(ebook) Squid Proxy Server.pdf 6b1f44

Disclaimer: This manual is NOT a Squid tutorial. It does not, for example, take the reader through step−by−step details of Squid installation and configuration. The objective of this manual is to explain, in as much detail as possible, every configuration parameter available in Squid. As such, the reader is required to have prior knowledge of basic Squid installation and configuration. The details presented in this manual are in the nature of reference material. For a complete tutorial on Squid, please visit http://www.squid−cache.org/ Table of Contents

I. Network This section explains ALL the network address parameters relevant to a Squid installation. Generally speaking, a Squid instance will need to communicate with: ♦ Local or remote web servers ♦ Other Cache servers ♦ Clients (desktop browsers or gateways) Squid configuration needs to define the addresses (IP address + port) for every relevant server and gateway This section focuses on communication with clients and web servers. The next section will detail the parameters required for communication with other cache servers in the network. A quick note on inter−server communication. Squid listens for T or I communication on specific ports. It uses T to communicate with web servers and clients, and I to talk to other cache servers. For every such server (or client), Squid configuration needs to assign a unique port number over which Squid would send requests (T or I) and listen for responses. An IP address is simply the network address at which the server is running. In short, the complete address for any server−to−server communication is determined by an IP−address+port combination. The following network parameters are relevant to Squid configuration:

• http_port • i_port • ht_port • mcast_groups • t_outgoing_address • udp_incoming_address • udp_outgoing_address II. Peer cache servers and Squid hierarchy The parameters described in this section are relevant when there is a Squid hierarchy in the network (i.e. more than one Squid instance running in the network with well−defined rules regarding which instance talks to which other instance, and so forth). Parameters of interest here are: number of cache servers, type of configuration (which instance communicates with which instance(s)), defining the primary cache server, mapping of specific domains to specific cache server instances, Timeouts, specification of objects that should not be cached locally etc. Relevant parameters covered by this section are:

• cache_peer • cache_peer_domain • neighbor_type_domain • i_query_timeout (msec) • maximum_i_query_timeout (msec) • mcast_i_query_timeout (msec) • dead_peer_timeout (seconds) • hierarchy_stoplist • no_cache

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III. Cache size This section describes parameters related to Cache Memory Size (real memory) as well as Cache Replacement Policy. Squid s more than one Cache replacement policy. This section also touches briefly on cache interaction with disk, but that subject is covered in greater detail in the next section. Relevant parameters for this section are

• Cache_mem (bytes) • cache_swap_low (percent, 0−100) • cache_swap_high (percent, 0−100) • maximum_object_size (bytes) • minimum_object_size (bytes) • maximum_object_size_in_memory (bytes) • ipcache_size (number of entries) • ipcache_low (percent) • ipcache_high (percent) • fqdncache_size (number of entries) • cache_replacement_policy • memory_replacement_policy IV. Log file path names and cache directories This section describes parameters for the configuration of cache directories (placement of caches in specific files and directories) AND Log file placement on disk (size, name, path, activity). Log files contain runtime information (relevant "successful" events as well as errors). Log files are used for system level debugging and runtime activity. Certain log file management issues, e.g. backups, restore, recycling etc. are not described here. For more information on controlling the log file size, see logfile_rotate directive, Squid command line option (−k rotate) and man page on logrotate in Linux.

• Cache_dir • cache_access_log • cache_log • cache_store_log • cache_swap_log • emulate_httpd_log on|off • log_ip_on_direct • mime_table • log_mime_hdrs on|off • agent_log • referer_log • pid_filename • debug_options • log_fqdn on|off • client_netmask V. for External functions Squid has the ability to invoke certain "externally defined' functions that are NOT part of the Squid binary. Such "external" executables (programs) are usually placed in a contrib directory for source code distribution. The most common "external" programs are FTP, DNS, Redirectors and Authenticators, and are usually contributed by sources other than Squid. External programs are invoked by Squid through the standard fork() and exec(). The number of such fork−able child processes for specific "external" processes can also be defined. Relevant parameters for this section are:

• ftp_ • ftp_list_width • ftp_ive • cache_dns_program 2

• dns_children • dns_retransmit_interval • dns_timeout • dns_defnames on|off • dns_nameservers • unlinkd_program • pinger_program • redirect_program • redirect_children • redirect_rewrites_host_header • redirector_access • authenticate_program • authenticate_children • authenticate_ttl • authenticate_ip_ttl • authenticate_ip_ttl_is_strict VI. Tuning the Squid Cache This section describes the important parameters that determine Squid cache performance. Notable among them are: Object refresh algorithm, size of the header and body for both reply and request, policy for aborting (server) connections when client closes connection etc. Relevant parameters are described below:

• wais_relay_host • wais_relay_port • request_header_max_size (KB) • request_body_max_size (KB) • reply_body_max_size (KB) • refresh_pattern • reference_age • quick_abort_min (KB) • quick_abort_max (KB) • quick_abort_pct (percent) • negative_ttl time−units • positive_dns_ttl time−units • negative_dns_ttl time−units • range_offset_limit (bytes) VII. Timeouts Timeout parameters in Squid can be based on overall connection timeouts, peer−specific timeouts, site/domain−specific timeouts, request−specific timeouts etc. Proper setting of timeout values is critical to optimal Squid performance. Relevant parameters for timeout settings are listed here.

• connect_timeout time−units • peer_connect_timeout time−units • site select_timeout time−units • read_timeout time−units • request_timeout • client_lifetime time−units • half_closed_clients • pconn_timeout • ident_timeout • shutdown_lifetime time−units VIII. Access controls Access control settings are among the most important features of Squid. You can configure Squid to set filters for various entities and at different granularities (e.g. filters for specific protocols, filters for certain types of commands, filters for specific routers, filters for specified domains, etc). The relevant parameters are described below:

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• acl • http_access • i_access • miss_access • cache_peer_access • proxy_auth_realm • ident_lookup_access IX. istrative parameters The parameters in this section allow the Squid to specify, for example, which s and groups have the right to run Squid , what host name should be displayed while displaying errors, which s have the authority to view Cache activity details, etc.

• Cache_mgr • cache_effective_ • cache_effective_group • visible_hostname • unique_hostname • hostname_aliases X. Options for the cache registration service Squid s have the option of ing their cache server with http://ircache.nlanr.net/Cache/Tracker/, a service that helps cache sites locate each other in order to create cache hierarchies. Relevant registration parameters are described by:

• announce_period • announce_host • announce_file • announce_port XI. Httpd−accelerator options Squid can act as a load balancer or load reducer for a particular webserver. Generally squid not only keeps clients happy but also the web servers by reducing load on server side. Some cache servers can act as web servers (or vice versa). These servers accept requests in both the standard web−request format (where only the path and filename are given), and in the proxy−specific format (where the entire URL is given). The Squid designers have decided not to let Squid to be configured in this way. This avoids various complicated issues, and reduces code complexity, making Squid more reliable. All in all, Squid is a web cache, not a web server. By adding a translation layer into Squid, we can accept (and understand) web requests, since the format is essentially the same. The additional layer can re−write incoming web requests, changing the destination server and port. This re−written request is then treated as a normal request: the remote server is ed, the data requested and the results cached. This lets Squid to pretend to be a web server, rewriting requests so that, they are ed on to some other web server. For Transparent caching, Squid can be configured to magically intercept outgoing web requests and cache them. Since the outgoing requests are in web−server format, it needs to translate them to cache−format requests. Transparent redirection is prohibited by internet standard #5 "Internet Protocol". And HTTP assumes no transparent redirection is taking place. This section allows various configurations related to the accelerator mode and the transparent mode.

• httpd_accel_host • httpd_accel_port • httpd_accel_single_host • httpd_accel_with_proxy on|off • httpd_accel_uses_host_header on|off

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XII. Miscellaneous As the title suggests, this section covers parameters that could not be explicitly bundled in with any of the previous categories. Examples of features covered here are: ♦ Limiting the growth of log fils. ♦ Displaying customized information to clients upon error conditions or access denial. ♦ Defining memory pools for Squid. ♦ Network management by enabling SNMP. ♦ Co−ordination with neighbor caches by enabling WC and ♦ Directing the requests either to the origin server or to the neighbor cache. The relevant parameters are:

• dns_test names • logfile_rotate • append_domain • t_recv_bufsize (bytes) • err_html_text • deny_info • memory_pools on|off • memory_pools_limit (bytes) • forwarded_for on|off • log_i_queries on|off • i_hit_stale on|off • minimum_direct_hops • minimum_direct_rtt • cachemgr_wd • store_avg_object_size (kbytes) • store_objects_per_bucket • client_db on|off • netdb_low • netdb_high • netdb_ping_period • query_icmp on|off • test_reachability on|off • buffered_logs on|off • reload_into_ims on|off • always_direct • never_direct • anonymize_headers • fake__agent • icon_directory • error_directory • minimum_retry_timeout (seconds) • maximum_single_addr_tries • snmp_port • snmp_access • snmp_incoming_address • snmp_outgoing_address • as_whois_server • wc_router • wc_version • wc_incoming_address • wc_outgoing_address XIII. Delaypool parameters (all require delay_pools compilation options) Conceptually, Delay pools are bandwidth limitations − "pools" of bandwidth that drain out as people browse the Web, and fill up at a rate we specify − this can be thought of as a leaky bucket that is continually being filled. This is useful when bandwidth charges are in place, if we want to reduce bandwidth usage for web traffic. Delay Pools can do wonders when combined with ACLs. These tags permit us to limit the bandwidth of

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certain requests, based on any criteria. Delay behavior is selected by ACLs (low and high priority traffic, staff Vs students or student Vs authenticated student or so on). In ISPs, delay pools can be implemented in a particular network to improve the quality of service. To enable this, Squid needs to be configured with the −−enable−delay−pools option. Relevant parameters are described below:

• delay_pools • delay_class • delay_access • delay_parameters • delay_initial_bucket_level (percent, 0−100) • incoming_i_average • incoming_http_average • incoming_dns_average • min_i_poll_cnt • min_dns_poll_cnt • min_http_poll_cnt • max_open_disk_fds • offline_mode • uri_whitespace • broken_posts • mcast_miss_addr • mcast_miss_ttl • mcast_miss_port • mcast_miss_encode_key • nonhierarchical_direct • prefer_direct • strip_query_ • coredump_dir • redirector_by • ignore_unknown_nameservers • digest_generation • digest_bits_per_entry • digest_rebuild_period (seconds) • digest_rewrite_period (seconds) • digest_swapout_chunk_size (bytes) • digest_rebuild_chunk_percentage (percent, 0−100) • chroot • client_persistent_connections • server_persistent_connections • pipeline_prefetch • extension_methods • high_response_time_warning • high_page_fault_warning • high_memory_warning • store_dir_select_algorithm • ie_refresh XIV. Glossary The Glossary provides a general explanation for various used in this guide.

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NETWORK OPTIONS Tag Name Usage

http_port http_port port hostname: port 1.2.3.4 : port

Description This tag name is used to specify the socket addresses where Squid will listen for HTTP client requests. Multiple socket addresses can be specified. There are three forms: port alone, hostname with port, and IP address with port. If hostname or IP address is specified, then Squid binds the socket to that specific address. This replaces the old "t_incoming_address" option. Most likely, there is no need to bind to a specific address, so the port number alone can be used. If Squid is to be run in accelerator mode, then it should listen on port 80 also, or instead. Default

http_port 3128

Example Give the port number in which you want squid to listen to http client requests. Like... http_port 8080 We can override the default port number by '−a ' command line option. #/usr/local/squid/bin/squid −a 8080 This will start squid with port 8080, which overrides the port number in squid.conf. However this option cannot be used to override IP address Caution Before changing the port number, make sure no application in your box is running in the same port. Note http_port can be used to specify the t_incoming_address through which the cache listens to requests from other remote servers. http_port can be listed multiple times.

Tag Name i_port Usage i_port port Description This specifies the port number from which Squid sends and receives I queries to and from neighbor caches. To disable "0" is used. I is a protocol used for communication among squid caches. I is primarily used within a cache hierarchy to locate specific objects in sibling caches. If a squid cache does not have a requested document, it sends an I query to its siblings, and the siblings respond with I replies indicating a ``HIT'' or a ``MISS.'' The cache then uses the replies to choose from which cache to resolve its own MISS. I is currently implemented on top of UDP. Squid also s I via multicast. Default

i_port 3130

Example The port number is given in which squid has to send and receive I queries from neighbor caches. Like... i_port 5050 May be overridden by −u command line option. #/usr/local/squid/bin/squid −u 5050 This will start squid with port 5050, which overrides the port number in squid.conf

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Caution Before changing this port number, make sure no application in the box is running in the same port.

Tag Name ht_port Usage ht_port port Description Used to specify the port number through which Squid sends and receives HT queries to and from neighbor caches. To disable "0" is used. Default

ht_port 4827

Example ht_port 5089 Caution To enable this option, you must use −−enable−ht with the configure script.

Tag Name mcast_groups Usage mcast_groups IPAddress Description This tag specifies a list of multicast groups, with which your server should to receive multicasted I queries. Multicast is essentially the ability to send one IP packet to multiple receivers. Multicast is often used for audio and video conferencing systems. If you are unsure about multicast, please read the Multicast chapter in the Squid FAQ (http://squid.nlanr.net/Squid/FAQ/). This option is to be set only if you want to RECEIVE multicast queries. I replies are always sent via unicast, so this option does not affect whether or not you will receive replies from multicast group . Be sure you understand the difference between an I _query_ and an I _reply_. Use cache_peer Directive for sending I queries. Default

none By default, Squid doesn't listen on any multicast groups

Example mcast_groups 239.128.16.128 224.0.1.20 Caution Should not use a multicast address, which is already in use by another group of caches. We should not set this option to SEND multicast I.

Tag Name t_outgoing_address Usage t_outgoing_address IPAddress Description It is used for connections made to remote servers. It is also used to communicate with other caches while using HT or CARP. Normally t_outgoing_address should not be specified. It is better to let the OS select a suitable address. There are some very specific network configurations where t_outgoing_address needs to be specified

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Default

t_outgoing_address 255.255.255.255

Example The t_incoming_address can be specified using http_port.

Tag Name udp_incoming_address Usage udp_incoming_address IPAddress Description It is used for the I socket receiving packets from other caches. Default

udp_incoming_address 0.0.0.0

Caution Cannot have the same value, since they both (udp_incoming_address and udp_outgoing_address) use the port 3130.

Tag Name udp_outgoing_address Usage udp_outgoing_address IPAddress Description It is used for the I packets sent out to the caches. Default

udp_outgoing_address 255.255.255.255

Caution Cannot have the same value, since they both (udp_incoming_address and udp_outgoing_address) use the port 3130.

PEER CACHE SERVERS AND SQUID HIERARCHY Tag Name cache_peer Usage cache_peer hostname type http_port i_port options Description This tag is used to specify the other caches in the hierarchy. The cache_peer option is split into five fields. The first field is the hostname or IP of the cache that is to be queried. The second field indicates the type of relationship. The third field sets the HTTP port of the destination server, while the fourth sets the I (UDP) query port. The fifth field can contain zero or more keywords. Here are the detailed explanations on each field. See cache_peer_access also. Hostname Hostname (FQDN) or IP address of the cache to be queried should be mentioned. For ex, cache_peer sib1.visolve.com sibling 3128 3130 [proxy−only] cache_peer 172.16.1.100 sibling 3128 3130 [proxy−only] Type Here cache hierarchy should be specified. This option plays an important role in deciding neighbor selection.

• parent • sibling • multicast

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Http_port The port number where the cache listens for proxy requests. See also http_port I_port Used for querying neighbor caches about objects. To have a non−I neighbor specify '7' for the I port and make sure the neighbor machine has the UDP echo port enabled in its /etc/inetd.conf file. See also i_port OPTIONS: proxy−only To specify that objects fetched from this cache should not be saved locally. Weight=n To specify a weighted parent. The weight must be an integer. The default weight is 1, larger weights are favoured more. ttl=n To specify a IP multicast Time To Live (ttl) value when sending I queries to multicast groups. We do not accept I replies from random hosts. So you must configure other group as peers with the multicast−responder option below. no−query This option is set for those peers, which do not I queries. It is obvious to have doubt about the I port specified in, while using this option. Squid does not care what digit has been given in the I port when no−query is specified. Using any number is fine. It is recommended to use 0 to emphasis the fact that I is not used in any way (not even to UDP echo port 7). This might be the typical example for this option : cache_peer hostname sibling 8080 0 proxy−only no−query By default, Port 3130 is typically where an I−aware proxy listens for I packets. Port 7 is the "echo" port (see /etc/services). It is typically handled by inetd as an internal process and simply "echoes" back what has been sent it. Since option "no−query" specified, port "7" is there so that if peer is queried, Squid gets an answer and not declares peer as dead and therefore stop using it. Port 7 is used when Squid has a non−I peer but still want to query it before sending requests there (no−query not specified). In such case, Squid will send the I queries to port 7 which is the UDP echo port. default If this is a parent cache which can be used as a "last−resort." and not I enabled then "default" would be the appropriate option. Simply adding default to a parent does not force all requests to be sent to that parent. The term default is perhaps a poor choice of words. If the cache is able to make direct connections, direct will be preferred over default. If needed to force all requests to parent cache(s), use the never_direct option. round−robin To define a set of parents which should be used in a round−robin fashion in the absence of any I queries. multicast−responder Indicates that the named peer is a member of a multicast group. I queries will not be sent directly to the peer, but I replies will be accepted from it. closest−only Indicates that, for I_OP_MISS replies, we'll only forward CLOSEST_PARENT_MISSes and never FIRST_PARENT_MISSes.

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no−digest To NOT request cache digests from this neighbor. no−netdb−exchange It disables requesting ICMP RTT database (NetDB) from the neighbor. no−delay To prevent access to this neighbor from influencing the delay pools. =: If this is a personal/workgroup proxy and your parent requires proxy authentication. connect−timeout=nn To specify a peer specific connect timeout (also see the peer_connect_timeout directive). digest−url=url To tell Squid to fetch the cache digest (if digests are enabled) for this host from the specified URL rather than the Squid default location. No cache peer is defined Default

none

Example cache_peer proxy.visolve.com parent 3128 3130 default cache_peer 172.16.1.100 sibling 3128 3130 proxy−only cache_peer 172.16.1.123 sibling 3129 5500 weight=2 Caution If you compiled Squid to HT, your cache will automatically attempt to connect to T port 4827 (there is currently no option to change this port value). Cache digests are transferred via the HTTP port specified on the cache_peer line. Non−I neighbors must be specified as 'parent'.

Tag Name cache_peer_domain Usage cache_peer_domain cache_host domain [domain ...] Description This tag is used to limit the domains for which the neighbor caches will be queried. It is used to communicate with different caches depending on the domain that the request is destined for

• Prefixing the domain name with '!' means that the cache will be queried for objects NOT in that domain. • Any number of domains may be given for a cache−host, either on the same or separate lines. • When multiple domains are given for a particular cache−host, the first matched domain is applied. • Cache hosts with no domain restrictions are queried for all requests. • There is also a 'cache_peer_access' tag in the ACL section . Default none Example cache_peer_domain parent.foo.net .edu It has the effect such that UDP query packets are sent to 'bigserver' only when the requested object exists on a server in the .edu domain.

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Tag Name neighbor_type_domain Usage neighbor_type_domain parent|sibling domain domain ... Description Modifying the neighbor type for specific domains is now possible. You can treat some domains differently than the default neighbor type specified on the 'cache_peer' line. Normally it should only be necessary to list domains, which should be treated differently because the default neighbor type applies for hostnames, which do not match domains listed here. Default

none

Example cache_peer proxy.visolve.com parent 3128 3130 neighbor_type_domain proxy.visolve.com sibling .com .net

Tag Name i_query_timeout (msecs) Usage i_query_timeout milliseconds Description Normally Squid will automatically determine an optimal I query timeout value based on the round−trip−time of recent I queries. If you want to override the value determined by Squid, set this 'i_query_timeout' to a non−zero value . Default

i_query_timeout 0

Example This value is specified in MILLISECONDS, so, to use a 2−second timeout (the old default), you would write: i_query_timeout 2000.

Tag Name maximum_i_query_timeout (msecs) Usage maximum_i_query_timeout milliseconds Description Normally the I query timeout is determined dynamically. But sometimes it can lead to very large values (say 5 seconds). Use this option to put an upper limit on the dynamic timeout value. If 'i_query_timeout' is set to zero, then this value is ignored. Default

maximum_i_query_timeout 2000

Caution Do NOT use this option to always use a fixed (instead of a dynamic) timeout value.

Tag Name mcast_i_query_timeout (msecs) Usage mcast_i_query_timeout milliseconds Description For Multicast peers, Squid regularly sends out I "probes" to count how many other peers are listening on the given multicast address. This value specifies how long Squid should wait to count all the replies. When Squid sends out a multicast query, it will wait at most mcast_i_query_timeout seconds (it's perfectly possible that one day a peer will be on the moon: and it would probably be a bad idea to peer with that cache seriously, unless it was a parent for the Mars top−level domain.) It's unlikely that you will want to increase this value, but you may wish to drop it, so that only reasonably speedy replies are considered. Default

mcast_i_query_timeout 2000

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Caution Do NOT use this option to always use a fixed (instead of a dynamic) timeout value.

Tag Name dead_peer_timeout (secs) Usage dead_peer_timeout seconds Description This controls how long Squid waits to declare a peer cache as "dead." If there are no I replies received in this amount of time, Squid will declare the peer dead and not expect to receive any further I replies. However, it continues to send I queries, and will mark the peer as alive upon receipt of the first subsequent I reply . Default

dead_peer_timeout 10 seconds

Caution This timeout also affects when Squid expects to receive I replies from peers. If more than 'dead_peer' seconds have ed since the last I reply was received, Squid will not expect to receive an I reply on the next query. Thus, if your time between requests is greater than this timeout, you will see a lot of requests sent DIRECT to origin servers instead of to your parents.

Tag Name hierarchy_stoplist Usage hierarchy_stoplist words Description A list of words which, if found in a URL, cause the object to be handled directly by this cache. In other words, use this when to query neighbor caches for certain objects. This option can be listed multiple times. As some times this functionality is affected by the directive never_direct, See also never_direct. Default

hierarchy_stoplist cgi−bin ? Squid will fetch URL's containing 'cgi−bin' or '?' from the origin servers directly without communicating with cache peers.

Example hierarchy_stoplist jsp asp If the URL contains the words jsp and asp, which indicate dynamic pages, then Squid will not query peers for the pages and will directly request the origin server. Note It is recommended to include all dynamic pages in this tag.

Tag Name no_cache Usage no_cache deny|allow aclname Description A list of ACL elements, which, if matched, cause the reply to be immediately, removed from the cache. In other words, use this to force certain objects to never be cached. Default

acl QUERY urlpath_regex cgi−bin \? no_cache deny QUERY The word 'DENY' is to indicate the ACL names, which should NOT be cached

Example acl DENYPAGE urlpath_regex Servlet no_cache deny DENYPAGE

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The DENYPAGE acl assures that the url containing Servlet will NOT be cached. Caution It is recommended to use this directive effectively. CACHE SIZE Tag Name cache_mem Usage cache_mem bytes Description 'cache_mem' specifies the ideal amount of memory to be used for :

• In−Transit objects • Hot Objects • Negative−Cached objects Data for these objects are stored in 4 KB blocks. This parameter specifies the ideal upper limit on the total size of 4 KB blocks allocated. In−transit objects have priority over the others. When additional space is needed for incoming data, negative−cached and hot objects will be released. In other words, the negative−cached and hot objects will fill up any unused space not needed for in−transit objects. If circumstances require, this limit will be exceeded. Specifically, if your incoming request rate requires more than 'cache_mem' of memory to hold in−transit objects, Squid will exceed this limit to satisfy the new requests. When the load decreases, blocks will be freed until the high−water mark is reached. Thereafter, blocks will be used to store hot objects. Default

cache_mem 8 MB

Example cache_mem 1 GB Caution This parameter does not specify the maximum process size. It places a limit on one aspect of squid's memory usage. Squid uses memory for other things as well. Process will probably become twice or three times bigger than the value put here.

Tag Name cache_swap_low (percent, 0−100) Usage cache_swap_low percentage Description This tag is used to specify the low−water mark for cache object replacement. Replacement begins when the swap (disk) usage is above the low−water mark and attempts to maintain utilization near the low−water mark. If utilization is close to the low−water mark, less replacement is done each time. Default

cache_swap_low 90

Example cache_swap_low 95 Caution If you have a large cache, 5% could be hundreds of MB. If this is the case, you may wish to set this number closer together.

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Tag Name cache_swap_high (percent, 0−100) Usage cache_swap_high percentage Description This tag is used to specify the high−water mark for cache object aggressive replacement. As swap utilization gets close to high−water mark, object eviction becomes more aggressive. Default

cache_swap_high 95

Example cache_swap_high 98 Caution If you have a large cache, 5% could be hundreds of MB. If this is the case, you may wish to set this number closer together.

Tag Name maximum_object_size (bytes) Usage maximum_object_size (bytes) Description Objects larger than this size will NOT be saved on disk. The value is specified in kilobytes, and the default is 4 MB. If you wish to get a high BYTES hit ratio, you should probably increase this (one 32 MB object hit counts for 3200 10 KB hits). If you wish to increase speed more than your want to save bandwidth, you should leave this low. During the initial ing of a file, the ing time seems to be a normal one, but if you the same file again, the time it takes for will be very minimum. This indicates that, the file comes from the Cache. Default

maximum_object_size 4096 KB

Example maximum_object_size 2000 KB Caution If using the LFUDA replacement policy you should increase this value to maximize the byte hit rate improvement of LFUDA. See replacement_policy for a discussion of this policy.

Tag Name minimum_object_size (bytes) Usage minimum_object_size (bytes) Description Objects smaller than this size will NOT be saved on disk. The value is specified in kilobytes, and the default is 0 KB, which means there is no minimum. See maximum_object_size for more information. Default

minimum_object_size 0 KB

Example minimum_object_size 2000 KB Note See maximum_object_size, which is reversibly applicable.

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Tag Name maximum_object_size_in_memory (bytes) Usage maximum_object_size_in_memory (bytes) Description Objects greater than this size will not be attempted to be kept in the memory cache. This should be set high enough to keep objects accessed frequently in memory to improve performance while, low enough to keep larger objects from hoarding cache_mem. Default

maximum_object_size_in_memory 8 KB

Example maximum_object_size_in_memory 20 KB

Tag Name ipcache_size (number of entries) Usage ipcache_size (number of entries) Description This tag is used to specify the size of the ipcache. Default

ipcache_size 1024

Tag Name ipcache_low (percent) Usage ipcache_low percentage Description This specifies the low water mark for caching IP addresses. Default

ipcache_low 90

Tag Name ipcache_high (percent) Usage ipcache_high percentage Description This specifies the high water mark for caching IP addresses. Default

ipcache_high 95

Tag Name fqdncache_size Usage fqdncache_size (number of entries) Description This specifies the maximum number of FQDN cache entries. Default

fqdncache_size 1024

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Tag Name cache_replacement_policy Usage cache_replacement_policy policy Description The cache replacement policy parameter decides which objects will remain in cache and which objects are evicted (replaced) to create space for the new objects.

• LRU : Squid's original list based LRU policy • heap GDSF : Greedy−Dual Size Frequency • heap LFUDA : Least Frequently Used with Dynamic Aging • heap LRU : LRU policy implemented using a heap This applies to any cache_dir lines listed below this. The LRU policies keep recently referenced objects. i.e., it replaces the object that has not been accessed for the longest time. The heap GDSF policy optimizes object−hit rate by keeping smaller popular objects in cache. So it has a better chance of getting a hit. It achieves a lower byte hit rate than LFUDA though, since it evicts larger (possibly popular) objects. The heap LFUDA ( Least Frequently Used with Dynamic Aging ) policy keeps popular objects in cache regardless of their size and thus optimizes byte hit rate at the expense of hit rate since one large, popular object will prevent many smaller, slightly less popular objects from being cached. Both policies utilize a dynamic aging mechanism that prevents cache pollution that can otherwise occur with frequency−based replacement policies. For more information about the GDSF and LFUDA cache replacement policies see http://www.hpl.hp.com/techreports/1999/HPL−1999−69.html and http://fog.hpl.external.hp.com/techreports/98/HPL−98−173.html . Default

cache_replacement_policy lru

Example cache_replacement_policy heap LFUDA To use this policy, Squid should be built with configure option −−enable−removal−policy=heap or simply −−enable−removal−policy. Caution If using the LFUDA replacement policy, the value of maximum_object_size should be increased above its default of 4096 KB to maximize the potential byte hit rate improvement of LFUDA. If needed to use other policies than default, squid should be built with configure option −−enable−removal−policies.

Tag Name memory_replacement_policy Usage memory_replacement_policy policy Description The memory replacement policy parameter determines which objects are purged from memory, when memory space is needed. See cache_replacement_policy for details Default

memory_replacement_policy lru

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LOG FILE PATH NAMES AND CACHE DIRECTORIES Tag Name Usage

cache_dir cache_dir Type Maxobjsize Directory−Name Mbytes Level−1 Level2 [..] DISKD : cache_dir diskd Maxobjsize Directory−Name MB L1 L2 Q1 Q2

Description Type specifies the kind of storage system to use. Most everyone will want to use "ufs" as the type. If you are using Async I/O (−−enable async−io) on Linux or Solaris, then you may want to try "aufs" as the type. Async IO may be buggy, however, so beware. Maxobjsize refers to the max object size this storedir s. It is used to initially choose the storedir to dump the object. −1 means 'any size'. 'Directory' is a top−level directory where cache swap files will be stored. If you want to use an entire disk for caching, then this can be the mount−point directory. The directory must exist and be writable by the Squid process. Squid will NOT create any directory. 'Mbytes' is the amount of disk space (MB) to use under this directory. 'Level−1' is the number of first−level subdirectories, which will be created under the 'Directory'. 'Level−2' is the number of second−level subdirectories, which will be created under each first−level directory. To create swap directory use /usr/local/squid/bin/squid –z option. For the diskd type, Q1 specifies the number of unacknowledged I/O requests when Squid stops opening new files. If this many messages are in the queues, Squid won't open new files. Q2 specifies the number of unacknowledged messages when Squid starts blocking. If this many messages are in the queues, Squid blocks until it receives some replies. Default

cache_dir ufs /usr/local/squid/cache 100 16 256

Example cache_dir ufs /cache1 5000 16 256 cache_dir ufs /cache2 7000 16 256 Note Can specify multiple cache_dir lines to spread the cache among different disk partitions. Click Here to find more informations on file systems and cache_dir.

Tag Name cache_access_log Usage cache_access_log Directory−path/filename Description This tag is used to specify the path of the access.log file, which logs the client request activity. It contains an entry for every HTTP and I queries received. Log Details can be customized using log_mime_hdrs, log_fqdn, client_netmask and emulate_httpd_log. See for Detailed information about this log file. See also log_i_queries. Default

cache_access_log /usr/local/squid/logs/access.log

Example cache_access_log /var/log/squid_access.log

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Caution It is safe to set log_mime_hdrs off.

Tag Name cache_log Usage cache_log Directory−path/filename Description This tag is used to set the path of the Cache logging file. This is where general information about the cache's behaviour goes. Amount of data logged to this file can be increased with the debug_options tag below. Default

cache_log /usr/local/squid/logs/cache.log

Example cache_log /var/log/squid_cache.log Caution Do not change the default value of debug_options unless otherwise needed. Because if debug_options value is high, then logging information goes high. This leads to undesirable growth in log file.

Tag Name cache_store_log Usage cache_store_log Directory−path/filename Description This tag is used to specify the location of the store.log, the file that logs the activities of the storage manager. The file shows which objects are ejected from the cache, and which objects are saved and for how long. Default

cache_store_log /usr/local/squid/logs/store.log

Example cache_store_log /var/log/squid_store.log Caution There are no real utilities to analyze this data. So it is recommended to disable this tag Note To disable, enter "none" instead of the filename.

Tag Name cache_swap_log Usage cache_ swap _log Directory−path/filename Description This tag specifies the location for the cache "swap.log." This log file holds the metadata of objects saved on disk. It is used to rebuild the cache during startup. Normally this file resides in the first 'cache_dir' directory, but you may specify an alternate pathname here. Note, you must give a full filename, not just a directory. Since this is the index for the whole object list you CANNOT periodically rotate it. If you have more than one 'cache_dir', these swap logs will have names such as:

• cache_swap_log.00 • cache_swap_log.01 • cache_swap_log.02 The numbered extension (which is added automatically) corresponds to the order of the 'cache_dir' lines in this configuration file.

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Default

cache_ swap _log /usr/local/squid/logs/ swap.log

Example cache_ swap _log /var/log/squid_ swap.log Caution If you change the order of the 'cache_dir' lines in this file, then these log files will NOT correspond to the correct 'cache_dir' entry (unless you manually rename them). We recommend that you do NOT use this option. It is better to keep these log files in each 'cache_dir' directory.

Tag Name emulate_httpd_log Usage emulate_httpd_log on|off Description The Cache can emulate the log file format, which many 'httpd' programs use. To disable/enable this emulation, set emulate_httpd_log to 'off' or 'on'. Default

emulate_httpd_log off (By Default Squid Native Log format is used. Since it includes useful information that Squid−specific log analyzers use).

Example emulate_httpd_log on Caution Before setting this to ON, make sure you have httpd_log file analyzers which will analyze log files and give us useful information.

Tag Name

log_ip_on_direct

Usage log_ip_on_direct on|off Description This tag is used to enable/disable logging of the destination IP address in the hierarchy log tag when the cache directs the request to the origin server. Default

log_ip_on_direct on

Example log_ip_on_direct off Note Earlier Squid versions logged the hostname here. If you prefer the old way, set this to off.

Tag Name mime_table Usage mime_table Directory−Path/filename Description This tag is used to set the pathname to Squid's MIME table. This file contains Squid's ed mime types. Default

mime_table /usr/local/squid/etc/mime.conf

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Caution Shouldn't need to change this, but the default file contains examples and formatting information if done.

Tag Name log_mime_hdrs Usage log_mime_hdrs on|off Description The Cache can record both the request and the response MIME headers for each HTTP transaction. The headers are encoded safely and will appear as two bracketed fields at the end of the access log (for either the native or httpd−emulated log formats). To enable this logging, set log_mime_hdrs to 'on'. Default

log_mime_hdrs off

Tag Name agent_log Usage agent_log Directory−path/filename Description If configured with the "−−enable−agent_log" configure option, Squid will write the −Agent field from HTTP requests to the filename specified here. Default

agent_log none (By default agent_log is disabled.)

Example agent_log /var/log/agent.log

Tag Name referer_log Usage referer_log Directory−path/filename Description If configured with the "−−enable−referer_log" configure option, Squid will write the Referer field from HTTP requests to the filename specified here. Default

referer_log none (By default referer_log is disabled.)

Example referer_log /var/log/referer.log

Tag Name pid_filename Usage pid_filename Directory−path/filename Description This tag specifies the location of the file in which Squid writes its process−ids. Default

pid_filename /usr/local/squid/logs/squid.pid

Example pid_filename /var/lock/squid.pid Caution To disable, enter "none".

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Tag Name debug_options Usage debug_options section, level Description Logging options are set as section, level, where each source file is assigned a unique section. Lower levels result in less output. The magic word "ALL" sets debugging levels for all sections. We recommend normally running with "ALL, 1". Default

debug_options ALL, 1

Example debug_options ALL, 9 Caution Full debugging (level 9) can result in a very large log file, so be careful. Normally, running with "ALL, 1" is recommended.

Tag Name log_fqdn Usage log_fqdn on|off Description This tag can be set to ON, if you wish to log fully qualified domain names in the access.log. Default

log_fqdn off

Example log_fqdn on Caution To do this, Squid does a DNS lookup of all IP's connecting to it. This can (in some situations) increase latency, which makes your cache seem slower for interactive browsing.

Tag Name client_netmask Usage client_netmask NETMASK Description A netmask for client addresses in log files and cachemgr output. Change this to protect the privacy of your cache clients. A netmaskof 255.255.255.0 will log all IP's in that range with the last digit set to '0'. Default

client_netmask 255.255.255.255

Example client_netmask 255.255.255.0 Caution When you enable this tag, then the client's visit pages cannot be identified.

FOR EXTERNAL FUNCTIONS

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Tag Name ftp_ Usage ftp_ name Description This tag can be used if you want the anonymous to be more informative. You can set this to something reasonable for your domain, like [email protected]. The reason why this is domain less by default is that the request can be made on the behalf of a in any domain, depending on how the cache is used. Some ftp servers also validate the email address. For detailed explanation Click Here Default

ftp_ Squid@

Example ftp_ [email protected]

Tag Name ftp_list_width Usage ftp_list_width number Description This tag is used to set the width of ftp listings. This should be set to fit in the width of a standard browser. Setting this too small can cut off long filenames when browsing ftp sites. Default

ftp_list_width 32

Example ftp_list_width 64

Tag Name ftp_ive Usage ftp_ive on|off Description If your firewall does not allow Squid to use ive connections, then turn off this option. Default

ftp_ive on

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Tag Name cache_dns_program Usage cache_dns_program program Description This tag is used to specify the location of the executable for dns lookup process. This option is only available if Squid is rebuilt with the −−disable−internal−dns option. The external dns program uses the normal resolver libraries which is a much more mature DNS client. The internal DNS client still has some problems with special cases in the DNS protocol. However, things has gotten a lot better compared to the early version so any of these issues are not likely to be noticed, and is heavily out weighted by the improved performance and reliability. But drawbacks of the external DNS helper are likely to be noticed when using external DNS. If DNS lookups are slow then the external DNS helper will hit the roof and no further DNS lookups can complete (some Squid versions even abort in such case). Recommendation: Use the internal DNS client unless an experience problem which forces to use the external one until a fix is provided. Default

cache_dns_program /usr/local/squid/libexec/squid/

Example cache_dns_program /usr/local/squid/bin/dnsserver

Tag Name dns_children Usage dns_children number (1 to 32) Description The number of processes spawn to service DNS name lookups are specified here. For heavily loaded caches on large servers, There is probably need to increase this value to at least 10. The maximum is 32. The default is 5. This option is only available if Squid is rebuilt with the −−disable−internal−dns option. The number of processes increases, the performance of DNS lookups also increases. It is recommended to use maximum child processes (32). The limitation that the external dnsserver helper can only handle one DNS lookup at a time and cannot be aborted prior to the 2 minutes DNS lookup time−out. The internal DNS client does not have this limitation and can handle any number of concurrent lookups. See the description of cache_dns_program. Default

dns_children 5

Example dns_children 10 Caution You must have at least one dnsserver process

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Tag Name dns_retransmit_interval Usage dns_retransmit_interval time−units Description This tag is used to set the initial retransmit interval for DNS queries. The interval is doubled each time all configured DNS servers have been tried Default

dns_retransmit_interval 5 seconds

Tag Name dns_timeout Usage dns_timeout time−units Description This tag is used to set the DNS Query time−out. If no response is received to a DNS query within this time then all DNS servers for the queried domain is assumed to be unavailable Default

dns_timeout 5 minutes

Tag Name dns_defnames Usage dns_defnames on|off Description Normally the 'dnsserver' disables the RES_DEFNAMES resolver option (see res_init(3)). This prevents caches in a hierarchy from interpreting single component hostnames locally. To allow dnsserver handle single component names, enable this option. This option is only available if Squid is rebuilt with the −−disable−internal−dnsoption. Default

dns_defnames off

Tag Name dns_nameservers Usage dns_nameservers IPaddress Description This tag can be used if you want to specify a list of DNS name servers (IP addresses) to use instead of those given in your /etc/resolv.conf file Default

dns_nameservers none

Example dns_nameservers 172.16.1.102 204.54.6.20

Tag Name diskd_program Usage diskd_program path/to/diskdfile Description To specify the location of the diskd executable. Note that this is only useful if you have compiled in diskd as one of the store io modules. Default

diskd_program /usr/local/squid/libexec/squid/diskd

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Example diskd_program /local/squid/bin/diskd

Tag Name unlinkd_program Usage unlinkd_program path/to/unlinkedfile Description This tag specifies the location of the unlinkd program. This isn't needed if you are using async−io since it's handled by a thread Default

unlinkd_program /usr/local/squid/libexec/squid/unlinkd

Example unlinkd_program /usr/local/squid/bin/unlinkd

Tag Name pinger_program Usage pinger_program path/to/pingerfile Description This tag is used to specify the location of the executable for the pinger process. This is only useful if you configured Squid (during compilation) with the '−−enable−icmp' option Default

pinger_program /usr/local/squid/libexec/squid/

Example pinger_program /usr/local/squid/bin/pinger

Tag Name redirect_program Usage redirect_program path/to/redirector Description This tag is used to specify the location of the executable for the URL redirector. Since they can perform almost any function there isn't one included. Click here for information on how to write one. By default, a redirector is not used Default

redirect_program none

Example redirect_program /usr/local/squirm/bin/squirm

Tag Name redirect_children Usage redirect_children number Description This tag is used to set the number of redirect processes to spawn Default

redirect_children 5

Example redirect_children 10 Caution If you start too few Squid will have to wait for them to process a back log of URLs, slowing it down. If you start too many they will use RAM and other system resources.

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Tag Name redirect_rewrites_host_header Usage redirect_rewrites_host_header on|off Description By default Squid rewrites any Host: header in redirected requests. If you are running a accelerator then this may not be a wanted effect of a redirector Default

redirect_rewrites_host_header on

Tag Name redirect_access Usage redirector_access allow|deny Description If defined, this access list specifies which requests are sent to the redirector processes Default

All requests are sent

Example redirector_access allow aclname

Tag Name authenticate_program Usage authenticate_program path/to/program path/to/wdfile Description This tag is used to specify the command for the external authenticator. Such a program reads a line containing "name " and replies "OK" or "ERR" in an endless loop. If you use an authenticator, make sure you have 1 acl of type proxy_auth. If you want to use the traditional proxy authentication, jump over to the ../auth_modules/NCSA directory and give # make # make install The source for this program is included in the source distribution, in the auth_modules/NCSA directory. You should now have an ncsa_authprogram in the same directory where your squid binary lives. You may need to create a file. If you have been using proxy authentication before, you probably already have such a file. You can get apache's htwd program from here. Pick a pathname for your file. We will assume you will want to put it in the same directory as your Squid.conf. Default

authenticate_program none By default, the authenticator_program is not used

Example authenticate_program /usr/local/squid/bin/ncsa_auth /usr/local/squid/etc/wd

Tag Name authenticate_children Usage authenticate_children number Description The number of authenticator processes to spawn (default 5). Default

authenticate_children 5

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Caution If you start too few Squid will have to wait for them to process aback log of code/ verifications, slowing it down. When verifications are done via a (slow) network you are likely to need lots of authenticator processes.

Tag Name authenticate_ttl Usage authenticate_ttl seconds Description This tag is used to specify the time a checked name/ combination remains cached (default 3600). If a wrong is given for a cached , the gets removed from the name/ cache forcing a revalidation. Default

authenticate_ttl 3600

Tag Name authenticate_ip_ttl Usage authenticate_ip_ttl number Description With this option you control how long a proxy authentication will be bound to a specific IP address. If a request using the same name is received during this time then access will be denied and both s are required to reauthenticate them selves. The idea behind this is to make it annoying for people to share their to their friends, but yet allow a dialup to reconnect on a different dialup port. The default is 0 to disable the check. Recommended values if you have dialup s are no more than 60 (seconds). If all your s are stationary then higher values may be used. Default

authenticate_ip_ttl 0

Example authenticate_ip_ttl 3600

Tag Name authenticate_ip_ttl_is_strict Usage authenticate_ip_ttl_is_strict on|off Description This option makes authenticate_ip_ttl a bit stricter. With this enabled authenticate_ip_ttl will deny all access from other IPaddresses until the TTL has expired, and the IP address "owning" the id will not be forced to reauthenticate. Default

authenticate_ip_ttl_is_strict on

OPTIONS FOR TUNING THE CACHE Tag Name Usage

wais_relay_host wais_relay_port wais_relay_host wais_relay_port

Description Relay WAIS request to host (1st arg) at port (2 arg). Default

wais_relay_port 0

Example wais_relay_host localhost

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wais_relay_port 8000

Tag Name request_header_max_size Usage request_header_max_size (KB) Description This specifies the maximum size for HTTP headers in a request. Request headers are usually relatively small (about 512 bytes). Placing a limit on the request header size will catch certain bugs (for example with persistent connections) and possibly buffer−overflow or denial−of−service attacks. Default

request_header_max_size 10 KB

Tag Name request_body_max_size Usage request_body_max_size (KB) Description This specifies the maximum size for an HTTP request body. In other words, the maximum size of a PUT/POST request. A , who attempts to send a request with a body larger than this limit receives an "Invalid Request" error message. If you set this parameter to a zero, there will be no limit imposed. Default

request_body_max_size 1 MB

Tag Name reply_body_max_size Usage reply_body_max_size (KB) Description This option specifies the maximum size of a reply body. It can be used to prevent s from ing very large files, such as MP3's and movies. The reply size is checked twice. First when we get the reply headers, we check the content−length value. If the content length value exists and is larger than this parameter, the request is denied and the receives an error message that says "the request or reply is too large." If there is no content−length, and the reply size exceeds this limit, the client's connection is just closed and they will receive a partial reply. Default

reply_body_max_size 0 If this parameter is set to zero (the default), there will be no limit imposed.

Caution Downstream caches probably cannot detect a partial reply if there is no content−length header, so they will cache partial responses and give them out as hits. You should NOT use this option, if you have downstream caches.

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Tag Name refresh_pattern Usage refresh_pattern [−i] regex min percent max [options] Description 'Min' is the time (in minutes) an object without an explicit expiry time should be considered fresh. The recommended value is 0; any higher values may cause dynamic applications to be erraneously cached unless the application designer has taken the appropriate actions. 'Percent' is a percentage of the objects age (time since last modification age) an object without explicit expiry time will be considered fresh. 'Max' is an upper limit on how long objects without an explicit expiry time will be considered fresh. Options: override−expire override−lastmod reload−into−ims ignore−reload override−expire enforces min age even if the server sent a Expires: header. Doing this VIOLATES the HTTP standard. Enabling this feature could make you liable for problems, which it causes. override−lastmod enforces min age even on objects that was modified recently. reload−into−ims changes client no−cache or ``reload'' to If−Modified−Since requests. Doing this VIOLATES the HTTP standard. Enabling this feature could make you liable for problems, which it causes.

ignore−reload ignores a client no−cache or ``reload'' header. Doing this VIOLATES the HTTP standard. Enabling this feature could make you liable for problems, which it causes.

Basically a cached object is: (the order is changed from 1.1.X) FRESH if expires br>STALE if age >max FRESH if lm−factor br>STALE FRESH if age else STALE The refresh_pattern lines are checked in the order listed here. The first entry which matches is used. If none of the entries match, then the default will be used. Default

refresh_pattern ^ftp: 1440 20% 10080 refresh_pattern ^gopher: 1440 0% 1440 refresh_pattern . 0 20% 4320

Tag Name

reference_age

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Usage reference_age time−units Description As a part of normal operation, Squid performs Least Recently Used removal of cached objects. The LRU age for removal is computed dynamically, based on the amount of disk space in use. The dynamic value can be seen in the Cache Manager 'info' output. The 'reference_age' parameter defines the maximum LRU age Default

reference_age 1 year

Example For example, setting reference_age to '1 week' will cause objects to be removed, if they have not been accessed for a week or more. The default value is one year. Specify a number here, followed by units of time. For example: 1 week 3.5 days 4 months 2.2 hours Caution This parameter is not used when using the enhanced replacement policies, GDSH or LFUDA.

Tag Name Usage

quick_abort_min quick_abort_max quick_abort_pct quick_abort_min (KB) quick_abort_max (KB) quick_abort_pct (percent)

Description The cache can be configured to continue ing aborted requests. This may be undesirable on slow (e.g. SLIP) links and/or very busy caches. Impatient s may tie up file descriptors and bandwidth by repeatedly requesting and immediately aborting s. When the aborts a request, Squid will check the quick_abort values to the amount of data transferred until then. If the transfer has less than 'quick_abort_min' KB remaining, it will finish the retrieval. Setting 'quick_abort_min' to –1 will disable the quick_abort feature. If the transfer has more than 'quick_abort_max' KB remaining, it will abort the retrieval. If more than 'quick_abort_pct' of the transfer has completed, it will finish the retrieval. Default

quick_abort_min 16 KB quick_abort_max 16 KB quick_abort_pct 95

Caution This may be undesirable on slow (e.g. SLIP) links and/or very busy caches.

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Tag Name negative_ttl Usage negative_ttl time−units Description Time−to−Live (TTL) for failed requests. Certain types of failures (such as "connection refused" and "404 Not Found") are negatively−cached for a configurable amount of time. Note that, this is different from negative caching of DNS lookups. Default

The default is 5 minutes. negative_ttl 5 minutes

Tag Name positive_dns_ttl Usage positive_dns_ttl time−units Description Time−to−Live (TTL) for positive caching of successful DNS lookups. If you want to minimize the use of Squid's ipcache, set this to 1, not 0. Default

Default is 6 hours (360 minutes). positive_dns_ttl 6 hours

Tag Name negative_dns_ttl Usage negative_dns_ttl time−units Description Time−to−Live (TTL) for negative caching of failed DNS lookups Default

negative_dns_ttl 5 minutes

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Tag Name range_offset_limit Usage range_offset_limit (bytes) Description Sets an upper limit on how far into the file a Range request may be to cause Squid to prefetch the whole file. If beyond this limit, then Squid forwards the Range request as it is and the result is NOT cached. This is to stop a far ahead range request (lets say start at 17MB) from making Squid fetch the whole object up to that point before sending anything to the client. A value of −1 causes Squid to always fetch the object from the beginning so that it may cache the result. (2.0 style). A value of 0 causes Squid to never fetch more than the client requested. (default) . Default

range_offset_limit 0 KB

TIMEOUTS Tag Name connect_timeout Usage connect_timeout seconds Description The time duration until which squid waits for the reply from the origin server. If it exceeds this squid will respond with the error message “Connection timed out” to the client Default

connect_timeout 120 seconds

Example connect_timeout 180 seconds Caution Increasing the time here will lead to annoying of browser .

Tag Name peer_connect_timeout Usage peer_connect_timeout time−units Description This parameter specifies how long to wait for a pending T connection to a peer cache. The default is 30 seconds. You may also set different timeout values for individual neighbors with the 'connect−timeout' option on a 'cache_peer' line Default

peer_connect_timeout 30 seconds

Example peer_connect_timeout 45 seconds Caution Setting of peer_connect_timeout to more than 30 seconds will be a performance issue.

Tag Name Usage

siteselect_timeout siteselect_timeout time−units

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Description Site select timeout is the timeout for URN to the multiple URLs selection. URN is a protocol designed for location−independent name resolution, specified in RFC 2169. This option configures the siteselect_timeout directive and defaults to 4 seconds. You do not need to change this. Default

siteselect_timeout 4 seconds

Example siteselect_timeout 6 seconds

Tag Name read_timeout Usage read_timeout time−units Description The read_timeout is applied on server−side connections. After each successful read(), the timeout will be extended by this amount. If no data is read again after this amount of time, the request is aborted and logged with ERR_READ_TIMEOUT. The default is 15 minutes. Default

read_timeout 15 minutes

Example read_timeout 10 minutes

Tag Name request_timeout Usage request_timeout seconds Description This tag specifies Squid the time in seconds to wait for an HTTP request after connection establishment. For persistent connections, Squid will wait this long after the previous request completes Default

request_timeout 30 seconds

Example request_timeout 20 seconds

Tag Name client_lifetime Usage client_lifetime time−units Description The maximum amount of time that a client (browser) is allowed to remain connected to the cache process. This protects the Cache from having a lot of sockets (and hence file descriptors) tied up in a CLOSE_WAIT state from remote clients that go away without properly shutting down (either because of a network failure or because of a poor client implementation). The default is one day, 1440 minutes Default

client_lifetime 1 day

Example client_lifetime 1000 minutes Caution The default value is intended to be much larger than any client would ever need to be connected to your cache. You should probably change client_lifetime only as a last resort. If you seem to have many client connections tying up filedescriptors, we recommend first tuning the read_timeout, request_timeout, pconn_timeout and quick_abort values. If the more file descriptors are in use then the memory in use will also increase, which is also a performance issue.

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Tag Name half_closed_clients Usage half_closed_clients on|off Description Some clients may shutdown the sending side of their T connections, while leaving their receiving sides open. Sometimes, Squid cannot tell the difference between a half−closed and a fully−closed T connection. By default, half−closed client connections are kept open until a read(2) or write(2) on the socket returns an error. Change this option to 'off' and Squid will immediately close client connections when read (2) returns "no more data to read Default

half_closed_clients on

Example half_closed_clients off

Tag Name pconn_timeout Usage pconn_timeout seconds Description Persistent timeout is the timeout value for persistent connections. Squid closes persistent connections if they are idle for this amount of time. Persistent connections are disabled entirely if this option is set to a value less than 10 seconds. The default is 120 seconds and likely does not need to be changed. Default

pconn_timeout 120 seconds

Example pconn_timeout 60 seconds

Tag Name ident_timeout Usage ident_timeout seconds Description Maximum time to wait for IDENT requests. If this is too high, and you enabled 'ident_lookup', then you might be susceptible to denial−of−service by having many ident requests going at once. Only src type ACL checks are fully ed. An src_domainACL might work at times, but it will not always provide the correct result. This option may be disabled by using −−disable−ident with the configure script Default

ident_timeout 10 seconds

Example ident_timeout 5 seconds

Tag Name shutdown_lifetime Usage shutdown_lifetime time−units Description When SIGTERM or SIGHUP is received, the cache is put into "shutdown pending" mode until all active sockets are closed. This value is the lifetime to set for all open descriptors during shutdown mode. Any active clients after this many seconds will receive a 'timeout' message Default

shutdown_lifetime 30 seconds

Example shutdown_lifetime 45 seconds

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Caution If this time is set to be too low then some file descriptors may remain open which will be a performance issue in memory usage.

ACCESS CONTROLS Tag Name acl Usage acl aclname acltype string1 ... | "file" Description This tag is used for defining an access List. When using "file" the file should contain one item per line By default, regular expressions are CASE−SENSITIVE. To make them case−insensitive, use the −i option.

Acl Type: src Description This will look client IP Address. Usage

acl aclname src ip−address/netmask.

Example 1.This refers to the whole Network with address 172.16.1.0 − acl aclname src 172.16.1.0/24 2.This refers specific single IP Address − acl aclname src 172.16.1.25/32 3.This refers range of IP Addresses from 172.16.1.25−172.16.1.35 − acl aclname src 172.16.1.25−172.16.1.35/32 Note While giving Netmask caution must be exerted in what value is given

Acl Type: dst Description This is same as src with only difference refers Server IPaddress. First Squid will dns−lookup for IPAddress from the domain−name, which is in request header. Then this acl is interpreted. Usage

acl aclname dst ip−address/netmask.

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Acl Type: srcdomain Description Since squid needs to reverse dns lookup (from client ip−address to client domain−name) before this acl is interpreted, it can cause processing delays. This lookup adds some delay to the request. Usage

acl aclname srcdomain domain−name

Example acl aclname srcdomain .kovaiteam.com Note Here "." is more important.

Acl Type: dstdomain Description This is the effective method to control specific domain Usage

acl aclname dstdomain domain−name

Example acl aclname dstdomain .kovaiteam.com Hence this looks for *.kovaiteam.com from URL Hence this looks for *.kovaiteam.com from URL Note Here "." is more important.

Acl Type: srcdom_regex Description Since squid needs to reverse dns lookup (from client ip−address to client domain−name) before this acl is interpreted, it can cause processing delays. This lookup adds some delay to the request Usage

acl aclname srcdom_regex pattern

Example acl aclname srcdom_regex kovai Hence this looks for the word kovai from the client domain name Note Better avoid using this acl type to be away from latency.

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Acl Type: dstdom_regex Description This is also an effective method as dstdomain Usage

acl aclname dstdom_regex pattern

Example acl aclname dstdom_regex kovai Hence this looks for the word kovai from the client domain name

Acl Type: time Description Time of day, and day of week Usage

acl aclname time [day−abbreviations] [h1:m1−h2:m2] day−abbreviations: S − Sunday M − Monday T − Tuesday W − Wednesday H − Thursday F − Friday A − Saturday h1:m1 must be less than h2:m2

Example acl ACLTIME time M 9:00−17:00 ACLTIME refers day of Monday from 9:00 to 17:00.

Acl Type: url_regex Description The url_regex means to search the entire URL for the regular expression you specify. Note that these regular expressions are case−sensitive. To make them case−insensitive, use the −i option. Usage

acl aclname url_regex pattern

Example acl ACLREG url_regex cooking ACLREG refers to the url containing "cooking" not "Cooking"

Acl Type: urpath_regex Description The urpath_regex regular expression pattern matching from URL but without protocol and hostname. Note that these regular expressions are case−sensitive Usage

acl aclname urlpath_regex pattern

Example acl ACLPATHREG urlpath_regex cooking

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ACLPATHREG refers only containing "cooking'' not "Cooking"; and without referring protocol and hostname. If URL is http://www.visolve.com/folder/subdir/cooking/first.html then this acltype only looks after http://www.visolve.com/ .

Acl Type: port Description Access can be controlled by destination (server) port address Usage

acl aclname port port−no

Example This example allows http_access only to the destination 172.16.1.115:80 from network 172.16.1.0 acl acceleratedhost dst 172.16.1.115/255.255.255.255 acl acceleratedport port 80 acl mynet src 172.16.1.0/255.255.255.0 http_access allow acceleratedhost acceleratedport mynet http_access deny all

Acl Type: proto Description This specifies the transfer protocol Usage

acl aclname proto protocol

Example acl aclname proto HTTP FTP This refers protocols HTTP and FTP

Acl Type: method Description This specifies the type of the method of the request Usage

acl aclname method method−type

Example acl aclname method GET POST This refers get and post methods only

Acl Type: browser Description Regular expression pattern matching on the request's −agent header Usage

acl aclname browser pattern

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Example acl aclname browser MOZILLA This refers to the requests, which are coming from the browsers who have "MOZILLA" keyword in the −agent header.

Acl Type: ident Description String matching on the 's name Usage

acl aclname ident name ...

Example You can use ident to allow specific s access to your cache. This requires that an ident server process runs on the 's machine(s). In your squid.conf configuration file you would write something like this: ident_lookup on acl friends ident kim lisa frank joe http_access allow friends http_access deny all

Acl Type: ident_regex Description Regular expression pattern matching on the 's name. String match on ident output. Use REQUIRED to accept any non−null ident Usage

acl aclname ident_regex pattern

Example You can use ident to allow specific s access to your cache. This requires that an ident server process run on the 's machine(s). In your squid.conf configuration file you would write something like this: ident_lookup on acl friends ident_regex joe This looks for the pattern "joe" in name

Acl Type: src_as Description source (client) Autonomous System number

Acl Type: dst_as Description destination (server) Autonomous System number

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Acl Type: proxy_auth Description authentication via external processes. proxy_auth requires an EXTERNAL authentication program to check name/ combinations (see authenticate_program ). Usage

acl aclname proxy_auth name... use REQUIRED instead of name to accept any valid name

Example acl ACLAUTH proxy_auth usha venkatesh balu deepa This acl is for authenticating s usha, venkatesh, balu and deepa by external programs. Warning proxy_auth can't be used in a transparent proxy. It collides with any authentication done by origin servers. It may seem like it works at first, but it doesn't. When a Proxy−Authentication header is sent but it is not needed during ACL checking the name is NOT logged in access.log.

Acl Type: proxy_auth_regex Description This is same as proxy_auth with a difference. That is it matches the pattern with names, which are given in authenticate_program Usage

acl aclname proxy_auth_regex [−i] pattern...

Acl Type: snmp_community Description SNMP community string matching Example acl aclname snmp_community public snmp_access aclname

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Acl Type: maxconn Description A limit on the maximum number of connections from a single client IP address. It is an ACL that will be true if the has more than maxconn connections open. It is used in http_access to allow/deny the request just like all the other acl types. Example acl some src 1.2.3.4 acl twoconn maxconn 5 http_access deny some twoconn http_access allow !twoconn Note maxconn acl requires client_db feature, so if you disabled that (client_db off) maxconn won't work.

Acl Type: req_mime_type Usage acl aclname req_mime_type pattern Description Regular expression pattern matching on the request content−type header Example acl aclname req_mime_type text This acl looks for the pattern "text" in request mime header

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Acl Type: arp Usage acl aclname arp ARP−ADDRESS Description Ethernet (MAC) address matching This acl is ed on Linux, Solaris, and probably BSD variants. To use ARP (MAC) access controls, you first need to compile in the optional code. Do this with the −−enable−arp−acl configure option: % ./configure −−enable−arp−acl ... % make clean % make If everything compiles, then you can add some ARP ACL lines to your squid.conf Default

acl all src 0.0.0.0/0.0.0.0 acl manager proto cache_object acl localhost src 127.0.0.1/255.255.255.255 acl SSL_ports port 443 563 acl Safe_ports port 80 21 443 563 70 210 1025−65535 acl Safe_ports port 280 # http−mgmt acl Safe_ports port 488 # gss−http acl Safe_ports port 591 # filemaker acl Safe_ports port 777 # multiling http acl CONNECT method CONNECT

Example acl ACLARP arp 11:12:13:14:15:16 ACLARP refers MACADDRESS of the ethernet 11:12:13:14:15:16 Note Squid can only determine the MAC address for clients that are on the same subnet. If the client is on a different subnet, then Squid cannot find out its MAC address.

Tag Name http_access Usage http_access allow|deny [!]aclname ... Description Allowing or denying http access based on defined access lists If none of the "access" lines cause a match, the default is the opposite of the last line in the list. If the last line was deny, then the default is allow. Conversely, if the last line is allow, the default will be deny. For these reasons, it is a good idea to have a "deny all" or "allow all" entry at the end of your access lists to avoid potential confusion Default

http_access allow manager localhost http_access deny manager http_access deny !Safe_ports http_access deny CONNECT !SSL_ports http_access deny all If there are no "access" lines present, the default is to allow the request

Example 1. To allow http_access for only one machine with MAC Address 00:08:c7:9f:34:41 2. To restrict access to work hours (9am − 5pm, Monday to Friday) from IP 192.168.2/24 3. Can i use multitime access control list for different s for different timing 4. Rules are read from top to bottom

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Caution The deny all line is very important. After all the http_access rules, if access isn't denied, it's ALLOWED !! So, specifying a LOT of http_access allow rules, and forget the deny all after them, is the same of NOTHING. If access isn't allowed by one of your rules, the default action ( ALLOW ) will be triggered. So, don't forget the deny all rule AFTER all the rules. And, finally, don't forget rules are read from top to bottom. The first rule matched will be used. Other rules won't be applied. Click here to See examples.

Tag Name i_access Usage i_access allow|deny [!]aclname ... Description i_access allow|deny [!]aclname ... Default

i_access deny all

Example i_access allow all − Allow I queries from everyone

Tag Name miss_access Usage miss_access allow|deny [!]aclname... Description Used to force your neighbors to use you as a sibling instead of a parent. For example: acl localclients src 172.16.0.0/16 miss_access allow localclients miss_access deny !localclients This means that only your local clients are allowed to fetch MISSES and all other clients can only fetch HITS. Default

By default, allow all clients who ed the http_access rules to fetch MISSES from us. miss_access allow all

Tag Name cache_peer_access Usage cache_peer_access cache−host allow|deny [!]aclname ... Description Similar to 'cache_peer_domain ' but provides more flexibility by using ACL elements. The syntax is identical to 'http_access' and the other lists of ACL elements. See 'http_access ' for further reference. Default

none

Example The following example could be used, if we want all requests from a specific IP address range to go to a specific cache server (for ing purposes, for example). Here, all the requests from the 10.0.1.* range are ed to proxy.visolve.com, but all other requests are handled directly.

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Using acls to select peers, acl myNet src 10.0.0.0/255.255.255.0 acl cusNet src 10.0.1.0/255.255.255.0 acl all src 0.0.0.0/0.0.0.0 cache_peer proxy.visolve.com parent 3128 3130 cache_peer_access proxy.visolve.com allow custNet cache_peer_access proxy.visolve.com deny all

Tag Name proxy_auth_realm Usage proxy_auth_realm string Description Specifies the realm name, which is to be reported to the client for proxy authentication (part of the text the will see when prompted for the name and ). Default

proxy_auth_realm Squid proxy−caching web server

Example proxy_auth_realm My Caching Server

Tag Name ident_lookup_access Usage ident_lookup_access allow|deny aclname... Description A list of ACL elements, which, if matched, cause an ident (RFC 931) lookup to be performed for this request. For example, you might choose to always perform ident lookups for your main multi− Unix boxes, but not for your Macs and PCs Default

By default, ident lookups are not performed for any requests ident_lookup_access deny all

Example To enable ident lookups for specific client addresses, you can follow this example: acl ident_aware_hosts src 198.168.1.0/255.255.255.0 ident_lookup_access allow ident_aware_hosts ident_lookup_access deny all Caution This option may be disabled by using −−disable−ident with the configure script.

Examples: (1) To allow http_access for only one machine with MAC Address 00:08:c7:9f:34:41 To use MAC address in ACL rules. Configure with option −enable−arp−acl. acl all src 0.0.0.0/0.0.0.0 acl pl800_arp arp 00:08:c7:9f:34:41 http_access allow pl800_arp http_access deny all

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(2) To restrict access to work hours (9am − 5pm, Monday to Friday) from IP 192.168.2/24 acl ip_acl src 192.168.2.0/24 acl time_acl time M T W H F 9:00−17:00 http_access allow ip_acl time_acl http_access deny all (3) Can i use multitime access control list for different s for different timing. AclDefnitions acl abc src 172.161.163.85 acl xyz src 172.161.163.86 acl asd src 172.161.163.87 acl morning time 06:00−11:00 acl lunch time 14:00−14:30 acl evening time 16:25−23:59

Access Controls http_access allow abc morning http_access allow xyz morning lunch http_access allow asd lunch This is wrong. The description follows: Here access line "http_access allow xyz morning lunch" will not work. So ACLs are interpreted like this ... http_access RULE statement1 AND statement2 AND statement3 OR http_access ACTION statement1 AND statement2 AND statement3 OR ........ So, the ACL "http_access allow xyz morning lunch" will never work, as pointed, because at any given time, morning AND lunch will ALWAYS be false, because both morning and lunch will NEVER be true at the same time. As one of them is false, and acl uses AND logical statement, 0/1 AND 0 will always be 0 (false). That's because this line is in two. If now read: http_access allow xyz AND morning OR http_access allow xyz lunch If request comes from xyz, and we're in one of the allowed time, one of the rules will match TRUE. The other will obviously match FALSE. TRUE OR FALSE will be TRUE, and access will be permitted. Finally Access Control looks... http_access allow abc morning http_access allow xyz morning http_access allow xyz lunch http_access allow asd lunch http_access deny all (4) Rules are read from top to bottom. The first rule matched will be used. Other rules won't be applied. Example: http_access allow xyz morning

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http_access deny xyz http_access allow xyz lunch If xyz tries to access something in the morning, access will be granted. But if he tries to access something at lunchtime, access will be denied. It will be denied by the deny xyz rule, that was matched before the 'xyz lunch' rule. ISTRATIVE PARAMETERS Tag Name cache_mgr Usage cache_mgr mailid Description Using this tag, we can specify the email−address of the local cache manager who will receive mail, if the cache dies. The default is "." In case squid dies, the mail will be sent to the given mailid. Default

cache_mgr

Example cache_mgr balu

Tag Name cache_effective_ Usage cache_effective_ id Description If the cache is run as root, it will change its effective/real UID to the UID specified below. The default is to change the UID to nobody. If Squid is not started as root, the default is to keep the current UID. Note that, if Squid is not started as root, then you cannot set http_port to a value lower than 1024. If Squid is started with the id squid, then the cache_effective_ will be given as squid. If it is started as root then the default value will be taken Default

cache_effective_ nobody

Example cache_effective_ squid Caution If the above directive is not configured properly then Squid will have problems in starting.

Tag Name cache_effective_group Usage cache_effective_group groupid Description If the cache is run as root, it will change its effective/real GID to the GID specified below. The default is to change the GID to nogroup. If Squid is not started as root, the default is to keep the current GID. Note that if Squid is not started as root then you cannot set http_port to a value lower than 1024. If the squid started with the groupid squid then the cache_effective_group will be given as squid. If it is started as root, then the default value will be taken. For further info on the above two tags, see Effective and group Default

cache_effective_group nogroup

Example cache_effective_group squid

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Caution If it is not configured properly, then squid may run in to problem.

Tag Name visible_hostname Usage visible_hostname anyhostname Description If you want to present a special hostname in error messages, etc then define this. Otherwise, the return value of gethostname () will be used. If you have multiple caches in a cluster and get errors about IP−forwarding, you must set them to have individual names with this setting. When the error message appears in the browser, it will show as it is generated from the visible_hostname. Default

none

Example visible_hostname www.visolve.com

Tag Name unique_hostname Usage unique_hostname hostname Description If you want to have multiple machines with the same 'visible_hostname' then you must give each machine a different unique_hostname' so that forwarding loops can be detected. In brief, Just set visible_hostname to the address the clients connects to, and unique_hostname to the externally visible address of each proxy. (address == ed domain name) Default

none

Example unique_hostname www.kovaiteam.com

Tag Name hostname_aliases Usage hostname_aliases Description A list of other DNS names that your cache has. This option is used to detect internal requests ( Cache Digests ), when a cache has more than one hostname in use. Default

none

Example hostname_aliases OPTIONS FOR THE CACHE REGISTRATION SERVICE This section contains parameters for the (optional) cache announcement service. This service is provided to help cache s locate one another in order to or create cache hierarchies. An 'announcement' message is sent (via UDP) to the registration service by Squid. By default, the announcement message is NOT SENT unless you enable it with 'announce_period' below. The announcement message includes your hostname, plus the following information from this configuration file:

• http_port 48

• i_port • cache_mgr All current information is processed regularly and made available on the Web at http://ircache.nlanr.net/Cache/Tracker/

Tag Name announce_period Usage announce_period time units Description This is how frequently to send cache announcements. To announce your cache, enable this tag. Default

The default is `0' which disables sending the announcement messages. announce_period 0

Example To send cache announcements every day, use this line announce_period 1 day

Tag Name Usage

announce_host announce_port announce_host hostname

announce_port port Description announce_host and announce_port set the hostname and port number where the registration message will be sent. Default

Hostname will default to 'tracker.ircache.net' and port will default to 3131. announce_host tracker.ircache.net announce_port 3131

Example announce_host cache.kovaiteam.com announce_port 3131

Tag Name announce_file Usage announce_file filename Description If the 'filename' argument is given, the contents of that file will be included in the announce message. See also announce_host and announce_port. Default

none

HTTPD−ACCELERATOR OPTIONS Tag Name httpd_accel_host Usage httpd_accel_host hostname(IP)|virtual Description This tag is used to set the hostname of the accelerated server. It is possible to have only one destination server and

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hence there can be only one occurrence of this line. If you are going to accelerate more than one server, or transparently cache traffic, you will have to use the word virtual instead of a hostname here Default

none

Example httpd_accel_host 172.16.1.115 httpd_accel_host virtual httpd_accel_host CACHE Caution Enabling httpd_accel_host disables proxy−caching and I. If you want these features enabled also, then set the httpd_accel_with_proxy' option.

Tag Name httpd_accel_port Usage httpd_accel_port port Description Accelerated requests can only be forwarded to one port: There is no table that associates accelerated hosts and a destination port. Squid will connect to the port that you set the httpd_accel_port value to. When acting as a front−end for a web server on the local machine, you will set up the web server to listen for connections on a different port (8000, for example), and set this squid.conf option to match the same value. If, on the other hand, you are forwarding requests to a set of slow backend servers, they will almost certainly be listening to port 80 (the default web−server port), and this option will need to be set to 80. If you want virtual port then specify the port as "0" Default

none

Example httpd_accel_port 80 httpd_accel_port 8000

Tag Name httpd_accel_single_host Usage httpd_accel_single_host on|off Description If you are running Squid as an accelerator and have a single backend server then set this to on. This causes Squid to forward the request to this server regardless of what any redirectors or Host headers says. Leave this at off if you have multiple backend servers, and use a redirector (or host table or private DNS) to map the requests to the appropriate backend servers. See also redirect_rewrites_host_header Default

httpd_accel_single_host off

Caution Note that the mapping needs to be a 1−1 mapping between requested and backend (from redirector) domain names or caching will fail, as caching is performed using the URL returned from the redirector.

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Tag Name httpd_accel_with_proxy Usage httpd_accel_with_proxy on|off Description If you use the httpd_accel_host option, Squid will stop recognizing cache requests. So that your cache can function both as an accelerator and as a web cache, you will need to set the httpd_accel_with_proxy option to on. Default

httpd_accel_with_proxy off

Tag Name httpd_accel_uses_host_header Usage httpd_accel_uses_host_header on|off Description HTTP/1.1 requests include a Host: header, which is basically the hostname from the URL. Squid can be an accelerator for different HTTP servers by looking at this header. However, Squid does NOT check the value of the Host header, so it opens a big security hole. It is recommended that this option remain disabled unless having good understanding. However, It is needed to enable this option if Squid run as a transparent proxy. Otherwise, virtual servers, which require the Host: header will not be properly cached. For detailed information, Click here Default

httpd_accel_uses_host_header off

Caution If Squid runs as a transparent proxy, It is needed to enable this option. MISCELLANEOUS Tag Name dns_testnames Usage dns_testnames URL Description The DNS tests exit as soon as the first site is successfully looked up This test can be disabled with the −D command line option. Default

dns_testnames netscape.com internic.net nlanr.net microsoft.com

Example dns_testnames visolve.com

Tag Name logfile_rotate Usage logfile_rotate NUMBER Description Specifies the number of logfile rotations to make when you type 'squid −k rotate'. The default is 10, which will rotate with extensions 0 through 9. Setting logfile_rotate to 0 will disable the rotation, but the logfiles are still closed and re−opened. This will enable you to rename the logfiles yourself just before sending the rotate signal. Default

logfile_rotate 10

Example logfile_rotate 5 Caution Note, the 'squid −k rotate' command normally sends a USR1 signal to the running squid process. In certain situations (e.g. on Linux with Async I/O), USR1 is used for other purposes; so −k rotate uses another signal. It is best to get in the habit of using 'squid −k rotate' instead of 'kill −USR1 '

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Tag Name append_domain Usage append_domain domainname Description Appends local domain name to hostnames without any dots in them. append_domain must begin with a period Default

none

Example append_domain .domain.com

Tag Name t_recv_bufsize Usage t_recv_bufsize (bytes) Description Size of receive buffer to set for T sockets. Probably just as easy to change your kernel's default. Default

Set to zero to use the default buffer size. By default, if this is set to zero, then it means it is using kernel's default. t_recv_bufsize 0 bytes

Tag Name err_html_text Usage err_html_text text Description This is used to specirfy the HTML text, which is to be included in error messages. Make this a "mailto" URL to your address, or may be just a link to your organizations Web page. To include this in your error messages, you must rewrite the error template files (found in the "$prefix/etc/errors" directory). Wherever you want the 'err_html_text' line to appear, insert a %L tag in the error template file Default

none

Example err_html_text [email protected] Consider you want to display this mail Id when access denied error occurs, then edit the corresponding file (ERR_ACCESS_DENIED in '$prefix/etc/errors' directory) with %L where this mail Id should be displayed.

Tag Name deny_info Usage deny_info err_page_name acl Description This can be used to return an ERR_ page for requests, which do not the 'http_access' rules. A single ACL will cause the http_access check to fail. If a 'deny_info' line exists for that ACL then Squid returns a corresponding error page. You may use ERR_ pages that come with Squid or create your own pages and put them into the configured errors/ directory Default

none

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Example If you want to deny domain 'deny.com' and want to display access denied message specifically, add these lines in conf. And add the file called ERR_CUSTOM_ACCESS_DENIED in $prefix/etc/errors/ directory with your own format. acl DSTDOMAIN dstdomain .deny.com http_access deny DSTDOMAIN http_access allow all deny_info ERR_CUSTOM_ACCESS_DENIED DSTDOMAIN So now if s try to browse 'deny.com' they will get your defined error message

Tag Name memory_pools Usage memory_pools on|off Description If set, Squid will keep pools of allocated (but unused) memory available for future use. If memory is a on your system and you believe your malloc library outperforms Squid routines, disable this. Default

memory_pools on

Tag Name memory_pools_limit Usage memory_pools_limit (bytes) Description If set to a non−zero value, Squid will keep at most the specified limit of allocated (but unused) memory in memory pools. All free() requests that exceed this limit will be handled by your malloc library. Squid does not pre−allocate any memory, just safe−keeps objects that otherwise would be free()d. Thus, it is safe to set memory_pools_limit to a reasonably high value even if your configuration will use less memory. If not set (default) or set to zero, Squid will keep all memory it can. That is, there will be no limit on the total amount of memory used for safe−keeping. Default

none By default, memory_pools is not set. So there is no default value for memory_pools_limit

Caution Used only with memory_pools on: To disable memory allocation optimization, do not set memory_pools_limit to 0. Set memory_pools to "off" instead. An overhead for maintaining memory pools is not taken into when the limit is checked. This overhead is close to four bytes per object kept. However, pools may actually _save_ memory because of reduced memory thrashing in your malloc library.

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Tag Name forwarded_for Usage forwarded_for on|off Description Current HTTP/1.1 does not provide any standard way of indicating the client address in the request. Since a number of people missed having the originating client address in the request, Squid now adds its own request header called "X−Forwarded−For" which looks like this: X−Forwarded−For: 192.1.2.3|unknown If set, Squid will include your system's IP address or name in the HTTP requests it forwards. By default it looks like this: X−Forwarded−For: 192.1.2.3 If you disable this, it will appear as X−Forwarded−For: unknown Default

forwarded_for on

Tag Name log_i_queries Usage log_i_queries on|off Description If set, I queries are logged to access.log. You may wish to disable this if your I load is very high to speed things up or to simplify log analysis Default

log_i_queries on

Tag Name i_hit_stale Usage i_hit_stale on|off Description If you want to return I_HIT for stale cache objects, set this option to 'on'. If you have sibling relationships with caches in other istrative domains, this should be 'off'. If you only have sibling relationships with caches under your control, then it is probably okay to set this to 'on' Default

i_hit_stale off

Tag Name minimum_direct_hops Usage minimum_direct_hops NUMBER Description If using the ICMP pinging stuff, do direct fetches for sites which are no more than this many hops away. This parameter plays a role in deciding latency Default

minimum_direct_hops 4

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Tag Name minimum_direct_rtt Usage minimum_direct_rtt time−units Description If using the ICMP pinging stuff, do direct fetches for sites which are no more than this many rtt milliseconds away. Default

minimum_direct_rtt 400

Tag Name cachemgr_wd Usage cachemgr_wd action action ... Description This tag is used to specify s for cachemgr operations. Some valid actions are (see cache manager menu for a full list): 5min 60min asndb authenticator cbdata client_list comm_incoming config * counters delay digest_stats dns events filedescriptors fqdncache histograms http_headers info io ipcache mem menu netdb non_peers objects pconn peer_select redirector refresh server_list shutdown * store_digest storedir utilization via_headers vm_objects * Indicates actions which will not be performed without a valid , others can be performed if not listed here. To disable an action, set the to "disable". To allow performing an action without a , set the to "none". Use the keyword "all" to set the same for all actions.

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cachemgr_wd secret shutdown cachemgr_wd lesssssssecret info stats/objects cachemgr_wd disable all Default

none

Tag Name store_avg_object_size Usage store_avg_object_size (kbytes) Description Average object size, used to estimate number of objects your cache can hold. To Estimate the number of objects your cache can hold: NUM_OBJ = cache_swap / store_avg_object_size Cache_swap is the size of the cache Default

The default is 13 KB. store_avg_object_size 13 KB

Tag Name store_objects_per_bucket Usage store_objects_per_bucket (kbytes) Description Target number of objects per bucket in the store hash table. Lowering this value increases the total number of buckets and also the storage maintenance rate. Then we estimate the number of hash buckets needed: NUM_BUCKETS = NUM_OBJ / store_objects_per_bucket NUM_OBJ is the number of objects your cache can hold, estimated by store_avg_object_size. Default

store_objects_per_bucket 20

Example store_objects_per_bucket 50

Tag Name client_db Usage client_db on|off Description If you want to disable collecting per−client statistics, then turn off client_db here Default

Tag Name Usage

client_db on

netdb_low netdb_high netdb_low entries

netdb_high entries Description The low and high water marks for the ICMP measurement database. These are counts, not percents. The defaults are 900 and1000. When the high water mark is reached, database entries will be deleted until the low mark is reached Default

netdb_low 900 netdb_high 1000

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Tag Name netdb_ping_period Usage netdb_ping_period time−units Description The minimum period for measuring a site. There will be at least this much delay between successive pings to the same network Default

netdb_ping_period 5 minutes

Tag Name query_icmp Usage query_icmp on|off Description If you want to ask your peers to include ICMP data in their I replies, enable this option. If your peer has configured Squid (during compilation) with '−−enable−icmp' then that peer will send ICMP pings to origin server sites of the URLs it receives. If you enable this option then the I replies from that peer will include the ICMP data (if available). Then, when choosing a parent cache, Squid will choose the parent with the minimal RTT to the origin server. When this happens, the hierarchy field of the access.log will be "CLOSEST_PARENT_MISS ". Default

query_icmp off

Tag Name test_reachability Usage test_reachability on|off Description When this is 'on', I MISS replies will be I_MISS_NOFETCH instead of I_MISS if the target host is NOT in the ICMP database, or has a zero RTT Default

test_reachability off

Tag Name buffered_logs Usage buffered_logs on|off Description Some log files (cache.log agent.log) are written with stdio functions, and as such they can be buffered or unbuffered. By default they will be unbuffered. Buffering them can speed up the writing slightly (though you are unlikely to need to worry). Default

buffered_logs off

Tag Name reload_into_ims Usage reload_into_ims on|off Description When you enable this option, client no−cache or "reload'' requests will be changed to If−Modified−Since requests. Doing this VIOLATES the HTTP standard. Enabling this feature could make you liable for problems, which it causes. See also refresh_pattern for a more selective approach. This option may be disabled by using −−disable−http−violations with the configure script. reload_into_ims off Default

reload_into_ims off

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Tag Name always_direct Usage always_direct allow|deny [!]aclname ... Description Here you can use ACL elements to specify requests, which should ALWAYS be forwarded directly to origin servers. This is mostly used while using cache_peer. See also never_direct . For Further reference on always_direct, please click here. Default

always_direct is by default deny.

Example For example, to always directly forward requests for local servers use something like: acl local−servers dstdomain .my.domain.net always_direct allow local−servers To always forward FTP requests directly, use acl FTP proto FTP always_direct allow FTP Example for denying specific domain acl local−external dstdomain .external.foo.net acl local−servers dstdomain .foo.net always_direct deny local−external always_direct allow local−servers Caution There is a similar, but opposite option named ' never_direct'. You need to be aware that "always_direct deny foo" is NOT the same thing as "never_direct allow foo". You may need to use a deny rule to exclude a more−specific case of some other rule.

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Tag Name never_direct Usage never_direct allow|deny [!]aclname ... Description never_direct is the opposite of always_direct. Please read the description for always_direct if you have not already. With 'never_direct' you can use ACL elements to specify requests, which should NEVER be forwarded directly to origin servers When always_direct and never_direct are deny (By default), Squid selects based on the request type and a number of other factors if a parent should be used or not, and if a parent could not be reached it will always fallback on direct. If always_direct is allow then Squid will always go direct to the source without considering any peers. If never_direct is allow then Squid will never attempt to go direct to the source. Instead it tries very hard to find a parent to send the request to. If no parent can be found then an error is returned. For Further reference on never_direct, please click here. Default

never_direct is by default deny.

Example For example, to force the use of a proxy for all requests, except those in your local domain use something like: acl local−servers dstdomain foo.net acl all src 0.0.0.0/0.0.0.0 never_direct deny local−servers never_direct allow all or if squid is inside a firewall and there are local intranet servers inside the firewall then use something like: acl local−intranet dstdomain .foo.net acl local−external dstdomain .external.foo.net always_direct deny local−external always_direct allow local−intranet never_direct allow all Caution It will be better to understand always_direct before enabling this tag

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Tag Name anonymize_headers Usage anonymize_headers allow|deny header_name ... Description This option replaces the old 'http_anonymizer' option with something that is much more configurable. You may now specify exactly which headers are to be allowed, or which are to be removed from outgoing requests. There are two methods of using this option. You may either allow specific headers (thus denying all others), or you may deny specific headers (thus allowing all others). For example, to achieve the same behavior as the old 'http_anonymizer standard' option, you should use: anonymize_headers deny From Referer Server anonymize_headers deny −Agent WWW−Authenticate Link Or, to reproduce the old 'http_anonymizer paranoid' feature you should use: anonymize_headers allow Allow Authorization Cache−Control anonymize_headers allow Content−Encoding Content−Length anonymize_headers allow Content−Type Date Expires Host anonymize_headers allow If−Modified−Since Last−Modified anonymize_headers allow Location Pragma Accept anonymize_headers allow Accept−Encoding Accept−Language anonymize_headers allow Content−Language Mime−Version anonymize_headers allow Retry−After Title Connection anonymize_headers allow Proxy−Connection Default

By default, all headers are allowed (no anonymizing is performed).

Example anonymize_headers deny Proxy−Connection Caution You cannot mix "allow" and "deny". All 'anonymize_headers' lines must have the same second argument.

Tag Name fake__agent Usage fake__agent String Description If you filter the −Agent header with ' anonymize_headers' it may cause some Web servers to refuse your request. Use this to fake one up. Default

none

Example fake__agent Nutscrape/1.0 (/M; 8−bit)

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Tag Name icon_directory Usage icon_directory directorypath/directoryname Description This tag is to specify the location where the icons are stored Default

These are normally kept in /usr/local/squid/etc/icons

Example icon_directory /etc/icons

Tag Name error_directory Usage error_directory directorypath/directoryname Description If you wish to create your own versions of the default (English) error files, either to customize them to suit your language or company, copy the template English files to another directory and point this tag at them Default

These are normally kept in /usr/local/squid/etc/errors

Example icon_directory /etc/errors

Tag Name minimum_retry_timeout Usage minimum_retry_timeout (seconds) Description This specifies the minimum connect timeout, when the connect timeout is reduced to compensate for the availability of multiple IP addresses. When a connection to a host is initiated, and that host has several IP addresses, the default connection timeout is reduced by dividing it by the number of addresses. So, a site with15 addresses would then have a timeout of 8 seconds for each address attempted. To avoid having the timeout reduced to the point where even a working host would not have a chance to respond, this setting is provided. Default

The default, and the minimum value, is five seconds, and the maximum value is sixty seconds, or half of connect_timeout, which ever is greater and less than connect_timeout. minimum_retry_timeout 5 seconds

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Tag Name maximum_single_addr_tries Usage maximum_single_addr_tries NUMBER Description This sets the maximum number of connection attempts for a host that only has one address (for multiple−address hosts, each address is tried once) Default

The default value is three tries, the (not recommended) maximum is 255 tries. maximum_single_addr_tries 3

Caution A warning message will be generated if it is set to a value greater than ten

Tag Name snmp_port Usage snmp_port port Description Squid can now serve statistics and status information via SNMP. If you don't wish to use SNMP, set this to "0". The snmpd daemon is a server that s both the Simple Network Management Protocol v2 and v1. It receives and responds to SNMP messages sent to the SNMP port on the local machine. snmpd.conf is the configuration file which defines how the ucd−smnp SNMP agent operates. Default

By default it listens to port 3401 on the machine. snmp_port 3401

Caution SNMP requires use of the −−enable−snmp configure command line option

Tag Name snmp_access Usage snmp_access allow|deny [!]aclname ... Description Allowing or denying access to the SNMP port. This option is only available if Squid is rebuilt with the −−enable−snmp option Default

All access to the agent is denied by default.

Example snmp_access allow snmppublic localhost snmp_access deny all

Tag Name Usage

snmp_incoming_address snmp_outgoing_address snmp_incoming_address IPAddress snmp_outgoing_address IPAddress

Description Just like 'udp_incoming_address' above, but for the SNMP port. This option is only available if Squid is rebuilt with the−−enable−snmp option

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snmp_incoming_address is used for the SNMP socket receiving messages from SNMP agents. snmp_outgoing_address is used for SNMP packets returned to SNMP agents. Default

The default behavior is to not bind to any specific address. snmp_incoming_address 0.0.0.0 snmp_outgoing_address 255.255.255.255

Example snmp_incoming_address 172.16.1.115 snmp_outgoing_address 172.16.1.114 Caution snmp_incoming_address and snmp_outgoing_address cannot have the same value since they both use port 3130.

Tag Name as_whois_server Usage as_whois_server Server−Name Description WHOIS server to query for AS numbers. NOTE: AS numbers are queried only when Squid starts up, not for every request. Default

as_whois_server whois.ra.net

Tag Name wc_router Usage wc_router Router−IPAddress Description This option is used to define the WC ``home'' router for Squid. Setting the 'wc_router' to 0.0.0.0 (the default) disables WC Default

wc_router 0.0.0.0

Tag Name wc_version Usage wc_version Version Description According to some s, Cisco IOS 11.2 only s WC version 3. If you're using that version of IOS, change this value to 3. Default

wc_version 4

Tag Name wc_incoming_address Usage wc_incoming_address IPAddress Description Use this option if you require WC messages to be received on only one interface. Do NOT use this option if you're unsure how many interfaces you have, or if you know you have only one interface Default

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The default behavior is to not bind to any specific address wc_incoming_address 0.0.0.0 Caution wc_incoming_address and wc_outgoing_address cannot have the same value since they both use port 2048.

Tag Name wc_outgoing_address Usage wc_outgoing_address IPAddress Description Use this option if you require WC messages to be sent out on only one interface. Do NOT use this option if you're unsure how many interfaces you have, or if you know you have only one interface Default

wc_outgoing_address 255.255.255.255 (The default behavior is to not bind to any specific address)

Caution wc_incoming_address and wc_outgoing_address cannot have the same value since they both use port 2048. DELAYPOOL PARAMETERS Tag Name delay_pools Usage delay_pools numbers Description This represents the number of delay pools to be used. For example, if you have one− class 2 delay pool and one− class 3 delay pool, you have a total of 2 delay pools. Delay pools allow you to limit traffic for clients or client groups, with various features. Objects retrieved from the cache will not be delayed. Only the object from the server will be delayed. Default

delay_pools 0

Example delay_pools 2 # 2 Delay pools Caution To enable this option, you must use −−enable−delay−pools with the # configure script.

Tag Name delay_class Usage delay_class number (delay−pool number), number (delay class) Description This defines the class of each delay pool. There must be exactly one delay_class line for each delay pool. For example, to define two delay pools, one of class 2 and one of class 3, the settings will be like as given in the example. For details on the delay pool classes see Glossary. Default

none

Example delay_pools 2 # 2 delay pools delay_class 1 2 # pool 1 is a class 2 pool delay_class 2 3 # pool 2 is a class 3 pool Caution To enable this option, you must use −−enable−delay−pools with the # configure script.

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Tag Name delay_access Usage delay_access allow acl name|deny acl name Description This is used to determine which delay pool a request falls into. The first matched delay pool is always used, i.e., if a request falls into delay pool number one, no more delay are checked, otherwise the rest are checked in order of their delay pool number until they have all been checked. For example, if you want pool_1_acl in delay pool 1 and pool_2_acl in delay pool 2, then look at the example below. Default

none

Example To specify which pool a client falls into, create ACLs which specifies the ip ranges for each pool, and use the following: delay_access 1 allow pool_1_acl delay_access 1 deny all delay_access 2 allow pool_2_acl delay_access 2 deny all Caution To enable this option, you must use −−enable−delay−pools with the # configure script.

Tag Name Usage

delay_parameters delay_parameters pool aggregate (for delay_class 1 networks) delay_parameters pool aggregate individual (for delay_class 2 networks) delay_parameters pool aggregate network individual (for delay_class 3 networks)

Description This defines the parameters for a delay pool. Each delay pool has number of "buckets" associated with it, as explained in the description of delay_class. For a class 1,2 and 3 delay pool, the syntax is given in the usage. For a Glossary of term related to delay_pool see Glossary . Default

none

Example 1: acl tech src 192.168.0.1−192.168.0.20/32 acl no_hotmail url_regex −i hotmail acl all src 0.0.0.0/0.0.0.0 delay_pools 1 #Number of delay_pool 1 delay_class 1 1 #pool 1 is a delay_class 1 delay_parameters 1 100/100 delay_access 1 allow no_hotmail !tech In the above example, hotmail s are limited to the speed specified in the delay_class. IP's in the ACL tech are allowed in the normal bandwidth. You can see the usage of bandwidth through cachemgr.cgi. Example 2: acl all src 0.0.0.0/0.0.0.0 # might already be defined delay_pools 1 delay_class 1 1 delay_access 1 allow all delay_parameters 1 64000/64000 # 512 kbits == 64 kbytes per second The above example tells that the squid is limited to the bandwidth of 512k. For ACL you can go here

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Caution To enable this option, you must use −−enable−delay−pools with the # configure script.

Tag Name delay_initial_bucket_level(percent, 0−100) Usage delay_initial_bucket_level bytes Description The initial bucket percentage is used to determine how much is put in each bucket when squid starts, is reconfigured, or first notices a host accessing it (in class 2 and class 3, individual hosts and networks only have buckets associated with them once they have been "seen" by squid). Default

delay_initial_bucket_level 50(bytes)

Caution This option is only available if Squid is rebuilt with the −−enable−delaypools option.

Tag Name

incoming_i_average incoming_http_average incoming_dns_average min_i_poll_cnt min_dns_poll_cnt min_http_poll_cnt TagName Number

Usage Description This describes the algorithms used for the above tags. INCOMING sockets are the I and HTTP ports. We need to check these fairly regularly, but how often? When the load increases, we want to check the incoming sockets more often. If we have a lot of incoming I, then we need to check these sockets more than if we just have HTTP. The variables 'incoming_i_interval' and 'incoming_http_interval'determine how many normal I/O events to process before checking incoming sockets again. Note we store the incoming_interval multiplied by a factor of (2^INCOMING_FACTOR) to have some pseudo−floating point precision. The variable 'i_io_events' and 'http_io_events' counts how many normal I/O events have been processed since the last check on the incoming sockets. When io_events >incoming_interval, its time to check incoming sockets. Every time we check incoming sockets, we count how many new messages or connections were processed. This is used to adjust the incoming_interval for the next iteration. The new incoming_interval is calculated as the current incoming_interval plus what we would like to see as an average number of events minus the number of events just processed. incoming_interval = incoming_interval + target_average − number_of_events_processed. There are separate incoming_interval counters for both HTTP and I events. You can see the current values of the incoming_interval, as well as a histogram of 'incoming_events' by asking the cache manager for 'comm_incoming', e.g.: % ./client mgr:comm_incoming Default

incoming_i_average 6 incoming_http_average 4 incoming_dns_average 4 min_i_poll_cnt 8 min_dns_poll_cnt 8 min_http_poll_cnt 8

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Caution −We have MAX_INCOMING_INTEGER as a magic upper limit on incoming_interval for both types of sockets. At the largest value the cache will effectively be idling. −The higher the INCOMING_FACTOR, the slower the algorithm will respond to load spikes/increases/decreases in demand. A value between 3 and 8 is recommended.

Tag Name max_open_disk_fds Usage max_open_disk_fds number Description This specifies the maximum file descriptor squid can use to open files. To avoid having disk as the I/O bottleneck, Squid can optionally by the on−disk cache if more than this amount of disk file descriptors are open. A value of 0 indicates no limit Default

max_open_disk_fds 0

Tag Name offline_mode Usage offline_mode on|off Description Enable this option and Squid will never try to validate cached objects. offline_mode gives access to more cached information than the proposed feature would allow (stale cached versions, where the origin server should have been ed). Default

offline_mode off

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Tag Name uri_whitespace Usage uri_whitespace options Description The action to be done on the requests that have whitespace characters in the URI is decided with this tag. Available options: strip: The whitespace characters are stripped out of the URL. This is the behavior recommended by RFC2616. deny: The request is denied. The receives an "Invalid Request" message. allow: The request is allowed and the URI is not changed. The whitespace characters remain in the URI. Note the whitespace is ed to redirector processes if they are in use. Encode: The request is allowed and the whitespace characters are encoded according to RFC1738. This could be considered a violation of the HTTP/1.1 RFC because proxies are not allowed to rewrite URI's. chop: The request is allowed and the URI is chopped at the first whitespace. This might also be considered as a violation. Default

uri_whitespace strip

Example uri_whitespace chop

Tag Name broken_posts Usage broken_posts allow|deny acl name Description A list of ACL elements which, if matched, causes Squid to send a extra CRLF pair after the body of a PUT/POST request. Some HTTP servers have broken implementations of PUT/POST, and rely on an extra CRLF pair sent by some WWW clients. Default

none

Example acl buggy_server url_regex ^http://.... broken_posts allow buggy_server

Tag Name mcast_miss_addr Usage mcast_miss_addr enable|disable Description If you enable this option, every "cache miss" URL will be sent out on the specified multicast address. This option is only available if Squid is rebuilt with the −DMULTICAST_MISS_STREAM option. Default

mcast_miss_addr 255.255.255.255

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Caution This option should be enabled only after a careful understanding. See multicast

Tag Name mcast_miss_ttl Usage mcast_miss_ttl time−units Description This is the time−to−live value for packets multicasted when multicasting off cache miss URLs is enabled. This option is only available if Squid is rebuilt with the −DMULTICAST_MISS_TTL option. Default

mcast_miss_ttl 16

Tag Name mcast_miss_port Usage mcast_miss_port port no Description This is the port number to be used in conjunction with 'mcast_miss_addr'. This option is only available if Squid is rebuilt with the −DMULTICAST_MISS_TTL option. Default

mcast_miss_port 3135

Caution This tag is used only when you enable mcast_miss_addr

Tag Name mcast_miss_encode_key Usage mcast_miss_encode_key enable|disable Description The URLs that are sent in the multicast miss stream are encrypted. This is the encryption key. This option is only available if Squid is rebuilt with the −DMULTICAST_MISS_STREAM option. Default

mcast_miss_encode_key XXXXXXXXXXXXXXX

Tag Name nonhierarchical_direct Usage nonhierarchical_direct on|off Description By default, Squid will send any non−hierarchical requests (matching hierarchy_stoplist or not cacheable request type) direct to origin servers. If you set this to off, then Squid will prefer to send these requests to parents. Note that in most configurations, by turning this off you will only add latency to this request without any improvement in global hit ratio. If you are inside a firewall then see never_direct instead of this directive. Default

nonhierarchical_direct on

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Tag Name prefer_direct Usage prefer_direct on|off Description Normally Squid tries to use parents for most requests. If you by some reason like it to first try going direct and only use a parent if going direct fails then set this to off. By combining non hierarchical_direct off and prefer_direct on you can set up Squid to use a parent as a backup path if going direct fails. Default

prefer_direct off

Tag Name strip_query_ Usage strip_query_ on|off Description Squid by default does not log query parameters. These parameters are however forwarded to the server verbatim. If we want to enable logging of query parameters, the strip_query_ directive can be used . By default, Squid strips query from requested URLs before logging. This protects your 's privacy Default

strip_query_ on

Tag Name coredump_dir Usage coredump_dir directory Description By default Squid leaves core files in the first cache_dir directory. If you set 'coredump_dir' to a directory that exists,Squid will chdir() to that directory at startup and coredump files will be left there. Default

none

Example coredump_dir /usr/local

Tag Name redirector_by Usage redirector_by on|off Description When this is 'on', a request will not go through the redirector if all redirectors are busy. If this is 'off' and the redirector queue grows too large, Squid will exit with a FATAL error and ask you to increase the number of redirectors. You should only enable this if the redirectors are not critical to your caching system.If you use redirectors for access control, and you enable this option,then s may have access to pages that they should not be allowed to request. Default

redirector_by off

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Tag Name digest_generation Usage digest_generation on|off Description This controls whether the server will generate a Cache Digest of its contents. By default, Cache Digest generation is enabled if Squid is compiled with USE_CACHE_DIGESTS defined. This option is only available if Squid is rebuilt with the −−enable−cache−digests option. Default

digest_generation on

Tag Name ignore_unknown_nameservers Usage ignore_unknown_nameservers on|off Description By default Squid checks that DNS responses are received from the same IP addresses that they are sent to. If they don't match, Squid ignores the response and writes a warning message to cache.log. You can allow responses from unknown nameservers by setting this option to 'off'. Default

ignore_unknown_nameservers on

Tag Name digest_bits_per_entry Usage digest_bits_per_entry number Description This is the number of bits of the server's Cache Digest, which will be associated with the Digest entry for a given HTTP Method and URL (public key) combination. The default is 5. This option is only available if Squid is rebuilt with the −−enable−cache−digests option. Default

digest_bits_per_entry 5

Tag Name digest_rebuild_period Usage digest_rebuild_period time−units Description This is the number of seconds between Cache Digest rebuilds. By default the server's Digest is rebuilt every hour. This option is only available if Squid is rebuilt with the −−enable−cache−digests option. Default

digest_rebuild_period 1 hour

Tag Name digest_rewrite_period Usage digest_rewrite_period time−units Description This is the number of seconds between Cache Digest writes to disk. By default the server's Digest is written to disk every hour. This option is only available if Squid is rebuilt with the−−enable−cache−digests option. Default

digest_rewrite_period 1 hour

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Tag Name digest_swapout_chunk_size Usage digest_swapout_chunk_size bytes Description This is the number of bytes of the Cache Digest to write to disk at a time. It defaults to 4096 bytes (4KB), the Squid default swap page. This option is only available if Squid is rebuilt with the −−enable−cache−digests option. Default

digest_swapout_chunk_size 4096 bytes

Tag Name digest_rebuild_chunk_percentage Usage digest_rebuild_chunk_percentage %(0 to 100) Description This is the percentage of the Cache Digest to be scanned at a time. By default it is set to 10% of the Cache Digest. This option is only available if Squid is rebuilt with the −−enable−cache−digests option. Default

digest_rebuild_chunk_percentage 10

Tag Name chroot Usage chroot enable|disable Description Squid by default does not fully drop root privileges because it may be required during reconfigure.So use this directive to have Squid do a chroot() while initializing. This also causes Squid to fully drop root privileges after initializing . Squid only drops all root privilegies when chroot_dir is used. Without chroot_dir it runs as root with effective nobody. This means, for example, that if you use a HTTP port less than 1024 and try to reconfigure, you will get an error . Default

none

Tag Name server_persistent_connections Usage server_persistent_connections on|off Description Persistent connection for clients and servers. By default, Squid uses persistent connections (when allowed) with its clients and servers. You can use these options to disable persistent connections with clients and/or servers. Default

server_persistent_connections on

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Tag Name client_persistent_connections Usage client_persistent_connections on|off Description Persistent connection for clients and servers. By default, Squid uses persistent connections (when allowed) with its clients and servers. You can use these options to disable persistent connections with clients and/or server. Related information : If the browser is talking to web server directly, socket can be closed after it is done using keep−alive directive in apache configuration file. The same thing can be done in Squid using these directives client_persistent_connections and server_persistent_connections. Default

client_persistent_connections on

Tag Name pipeline_prefetch Usage pipeline_prefetch on|off Description To boost the performance of pipelined requests to closer match that of a non−proxied environment Squid tries to fetch up to two requests in parallell from a pipeline. Default

pipeline_prefetch on

Tag Name extension_methods Usage extension_methods request method Description Squid only knows about standard HTTP request methods. Unknown methods are denied, unless you add them to this list. You can add up to 20 additional "extension" methods here. Default

none

Tag Name high_response_time_warning Usage high_response_time_warning msec Description If the one−minute median response time exceeds this value, Squid prints a WARNING with debug level 0 to get the s attention. The value is in milliseconds. Default

high_response_time_warning 0

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Tag Name high_page_fault_warning Usage high_page_fault_warning time−units Description If the one−minute average page fault rate exceeds this value, Squid prints a WARNING with debug level 0 to get the s attention. The value is in page faults per second. Default

high_page_fault_warning 0

Tag Name high_memory_warning Usage high_memory_warning number Description If the memory usage (as determined by mallinfo) exceeds value, Squid prints a WARNING with debug level 0 to get the s attention. Default

high_memory_warning 0

Tag Name store_dir_select_algorithm Usage store_dir_select_algorithm algorithm type Description Squid currently s two algorithms for selecting cache directories for new objects: least−load and round−robin. Set this to 'round−robin' as an alternative. Default

store_dir_select_algorithm least_load

Tag Name ie_refresh Usage ie_refresh on|off Description Microsoft Internet Explorer up until version 5.5 Service Pack 1 has an issue with transparent proxies, where in it is impossible to force a refresh. Turning this on provides a partial fix to the problem, by causing all IMS−REFRESH requests from older IE versions to check the origin server for fresh content. This reduces hit ratio by some amount (~10%), but allows s to actually get fresh content when they want it. Note that because Squid cannot tell if the is using 5.5 or 5.5SP1, the behavior of 5.5 is unchanged from old versions of Squid (i.e. a forced refresh is impossible).Newer versions of IE will, hopefully, continue to have the new behavior and will be handled based on that assumption. This option defaults to the old Squid behavior, which is better for hit ratios but worse for clients using IE, if they need to be able to force fresh content. Default

ie_refresh off

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GLOSSARY parent In a parent relationship, the child cache will forward requests to its parent cache. If the parent does not hold a requested object, it will forward the request on behalf of the child. A cache hierarchy should closely follow the underlying network topology. Parent caches should be located along the network paths towards the greater Internet. For example, if your Internet Service Provider (ISP) operates a cache, it should probably be a parent to yours, since your Web traffic will have to travel along your ISP's infra structure anyway.

sibling In a sibling relationship, a peer may only request objects already held in the cache; a sibling can not forward cache misses on behalf of the peer. The sibling relationship should be used for caches ``nearby'' but not in the direction of your route to the Internet. For example, it may make sense for a number of department−specific caches within an organization to have sibling relationships among them. This approach is even more compelling when there is no parent cache available for the organization as a whole.

Multicast and Unicast A unicast packet is the complete opposite: one machine is talking to only one other machine. All T connections are unicast, since they can only have one destination host for each source host. UDP packets are almost always unicast too, though they can be sent to the broadcast address so that they reach every single machine in some cases. A multicast packet is from one machine to one or more. The difference between a multicast packet and a broadcast packet is that hosts receiving multicast packets can be on different lans, and that each multicast data−stream is only transmitted between networks once, not once per machine on the remote network. Rather than each machine connecting to a video server, the multicast data is streamed per−network, and multiple machines just listen−in on the multicast data once it's on the network.

Netmask An IP address has two components, the network address and the host address. For example, consider the IP address 172.16.1.25. Assuming this is part of a Class B network, the first two numbers (172.16) represent the Class B network address, and the second two numbers (1.25) identify a particular host on this network. Subnetting enables the network to further divide the host part of the address into two or more subnets. In this case, a part of the host address is reserved to identify the particular subnet. This is easier to see if we show the IP address in binary format. The full address is: 11111000.00001000.00000001.00011001 The Class B network part is: 11111000.00001000 and the host address is 00000001.00011001 If the subnetmask for this IP Address is 255.255.255.0,11111111.11111111.11111111.00000000 (binary). The resultant Subnet Address is got by bitwise AND operations. If this network is divided into 255 subnets, then the first 8 bits of the host address (00000000) are reserved for identifying the subnet. 11111000.00001000.00000001.00000000 Hence, resultant is 172.16.1.0. It refers IPAddress from 172.16.1.1 to172.16.1.255.

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FileSystems in Squid The cache_dir type in Squid has nothing to do with the underlying filesystem type, it defines the storage method / implementation. Currently Squid has 4 different implementations: ufs :− On top of a normal filesystem ing directories and files. aufs :− As "ufs", but using threads to implement non−blocking disk I/O diskd :− As "ufs", but using a separate process to implement non−blocking disk I/O coss :− An experimental "raw" filesystem, where all objects are stored in one big file. Other storage methods are being worked upon Kind of diskd is designed to work around the problem of blocking IO in a unix process. async ufs gets around this by using threads to complete disk IO. diskd uses external processes to complete disk IO. Asyncufs works just that little bit faster, but only works on systems where threads can do async disk IO without blocking the main process. Systems with −threads (eg FreeBSD) can not use this effectively. Diskd, being implemented as an external process, gets around this. If cache is slightly active, then the difference cannot be noticed. diskd/aufs are only useful when the cache is under high load. In case it was not clear, asyncronous I/O (diskd/aufs) is beneficial for single drive configurations with "higher" request loads, in many cases allowing you to push about 100% more I/O thru the drive before latency creeps up too high. For multiple drive configurations, it is almost a requirement to be able to use the I/O capacity of the extra drives. Without it, a multiple disk configuration is effectively limited to almost the speed of a single disk configuration. With asyncronous I/O, the disk I/O scales quite well (at least for the first few drives, other limits gets very apparent when you have more than ~3 drives).

Cache peer Options proxy−only

Data retrieved from this remote cache will not be stored locally, but retrieved again on any subsequent request. By default, Squid will store objects it retrieves from other caches: by having the object available locally it can return the object fast, if it is requested again. This feature is often useful in a cluster of sibling caches to prevent each cache from holding every object. When the caches are close to each other (e.g. on the same ethernet segment), then it costs relatively little to transfer an object from one to the other. While this is good for latency, it can be a waste of bandwidth, especially if the other cache is on the same piece of ethernet. In the examples section of this chapter,we use this option when load−balancing between two cache servers.

Weight

If more than one cache server has an object (based on the result of an I query), Squid decides which cache to get the data from the cache that responded fastest. If you want to prefer one cache over another, you can add a weight value to the preferred cache's config line. Larger values are preferred. Squid times how long each I request takes (in milliseconds), and divides the time by the weight value, using the cache with the smallest result. A higher weight will artificially lower the calculated RTT between peers, thereby favoring it in the selection algorithm. Your weight value should thus not be an unreasonable value. ttl

An outgoing multicast packet has a ttl (Time To Live) value, which is used to ensure that loops are not created. Each time a packet es through a router, the router decrements this ttl value, and the value is then checked. Once the value reaches zero, the packet is dropped. If you want multicast packets to stay on your local network, you would set

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the ttl value to 1. The first router to see the packet would decrement the packet, discover the ttl was zero and discard it. This value gives you a level of control on how many multicast routers will see the packet. You should set this value carefully, so that you limit packets to your local network or immediate multicast peers (larger multicast groups are seldom of any use: they generate too many responses, and when geographically dispersed, may simply add latency. You also don't want crackers picking up all your I requests by ing the appropriate multicast group.) no− query

Squid will send I requests to all configured caches. The response time is measured, and used to decide which parent to send the HTTP request to. There is another function of these requests: if there is no response to a request, the cache is marked down. If you are communicating with a cache that does not I, you must use the no−query option: if you don't, Squid will consider that cache down, and attempt to go directly to the destination server. (If you want, you can set the I port on the config line to point to the echo port, port 7. Squid will then use this port to check if the machine is available. Note that you will have to configure inetd.conf to the UDP echo port.) This option is normally used in conjunction with the default option and round−robin option. cache_peer proxy.visolve.com1 parent 3128 3130 no−query default Default

This sets the host to be the proxy of last resort. If no other cache matches a rule (due to acl or domain filtering), this cache is used. If you have only one way of reaching the outside world, and it doesn't I, you can use the default and no−query options to ensure that, all queries are ed through it. If this cache is then down, the client will see an error message (without these options, Squid would attempt to route around the problem.) round−robin This option must be used on more than one cache_peer line to be useful. Connections to caches configured with this options are spread evenly (round−robined) among the caches. This can be used by client caches to communicate with a group of loaded parents, so that load is spread evenly. If you have multiple Internet connections, with a parent cache on each side, you can use this option to do some basic load−balancing of the connections. In other words,the round−robin option is similar to default, except that Squid forwards the request to the parent with the lowest use count. The cache_peer_domain restrictions still apply, of course. A typical configuration might look like: cache_peer proxy.visolve.com1 parent 3128 3130 round−robin no−query cache_peer proxy.visolve.com2 parent 3128 3130 round−robin no−query cache_peer proxy.visolve.com3 parent 3128 3130 round−robin no−query Squid treats all round−robin parents equally. It is not currently possible to, e.g., forward 25% of the requests to one parent and 75% to another. no−net−dbexchange

If your cache was configured to keep ICMP (ping) timing information with the −−enable−icmp configure option, your cache will attempt to retrieve the remote machine's ICMP timing information from any peers. If you don't want this to happen (or the remote cache doesn't it), you can use the no−netdb−exchange option to stop Squid from requesting this information from the cache no−delay

Hits from other caches will normally be included into a client's delay−pool information. If you have two caches load−balancing, you don't want the hits from the other cache to be limited. You may also want hits from caches in a nearby hierarchy to come down at full speed, not to be limited as if they were misses. Use the no−delay option to ensure that requests come down at their full speed.

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Caches can be configured to use names and s on accesses. To authenticate with a parent cache, you can enter a name and using this tag. Note that, the HTTP protocol makes authenticating to multiple cache servers impossible: you cannot chain together a string of proxies, each one requiring authentication. You should only use this option if this is a personal proxy. Round Trip time

It is the time interval between the sending of the first byte of an HTTP request for the request, until the last bytes of the server response has arrived at the requesting web client.

Probe Squid will wait for up to dead_peer_timeout seconds after sending out an I request before deciding to ignore a peer. With a multicast group, peers can leave and at will, and it should make no difference to a client. This presents a problem for Squid: it can't wait for a number of seconds each time (whatif thecaches are on the same network, and responses come back in milliseconds: the waiting just adds latency.) Squid gets around this problem by sending I probes to the multicast address occasionally. Each host in the group responds to the probe, and Squid will know how many machines are currently in the group. When sending a real request, Squid will wait until it gets atleast as many responses as were returned in the last probe: if more arrive, great. If less arrive, though, Squid will wait until the dead_peer_timeout value is reached. If there is still no reply, Squid marks that peer as down, so that all connections are not held up by one peer.

What is the httpd−accelerator mode? An accelerator caches incoming requests for outgoing data (i.e., that which you publish to the world). It takes load away from your HTTP server and internal network. You move the server away from port 80 (or whatever your published port is), and substitute the accelerator, which then pulls the HTTP data from the ``real" HTTP server (only the accelerator needs to know where the real server is). The outside world sees no difference (apart from an increase in speed, with luck).

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The httpd_accel_uses_host_header Option The httpd_accel_uses_host_header option. A normal HTTP request consists of three values: the type of transfer (normally a GET, which is used for s); the path and filename to be retrieved (or executed, in the case of a cgi program); and the HTTP version. This layout is fine if you only have one web site on a machine. On systems where you have more than one site, though, it makes life difficult: the request does not contain enough information, since it doesn't include information about the destination domain. Most operating systems allow you to have IP aliases, where you have more than one IP address per network card. By allocating one IP per hosted site, you could run one web server per IP address. Once the programs were made more efficient, one running program could act as a server for many sites: the only requirement was that you had one IP address per domain. Server programs would find out which of the IP addresses clients were connected to, and would serve data from different directories for each IP. There are a limited number of IP addresses, and they are fast running out. Some systems also have a limited number of IP aliases, which means that you cannot host more than a (fairly arbitrary) number of web sites on machine. If the client were to the destination host name along with the path and filename, the web server could listen to only one IP address, and would find the right destination directores by looking in a simple hostname table. From version 1.1 on, the HTTP standard s a special Host header, which is ed along with every outgoing request. This header also makes transparent caching and acceleration easier: by pulling the host value out of the headers, Squid can translate a standard HTTP request to a cache−specific HTTP request, which can then be handled by the standard Squid code. Turning on the httpd_accel_uses_host_header option enables this translation. You will need to use this option when doing transparent caching. It's important to note that acls are checked before this translation. You must combine this option with strict source−address checks, so you cannot use this option to accelerate multiple backend servers (this is certain to change in a later version of Squid).

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The "always direct" and "never direct" tags Squid checks all always_direct tags before it checks any never_direct tags. If a matching 'always_direct tag' is found, Squid will not check the never_direct tags, but decides which cache to talk to immediately. This behavior is demonstrated by the following example here, Squid will attempt to go the machine intranet, even though the same host is also matched by all acl. Bying a parent for a local machine cache_peer proxy.visolve.com parent 3128 3130 acl all src 0.0.0.0/0.0.0 acl localmachines dstdomain intranet.mydomain.example never_direct allow all always_direct allow localmachines i.e., Let's consider a request destined for the web server intranet.mydomain.example. Squid first works through all the always_direct lines; the request is matched by the first (and only) line. The never_direct and always_direct tags are acl−operators, which means that the first match is considered. In this illustration, the matching line instructs Squid to go directly when the acl matches, so all neighboring peers are ignored for this request. If the line used the deny keyword instead of allow, Squid would have simply skipped on to checking of the former never_direct lines. Now, suppose, a request arrives for an external host. Squid works through the always_direct lines, and finds that none of them match. The never_direct lines are then checked. The all acl matches the connection, so Squid marks the connection as never to be forwarded directly to the origin server.

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Access.log details The native access.log has ten (10) fields.There is one entry here for each HTTP (client) request and each I Query. HTTP requests are logged when the client socket is closed. A singledash (−) indicates unavailable data. 1. Timestamp The time when the client socket is closed. The format is 'Unix time' (seconds since Jan 1, 1970) with millisecond resolution. This can be modified to visible format by 'cat access.log | perl −nwe 's/^(\d+)/localtime($1)/e; print';. 2. Elapsed Time The elapsed time of the request, in milliseconds. This is time between the accept() and close() of the client socket. 3. Client Address The IP address of the connecting client, or the FQDN if the 'log_fqdn' option is enabled in the config file. 4. Log Tag / HTTP Code The Log Tag describes how the request was treated locally (hit, miss, etc). All the tags are described below. The HTTP code is the reply code taken from the first line of the HTTP reply header. Non−HTTP requests may have zero reply codes. 5. Size The number of bytes written to the client. 6. Request Method The HTTP request method, or I_QUERY for I requests. 7. URL The requested URL. 8. Ident If ident_lookup is on, this field may contain the name associated with the client connection as derived from the ident service. 9. Hierarchy Data / Hostname A description of how and where the requested object was fetched. 10. Content Type The Content−type field from the HTTP reply.

Access Log Tag / HTTP Code "T_" refers to requests on the HTTP port. T_ HIT A valid copy of the requested object was in the cache. T_MISS The requested object was not in the cache.

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T_REFRESH_HIT The object was in the cache, but STALE. An If−Modified−Since request was made and a '304 Not Modified' reply was received. T_REF_FAIL_HIT The object was in the cache, but STALE. The request to validate the object failed, so the old (stale) object was returned. T_REFRESH_MISS The object was in the cache, but STALE. An If−Modified−Since request was made and the reply contained new content. T_CLIENT_REFRESH The client issued a request with the 'no−cache' pragma. T_CLIENT_REFRESH_MISS The client issued a "no−cache" pragma, or some analogous cache control command along with the request. Thus, the cache has to refetch the object from origin server. It is s pushing that reload−button forcing the proxy to check for a new copy (also triggered by selecting a bookmark in some browser versions). In short, the browser forced the proxy to check for a new version T_IMS_HIT The client issued an If−Modified−Since request and the object was in the cache and still fresh. T_HIT and T_IMS_HIT are hits, the only difference is that in the T_IMS_HIT case, the browser already had an up to date version, so there was no need to send the Squid cached copy to the requestor. T_IMS_MISS The client issued an If−Modified−Since request for a stale object. T_SWAPFAIL The object was believed to be in the cache, but could not be accessed. T_DENIED Access was denied for this request "UDP_" refers to requests on the I port UDP_HIT A valid copy of the requested object was in the cache. UDP_HIT_OBJ Same as UDP_HIT, but the object data was small enough to be sent in the UDP reply packet. Saves the following T request. UDP_MISS The requested object was not in the cache. UDP_DENIED Access was denied for this request. UDP_INVALID An invalid request was received. UDP_RELOADING The I request was "refused" because the cache is busy, reloading its metadata. SIBLING_HIT

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The object was fetched from a sibling cache which replied with UDP_HIT. PARENT_HIT The object was requested from a parent cache which replied with UDP_HIT. DEFAULT_PARENT No I queries were sent. This parent was chosen because it was marked ``default'' in the config file. FIRST_UP_PARENT The object was fetched from the first parent in the list of parents. NO_PARENT_DIRECT The object was fetched from the origin server, because no parents existed for the given URL. FIRST_PARENT_MISS The object was fetched from the parent with the fastest (possibly weighted) round trip time. CLOSEST_PARENT_MISS This parent was chosen, because it included the the lowest RTT measurement to the origin server. See also the closests−only peer configuration option. CLOSEST_PARENT The Parent selection was based on our own RTT measurements.

Refresh Pattern Squid switched from a Time−To−Live based expiration model to a Refresh−Rate model. Objects are no longer purged from the cache when they expire. Instead of asg TTL's when the object enters the cache, we now check freshness requirements when objects are requested. If an object is 'fresh' it is given directly to the client. If it is 'stale' then we make an If−Modified−Since request for it.

in delay pool Pool: A collection of bucket groups as appropriate to a given class. bucket Pool: a group of buckets within a pool, such as the per−host bucket group, the per−network bucket group or the aggregate bucket group (the aggregate bucket group is actually a single bucket). bucket: an individual delay bucket represents a traffic allocation, which is replenished at a given rate (up to a given limit) and causes traffic to be delayed when empty. Classes: There are 3 classes of delay pools − class 1 is a single aggregate bucket, class 2 is an aggregate bucket with an individual bucket for each host in the class C, and class 3 is an aggregate bucket, with a network bucket (for each class B) and an individual bucket for each host. class:− Class of a delay pool determines how the delay is applied, ie, whether the different client IPs are treated separately or as a group (or both). class1:− Class 1 delay pool contains a single unified bucket, which is used for all requests from hosts subject to the pool.

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calss2:− Class 2 delay pool contains one unified bucket and 255 buckets,one for each host on an 8−bit network class3:− It contains 255 buckets for the subnets in a 16−bit network, and individual buckets for every host on these networks (IPv4 class B)

Setting the parameters for each pool is done by : delay_parameters pool aggregate network individual. The variables here are: where pool is a pool number , i.e., a number between 1 and the number specified in delay_pools as used in delay_class lines, aggregate is the parameter for the aggregate bucket, network for the network bucket, and individual for the individual bucket. Aggregate is only useful for classes 1, 2 and 3, individual for classes 2 and 3, and network for class 3. Each of these parameters is specified as restore / maximum − restore being the bytes per second restored to the bucket, and maximum being the amount of bytes that can be in the bucket at any time. It is important to that they are in bytes per second, not bits. To specify that a parameter is unlimited, use a −1. If we wish to limit any parameter in bits per second, divide this amount by 8, and use the value for both the restore and the maximum. For example, to restrict the entire proxy to 64kbps, use: delay_parameters 1 8000/8000

Ftp Information Squid can act as a proxy server for various Internet protocols. The most commonly used protocol is HTTP, but the File Transfer Protocol (FTP) is still alive and well. FTP was written for authenticated file transfer (it requires a name and ). To provide public access, a special is created: the anonymous . When you to an FTP server you use this as your name. As a , you generally use your email address. Most browsers these days automatically enter a useless email address. It's polite to give an address that works, though. If one of your s abuses a site, it allows the site get hold of you easily. Squid allows you to set the email address that is used with the ftp_ tag. You should probably create a [email protected] email address specifically for people to you on. There is another reason to enter a proper address here: some servers require a real email address. For your proxy to to these ftp servers, you will have to enter a real email address here.

Effective and Group ID Squid can only bind to low numbered ports (such as port 80) if it is started as root. Squid is normally started by your system's rc scripts when the machine boots. Since these scripts run as root, Squid is started as root at bootup time. Once Squid has been started, however, there is no need to run it as root. Good security practice is to run programs as root only when it's absolutely necessary, and for this reason Squid changes and group ID's once it has bound to the incoming network port.

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The cache_effective_ and cache_effective_group tags tell Squid what ID's to change to. The Unix security system would be useless if it allowed all s to change their ID's will, so Squid only attempts to change ID's if the main program is started as root. If you do not have root access to the machine, and are thus not starting Squid as root, you can simply leave this option commented out. Squid will then run with whatever ID starts the actual Squid binary. Now let us assume that, you have created both a squid and a squid group on your cache machine. The above tags should thus both be set to 'squid' .

Timeouts Half closed clients: The clients that shutsdown the sending side of their T connections, while leaving their receiving sides open, we term it as halfclosed clients. ie., the clients closes while the handshaking is in progress. Fully closed clients: The clients and servers have shared their acknowledgements(request and responses) before closing. Persistent Connection: Persistent Connection (keep alive) feature allows the same Connection to remain open for multiple requests. Obviously the drawback is that, the next request processing cannot start before the previous response has been sent by the server. IDENT: Squid will make an RFC931/ident request for client connections if 'ident_lookup' is enabled in the config file. Currently, the ident value is only logged with the request in the access.log. It is not currently possible to use the ident return value for access control purposes. URN: The URI architecture requires that a resource be named by a URN (Uniform Resource Name) and be retrieved by a URL (Uniform Resource Locator). A URC (Uniform Resource Characterstitic) binds the URN of a resource to one or more URLs. Once this system is activated, URNs will be used to "reference" information resources. World Wide Web clients will then send the URN for a desired resource to an international network of URN to URL resolvers (the URC service) that will return to the client one or more URLs that can be used to access the resource. SIGHUP or SIGTERM: The system signal sent to processes running in linux OS to shutdown.

External Programs Htwd: It is apache type wd ,You can use this to create wd for squid also. The Syntax is: htwd [ −c ] wdfile name . Redirector: Squid now has the ability to rewrite requested URLs. Implemented as an external process (similar to a dns server), Squid can be configured to every incoming URL through a 'redirector' process that returns either a new URL, or a blank line to indicate no change. The redirector program is NOT a standard part of the Squid package. However there are a couple of −contributed redirectors in the "contrib/" directory. Since everyone has different needs, it is up to the individual s to

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write their own implementation. For testing, and a place to start, this very simple Perl script can be used: #!/usr/local/bin/perl $|=1; print while (<>); The redirector program must read URLs (one per line) on standard input, and write rewritten URLs or blank lines on standard output. Note that the redirector program can not use buffered I/O. Ftp ive Connections: Ftp uses two data streams, one for ing commands around, the other for moving data. The command channel is handled by the ftpd listening on port 21. The data channel varies depending on whether you ask for ive ftp or not. When you request data in a non−ive environment, you client tells the server ``I am listening on .'' The server then connects FROM port 20 to the ip address and port specified by your client. This requires your "security device" to permit any host outside from port 20 to any host inside on any port >1023. Somewhat of a hole. In ive mode, when you request a data transfer, the server tells the client ``I am listening on .'' Your client then connects to the server on that IP and port and data flows. Unlinkd Program: Unlinkd is an external process used for unlinking old files in the cache to make room for newer object. Pinger Process: Squid ping program is an external program that provides Squid with icmp RTT information so that, it can more effectively choose between multiple remote parent caches for request fulfillment. There are special cases when this option is required, and your Squid must have been compiled with the −−enable−icmp configure option for it to work. This option should only be used on caches with multiple parent caches on different networks that it must choose between. The default program to use for this task is called pinger. This option configures the pinger_program directive.

BYTES−hit ratio The byte−hit ratio measures the ratio of total bytes from cached objects over the total bytes of objects requested.

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© ViSolve.com 2002 Created By: [email protected] Date: May 15,2002 Revision No:0.0 Modified By Date

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