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Disclaimer: This manual is NOT a Squid tutorial. It is only a reference material that provides detailed explanation of all configuration parameters available in Squid 2.6. The reader is expected to have prior knowledge of basic Squid installation and configuration. For Complete tutorial on Squid, please visit http://www.squid-cache.org

Squid 2.6 Configuration Manual OPTIONS FOR TUNING THE CACHE This section describes the important parameters that determine Squid cache performance. wais_relay_host wais_relay_port request_header_max_size request_body_max_size   refresh_pattern quick_abort_min quick_abort_max quick_abort_pct read_ahead_gap negative_ttl positive_dns_ttl negative_dns_ttl range_offset_limit collapsed_forwarding refresh_stale_hit

TAG NAME                   wais_relay_host, wais_relay_port Description  Defines WAIS host and port to relay WAIS requests Build Option  Default Usage  wais_relay_host hostname  wais_relay_port portnumber Default  wais_relay_host localhost  wais_relay_port 8000 Synopsis WAIS, or Wide Area Information System, is a system to catalog and search large amounts of data via a WAIS or WWW browser. This defaults to localhost and 8000. Arguments hostname  Machine name portnumber  Port where to bind the socket Example(s) wais_relay_host localhost wais_relay_port 8000       TAG NAME                   request_header_max_size Description  This specifies the maximum size for HTTP headers in a request Build Option  Default Usage  request_header_max_size size(KB) Default  request_header_max_size 10 KB Synopsis Size of HTTP headers in a request can be controlled using this tag. 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. Arguments size  Maximum size of request header Example(s) request_header_max_size 100 KB       TAG NAME                   request_body_max_size Description  Specifies the maximum size for an HTTP request body Build Option  Default Usage  request_body_max_size size(KB) Default  request_body_max_size 0 KB Synopsis This is the maximum size of a PUT/POST request. A user 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 (the default), there will be no limit imposed. Arguments size  Maximum size of request body Example(s) request_body_max_size 10 KB       TAG NAME                   refresh_pattern Description  Used to define the manner how Squid treats the objects in the cache Build Option  Default Usage  refresh_pattern [-i] regex min percent max [options] Default (Suggested)  refresh_pattern ^ftp:           1440    20%    10080  refresh_pattern ^gopher:      1440    0%      1440  refresh_pattern .                      0    20%    4320 Synopsis The way how the objects in the cache be refreshed is defined using this tag. By default, regular expressions are CASE-SENSITIVE.  To make them case-insensitive, use the -i option. Basically a cached object is: FRESH  if expires < now, else STALE STALE  if age > max FRESH  if lm-factor < percent, else STALE FRESH  if age < min 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. Arguments regex  regular expression Min  time (in minutes), an object without an explicit expire time should be considered fresh. percent  percentage of the objects age (time since last modification age) an object without explicit expire time will be considered fresh. Max  upper limit on how long objects without an explicit expiry time will be considered fresh. Options: 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. ignore-no-cache  ignores any ``Pragma: no-cache'' and ``Cache-control: no-cache'' headers received from a server. ignore-private  ignores any ``Cache-control: private'' headers received from a server. Doing this VIOLATES the HTTP standard.   Enabling this feature  could make you liable for problems which it causes. ignore-auth  caches responses to requests with authorization, irrespective of ``Cache-control'' headers received from a  server. Doing this VIOLATES the HTTP standard. Enabling this feature could make you liable for problems which it  causes. Example(s) refresh_pattern ^ftp:        1440    20%    10080 refresh_pattern ^gopher:    1440    0%    1440 refresh_pattern .        0    20%    4320       TAG NAME                   quick_abort_min, quick_abort_max, quick_abort_pct Description  Signals the cache how to continue downloads during abort signals sent by the clients Buid Option  Default Usage  quick_abort_min size  quick_abort_max size  quick_abort_pct percent Default  quick_abort_min 16 KB  quick_abort_max 16 KB  quick_abort_pct 95 Synopsis The cache by default continues downloading aborted requests which are almost completed (less than 16 KB remaining). This may be undesirable on slow (e.g. SLIP) links and/or very busy caches.  Impatient users may tie up file descriptors and bandwidth by repeatedly requesting and immediately aborting downloads. Arguments size  Minimum and maximum transfer size percent  Percentage of transfer When the user 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. 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. If you do not want any retrieval to continue after the client has aborted, set both quick_abort_min and quick_abort_max to '0 KB'. If you want retrievals to always continue if they are being cached then set quick_abort_min to '-1 KB'. Example(s) quick_abort_min 30 KB quick_abort_max 30 KB quick_abort_pct 80       TAG NAME                  read_ahead_gap Description  Define the amount of data the cache will buffer ahead of what has been sent to the client when retrieving an object from  another server Buid Option  Default Usage  read_ahead_gap buffer-size Default  read_ahead_gap 17 KB Synopsis This tag determines the prefetch cache buffer size for holding objects from another server while sending to the client. Arguments buffer-size  Size of the cache buffer Example(s) read_ahead_gap 30 KB       TAG NAME                   negative_ttl Description  Defines Time-to-Live (TTL) for failed requests Buid Option  Default Usage  negative_ttl time-units Default  negative_ttl 5 minutes Synopsis Certain types of failures (such as "connection refused" and "404 Not Found") are negatively-cached for a configurable amount of time. The default is 5 minutes.  Note that this is different from negative caching of DNS lookups. Arguments time-units  Timeout for negatively cached objects Example(s) negative_ttl 1 minutes       TAG NAME                   positive_dns_ttl Description  Defines Time-to-Live (TTL) for positive caching of successful DNS lookups Buid Option  Default Usage  positive_dns_ttl time-units Default  positive_dns_ttl 6 hours Synopsis For positive caching of successful DNS lookups, this defines Time-to-Live period. Default is 6 hours (360 minutes).  If you want to minimize the use of Squid's ipcache, set this to 1, not 0. Arguments time-units  Timeout for positive cachings Example(s) positive_dns_ttl 24 hours       TAG NAME                   negative_dns_ttl Description  Time-to-Live (TTL) for negative caching of failed DNS lookups Buid Option  Default Usage  negative_dns_ttl time-units Default  negative_dns_ttl 1 minutes Synopsis Sometimes DNS lookups may get failed. This parameter defines the Time-To-Live period for failed DNS lookups. Normally this will be a small value. Arguments time-units  Timeout period Example(s) negative_dns_ttl 1 minutes       TAG NAME                   range_offset_limit Description  Sets a upper limit on how far into the file a Range request may be to cause Squid to prefetch the whole file Buid Option  Default Usage  range_offset_limit bytes Default  range_offset_limit 0 KB Synopsis 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) Arguments bytes  Upper limit for the range request Example(s) range_offset_limit 17 MB       TAG NAME                   collapsed_forwarding Description  Enables multiple requests for the same URI to be processed as one request. Buid Option  Default Usage  collapsed_forwarding on | off Default  collapsed_forwarding off Synopsis This option enables multiple requests for the same URI to be processed as one request. Normally disabled to avoid increased latency on dynamic content, but there can be benefit from enabling this in accelerator setups where the web servers are the bottleneck and reliable and returns mostly cacheable information. Arguments on/off  Enable or disable this process       TAG NAME                   refresh_stale_hit Description  Changes the refresh algorithm to allow concurrent requests while an object is being refreshed to be processed. Buid Option  Default Usage  collapsed_forwarding on | off Default  collapsed_forwarding off Synopsis This option changes the refresh algorithm to allow concurrent requests while an object is being refreshed to be processed as cache hits if the object expired less than X seconds ago. Default is 0 to disable this feature. This option is mostly interesting in accelerator setups where a few objects is accessed very frequently. Arguments time-units  Timeout for refresh