
.. The following is the autogenerated output from varnishd -x parameter

.. _ref_param_accept_filter:

accept_filter
~~~~~~~~~~~~~

NB: This parameter depends on a feature which is not available on all platforms.

	* Units: bool
	* Default: off
	* Flags: 

Enable kernel accept-filters.

.. _ref_param_acceptor_sleep_decay:

acceptor_sleep_decay
~~~~~~~~~~~~~~~~~~~~
	* Default: 0.9
	* Minimum: 0
	* Maximum: 1
	* Flags: experimental

If we run out of resources, such as file descriptors or worker threads, the acceptor will sleep between accepts.
This parameter (multiplicatively) reduce the sleep duration for each successful accept. (ie: 0.9 = reduce by 10%)

.. _ref_param_acceptor_sleep_incr:

acceptor_sleep_incr
~~~~~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 0.000
	* Minimum: 0.000
	* Maximum: 1.000
	* Flags: experimental

If we run out of resources, such as file descriptors or worker threads, the acceptor will sleep between accepts.
This parameter control how much longer we sleep, each time we fail to accept a new connection.

.. _ref_param_acceptor_sleep_max:

acceptor_sleep_max
~~~~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 0.050
	* Minimum: 0.000
	* Maximum: 10.000
	* Flags: experimental

If we run out of resources, such as file descriptors or worker threads, the acceptor will sleep between accepts.
This parameter limits how long it can sleep between attempts to accept new connections.

.. _ref_param_auto_restart:

auto_restart
~~~~~~~~~~~~
	* Units: bool
	* Default: on

Automatically restart the child/worker process if it dies.

.. _ref_param_backend_idle_timeout:

backend_idle_timeout
~~~~~~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 60.000
	* Minimum: 1.000

Timeout before we close unused backend connections.

.. _ref_param_backend_local_error_holddown:

backend_local_error_holddown
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 10.000
	* Minimum: 0.000
	* Flags: experimental

When connecting to backends, certain error codes (EADDRNOTAVAIL, EACCESS, EPERM) signal a local resource shortage or configuration issue for which retrying connection attempts may worsen the situation due to the complexity of the operations involved in the kernel.
This parameter prevents repeated connection attempts for the configured duration.

.. _ref_param_backend_remote_error_holddown:

backend_remote_error_holddown
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 0.250
	* Minimum: 0.000
	* Flags: experimental

When connecting to backends, certain error codes (ECONNREFUSED, ENETUNREACH) signal fundamental connection issues such as the backend not accepting connections or routing problems for which repeated connection attempts are considered useless
This parameter prevents repeated connection attempts for the configured duration.

.. _ref_param_ban_cutoff:

ban_cutoff
~~~~~~~~~~
	* Units: bans
	* Default: 0
	* Minimum: 0
	* Flags: experimental

Expurge long tail content from the cache to keep the number of bans below this value. 0 disables.

When this parameter is set to a non-zero value, the ban lurker continues to work the ban list as usual top to bottom, but when it reaches the ban_cutoff-th ban, it treats all objects as if they matched a ban and expurges them from cache. As actively used objects get tested against the ban list at request time and thus are likely to be associated with bans near the top of the ban list, with ban_cutoff, least recently accessed objects (the "long tail") are removed.

This parameter is a safety net to avoid bad response times due to bans being tested at lookup time. Setting a cutoff trades response time for cache efficiency. The recommended value is proportional to rate(bans_lurker_tests_tested) / n_objects while the ban lurker is working, which is the number of bans the system can sustain. The additional latency due to request ban testing is in the order of ban_cutoff / rate(bans_lurker_tests_tested). For example, for rate(bans_lurker_tests_tested) = 2M/s and a tolerable latency of 100ms, a good value for ban_cutoff may be 200K.

.. _ref_param_ban_dups:

ban_dups
~~~~~~~~
	* Units: bool
	* Default: on

Eliminate older identical bans when a new ban is added.  This saves CPU cycles by not comparing objects to identical bans.
This is a waste of time if you have many bans which are never identical.

.. _ref_param_ban_lurker_age:

ban_lurker_age
~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 60.000
	* Minimum: 0.000

The ban lurker will ignore bans until they are this old.  When a ban is added, the active traffic will be tested against it as part of object lookup.  Because many applications issue bans in bursts, this parameter holds the ban-lurker off until the rush is over.
This should be set to the approximate time which a ban-burst takes.

.. _ref_param_ban_lurker_batch:

ban_lurker_batch
~~~~~~~~~~~~~~~~
	* Default: 1000
	* Minimum: 1

The ban lurker sleeps ${ban_lurker_sleep} after examining this many objects.  Use this to pace the ban-lurker if it eats too many resources.

.. _ref_param_ban_lurker_holdoff:

ban_lurker_holdoff
~~~~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 0.010
	* Minimum: 0.000
	* Flags: experimental

How long the ban lurker sleeps when giving way to lookup due to lock contention.

.. _ref_param_ban_lurker_sleep:

ban_lurker_sleep
~~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 0.010
	* Minimum: 0.000

How long the ban lurker sleeps after examining ${ban_lurker_batch} objects.  Use this to pace the ban-lurker if it eats too many resources.
A value of zero will disable the ban lurker entirely.

.. _ref_param_between_bytes_timeout:

between_bytes_timeout
~~~~~~~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 60.000
	* Minimum: 0.000

We only wait for this many seconds between bytes received from the backend before giving up the fetch.
A value of zero means never give up.
VCL values, per backend or per backend request take precedence.
This parameter does not apply to pipe'ed requests.

.. _ref_param_cc_command:

cc_command
~~~~~~~~~~
	* Default: exec clang -g -O2 -Wall -Werror -Wno-error=unused-result  \t-Werror \t-Wall \t-Wno-format-y2k \t-W \t-Wstrict-prototypes \t-Wmissing-prototypes \t-Wpointer-arith \t-Wreturn-type \t-Wcast-qual \t-Wwrite-strings \t-Wswitch \t-Wshadow \t-Wunused-parameter \t-Wcast-align \t-Wchar-subscripts \t-Wnested-externs \t-Wextra \t-Wno-sign-compare  -fstack-protector -Wno-missing-field-initializers -pthread -fpic -shared -Wl,-x -o %o %s
	* Flags: must_reload

Command used for compiling the C source code to a dlopen(3) loadable object.  Any occurrence of %s in the string will be replaced with the source file name, and %o will be replaced with the output file name.

.. _ref_param_cli_limit:

cli_limit
~~~~~~~~~
	* Units: bytes
	* Default: 48k
	* Minimum: 128b
	* Maximum: 99999999b

Maximum size of CLI response.  If the response exceeds this limit, the response code will be 201 instead of 200 and the last line will indicate the truncation.

.. _ref_param_cli_timeout:

cli_timeout
~~~~~~~~~~~
	* Units: seconds
	* Default: 60.000
	* Minimum: 0.000

Timeout for the childs replies to CLI requests from the mgt_param.

.. _ref_param_clock_skew:

clock_skew
~~~~~~~~~~
	* Units: seconds
	* Default: 10
	* Minimum: 0

How much clockskew we are willing to accept between the backend and our own clock.

.. _ref_param_clock_step:

clock_step
~~~~~~~~~~
	* Units: seconds
	* Default: 1.000
	* Minimum: 0.000

How much observed clock step we are willing to accept before we panic.

.. _ref_param_connect_timeout:

connect_timeout
~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 3.500
	* Minimum: 0.000

Default connection timeout for backend connections. We only try to connect to the backend for this many seconds before giving up. VCL can override this default value for each backend and backend request.

.. _ref_param_critbit_cooloff:

critbit_cooloff
~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 180.000
	* Minimum: 60.000
	* Maximum: 254.000
	* Flags: wizard

How long the critbit hasher keeps deleted objheads on the cooloff list.

.. _ref_param_debug:

debug
~~~~~
	* Default: none

Enable/Disable various kinds of debugging.

	*none*
		Disable all debugging

Use +/- prefix to set/reset individual bits:

	*req_state*
		VSL Request state engine

	*workspace*
		VSL Workspace operations

	*waiter*
		VSL Waiter internals

	*waitinglist*
		VSL Waitinglist events

	*syncvsl*
		Make VSL synchronous

	*hashedge*
		Edge cases in Hash

	*vclrel*
		Rapid VCL release

	*lurker*
		VSL Ban lurker

	*esi_chop*
		Chop ESI fetch to bits

	*flush_head*
		Flush after http1 head

	*vtc_mode*
		Varnishtest Mode

	*witness*
		Emit WITNESS lock records

	*vsm_keep*
		Keep the VSM file on restart

	*drop_pools*
		Drop thread pools (testing)

	*slow_acceptor*
		Slow down Acceptor

	*h2_nocheck*
		Disable various H2 checks

	*vmod_so_keep*
		Keep copied VMOD libraries

	*processors*
		Fetch/Deliver processors

	*protocol*
		Protocol debugging

	*vcl_keep*
		Keep VCL C and so files

.. _ref_param_default_grace:

default_grace
~~~~~~~~~~~~~
	* Units: seconds
	* Default: 10.000
	* Minimum: 0.000
	* Flags: obj_sticky

Default grace period.  We will deliver an object this long after it has expired, provided another thread is attempting to get a new copy.

.. _ref_param_default_keep:

default_keep
~~~~~~~~~~~~
	* Units: seconds
	* Default: 0.000
	* Minimum: 0.000
	* Flags: obj_sticky

Default keep period.  We will keep a useless object around this long, making it available for conditional backend fetches.  That means that the object will be removed from the cache at the end of ttl+grace+keep.

.. _ref_param_default_ttl:

default_ttl
~~~~~~~~~~~
	* Units: seconds
	* Default: 120.000
	* Minimum: 0.000
	* Flags: obj_sticky

The TTL assigned to objects if neither the backend nor the VCL code assigns one.

.. _ref_param_esi_iovs:

esi_iovs
~~~~~~~~
	* Units: struct iovec
	* Default: 10
	* Minimum: 3
	* Maximum: 1024
	* Flags: wizard

Number of io vectors to allocate on the thread workspace for ESI requests.

.. _ref_param_feature:

feature
~~~~~~~
	* Default: none

Enable/Disable various minor features.

	*none*
		Disable all features.

Use +/- prefix to enable/disable individual feature:

	*short_panic*
		Short panic message.

	*wait_silo*
		Wait for persistent silo.

	*no_coredump*
		No coredumps.

	*esi_ignore_https*
		Treat HTTPS as HTTP in ESI:includes

	*esi_disable_xml_check*
		Don't check of body looks like XML

	*esi_ignore_other_elements*
		Ignore non-esi XML-elements

	*esi_remove_bom*
		Remove UTF-8 BOM

	*https_scheme*
		Also split https URIs

	*http2*
		Support HTTP/2 protocol

	*http_date_postel*
		Relax parsing of timestamps in HTTP headers

.. _ref_param_fetch_chunksize:

fetch_chunksize
~~~~~~~~~~~~~~~
	* Units: bytes
	* Default: 16k
	* Minimum: 4k
	* Flags: experimental

The default chunksize used by fetcher. This should be bigger than the majority of objects with short TTLs.
Internal limits in the storage_file module makes increases above 128kb a dubious idea.

.. _ref_param_fetch_maxchunksize:

fetch_maxchunksize
~~~~~~~~~~~~~~~~~~
	* Units: bytes
	* Default: 0.25G
	* Minimum: 64k
	* Flags: experimental

The maximum chunksize we attempt to allocate from storage. Making this too large may cause delays and storage fragmentation.

.. _ref_param_first_byte_timeout:

first_byte_timeout
~~~~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 60.000
	* Minimum: 0.000

Default timeout for receiving first byte from backend. We only wait for this many seconds for the first byte before giving up. A value of 0 means it will never time out. VCL can override this default value for each backend and backend request. This parameter does not apply to pipe.

.. _ref_param_gzip_buffer:

gzip_buffer
~~~~~~~~~~~
	* Units: bytes
	* Default: 32k
	* Minimum: 2k
	* Flags: experimental

Size of malloc buffer used for gzip processing.
These buffers are used for in-transit data, for instance gunzip'ed data being sent to a client.Making this space to small results in more overhead, writes to sockets etc, making it too big is probably just a waste of memory.

.. _ref_param_gzip_level:

gzip_level
~~~~~~~~~~
	* Default: 6
	* Minimum: 0
	* Maximum: 9

Gzip compression level: 0=debug, 1=fast, 9=best

.. _ref_param_gzip_memlevel:

gzip_memlevel
~~~~~~~~~~~~~
	* Default: 8
	* Minimum: 1
	* Maximum: 9

Gzip memory level 1=slow/least, 9=fast/most compression.
Memory impact is 1=1k, 2=2k, ... 9=256k.

.. _ref_param_h2_header_table_size:

h2_header_table_size
~~~~~~~~~~~~~~~~~~~~
	* Units: bytes
	* Default: 4k
	* Minimum: 0b

HTTP2 header table size.
This is the size that will be used for the HPACK dynamic
decoding table.

.. _ref_param_h2_initial_window_size:

h2_initial_window_size
~~~~~~~~~~~~~~~~~~~~~~
	* Units: bytes
	* Default: 65535b
	* Minimum: 0b
	* Maximum: 2147483647b

HTTP2 initial flow control window size.

.. _ref_param_h2_max_concurrent_streams:

h2_max_concurrent_streams
~~~~~~~~~~~~~~~~~~~~~~~~~
	* Units: streams
	* Default: 100
	* Minimum: 0

HTTP2 Maximum number of concurrent streams.
This is the number of requests that can be active
at the same time for a single HTTP2 connection.

.. _ref_param_h2_max_frame_size:

h2_max_frame_size
~~~~~~~~~~~~~~~~~
	* Units: bytes
	* Default: 16k
	* Minimum: 16k
	* Maximum: 16777215b

HTTP2 maximum per frame payload size we are willing to accept.

.. _ref_param_h2_max_header_list_size:

h2_max_header_list_size
~~~~~~~~~~~~~~~~~~~~~~~
	* Units: bytes
	* Default: 2147483647b
	* Minimum: 0b

HTTP2 maximum size of an uncompressed header list.

.. _ref_param_h2_rx_window_increment:

h2_rx_window_increment
~~~~~~~~~~~~~~~~~~~~~~
	* Units: bytes
	* Default: 1M
	* Minimum: 1M
	* Maximum: 1G
	* Flags: wizard

HTTP2 Receive Window Increments.
How big credits we send in WINDOW_UPDATE frames
Only affects incoming request bodies (ie: POST, PUT etc.)

.. _ref_param_h2_rx_window_low_water:

h2_rx_window_low_water
~~~~~~~~~~~~~~~~~~~~~~
	* Units: bytes
	* Default: 10M
	* Minimum: 65535b
	* Maximum: 1G
	* Flags: wizard

HTTP2 Receive Window low water mark.
We try to keep the window at least this big
Only affects incoming request bodies (ie: POST, PUT etc.)

.. _ref_param_http_gzip_support:

http_gzip_support
~~~~~~~~~~~~~~~~~
	* Units: bool
	* Default: on

Enable gzip support. When enabled Varnish request compressed objects from the backend and store them compressed. If a client does not support gzip encoding Varnish will uncompress compressed objects on demand. Varnish will also rewrite the Accept-Encoding header of clients indicating support for gzip to:
  Accept-Encoding: gzip

Clients that do not support gzip will have their Accept-Encoding header removed. For more information on how gzip is implemented please see the chapter on gzip in the Varnish reference.

When gzip support is disabled the variables beresp.do_gzip and beresp.do_gunzip have no effect in VCL.

.. _ref_param_http_max_hdr:

http_max_hdr
~~~~~~~~~~~~
	* Units: header lines
	* Default: 64
	* Minimum: 32
	* Maximum: 65535

Maximum number of HTTP header lines we allow in {req|resp|bereq|beresp}.http (obj.http is autosized to the exact number of headers).
Cheap, ~20 bytes, in terms of workspace memory.
Note that the first line occupies five header lines.

.. _ref_param_http_range_support:

http_range_support
~~~~~~~~~~~~~~~~~~
	* Units: bool
	* Default: on

Enable support for HTTP Range headers.

.. _ref_param_http_req_hdr_len:

http_req_hdr_len
~~~~~~~~~~~~~~~~
	* Units: bytes
	* Default: 8k
	* Minimum: 40b

Maximum length of any HTTP client request header we will allow.  The limit is inclusive its continuation lines.

.. _ref_param_http_req_size:

http_req_size
~~~~~~~~~~~~~
	* Units: bytes
	* Default: 32k
	* Minimum: 0.25k

Maximum number of bytes of HTTP client request we will deal with.  This is a limit on all bytes up to the double blank line which ends the HTTP request.
The memory for the request is allocated from the client workspace (param: workspace_client) and this parameter limits how much of that the request is allowed to take up.

.. _ref_param_http_resp_hdr_len:

http_resp_hdr_len
~~~~~~~~~~~~~~~~~
	* Units: bytes
	* Default: 8k
	* Minimum: 40b

Maximum length of any HTTP backend response header we will allow.  The limit is inclusive its continuation lines.

.. _ref_param_http_resp_size:

http_resp_size
~~~~~~~~~~~~~~
	* Units: bytes
	* Default: 32k
	* Minimum: 0.25k

Maximum number of bytes of HTTP backend response we will deal with.  This is a limit on all bytes up to the double blank line which ends the HTTP response.
The memory for the response is allocated from the backend workspace (param: workspace_backend) and this parameter limits how much of that the response is allowed to take up.

.. _ref_param_idle_send_timeout:

idle_send_timeout
~~~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 60.000
	* Minimum: 0.000
	* Flags: delayed

Send timeout for individual pieces of data on client connections. May get extended if 'send_timeout' applies.

When this timeout is hit, the session is closed.

See the man page for `setsockopt(2)` under ``SO_SNDTIMEO`` for more information.

.. _ref_param_listen_depth:

listen_depth
~~~~~~~~~~~~
	* Units: connections
	* Default: 1024
	* Minimum: 0
	* Flags: must_restart

Listen queue depth.

.. _ref_param_lru_interval:

lru_interval
~~~~~~~~~~~~
	* Units: seconds
	* Default: 2.000
	* Minimum: 0.000
	* Flags: experimental

Grace period before object moves on LRU list.
Objects are only moved to the front of the LRU list if they have not been moved there already inside this timeout period.  This reduces the amount of lock operations necessary for LRU list access.

.. _ref_param_max_esi_depth:

max_esi_depth
~~~~~~~~~~~~~
	* Units: levels
	* Default: 5
	* Minimum: 0

Maximum depth of esi:include processing.

.. _ref_param_max_restarts:

max_restarts
~~~~~~~~~~~~
	* Units: restarts
	* Default: 4
	* Minimum: 0

Upper limit on how many times a request can restart.

.. _ref_param_max_retries:

max_retries
~~~~~~~~~~~
	* Units: retries
	* Default: 4
	* Minimum: 0

Upper limit on how many times a backend fetch can retry.

.. _ref_param_max_vcl:

max_vcl
~~~~~~~
	* Default: 100
	* Minimum: 0

Threshold of loaded VCL programs.  (VCL labels are not counted.)  Parameter max_vcl_handling determines behaviour.

.. _ref_param_max_vcl_handling:

max_vcl_handling
~~~~~~~~~~~~~~~~
	* Default: 1
	* Minimum: 0
	* Maximum: 2

Behaviour when attempting to exceed max_vcl loaded VCL.

*  0 - Ignore max_vcl parameter.

*  1 - Issue warning.

*  2 - Refuse loading VCLs.

.. _ref_param_nuke_limit:

nuke_limit
~~~~~~~~~~
	* Units: allocations
	* Default: 50
	* Minimum: 0
	* Flags: experimental

Maximum number of objects we attempt to nuke in order to make space for a object body.

.. _ref_param_pcre_match_limit:

pcre_match_limit
~~~~~~~~~~~~~~~~
	* Default: 10000
	* Minimum: 1

The limit for the number of calls to the internal match() function in pcre_exec().

(See: PCRE_EXTRA_MATCH_LIMIT in pcre docs.)

This parameter limits how much CPU time regular expression matching can soak up.

.. _ref_param_pcre_match_limit_recursion:

pcre_match_limit_recursion
~~~~~~~~~~~~~~~~~~~~~~~~~~
	* Default: 20
	* Minimum: 1

The recursion depth-limit for the internal match() function in a pcre_exec().

(See: PCRE_EXTRA_MATCH_LIMIT_RECURSION in pcre docs.)

This puts an upper limit on the amount of stack used by PCRE for certain classes of regular expressions.

We have set the default value low in order to prevent crashes, at the cost of possible regexp matching failures.

Matching failures will show up in the log as VCL_Error messages with regexp errors -27 or -21.

Testcase r01576 can be useful when tuning this parameter.

.. _ref_param_ping_interval:

ping_interval
~~~~~~~~~~~~~
	* Units: seconds
	* Default: 3
	* Minimum: 0
	* Flags: must_restart

Interval between pings from parent to child.
Zero will disable pinging entirely, which makes it possible to attach a debugger to the child.

.. _ref_param_pipe_timeout:

pipe_timeout
~~~~~~~~~~~~
	* Units: seconds
	* Default: 60.000
	* Minimum: 0.000

Idle timeout for PIPE sessions. If nothing have been received in either direction for this many seconds, the session is closed.

.. _ref_param_pool_req:

pool_req
~~~~~~~~
	* Default: 10,100,10

Parameters for per worker pool request memory pool.
The three numbers are:

	*min_pool*
		minimum size of free pool.

	*max_pool*
		maximum size of free pool.

	*max_age*
		max age of free element.

.. _ref_param_pool_sess:

pool_sess
~~~~~~~~~
	* Default: 10,100,10

Parameters for per worker pool session memory pool.
The three numbers are:

	*min_pool*
		minimum size of free pool.

	*max_pool*
		maximum size of free pool.

	*max_age*
		max age of free element.

.. _ref_param_pool_vbo:

pool_vbo
~~~~~~~~
	* Default: 10,100,10

Parameters for backend object fetch memory pool.
The three numbers are:

	*min_pool*
		minimum size of free pool.

	*max_pool*
		maximum size of free pool.

	*max_age*
		max age of free element.

.. _ref_param_prefer_ipv6:

prefer_ipv6
~~~~~~~~~~~
	* Units: bool
	* Default: off

Prefer IPv6 address when connecting to backends which have both IPv4 and IPv6 addresses.

.. _ref_param_rush_exponent:

rush_exponent
~~~~~~~~~~~~~
	* Units: requests per request
	* Default: 3
	* Minimum: 2
	* Flags: experimental

How many parked request we start for each completed request on the object.
NB: Even with the implict delay of delivery, this parameter controls an exponential increase in number of worker threads.

.. _ref_param_send_timeout:

send_timeout
~~~~~~~~~~~~
	* Units: seconds
	* Default: 600.000
	* Minimum: 0.000
	* Flags: delayed

Total timeout for ordinary HTTP1 responses. Does not apply to some internally generated errors and pipe mode.

When 'idle_send_timeout' is hit while sending an HTTP1 response, the timeout is extended unless the total time already taken for sending the response in its entirety exceeds this many seconds.

When this timeout is hit, the session is closed

.. _ref_param_shm_reclen:

shm_reclen
~~~~~~~~~~
	* Units: bytes
	* Default: 255b
	* Minimum: 16b
	* Maximum: 4084

Old name for vsl_reclen, use that instead.

.. _ref_param_shortlived:

shortlived
~~~~~~~~~~
	* Units: seconds
	* Default: 10.000
	* Minimum: 0.000

Objects created with (ttl+grace+keep) shorter than this are always put in transient storage.

.. _ref_param_sigsegv_handler:

sigsegv_handler
~~~~~~~~~~~~~~~
	* Units: bool
	* Default: on
	* Flags: must_restart

Install a signal handler which tries to dump debug information on segmentation faults, bus errors and abort signals.

.. _ref_param_syslog_cli_traffic:

syslog_cli_traffic
~~~~~~~~~~~~~~~~~~
	* Units: bool
	* Default: on

Log all CLI traffic to syslog(LOG_INFO).

.. _ref_param_tcp_fastopen:

tcp_fastopen
~~~~~~~~~~~~
	* Units: bool
	* Default: off
	* Flags: must_restart

Enable TCP Fast Open extension.

.. _ref_param_tcp_keepalive_intvl:

tcp_keepalive_intvl
~~~~~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 75.000
	* Minimum: 1.000
	* Maximum: 100.000
	* Flags: experimental

The number of seconds between TCP keep-alive probes. Ignored for Unix domain sockets.

.. _ref_param_tcp_keepalive_probes:

tcp_keepalive_probes
~~~~~~~~~~~~~~~~~~~~
	* Units: probes
	* Default: 9
	* Minimum: 1
	* Maximum: 100
	* Flags: experimental

The maximum number of TCP keep-alive probes to send before giving up and killing the connection if no response is obtained from the other end. Ignored for Unix domain sockets.

.. _ref_param_tcp_keepalive_time:

tcp_keepalive_time
~~~~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 7200.000
	* Minimum: 1.000
	* Maximum: 7200.000
	* Flags: experimental

The number of seconds a connection needs to be idle before TCP begins sending out keep-alive probes. Ignored for Unix domain sockets.

.. _ref_param_thread_pool_add_delay:

thread_pool_add_delay
~~~~~~~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 0.000
	* Minimum: 0.000
	* Flags: experimental

Wait at least this long after creating a thread.

Some (buggy) systems may need a short (sub-second) delay between creating threads.
Set this to a few milliseconds if you see the 'threads_failed' counter grow too much.

Setting this too high results in insufficient worker threads.

.. _ref_param_thread_pool_destroy_delay:

thread_pool_destroy_delay
~~~~~~~~~~~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 1.000
	* Minimum: 0.010
	* Flags: delayed, experimental

Wait this long after destroying a thread.

This controls the decay of thread pools when idle(-ish).

.. _ref_param_thread_pool_fail_delay:

thread_pool_fail_delay
~~~~~~~~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 0.200
	* Minimum: 0.010
	* Flags: experimental

Wait at least this long after a failed thread creation before trying to create another thread.

Failure to create a worker thread is often a sign that  the end is near, because the process is running out of some resource.  This delay tries to not rush the end on needlessly.

If thread creation failures are a problem, check that thread_pool_max is not too high.

It may also help to increase thread_pool_timeout and thread_pool_min, to reduce the rate at which treads are destroyed and later recreated.

.. _ref_param_thread_pool_max:

thread_pool_max
~~~~~~~~~~~~~~~
	* Units: threads
	* Default: 5000
	* Minimum: 100
	* Flags: delayed

The maximum number of worker threads in each pool. The minimum value depends on thread_pool_min.

Do not set this higher than you have to, since excess worker threads soak up RAM and CPU and generally just get in the way of getting work done.

.. _ref_param_thread_pool_min:

thread_pool_min
~~~~~~~~~~~~~~~
	* Units: threads
	* Default: 100
	* Minimum: 5
	* Maximum: 5000
	* Flags: delayed

The minimum number of worker threads in each pool. The maximum value depends on thread_pool_max.

Increasing this may help ramp up faster from low load situations or when threads have expired.

Technical minimum is 5 threads, but this parameter is strongly recommended to be at least 10

.. _ref_param_thread_pool_reserve:

thread_pool_reserve
~~~~~~~~~~~~~~~~~~~
	* Units: threads
	* Default: 0
	* Maximum: 95
	* Flags: delayed

The number of worker threads reserved for vital tasks in each pool.

Tasks may require other tasks to complete (for example, client requests may require backend requests, http2 sessions require streams, which require requests). This reserve is to ensure that lower priority tasks do not prevent higher priority tasks from running even under high load.

The effective value is at least 5 (the number of internal priority classes), irrespective of this parameter.
Default is 0 to auto-tune (5% of thread_pool_min).
Minimum is 1 otherwise, maximum is 95% of thread_pool_min.

.. _ref_param_thread_pool_stack:

thread_pool_stack
~~~~~~~~~~~~~~~~~
	* Units: bytes
	* Default: 48k
	* Minimum: 16k
	* Flags: delayed

Worker thread stack size.
This will likely be rounded up to a multiple of 4k (or whatever the page_size might be) by the kernel.

The required stack size is primarily driven by the depth of the call-tree. The most common relevant determining factors in varnish core code are GZIP (un)compression, ESI processing and regular expression matches. VMODs may also require significant amounts of additional stack. The nesting depth of VCL subs is another factor, although typically not predominant.

The stack size is per thread, so the maximum total memory required for worker thread stacks is in the order of size = thread_pools x thread_pool_max x thread_pool_stack.

Thus, in particular for setups with many threads, keeping the stack size at a minimum helps reduce the amount of memory required by Varnish.

On the other hand, thread_pool_stack must be large enough under all circumstances, otherwise varnish will crash due to a stack overflow. Usually, a stack overflow manifests itself as a segmentation fault (aka segfault / SIGSEGV) with the faulting address being near the stack pointer (sp).

Unless stack usage can be reduced, thread_pool_stack must be increased when a stack overflow occurs. Setting it in 150%-200% increments is recommended until stack overflows cease to occur.

.. _ref_param_thread_pool_timeout:

thread_pool_timeout
~~~~~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 300.000
	* Minimum: 10.000
	* Flags: delayed, experimental

Thread idle threshold.

Threads in excess of thread_pool_min, which have been idle for at least this long, will be destroyed.

.. _ref_param_thread_pool_watchdog:

thread_pool_watchdog
~~~~~~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 60.000
	* Minimum: 0.100
	* Flags: experimental

Thread queue stuck watchdog.

If no queued work have been released for this long, the worker process panics itself.

.. _ref_param_thread_pools:

thread_pools
~~~~~~~~~~~~
	* Units: pools
	* Default: 2
	* Minimum: 1
	* Maximum: 32
	* Flags: delayed, experimental

Number of worker thread pools.

Increasing the number of worker pools decreases lock contention. Each worker pool also has a thread accepting new connections, so for very high rates of incoming new connections on systems with many cores, increasing the worker pools may be required.

Too many pools waste CPU and RAM resources, and more than one pool for each CPU is most likely detrimental to performance.

Can be increased on the fly, but decreases require a restart to take effect.

.. _ref_param_thread_queue_limit:

thread_queue_limit
~~~~~~~~~~~~~~~~~~
	* Default: 20
	* Minimum: 0
	* Flags: experimental

Permitted request queue length per thread-pool.

This sets the number of requests we will queue, waiting for an available thread.  Above this limit sessions will be dropped instead of queued.

.. _ref_param_thread_stats_rate:

thread_stats_rate
~~~~~~~~~~~~~~~~~
	* Units: requests
	* Default: 10
	* Minimum: 0
	* Flags: experimental

Worker threads accumulate statistics, and dump these into the global stats counters if the lock is free when they finish a job (request/fetch etc.)
This parameters defines the maximum number of jobs a worker thread may handle, before it is forced to dump its accumulated stats into the global counters.

.. _ref_param_timeout_idle:

timeout_idle
~~~~~~~~~~~~
	* Units: seconds
	* Default: 5.000
	* Minimum: 0.000

Idle timeout for client connections.

A connection is considered idle until we have received the full request headers.

This parameter is particularly relevant for HTTP1 keepalive  connections which are closed unless the next request is received before this timeout is reached.

.. _ref_param_timeout_linger:

timeout_linger
~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 0.050
	* Minimum: 0.000
	* Flags: experimental

How long the worker thread lingers on an idle session before handing it over to the waiter.
When sessions are reused, as much as half of all reuses happen within the first 100 msec of the previous request completing.
Setting this too high results in worker threads not doing anything for their keep, setting it too low just means that more sessions take a detour around the waiter.

.. _ref_param_vcc_allow_inline_c:

vcc_allow_inline_c
~~~~~~~~~~~~~~~~~~
	* Units: bool
	* Default: off

Allow inline C code in VCL.

.. _ref_param_vcc_err_unref:

vcc_err_unref
~~~~~~~~~~~~~
	* Units: bool
	* Default: on

Unreferenced VCL objects result in error.

.. _ref_param_vcc_unsafe_path:

vcc_unsafe_path
~~~~~~~~~~~~~~~
	* Units: bool
	* Default: on

Allow '/' in vmod & include paths.
Allow 'import ... from ...'.

.. _ref_param_vcl_cooldown:

vcl_cooldown
~~~~~~~~~~~~
	* Units: seconds
	* Default: 600.000
	* Minimum: 0.000

How long a VCL is kept warm after being replaced as the active VCL (granularity approximately 30 seconds).

.. _ref_param_vcl_dir:

vcl_dir
~~~~~~~
	* Default: /opt/varnish/etc/varnish:/opt/varnish/share/varnish/vcl

Old name for vcl_path, use that instead.

.. _ref_param_vcl_path:

vcl_path
~~~~~~~~
	* Default: /opt/varnish/etc/varnish:/opt/varnish/share/varnish/vcl

Directory (or colon separated list of directories) from which relative VCL filenames (vcl.load and include) are to be found.  By default Varnish searches VCL files in both the system configuration and shared data directories to allow packages to drop their VCL files in a standard location where relative includes would work.

.. _ref_param_vmod_dir:

vmod_dir
~~~~~~~~
	* Default: /opt/varnish/lib/varnish/vmods

Old name for vmod_path, use that instead.

.. _ref_param_vmod_path:

vmod_path
~~~~~~~~~
	* Default: /opt/varnish/lib/varnish/vmods

Directory (or colon separated list of directories) where VMODs are to be found.

.. _ref_param_vsl_buffer:

vsl_buffer
~~~~~~~~~~
	* Units: bytes
	* Default: 4k
	* Minimum: 267

Bytes of (req-/backend-)workspace dedicated to buffering VSL records.
When this parameter is adjusted, most likely workspace_client and workspace_backend will have to be adjusted by the same amount.

Setting this too high costs memory, setting it too low will cause more VSL flushes and likely increase lock-contention on the VSL mutex.

The minimum tracks the vsl_reclen parameter + 12 bytes.

.. _ref_param_vsl_mask:

vsl_mask
~~~~~~~~
	* Default: -ObjProtocol,-ObjStatus,-ObjReason,-ObjHeader,-VCL_trace,-WorkThread,-Hash,-VfpAcct,-H2RxHdr,-H2RxBody,-H2TxHdr,-H2TxBody

Mask individual VSL messages from being logged.

	*default*
		Set default value

Use +/- prefix in front of VSL tag name, to mask/unmask individual VSL messages.

.. _ref_param_vsl_reclen:

vsl_reclen
~~~~~~~~~~
	* Units: bytes
	* Default: 255b
	* Minimum: 16b
	* Maximum: 4084b

Maximum number of bytes in SHM log record.

The maximum tracks the vsl_buffer parameter - 12 bytes.

.. _ref_param_vsl_space:

vsl_space
~~~~~~~~~
	* Units: bytes
	* Default: 80M
	* Minimum: 1M
	* Maximum: 4G
	* Flags: must_restart

The amount of space to allocate for the VSL fifo buffer in the VSM memory segment.  If you make this too small, varnish{ncsa|log} etc will not be able to keep up.  Making it too large just costs memory resources.

.. _ref_param_vsm_free_cooldown:

vsm_free_cooldown
~~~~~~~~~~~~~~~~~
	* Units: seconds
	* Default: 60.000
	* Minimum: 10.000
	* Maximum: 600.000

How long VSM memory is kept warm after a deallocation (granularity approximately 2 seconds).

.. _ref_param_vsm_space:

vsm_space
~~~~~~~~~
	* Units: bytes
	* Default: 1M
	* Minimum: 1M
	* Maximum: 1G

DEPRECATED: This parameter is ignored.
There is no global limit on amount of shared memory now.

.. _ref_param_workspace_backend:

workspace_backend
~~~~~~~~~~~~~~~~~
	* Units: bytes
	* Default: 64k
	* Minimum: 1k
	* Flags: delayed

Bytes of HTTP protocol workspace for backend HTTP req/resp.  If larger than 4k, use a multiple of 4k for VM efficiency.

.. _ref_param_workspace_client:

workspace_client
~~~~~~~~~~~~~~~~
	* Units: bytes
	* Default: 64k
	* Minimum: 9k
	* Flags: delayed

Bytes of HTTP protocol workspace for clients HTTP req/resp.  Use a multiple of 4k for VM efficiency.
For HTTP/2 compliance this must be at least 20k, in order to receive fullsize (=16k) frames from the client.   That usually happens only in POST/PUT bodies.  For other traffic-patterns smaller values work just fine.

.. _ref_param_workspace_session:

workspace_session
~~~~~~~~~~~~~~~~~
	* Units: bytes
	* Default: 0.50k
	* Minimum: 0.25k
	* Flags: delayed

Allocation size for session structure and workspace.    The workspace is primarily used for TCP connection addresses.  If larger than 4k, use a multiple of 4k for VM efficiency.

.. _ref_param_workspace_thread:

workspace_thread
~~~~~~~~~~~~~~~~
	* Units: bytes
	* Default: 2k
	* Minimum: 0.25k
	* Maximum: 8k
	* Flags: delayed

Bytes of auxiliary workspace per thread.
This workspace is used for certain temporary data structures during the operation of a worker thread.
One use is for the IO-vectors used during delivery. Setting this parameter too low may increase the number of writev() syscalls, setting it too high just wastes space.  ~0.1k + UIO_MAXIOV * sizeof(struct iovec) (typically = ~16k for 64bit) is considered the maximum sensible value under any known circumstances (excluding exotic vmod use).

