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VARNISHD(1)		     General Commands Manual		     VARNISHD(1)

NAME
     varnishd - HTTP accelerator daemon

SYNOPSIS
     varnishd
	    [-a      [name=][listen_address[,PROTO|,option=value,...]]	     [-b
	    [host[:port]|path]] [-C] [-d] [-F] [-f config]  [-h  type[,options]]
	    [-I  clifile] [-i identity] [-j jail[,jailoptions]] [-l vsl] [-M ad-
	    dress:port]  [-n   workdir]   [-P	file]	[-p   param=value]   [-r
	    param[,param...]]	[-S  secret-file] [-s [name=]kind[,options]] [-T
	    address[:port]] [-t TTL] [-V] [-W waiter]

     varnishd [-x parameter|vsl|cli|builtin|optstring]

     varnishd [-?]

DESCRIPTION
     The varnishd daemon accepts HTTP requests from clients, passes them on to a
     backend server and caches the returned documents to better  satisfy  future
     requests for the same document.

OPTIONS
   Basic options
     -a <[name=][listen_address[,PROTO|,option=value,...]]>
	    Generic  syntax  to  accept client requests on a listen_address. See
	    below for details.

	    Name is referenced in logs and available to vcl as local.socket.  If
	    name  is  not  specified,  a  with a numerical sequence ("a0", "a1",
	    etc.) is used.

	    Any arguments after the listen_address separated by comma are  taken
	    as	either	an acceptor option=value pair if containing a =, or as a
	    PROTO(col) selection otherwise.

	    Valid options depend on the acceptor type, see below.

	    PROTO can be "HTTP" (the default) or "PROXY".  Both version 1 and  2
	    of the proxy protocol can be used.

	    Multiple -a arguments are allowed.

	    If	no  -a	argument is given, the default -a :80 will listen on all
	    IPv4 and IPv6 interfaces.

     -a <[name=][ip_address][:port][,PROTO]>
	    The ip_address can be a host name ("localhost"), an IPv4 dotted-quad
	    ("127.0.0.1")  or  an  IPv6  address  enclosed  in	square	brackets
	    ("[::1]")

	    The port can be a port number (80), a service name (http), or a port
	    range (80-81). Port ranges are inclusive and cannot overlap. If port
	    is not specified, port 80 (http) is used.

	    At least one of ip_address or port is required.

     -a <[name=][path][,PROTO][,user=name][,group=name][,mode=octal]>
	    (VCL4.1 and higher)

	    Accept  connections  on a Unix domain socket.  Path must be absolute
	    ("/path/to/listen.sock") or "@" followed by the name of an	abstract
	    socket ("@myvarnishd").

	    The  user,	group  and mode sub-arguments may be used to specify the
	    permissions of the socket file -- use names for user and group,  and
	    a  3-digit octal value for mode. These sub-arguments do not apply to
	    abstract sockets.

     -b <[host[:port]|path]>
	    Use the specified host as backend server. If port is not  specified,
	    the default is 8080.

	    If	the value of -b begins with /, it is interpreted as the absolute
	    path of a Unix domain socket to  which  Varnish  connects.	In  that
	    case,  the	value of -b must satisfy the conditions required for the
	    .path field of a backend declaration,  see	vcl(7).   Backends  with
	    Unix socket addresses may only be used with VCL versions >= 4.1.

	    -b can be used only once, and not together with f.

     -f config
	    Use  the specified VCL configuration file instead of the builtin de-
	    fault.  See vcl(7) for details on VCL syntax.

	    If a single -f option is used, then the VCL instance loaded from the
	    file is named "boot" and immediately becomes active.  If  more  than
	    one  -f option is used, the VCL instances are named "boot0", "boot1"
	    and so forth, in the order corresponding to the  -f  arguments,  and
	    the last one is named "boot", which becomes active.

	    Either -b or one or more -f options must be specified, but not both,
	    and  they  cannot  both be left out, unless -d is used to start var-
	    nishd in debugging mode. If the empty string  is  specified  as  the
	    sole  -f  option,  then  varnishd starts without starting the worker
	    process, and the management process will accept CLI  commands.   You
	    can  also  combine	an empty -f option with an initialization script
	    (-I option) and the child process will be started if there is an ac-
	    tive VCL at the end of the initialization.

	    When used with a relative file  name,  config  is  searched  in  the
	    vcl_path.  It is possible to set this path prior to using -f options
	    with a -p option. During startup, varnishd	doesn't  complain  about
	    unsafe  VCL paths: unlike the varnish-cli(7) that could later be ac-
	    cessed remotely, starting varnishd requires local privileges.

     -n workdir
	    Runtime directory for the shared memory, compiled VCLs etc.

	    In performance critical applications, this directory should be on  a
	    RAM backed filesystem.

	    When  running multiple varnishd instances, separate directories need
	    to be used.

	    The default is taken from the  VARNISH_DEFAULT_N  environment  vari-
	    able.

	    Relative paths will be appended to /usr/local/varnish.

	    If	neither  VARNISH_DEFAULT_N  nor  -n  are  present,  the value is
	    /usr/local/varnish/varnishd.

	    Note: These defaults may be distribution specific.

   Documentation options
     For these options, varnishd prints information to standard output	and  ex-
     its. When a -x option is used, it must be the only option (it outputs docu-
     mentation in reStructuredText, aka RST).

     -?
	Print the usage message.

     -x parameter
	    Print documentation of the runtime parameters (-p options), see List
	    of Parameters.

     -x vsl
	    Print  documentation  of  the tags used in the Varnish shared memory
	    log, see vsl(7).

     -x cli
	    Print  documentation  of  the  command  line  interface,  see   var-
	    nish-cli(7).

     -x builtin
	    Print the contents of the default VCL program builtin.vcl.

     -x optstring
	    Print  the	optstring parameter to getopt(3) to help writing wrapper
	    scripts.

   Operations options
     -F     Do not fork, run in the foreground. Only one of  -F  or  -d  can  be
	    specified, and -F cannot be used together with -C.

     -T <address[:port]>
	    Offer  a management interface on the specified address and port. See
	    varnish-cli(7) for documentation of  the  management  commands.   To
	    disable the management interface use none.

     -M <address:port>
	    Connect to this port and offer the command line interface.	Think of
	    it	as a reverse shell. When running with -M and there is no backend
	    defined the child process (the cache) will not start initially.

     -P file
	    Write the PID of the process to the specified file.

     -i identity
	    Specify the identity of the Varnish server. This can be accessed us-
	    ing server.identity from VCL.

	    The server identity is used for the received-by field of Via headers
	    generated by Varnish. For this reason, it must be a valid  token  as
	    defined by the HTTP grammar.

	    If not specified the output of gethostname(3) is used, in which case
	    the syntax is assumed to be correct.

     -I clifile
	    Execute  the management commands in the file given as clifile before
	    the worker process starts, see CLI Command File.

   Tuning options
     -t TTL
	    Specifies the default time to live (TTL) for cached objects. This is
	    a shortcut for specifying the default_ttl run-time parameter.

     -p <param=value>
	    Set the parameter specified by param to  the  specified  value,  see
	    List  of  Parameters  for  details. This option can be used multiple
	    times to specify multiple parameters.

     -s <[name=]type[,options]>
	    Use the specified storage backend. See Storage Backend section.

	    This option can be used multiple times to specify  multiple  storage
	    files.  Name is referenced in logs, VCL, statistics, etc. If name is
	    not specified, "s0", "s1" and so forth is used.

     -l <vsl>
	    Specifies size of the space for the VSL records,  shorthand  for  -p
	    vsl_space=<vsl>. Scaling suffixes like 'K' and 'M' can be used up to
	    (G)igabytes. See vsl_space for more information.

   Security options
     -r <param[,param...]>
	    Make the listed parameters read only. This gives the system adminis-
	    trator  a way to limit what the Varnish CLI can do.  Consider making
	    parameters such as cc_command, vcc_allow_inline_c and vmod_path read
	    only as these can potentially be used to  escalate	privileges  from
	    the CLI.

     -S secret-file
	    Path  to  a  file containing a secret used for authorizing access to
	    the management port. To disable authentication use none.

	    If this argument is not provided, a secret	drawn  from  the  system
	    PRNG will be written to a file called _.secret in the working direc-
	    tory  (see opt_n) with default ownership and permissions of the user
	    having started varnish.

	    Thus, users wishing to delegate control over varnish  will	probably
	    want  to  create  a  custom secret file with appropriate permissions
	    (ie. readable by a unix group to delegate control to).

     -j <jail[,jailoptions]>
	    Specify the jailing mechanism to use. See Jail section.

   Advanced, development and debugging options
     -d     Enables debugging mode: The parent process runs  in  the  foreground
	    with a CLI connection on stdin/stdout, and the child process must be
	    started  explicitly  with  a  CLI  command.  Terminating  the parent
	    process will also terminate the child.

	    Only one of -d or -F can be specified, and -d  cannot  be  used  to-
	    gether with -C.

     -C     Print VCL code compiled to C language and exit. Specify the VCL file
	    to compile with the -f option. Either -f or -b must be used with -C,
	    and -C cannot be used with -F or -d.

     -V     Display the version number and exit. This must be the only option.

     -h <type[,options]>
	    Specifies  the hash algorithm. See Hash Algorithm section for a list
	    of supported algorithms.

     -W waiter
	    Specifies the waiter type to use.

   Hash Algorithm
     The following hash algorithms are available:

     -h critbit
	    self-scaling tree structure. The default hash algorithm  in  Varnish
	    Cache  2.1	and  onwards. In comparison to a more traditional B tree
	    the critbit tree is almost completely lockless. Do not  change  this
	    unless you are certain what you're doing.

     -h simple_list
	    A simple doubly-linked list.  Not recommended for production use.

     -h <classic[,buckets]>
	    A standard hash table. The hash key is the CRC32 of the object's URL
	    modulo  the  size  of  the hash table.  Each table entry points to a
	    list of elements which share the same hash key. The buckets  parame-
	    ter  specifies the number of entries in the hash table.  The default
	    is 16383.

   Storage Backend
     Multiple storage backends (where the cached and in-flight objects are held)
     can be defined, and VCL can pilot	which  store  is  used	by  setting  the
     beresp.storage variable (see man vcl-var for more information).

     The argument format to define storage backends is:

     -s <[name]=kind[,options]>
	    If	name is omitted, Varnish will name storages sN, starting with s0
	    and incrementing N for every new storage.

	    For kind and options see details below.

     Storages can be used in vcl as storage.name, so, for example  if  myStorage
     was defined by -s myStorage=malloc,5G, it could be used in VCL like so:

	set beresp.storage = storage.myStorage;

     A	special  name  is Transient which is the default storage for uncacheable
     objects as resulting from a pass, hit-for-miss or hit-for-pass.

     If no -s options are given, the default is:

	-s default,100m

     If no Transient storage is defined, the default is an unbound default stor-
     age as if defined as:

	-s Transient=default

     The following storage types and options are available:

     -s <default[,size]>
	    The default storage type resolves to umem where available and malloc
	    otherwise.

     -s <malloc[,size]>
	    malloc is a memory based backend.

     -s <umem[,size]>
	    umem is a storage backend which is more  efficient	than  malloc  on
	    platforms where it is available.

	    See  the  section on umem in chapter Storage backends of The Varnish
	    Users Guide for details.

     -s <file,path[,size[,granularity[,advice]]]>
	    The file backend stores data in a file on disk. The file will be ac-
	    cessed using mmap. Note that this storage provide no  cache  persis-
	    tence.

	    The  path  is  mandatory. If path points to a directory, a temporary
	    file will be created in that directory and immediately unlinked.  If
	    path points to a non-existing file, the file will be created.

	    If	size is omitted, and path points to an existing file with a size
	    greater than zero, the size of that file will be used.  If	not,  an
	    error is reported.

	    Granularity  sets  the allocation block size. Defaults to the system
	    page size or the filesystem block size, whichever is larger.

	    Advice tells the kernel how varnishd expects to use this mapped  re-
	    gion  so  that  the kernel can choose the appropriate read-ahead and
	    caching techniques. Possible values are normal, random  and  sequen-
	    tial,  corresponding to MADV_NORMAL, MADV_RANDOM and MADV_SEQUENTIAL
	    madvise() advice argument, respectively. Defaults to random.

     -s <persistent,path,size>
	    Persistent storage. Varnish will store objects in a file in a manner
	    that will secure the survival of most of the objects in the event of
	    a planned or unplanned shutdown of Varnish. The  persistent  storage
	    backend  has multiple issues with it and will likely be removed from
	    a future version of Varnish.

   Jail
     Varnish jails are a generalization over various platform  specific  methods
     to  reduce  the privileges of varnish processes. They may have specific op-
     tions. Available jails are:

     -j <solaris[,worker=`privspec`]>
	    Reduce privileges(5) for varnishd and sub-processes to the minimally
	    required set. Only available on platforms which have the setppriv(2)
	    call.

	    The optional worker argument can be used to pass a	privilege-speci-
	    fication  (see ppriv(1)) by which to extend the effective set of the
	    varnish worker process. While extended privileges may be required by
	    custom vmods, not using the worker option is always more secure.

	    Example to grant basic privileges to the worker process:

	       -j solaris,worker=basic

     -j <linux[,transparent_hugepage=`thp_setting`][,`unixjailoption`...]>
	    Default on Linux platforms, it extends the UNIX jail with Linux-spe-
	    cific mechanisms:

	    * It warns when workdir is not on a tmpfs.

	    * It tries to keep the process dumpable after dropping privileges.

	    * It adds control over the transparent hugepage (THP) setting.

	    thp_setting can take these values:

	    * ignore: Do nothing

	    * enable: Enable THP (see Note below)

	    * disable: Disable THP

	    * try-disable (default): Try to disable, ignore failure (but emit  a
	      warning)

	    Note:  Technically,  enable is "disable the disable", so it does not
	    necessarily enable THP. The setting names have been chosen to  avoid
	    a confusing double negation.

     -j <unix[,user=`user`][,ccgroup=`group`][,workuser=`user`]>
	    Default  on all other platforms when varnishd is started with an ef-
	    fective uid of 0 ("as root").

	    With the unix jail mechanism activated, varnish will  switch  to  an
	    alternative  user  for  subprocesses and change the effective uid of
	    the master process whenever possible.

	    The optional user argument specifies which alternative user to  use.
	    It defaults to varnish.

	    The  optional  ccgroup  argument specifies a group to add to varnish
	    subprocesses requiring access to a c-compiler. There is no default.

	    The optional workuser argument specifies an alternative user to  use
	    for the worker process. It defaults to vcache.

	    The users given for the user and workuser arguments need to have the
	    same primary ("login") group.

	    To	set up a system for the default users with a group name varnish,
	    shell commands similar to these may be used:

	       groupadd varnish
	       useradd -g varnish -d /nonexistent -s /bin/false \
		 -c "Varnish-Cache Daemon User" varnish
	       useradd -g varnish -d /nonexistent -s /bin/false \
		 -c "Varnish-Cache Worker User" vcache

     -j none
	    last resort jail choice: With jail mechanism none, varnish will  run
	    all processes with the privileges it was started with.

   Management Interface
     If  the -T option was specified, varnishd will offer a command-line manage-
     ment interface on the specified address and port.	The recommended  way  of
     connecting  to  the  command-line	management  interface  is  through  var-
     nishadm(1).

     The commands available are documented in varnish-cli(7).

   CLI Command File
     The -I option makes it possible to run arbitrary management  commands  when
     varnishd  is launched, before the worker process is started. In particular,
     this is the way to load configurations, apply labels to them,  and  make  a
     VCL instance active that uses those labels on startup:

	vcl.load panic /etc/varnish_panic.vcl
	vcl.load siteA0 /etc/varnish_siteA.vcl
	vcl.load siteB0 /etc/varnish_siteB.vcl
	vcl.load siteC0 /etc/varnish_siteC.vcl
	vcl.label siteA siteA0
	vcl.label siteB siteB0
	vcl.label siteC siteC0
	vcl.load main /etc/varnish_main.vcl
	vcl.use main

     Every  line  in  the file, including the last line, must be terminated by a
     newline or carriage return or is otherwise considered truncated, which is a
     fatal error.

     If a command in the file is prefixed with '-', failure will not  abort  the
     startup.

     Note  that it is necessary to include an explicit vcl.use command to select
     which VCL should be the active VCL when relying on CLI Command File to load
     the configurations at startup.

RUN TIME PARAMETERS
     Runtime parameters can either be set during startup  with	the  -p  command
     line  option  for	varnishd(1)  or  through  the CLI using the param.set or
     param.reset commands. They can be locked during startup with the -r command
     line option.

   Run Time Parameter Units
     There are different types of parameters that may accept a list of	specific
     values, or optionally take a unit suffix.

   bool
     A boolean parameter accepts the values on and off.

     It will also recognize the following values:

     * yes and no

     * true and false

     * enable and disable

   bytes
     A bytes parameter requires one of the following units suffixes:

     * b (bytes)

     * k (kibibytes, 1024 bytes)

     * m (mebibytes, 1024 kibibytes)

     * g (gibibytes, 1024 mebibytes)

     * t (tebibytes, 1024 gibibytes)

     * p (pebibytes, 1024 tebibytes)

     Multiplicator  units  may	be  appended with an extra b. For example 32k is
     equivalent to 32kb. Bytes units are case-insensitive.

   seconds
     A duration parameter may accept the following units suffixes:

     * ms (milliseconds)

     * s (seconds)

     * m (minutes)

     * h (hours)

     * d (days)

     * w (weeks)

     * y (years)

     If the parameter is a timeout or a deadline, a value of "never"  (when  al-
     lowed) disables the effect of the parameter.

   Run Time Parameter Flags
     Runtime  parameters  are marked with shorthand flags to avoid repeating the
     same text over and over in the table below. The meaning of the flags are:

     * experimental

       We have no solid information about good/bad/optimal values for this para-
       meter. Feedback with experience and observations are most welcome.

     * delayed

       This parameter can be changed on the fly, but will not take effect  imme-
       diately.

     * restart

       The  worker  process must be stopped and restarted, before this parameter
       takes effect.

     * reload

       The VCL programs must be reloaded for this parameter to take effect.

     * wizard

       Do not touch unless you really know what you're doing.

     * only_root

       Only works if varnishd is running as root.

   Default Value Exceptions on 32 bit Systems
     Be aware that on 32 bit systems, certain default or maximum values are  re-
     duced relative to the values listed below, in order to conserve VM space:

     * workspace_client: 24k

     * workspace_backend: 20k

     * http_resp_size: 8k

     * http_req_size: 12k

     * gzip_buffer: 4k

     * vsl_buffer: 4k

     * vsl_space: 1G (maximum)

     * thread_pool_stack: 64k

   List of Parameters
     This  text  is  produced from the same text you will find in the CLI if you
     use the param.show command:

   accept_filter
     NB: This parameter depends on a feature which is not available on all plat-
     forms.

	* Units: bool

	* Default: on (if your platform supports accept filters)

	* Flags: must_restart

     Enable kernel accept-filters. This may require a kernel module to be loaded
     to have an effect when enabled.

     Enabling accept_filter may prevent some requests to reach	Varnish  in  the
     first  place.  Malformed  requests  may  go  unnoticed and not increase the
     client_req_400 counter. GET or HEAD requests with a body may be blocked al-
     together.

   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) re-
     duce the sleep duration for each successful accept. (ie: 0.9  =  reduce  by
     10%)

   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.

   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.

   auto_restart
	* Units: bool

	* Default: on

     Automatically restart the child/worker process if it dies.

   backend_idle_timeout
	* Units: seconds

	* Default: 60.000

	* Minimum: 1.000

     Timeout before we close unused backend connections.

   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.

   backend_remote_error_holddown
	* Units: seconds

	* Default: 0.250

	* Minimum: 0.000

	* Flags: experimental

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

   backend_wait_limit
	* Default: 0

	* Minimum: 0

	* Flags: experimental

     Maximum number of transactions that can queue waiting for a backend connec-
     tion to become available.	This default of 0 (zero) means that there is  no
     transaction queueing. VCL can override this default value for each backend.

     Note  that  this feature must be used with caution, as it can cause threads
     to pile up and increase response times.

   backend_wait_timeout
	* Units: seconds

	* Default: 0.000

	* Minimum: 0.000

	* Flags: timeout, experimental

     When a backend has no connections available for a transaction, the transac-
     tion can be queued (see backend_wait_limit) to wait for a connection.  This
     is the default time that the transaction will wait before	giving	up.  VCL
     can override this default value for each backend.

     It is strongly advised to never set this higher than a couple of seconds.

   ban_any_variant
	* Units: checks

	* Default: 10000

	* Minimum: 0

     Maximum  number  of possibly non matching variants that we evaluate against
     the ban list during a lookup.  Setting this to 0 means that only the match-
     ing variants will be evaluated against the current ban list.

   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_cut-
     off-th ban, it treats all objects as if they matched  a  ban  and	expunges
     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 be-
     ing 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.

   ban_dups
	* Units: bool

	* Default: on

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

   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.

   ban_lurker_batch
	* Default: 1000

	* Minimum: 1

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

   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 con-
     tention.

   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.

   between_bytes_timeout
	* Units: seconds

	* Default: 60.000

	* Minimum: 0.000

	* Flags: timeout

     We  only wait for this many seconds between bytes received from the backend
     before giving up the fetch.  VCL values, per backend or per backend request
     take precedence.  This parameter does not apply to pipe'ed requests.

   cc_command
     NB: The actual default value for this  parameter  depends	on  the  Varnish
     build environment and options.

	* Default: exec $CC $CFLAGS %w -shared -o %o %s

	* Flags: must_reload

     The  command  used  for compiling the C source code to a dlopen(3) loadable
     object. The following expansions can be used:

     * %s: the source file name

     * %o: the output file name

     * %w: the cc_warnings parameter

     * %d: the raw default cc_command

     * %D: the expanded default cc_command

     * %n: the working directory (-n option)

     * %%: a percent sign

     Unknown percent expansion sequences are ignored, and to avoid future incom-
     patibilities percent characters should be escaped with a double percent se-
     quence.

     The %d and %D expansions allow passing the parameter's default value  to  a
     wrapper script to perform additional processing.

   cc_warnings
     NB:  The  actual  default	value  for this parameter depends on the Varnish
     build environment and options.

	* Default: -Wall -Werror

	* Flags: must_reload

     Warnings used when compiling the C source code with the cc_command  parame-
     ter.  By  default, VCL is compiled with the same set of warnings as Varnish
     itself.

   cli_limit
	* Units: bytes

	* Default: 64k

	* Minimum: 128b

	* Maximum: 99999999b

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

   cli_timeout
	* Units: seconds

	* Default: 60.000

	* Minimum: 0.000

	* Flags: timeout

     Timeout for the child's replies to CLI requests.

   clock_skew
	* Units: seconds

	* Default: 10

	* Minimum: 0

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

   clock_step
	* Units: seconds

	* Default: 1.000

	* Minimum: 0.000

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

   connect_timeout
	* Units: seconds

	* Default: 3.500

	* Minimum: 0.000

	* Flags: timeout

     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.

   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.

   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

	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

	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

	lck    Additional lock statistics

   default_grace
	* Units: seconds

	* Default: 10s

	* Minimum: 0.000

	* Flags: obj_sticky

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

   default_keep
	* Units: seconds

	* Default: 0s

	* Minimum: 0.000

	* Flags: obj_sticky

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

   default_ttl
	* Units: seconds

	* Default: 2m

	* Minimum: 0.000

	* Flags: obj_sticky

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

   experimental
	* Default: none

     Enable/Disable experimental features.

	none   Disable all experimental features

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

	drop_pools
	       Drop thread pools

   feature
	* Default: none,+validate_headers,+vcl_req_reset

     Enable/Disable various minor features.

	default
	       Set default value (deprecated: use param.reset)

	none   Disable all features.

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

	http2  Enable HTTP/2 protocol support.

	short_panic
	       Short panic message.

	no_coredump
	       No coredumps.  Must be set before child process starts.

	https_scheme
	       Extract host from full URI in the HTTP/1  request  line,  if  the
	       scheme is https.

	http_date_postel
	       Tolerate  non  compliant  timestamp headers like Date, Last-Modi-
	       fied, Expires etc.

	esi_ignore_https
	       Convert <esi:include src"https://... to http://...

	esi_disable_xml_check
	       Allow ESI processing on non-XML ESI bodies

	esi_ignore_other_elements
	       Ignore XML syntax errors in ESI bodies.

	esi_remove_bom
	       Ignore UTF-8 BOM in ESI bodies.

	esi_include_onerror
	       Parse the onerror attribute of <esi:include> tags.

	wait_silo
	       Wait for persistent silos to completely load before  serving  re-
	       quests.

	validate_headers
	       Validate  all header set operations to conform to RFC9110 section
	       5.5.

	busy_stats_rate
	       Make busy workers comply with thread_stats_rate.

	trace  Enable VCL tracing by default  (enable  (be)req.trace).	Required
	       for tracing vcl_init / vcl_fini

	vcl_req_reset
	       Stop  processing  client  VCL  once the client is gone. When this
	       happens MAIN.req_reset is incremented.

   fetch_chunksize
	* Units: bytes

	* Default: 16k

	* Minimum: 4k

	* Flags: experimental

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

   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.

   first_byte_timeout
	* Units: seconds

	* Default: 60.000

	* Minimum: 0.000

	* Flags: timeout

     Default  timeout  for  receiving  first byte from backend. We only wait for
     this many seconds for the first byte before giving up.   VCL  can	override
     this  default  value  for each backend and backend request.  This parameter
     does not apply to pipe'ed requests.

   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.

   gzip_level
	* Default: 6

	* Minimum: 0

	* Maximum: 9

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

   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.

   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.

     The  value of this parameter defines SETTINGS_HEADER_TABLE_SIZE in the ini-
     tial SETTINGS frame sent to the client when a new HTTP2 session  is  estab-
     lished.

   h2_initial_window_size
	* Units: bytes

	* Default: 65535b

	* Minimum: 65535b

	* Maximum: 2147483647b

     HTTP2 initial flow control window size.

     The  value  of  this  parameter defines SETTINGS_INITIAL_WINDOW_SIZE in the
     initial SETTINGS frame sent to the client when a new HTTP2 session  is  es-
     tablished.

   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.

     The  value of this parameter defines SETTINGS_MAX_CONCURRENT_STREAMS in the
     initial SETTINGS frame sent to the client when a new HTTP2 session  is  es-
     tablished.

   h2_max_frame_size
	* Units: bytes

	* Default: 16k

	* Minimum: 16k

	* Maximum: 16777215b

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

     The  value of this parameter defines SETTINGS_MAX_FRAME_SIZE in the initial
     SETTINGS frame sent to the client when a new HTTP2 session is established.

   h2_max_header_list_size
	* Units: bytes

	* Default: 0b

	* Minimum: 0b

	* Maximum: 2147483647b

     HTTP2 maximum size of an uncompressed header list. This  parameter  is  not
     mapped  to SETTINGS_MAX_HEADER_LIST_SIZE in the initial SETTINGS frame, the
     http_req_size parameter is instead.

     The http_req_size advises HTTP2 clients of the maximum size for the  header
     list.  Exceeding  http_req_size  results in a reset stream after processing
     the   HPACK   block   to	preserve   the	 connection,	but    exceeding
     h2_max_header_list_size  results in the HTTP2 connection going away immedi-
     ately.

     If h2_max_header_list_size is lower than http_req_size, it has  no  effect,
     except for the special value zero interpreted as 150% of http_req_size.

   h2_rapid_reset
	* Units: seconds

	* Default: 1.000

	* Minimum: 0.000

	* Flags: delayed, experimental

     The  upper  threshold  for  how  soon  an http/2 RST_STREAM frame has to be
     parsed after a HEADERS frame for it to be treated as suspect and  subjected
     to the rate limits specified by h2_rapid_reset_limit and h2_rapid_reset_pe-
     riod.  Changes to this parameter affect the default for new HTTP2 sessions.
     vmod_h2(3) can be used to adjust it from VCL.

   h2_rapid_reset_limit
	* Default: 100

	* Minimum: 0

	* Flags: delayed, experimental

     HTTP2 RST Allowance.  Specifies the maximum number of allowed stream resets
     issued  by  a  client  over  a time period before the connection is closed.
     Setting this parameter to 0 disables the limit.  Changes to this  parameter
     affect the default for new HTTP2 sessions. vmod_h2(3) can be used to adjust
     it from VCL.

   h2_rapid_reset_period
	* Units: seconds

	* Default: 60.000

	* Minimum: 1.000

	* Flags: delayed, experimental, wizard

     HTTP2  sliding  window  duration for h2_rapid_reset_limit.  Changes to this
     parameter affect the default for new HTTP2 sessions. vmod_h2(3) can be used
     to adjust it from VCL.

   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.)

   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.)

   h2_rxbuf_storage
	* Default: Transient

	* Flags: must_restart

     The name of the storage backend that HTTP/2 receive buffers should be allo-
     cated from.

   h2_window_timeout
	* Units: seconds

	* Default: 5.000

	* Minimum: 0.000

	* Flags: timeout, wizard

     HTTP2 time limit without window credits. How long a stream may wait for the
     client to credit the window and allow for more DATA frames to be sent.

   http1_iovs
	* Units: struct iovec (=16 bytes)

	* Default: 64

	* Minimum: 5

	* Maximum: 1024

	* Flags: wizard

     Number of io vectors to allocate for HTTP1 protocol transmission.	A  HTTP1
     header needs 7 + 2 per HTTP header field.	Allocated from workspace_thread.
     This parameter affects only io vectors used for client delivery.  For back-
     end fetches, the maximum number of io vectors (up to IOV_MAX)  is allocated
     from available workspace_thread memory.

   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 re-
     moved. For more information on how gzip is implemented please see the chap-
     ter 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.

   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.

   http_range_support
	* Units: bool

	* Default: on

     Enable support for HTTP Range headers.

   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.

   http_req_overflow_status
	* Units: HTTP status code or 0 to disable

	* Default: 0

	* Minimum: 400

	* Maximum: 499

     HTTP status code to be returned if http_req_size is exceeded.  The  default
     value  of 0 closes the connection silently without sending a HTTP response.
     Note that there is no standard HTTP status which exactly matches the imple-
     mentation of http_req_size. 414 applies to the URL only, while 413  applies
     to  the request body. 400 is probably the least incorrect alternative value
     to sending no response at all (0).

   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.

     For  HTTP2 clients, it is advertised as MAX_HEADER_LIST_SIZE in the initial
     SETTINGS frame.

   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.

   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 re-
     sponse.  The memory for the response is allocated from  the  backend  work-
     space (param: workspace_backend) and this parameter limits how much of that
     the response is allowed to take up.

   idle_send_timeout
	* Units: seconds

	* Default: 60.000

	* Minimum: 0.000

	* Maximum: 3600.000

	* Flags: timeout, 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) or socket(7) under SO_SNDTIMEO for  more
     information.

   listen_depth
	* Units: connections

	* Default: 1024

	* Minimum: 0

	* Flags: must_restart

     Listen queue depth.

   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.

   max_esi_depth
	* Units: levels

	* Default: 5

	* Minimum: 0

     Maximum depth of esi:include processing.

   max_restarts
	* Units: restarts

	* Default: 4

	* Minimum: 0

	* Flags: delayed

     Upper limit on how many times a request can restart.

   max_retries
	* Units: retries

	* Default: 4

	* Minimum: 0

	* Flags: delayed

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

   max_vcl
	* Default: 100

	* Minimum: 0

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

   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.

   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.

   panic_buffer
	* Units: bytes

	* Default: 64k

	* Minimum: 4k

	* Maximum: 10M

	* Flags: must_restart

     Size  of  the  panic  message buffer.  The panic buffer is allocated in the
     working directory as  memory  shared  between  the  management  and  worker
     process,  so  sufficient working directory space should be accounted for if
     this value is adjusted. Panic messages  are  truncated  to  the  configured
     size.

   pcre2_depth_limit
	* Default: 20

	* Minimum: 1

     The recursion depth-limit for the internal match logic in a pcre2_match().

     (See: pcre2_set_depth_limit() in pcre2 docs.)

     This  puts  an upper limit on the amount of stack used by PCRE2 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.

   pcre2_jit_compilation
	* Units: bool

	* Default: on

     Use the pcre2 JIT compiler if available.

   pcre2_match_limit
	* Default: 10000

	* Minimum: 1

     The  limit  for  the  number  of  calls  to  the  internal  match	logic in
     pcre2_match().

     (See: pcre2_set_match_limit() in pcre2 docs.)

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

   ping_interval
	* Units: seconds

	* Default: 3

	* Minimum: 0

	* Flags: must_restart

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

   pipe_sess_max
	* Units: connections

	* Default: 0

	* Minimum: 0

     Maximum number of sessions dedicated to pipe transactions.

   pipe_task_deadline
	* Units: seconds

	* Default: 0.000

	* Minimum: 0.000

	* Flags: timeout

     Deadline  for PIPE sessions. Regardless of activity in either direction af-
     ter this many seconds, the session is closed.

   pipe_timeout
	* Units: seconds

	* Default: 60.000

	* Minimum: 0.000

	* Flags: timeout

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

   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.

   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.

   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.

   prefer_ipv6
	* Units: bool

	* Default: off

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

   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 implicit delay of delivery, this  parameter  controls  an
     exponential increase in number of worker threads.

   send_timeout
	* Units: seconds

	* Default: 600.000

	* Minimum: 0.000

	* Flags: timeout, delayed

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

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

     When this timeout is hit, the session is closed

   shortlived
	* Units: seconds

	* Default: 10.000

	* Minimum: 0.000

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

   sigsegv_handler
	* Units: bool

	* Default: on

	* Flags: must_restart

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

   startup_timeout
	* Units: seconds

	* Default: 0.000

	* Minimum: 0.000

	* Flags: timeout

     Alternative timeout for the initial worker process startup.  If cli_timeout
     is longer than startup_timeout, it is used instead.

   syslog_cli_traffic
	* Units: bool

	* Default: on

     Log all CLI traffic to syslog(LOG_INFO).

   tcp_fastopen
     NB: This parameter depends on a feature which is not available on all plat-
     forms.

	* Units: bool

	* Default: off

	* Flags: must_restart

     Enable TCP Fast Open extension.

   tcp_keepalive_intvl
     NB: This parameter depends on a feature which is not available on all plat-
     forms.

	* Units: seconds

	* Default: platform dependent

	* Minimum: 1.000

	* Maximum: 100.000

	* Flags: experimental

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

   tcp_keepalive_probes
     NB: This parameter depends on a feature which is not available on all plat-
     forms.

	* Units: probes

	* Default: platform dependent

	* 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. Ig-
     nored for Unix domain sockets.

   tcp_keepalive_time
     NB: This parameter depends on a feature which is not available on all plat-
     forms.

	* Units: seconds

	* Default: platform dependent

	* Minimum: 1.000

	* Maximum: 7200.000

	* Flags: experimental

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

   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.

   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).

   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.

   thread_pool_max
	* Units: threads

	* Default: 5000

	* Minimum: thread_pool_min

	* Flags: delayed

     The maximum number of worker threads in each pool.

     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.

   thread_pool_min
	* Units: threads

	* Default: 100

	* Minimum: 5

	* Maximum: thread_pool_max

	* Flags: delayed

     The minimum number of worker threads in each pool.

     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

   thread_pool_reserve
	* Units: threads

	* Default: 0 (auto-tune: 5% of thread_pool_min)

	* Maximum: 95% of thread_pool_min

	* 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 re-
     quests). 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.

   thread_pool_stack
	* Units: bytes

	* Default: 80k

	* Minimum: sysconf(_SC_THREAD_STACK_MIN)

	* 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 circum-
     stances, 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.

   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.

   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 pan-
     ics itself.

   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 ef-
     fect, unless the drop_pools experimental debug flag is set.

   thread_queue_limit
	* Units: requests

	* 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.

   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 han-
     dle,  before  it  is  forced  to dump its accumulated stats into the global
     counters.

   timeout_idle
	* Units: seconds

	* Default: 5.000

	* Minimum: 0.000

	* Maximum: 3600.000

     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.

   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.

   transit_buffer
	* Units: bytes

	* Default: 0b

	* Minimum: 0b

     The number of bytes which Varnish buffers for uncacheable backend streaming
     fetches - in other words, how many bytes Varnish  reads  from  the  backend
     ahead  of	what  has been sent to the client.  A zero value means no limit,
     the object is fetched as fast as possible.

     When dealing with slow clients, setting this parameter to non-zero can pre-
     vent large uncacheable objects from being stored in full when the intent is
     to simply stream them to the client. As a result, a slow client transaction
     holds onto a backend connection until the end of the delivery.

     This parameter is the default to the  VCL	variable  beresp.transit_buffer,
     which can be used to control the transit buffer per backend request.

   vary_notice
	* Units: variants

	* Default: 10

	* Minimum: 1

     How  many variants need to be evaluated to log a Notice that there might be
     too many variants.

   vcc_allow_inline_c
     Deprecated alias for the vcc_feature parameter.

   vcc_err_unref
     Deprecated alias for the vcc_feature parameter.

   vcc_feature
	* Default: none,+err_unref,+unsafe_path

     Enable/Disable various VCC behaviors.

	default
	       Set default value (deprecated: use param.reset)

	none   Disable all behaviors.

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

	err_unref
	       Unreferenced VCL objects result in error.

	allow_inline_c
	       Allow inline C code in VCL.

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

   vcc_unsafe_path
     Deprecated alias for the vcc_feature parameter.

   vcl_cooldown
	* Units: seconds

	* Default: 600.000

	* Minimum: 1.000

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

   vcl_path
     NB:  The  actual  default	value  for this parameter depends on the Varnish
     build environment and options.

	* Default: ${sysconfdir}/varnish:${datadir}/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  direc-
     tories  to  allow	packages  to drop their VCL files in a standard location
     where relative includes would work. Includes using +glob cannot be searched
     in vcl_path.

   vmod_path
     NB: The actual default value for this  parameter  depends	on  the  Varnish
     build environment and options.

	* Default: ${libdir}/varnish/vmods

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

   vsl_buffer
	* Units: bytes

	* Default: 16k

	* Minimum: vsl_reclen + 12 bytes

     Bytes of (req-/backend-)workspace dedicated to buffering VSL records.  When
     this  parameter  is  adjusted,  most  likely  workspace_client  and   work-
     space_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.

   vsl_mask
	* Default: all,-Debug,-ObjProtocol,-ObjStatus,-ObjReason,-ObjHeader,-Ex-
	  pKill,-WorkThread,-Hash,-VfpAcct,-H2RxHdr,-H2RxBody,-H2TxHdr,-H2Tx-
	  Body,-VdpAcct

     Mask individual VSL messages from being logged.

	all    Enable all tags

	default
	       Set default value (deprecated: use param.reset)

     Use +/- prefix in front of VSL tag name to unmask/mask individual VSL  mes-
     sages. See vsl(7) for possible values.

   vsl_reclen
	* Units: bytes

	* Default: 255b

	* Minimum: 16b

	* Maximum: vsl_buffer - 12 bytes

     Maximum number of bytes in SHM log record.

   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.

   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 approxi-
     mately 2 seconds).

   workspace_backend
	* Units: bytes

	* Default: 96k

	* 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.

   workspace_client
	* Units: bytes

	* Default: 96k

	* 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.

   workspace_session
	* Units: bytes

	* Default: 0.75k

	* Minimum: 384b

	* Flags: delayed

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

   workspace_thread
	* Units: bytes

	* Default: 2k

	* Minimum: 0.25k

	* Maximum: 8k

	* Flags: delayed

     Bytes of auxiliary workspace per thread.  This workspace is used  for  cer-
     tain  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).

EXIT CODES
     Varnish and bundled tools will, in most cases, exit with one of the follow-
     ing codes

     * 0 OK

     * 1 Some error which could be system-dependent and/or transient

     * 2 Serious configuration / parameter error - retrying with the  same  con-
       figuration / parameters is most likely useless

     The varnishd master process may also OR its exit code

     * with 0x20 when the varnishd child process died,

     * with 0x40 when the varnishd child process was terminated by a signal and

     * with 0x80 when a core was dumped.

SEE ALSO
     * varnishlog(1)

     * varnishhist(1)

     * varnishncsa(1)

     * varnishstat(1)

     * varnishtop(1)

     * varnish-cli(7)

     * vcl(7)

HISTORY
     The  varnishd daemon was developed by Poul-Henning Kamp in cooperation with
     Verdens Gang AS and Varnish Software.

     This manual page was written by Dag-Erling SmA,rgrav with updates	by  Stig
     Sandbeck Mathisen < <ssm@debian.org> >, Nils Goroll and others.

COPYRIGHT
     This document is licensed under the same licence as Varnish itself. See LI-
     CENCE for details.

     * Copyright (c) 2007-2015 Varnish Software AS

								     VARNISHD(1)

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