Ubuntu Manpage: varnishd - HTTP accelerator daemon

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
              address: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 default. 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 varnishd 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 active 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 accessed 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 variable.

Relative paths will be appended to /var/lib/varnish.

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

Note: These defaults may be distribution specific.

Documentation options
For these options, varnishd prints information to standard output and exits. When a -x option is used, it
must be the only option (it outputs documentation 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 varnish-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 using 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 administrator 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 directory (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 together 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
parameter 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 storage 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 accessed using mmap. Note that
this storage provide no cache persistence.

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 region so that the kernel can
choose the appropriate read-ahead and caching techniques. Possible values are normal, random and
sequential, 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 options. 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-specification (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-specific 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 effective 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 management interface on the specified
address and port. The recommended way of connecting to the command-line management interface is through
varnishadm(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 allowed) 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 parameter. Feedback with experience
and observations are most welcome.

• delayed

This parameter can be changed on the fly, but will not take effect immediately.

• 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 reduced 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 platforms.

• Units: bool

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

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 altogether.

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%)

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, 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.

backend_wait_limit
• Default: 0

• Minimum: 0

• Flags: experimental

Maximum number of transactions that can queue waiting for a backend connection 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 transaction 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 matching 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_cutoff-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 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.

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.

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 objects. 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 contention.

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 incompatibilities percent characters
should be escaped with a double percent sequence.

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 parameter. 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 response 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 expired, 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, 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.

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-Modified, 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 requests.

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 majority 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 initial SETTINGS frame sent to the
client when a new HTTP2 session is established.

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 established.

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 established.

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 immediately.

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_period. 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 allocated 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 backend 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 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.

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 implementation 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 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.

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 entirely, 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 after 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 direction 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 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

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 segmentation 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 platforms.

• 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 platforms.

• 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 domain sockets.

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

• 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. Ignored for Unix domain sockets.

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

• 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 sending 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 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.

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 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.

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 panics 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 effect, 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 handle, 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 prevent 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 (granularity 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 directories 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 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.

vsl_mask
• Default:
all,-Debug,-ObjProtocol,-ObjStatus,-ObjReason,-ObjHeader,-ExpKill,-WorkThread,-Hash,-VfpAcct,-H2RxHdr,-H2RxBody,-H2TxHdr,-H2TxBody,-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 messages. 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 approximately 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 multiple 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 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).

EXIT CODES

       Varnish and bundled tools will, in most cases, exit with one of the following codes

       • 0 OK

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

       • 2  Serious  configuration / parameter error - retrying with the same configuration / 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.

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  Smørgrav  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 LICENCE for details.

       • Copyright (c) 2007-2015 Varnish Software AS

                                                                                                     VARNISHD(1)

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

RUN TIME PARAMETERS

EXIT CODES

SEE ALSO

HISTORY

COPYRIGHT