VARNISHD(1)                                                        VARNISHD(1)

       varnishd - HTTP accelerator daemon

       varnishd [-a
       [-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 name] [-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 [-?]

       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.

   Basic options
          Listen for client requests on the specified address and port. The
          address can be a host name ("localhost"), an IPv4 dotted-quad
          (""), an IPv6 address enclosed in square brackets
          ("[::1]"), or a path beginning with a '/' for a Unix domain socket
          ("/path/to/listen.sock"). If address is not specified, varnishd will
          listen on all available IPv4 and IPv6 interfaces. If port is not
          specified, port 80 (http) is used. At least one of address or port
          is required.

          If a Unix domain socket is specified as the listen address, then 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 are not
          permitted if an IP address is specified. When Unix domain socket
          listeners are in use, all VCL configurations must have version >=

          Name is referenced in logs. If name is not specified, "a0", "a1",
          etc. is used. An additional protocol type can be set for the
          listening socket with PROTO. Valid protocol types are: HTTP
          (default), and PROXY.

          Multiple listening addresses can be specified by using different -a

       -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

              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

              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 name
              Specify the name for this instance.  This name is used to
              construct the name of the directory in which varnishd keeps
              temporary files and persistent state. If the specified name
              begins with a forward slash, it is interpreted as the absolute
              path to the directory.

   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

       -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 and with VSM_Name() from
              utilities.  If not specified the output of gethostname(3) is

       -I clifile
              Execute the management commands in the file given as clifile
              before the 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

       -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

       -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

       -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

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

       -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
       The following storage types 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

              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

              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.

       You can also prefix the type with NAME= to explicitly name a storage:

          -s myStorage=malloc,5G

       This allows to address it more easily in VCL:

          set = storage.myStorage;

       If the name is omitted, Varnish will name storages sN, starting with s0
       and incrementing N for every new storage.

       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
              Reduce privileges(5) for varnishd and sub-process to the
              minimally required set. Only available on platforms which have
              the setppriv(2) call.

       -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.

       -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.

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

   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

       • delayed

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

       • 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.

       • experimental

         We're not really sure about this parameter, tell us what you find.

       • 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 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_space: 1G

       • thread_pool_stack: 52k

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

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

          • Units: bool

          • Default: off

          • Flags:

       Enable kernel accept-filters.

          • 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%)

          • 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.

          • 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.

          • Units: bool

          • Default: on

       Automatically restart the child/worker process if it dies.

          • Units: seconds

          • Default: 60.000

          • Minimum: 1.000

       Timeout before we close unused backend connections.

          • 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

          • 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.

          • Units: bans

          • Default: 0

          • Minimum: 0

          • Flags: experimental

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

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

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

          • 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.

          • 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.

          • 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

          • Units: seconds

          • Default: 0.010

          • Minimum: 0.000

          • Flags: experimental

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

          • 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.

          • Units: seconds

          • Default: 60.000

          • Minimum: 0.000

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

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

          • Flags: must_reload

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

          • Units: bytes

          • Default: 48k

          • Minimum: 128b

          • Maximum: 99999999b

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

          • Units: seconds

          • Default: 60.000

          • Minimum: 0.000

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

          • Units: seconds

          • Default: 10

          • Minimum: 0

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

          • Units: seconds

          • Default: 1.000

          • Minimum: 0.000

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

          • Units: seconds

          • Default: 3.500

          • Minimum: 0.000

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

          • 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.

          • Default: none

       Enable/Disable various kinds of debugging.

          none   Disable all debugging

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

                 VSL Request state engine

                 VSL Workspace operations

                 VSL Waitinglist events

                 Make VSL synchronous

                 Edge cases in Hash

          vclrel Rapid VCL release

          lurker VSL Ban lurker

                 Chop ESI fetch to bits

                 Flush after http1 head

                 Varnishtest Mode

                 Emit WITNESS lock records

                 Keep the VSM file on restart

                 Drop thread pools (testing)

                 Slow down Acceptor

                 Disable various H2 checks

                 Keep copied VMOD libraries

                 Fetch/Deliver processors

                 Protocol debugging

                 Keep VCL C and so files

          lck    Additional lock statistics

          • Units: seconds

          • Default: 10.000

          • Minimum: 0.000

          • Flags: obj_sticky

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

          • Units: seconds

          • Default: 0.000

          • Minimum: 0.000

          • Flags: obj_sticky

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

          • Units: seconds

          • Default: 120.000

          • Minimum: 0.000

          • Flags: obj_sticky

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

          • Default: none

       Enable/Disable various minor features.

          none   Disable all features.

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

                 Short panic message.

                 Wait for persistent silo.

                 No coredumps.

                 Treat HTTPS as HTTP in ESI:includes

                 Don't check of body looks like XML

                 Ignore non-esi XML-elements

                 Remove UTF-8 BOM

                 Also split https URIs

          http2  Support HTTP/2 protocol

                 Relax parsing of timestamps in HTTP headers

          • 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.

          • 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.

          • Units: seconds

          • Default: 60.000

          • Minimum: 0.000

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

          • 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.

          • Default: 6

          • Minimum: 0

          • Maximum: 9

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

          • 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.

          • Units: bytes

          • Default: 4k

          • Minimum: 0b

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

          • Units: bytes

          • Default: 65535b

          • Minimum: 0b

          • Maximum: 2147483647b

       HTTP2 initial flow control window size.

          • 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

          • Units: bytes

          • Default: 16k

          • Minimum: 16k

          • Maximum: 16777215b

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

          • Units: bytes

          • Default: 2147483647b

          • Minimum: 0b

       HTTP2 maximum size of an uncompressed header list.

          • 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.)

          • 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

          • 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

          • 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.

          • 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.

          • Units: bool

          • Default: on

       Enable support for HTTP Range headers.

          • Units: bytes

          • Default: 8k

          • Minimum: 40b

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

          • 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.

          • Units: bytes

          • Default: 8k

          • Minimum: 40b

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

          • 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.

          • Units: seconds

          • Default: 60.000

          • Minimum: 0.000

          • Flags: delayed

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

       When this timeout is hit, the session is closed.

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

          • Units: connections

          • Default: 1024

          • Minimum: 0

          • Flags: must_restart

       Listen queue depth.

          • 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.

          • Units: levels

          • Default: 5

          • Minimum: 0

       Maximum depth of esi:include processing.

          • Units: restarts

          • Default: 4

          • Minimum: 0

       Upper limit on how many times a request can restart.

          • Units: retries

          • Default: 4

          • Minimum: 0

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

          • Default: 100

          • Minimum: 0

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

          • 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.

          • 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.

          • Default: 10000

          • Minimum: 1

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

       (See: PCRE_EXTRA_MATCH_LIMIT in pcre docs.)

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

          • Default: 20

          • Minimum: 1

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

       (See: PCRE_EXTRA_MATCH_LIMIT_RECURSION in pcre docs.)

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

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

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

       Testcase r01576 can be useful when tuning this parameter.

          • 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.

          • Units: connections

          • Default: 0

          • Minimum: 0

       Maximum number of sessions dedicated to pipe transactions.

          • Units: seconds

          • Default: 60.000

          • Minimum: 0.000

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

          • Default: 10,100,10

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

                 minimum size of free pool.

                 maximum size of free pool.

                 max age of free element.

          • Default: 10,100,10

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

                 minimum size of free pool.

                 maximum size of free pool.

                 max age of free element.

          • Default: 10,100,10

       Parameters for backend object fetch memory pool.  The three numbers

                 minimum size of free pool.

                 maximum size of free pool.

                 max age of free element.

          • Units: bool

          • Default: off

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

          • Units: requests per request

          • Default: 3

          • Minimum: 2

          • Flags: experimental

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

          • Units: seconds

          • Default: 600.000

          • Minimum: 0.000

          • Flags: delayed

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

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

       When this timeout is hit, the session is closed

          • Units: seconds

          • Default: 10.000

          • Minimum: 0.000

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

          • 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.

          • Units: bool

          • Default: on

       Log all CLI traffic to syslog(LOG_INFO).

          • Units: bool

          • Default: off

          • Flags: must_restart

       Enable TCP Fast Open extension.

          • Units: seconds

          • Default: 75.000

          • Minimum: 1.000

          • Maximum: 100.000

          • Flags: experimental

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

          • Units: probes

          • Default: 9

          • Minimum: 1

          • Maximum: 100

          • Flags: experimental

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

          • Units: seconds

          • Default: 7200.000

          • Minimum: 1.000

          • Maximum: 7200.000

          • Flags: experimental

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

          • 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.

          • 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).

          • 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.

          • Units: threads

          • Default: 5000

          • Minimum: 100

          • Flags: delayed

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

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

          • Units: threads

          • Default: 100

          • Maximum: 5000

          • Flags: delayed

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

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

       Minimum is 10 threads.

          • Units: threads

          • Default: 0

          • Maximum: 95

          • Flags: delayed

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

       Tasks may require other tasks to complete (for example, client requests
       may require backend requests). This reserve is to ensure that such
       tasks still get to run even under high load.

       Increasing the reserve may help setups with a high number of backend
       requests at the expense of client performance. Setting it too high will
       waste resources by keeping threads unused.

       Default is 0 to auto-tune (currently 5% of thread_pool_min).  Minimum
       is 1 otherwise, maximum is 95% of thread_pool_min.

          • Units: bytes

          • Default: 56k

          • Minimum: 16k

          • Flags: delayed

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

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

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

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

       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.

          • 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.

          • 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.

          • 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

          • 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

          • 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.

          • Units: seconds

          • Default: 5.000

          • Minimum: 0.000

       Idle timeout for client connections.

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

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

          • 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.

          • Units: bool

          • Default: off

       Allow inline C code in VCL.

          • Units: bool

          • Default: on

       Unreferenced VCL objects result in error.

          • Units: bool

          • Default: on

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

          • Units: seconds

          • Default: 600.000

          • Minimum: 0.000

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

          • Default: /opt/varnish/etc/varnish:/opt/varnish/share/varnish/vcl

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

          • Default: /opt/varnish/lib/varnish/vmods

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

          • Units: bytes

          • Default: 4k

          • Minimum: 267

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

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

       The minimum tracks the vsl_reclen parameter + 12 bytes.

          • Default:

       Mask individual VSL messages from being logged.

                 Set default value

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

          • Units: bytes

          • Default: 255b

          • Minimum: 16b

          • Maximum: 4084b

       Maximum number of bytes in SHM log record.

       The maximum tracks the vsl_buffer parameter - 12 bytes.

          • 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

          • 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).

          • Units: bytes

          • Default: 1M

          • Minimum: 1M

          • Maximum: 1G

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

          • Units: bytes

          • Default: 64k

          • Minimum: 1k

          • Flags: delayed

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

          • Units: bytes

          • Default: 64k

          • Minimum: 9k

          • Flags: delayed

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

          • Units: bytes

          • Default: 0.50k

          • Minimum: 0.25k

          • Flags: delayed

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

          • 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).

       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

       • with 0x80 when a core was dumped.

SEE ALSOvarnishlog(1)varnishhist(1)varnishncsa(1)varnishstat(1)varnishtop(1)varnish-cli(7)vcl(7)

       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 <>, Nils Goroll and others.

       This document is licensed under the same licence as Varnish itself. See
       LICENCE for details.

       • Copyright (c) 2007-2015 Varnish Software AS