Varnish Command Line Interface

Author:Per Buer
Manual section:7


Varnish as a command line interface (CLI) which can control and change most of the operational parameters and the configuration of Varnish, without interrupting the running service.

The CLI can be used for the following tasks:

You can upload, change and delete VCL files from the CLI.
You can inspect and change the various parameters Varnish has available through the CLI. The individual parameters are documented in the varnishd(1) man page.
Bans are filters that are applied to keep Varnish from serving stale content. When you issue a ban Varnish will not serve any banned object from cache, but rather re-fetch it from its backend servers.
process management
You can stop and start the cache (child) process though the CLI. You can also retrieve the lastst stack trace if the child process has crashed.

If you invoke varnishd(1) with -T, -M or -d the CLI will be available. In debug mode (-d) the CLI will be in the foreground, with -T you can connect to it with varnishadm or telnet and with -M varnishd will connect back to a listening service pushing the CLI to that service. Please see varnishd(1) for details.


Commands are usually terminated with a newline. Long command can be entered using sh style here documents. The format of here-documents is:

<< word
     here document

word can be any continuous string choosen to make sure it doesn't appear naturally in the following here document.

When using the here document style of input there are no restrictions on lenght. When using newline-terminated commands maximum lenght is limited by the varnishd parameter cli_buffer.

When commands are newline terminated they get tokenized before parsing so if you have significant spaces enclose your strings in double quotes. Within the quotes you can escape characters with \. The n, r and t get translated to newlines, carrage returns and tabs. Double quotes themselves can be escaped with a backslash.

To enter characters in octals use the \nnn syntax. Hexadecimals can be entered with the \xnn syntax.


Lists the defined backends including health state.
backend.set_health matcher state
Sets the health state on a specific backend. This is useful if you want to take a certain backend out of sirculations.
ban field operator argument [&& field operator argument [...]]
Immediately invalidate all documents matching the ban expression. See Ban Expressions for more documentation and examples.

All requests for objects from the cache are matched against items on the ban list. If an object in the cache is older than a matching ban list item, it is considered "banned", and will be fetched from the backend instead.

When a ban expression is older than all the objects in the cache, it is removed from the list.

ban.list displays the ban list. The output looks something like this (broken into two lines):

0x7fea4fcb0580 1303835108.618863 131G ~ && req.url ~ /some/url

The first field is the address of the ban.

The second is the time of entry into the list, given as a high precision timestamp.

The third field describes many objects point to this ban. When an object is compared to a ban the object is marked with a reference to the newest ban it was tested against. This isn't really useful unless you're debugging.

A "G" marks that the ban is "Gone". Meaning it has been marked as a duplicate or it is no longer valid. It stays in the list for effiency reasons.

Then follows the actual ban it self.

ban.url regexp
Immediately invalidate all documents whose URL matches the specified regular expression. Please note that the Host part of the URL is ignored, so if you have several virtual hosts all of them will be banned. Use ban to specify a complete ban if you need to narrow it down.
help [command]
Display a list of available commands. If the command is specified, display help for this command.
param.set param value
Set the parameter specified by param to the specified value. See Run-Time Parameters for a list of parame‐ ters. [-l] [param]

Display a list if run-time parameters and their values.

If the -l option is specified, the list includes a brief explanation of each parameter.

If a param is specified, display only the value and explanation for this parameter.

ping [timestamp]
Ping the Varnish cache process, keeping the connection alive.
Close the connection to the varnish admin port.
Start the Varnish cache process if it is not already running.
Check the status of the Varnish cache process.
Stop the Varnish cache process.
Lists the defined storage backends.
vcl.discard configname
Discard the configuration specified by configname. This will have no effect if the specified configuration has a non-zero reference count.
vcl.inline configname vcl
Create a new configuration named configname with the VCL code specified by vcl, which must be a quoted string.
List available configurations and their respective reference counts. The active configuration is indicated with an asterisk ("*").
vcl.load configname filename
Create a new configuration named configname with the contents of the specified file. configname
Display the source code for the specified configuration.
vcl.use configname
Start using the configuration specified by configname for all new requests. Existing requests will con‐ tinue using whichever configuration was in use when they arrived.

Ban Expressions

A ban expression consists of one or more conditions. A condition consists of a field, an operator, and an argument. Conditions can be ANDed together with "&&".

A field can be any of the variables from VCL, for instance req.url, or obj.http.set-cookie.

Operators are "==" for direct comparision, "~" for a regular expression match, and ">" or "<" for size comparisons. Prepending an operator with "!" negates the expression.

The argument could be a quoted string, a regexp, or an integer. Integers can have "KB", "MB", "GB" or "TB" appended for size related fields.


If you are going to write a script that talks CLI to varnishd, the include/cli.h contains the relevant magic numbers.

One particular magic number to know, is that the line with the status code and length field always is exactly 13 characters long, including the NL character.

For your reference the sourcefile lib/libvarnish/cli_common.h contains the functions varnish code uses to read and write CLI response.

Details on authentication

If the -S secret-file is given as argument to varnishd, all network CLI connections must authenticate, by proving they know the contents of that file.

The file is read at the time the auth command is issued and the contents is not cached in varnishd, so it is possible to update the file on the fly.

Use the unix file permissions to control access to the file.

An authenticated session looks like this:

critter phk> telnet localhost 1234
Trying ::1...
Connected to localhost.
Escape character is '^]'.
107 59

Authentication required.

auth 455ce847f0073c7ab3b1465f74507b75d3dc064c1e7de3b71e00de9092fdc89a
200 193
Varnish HTTP accelerator CLI.
Type 'help' for command list.
Type 'quit' to close CLI session.
Type 'start' to launch worker process.

The CLI status of 107 indicates that authentication is necessary. The first 32 characters of the reponse text is the challenge "ixsl...mpg". The challenge is randomly generated for each CLI connection, and changes each time a 107 is emitted.

The most recently emitted challenge must be used for calculating the authenticator "455c...c89a".

The authenticator is calculated by applying the SHA256 function to the following byte sequence:

  • Challenge string
  • Newline (0x0a) character.
  • Contents of the secret file
  • Challenge string
  • Newline (0x0a) character.

and dumping the resulting digest in lower-case hex.

In the above example, the secret file contained foon and thus:

critter phk> cat > _
critter phk> hexdump -C _
00000000  69 78 73 6c 76 76 78 72  67 6b 6a 70 74 78 6d 63  |ixslvvxrgkjptxmc|
00000010  67 6e 6e 73 64 78 73 76  64 6d 76 66 79 6d 70 67  |gnnsdxsvdmvfympg|
00000020  0a 66 6f 6f 0a 69 78 73  6c 76 76 78 72 67 6b 6a  |.foo.ixslvvxrgkj|
00000030  70 74 78 6d 63 67 6e 6e  73 64 78 73 76 64 6d 76  |ptxmcgnnsdxsvdmv|
00000040  66 79 6d 70 67 0a                                 |fympg.|
critter phk> sha256 _
SHA256 (_) = 455ce847f0073c7ab3b1465f74507b75d3dc064c1e7de3b71e00de9092fdc89a
critter phk> openssl dgst -sha256 < _

The sourcefile lib/libvarnish/cli_auth.c contains a useful function which calculates the response, given an open filedescriptor to the secret file, and the challenge string.


Simple example: All requests where req.url exactly matches the string /news are banned from the cache:

req.url == "/news"

Example: Ban all documents where the name does not end with ".ogg", and where the size of the object is greater than 10 megabytes:

req.url !~ "\.ogg$" && obj.size > 10MB

Example: Ban all documents where the serving host is "" or "", and where the Set-Cookie header received from the backend contains "USERID=1663": ~ "^(?i)(www\.)$" && obj.http.set-cookie ~ "USERID=1663"


  • varnishd(1)
  • vanrishadm(1)
  • vcl(7)


The varnish manual page was written by Per Buer in 2011. Some of the text was taken from the Varnish Cache wiki, the varnishd(7) man page or the varnish source code.

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