Resource Type: exec

NOTE: This page was generated from the Puppet source code on 2024-10-18 10:08:53 -0700

exec

Description

Executes external commands.

Any command in an exec resource must be able to run multiple times without causing harm --- that is, it must be idempotent. There are three main ways for an exec to be idempotent:

  • The command itself is already idempotent. (For example, apt-get update.)

  • The exec has an onlyif, unless, or creates attribute, which prevents Puppet from running the command unless some condition is met. The onlyif and unless commands of an exec are used in the process of determining whether the exec is already in sync, therefore they must be run during a noop Puppet run.

  • The exec has refreshonly => true, which allows Puppet to run the command only when some other resource is changed. (See the notes on refreshing below.)

The state managed by an exec resource represents whether the specified command needs to be executed during the catalog run. The target state is always that the command does not need to be executed. If the initial state is that the command does need to be executed, then successfully executing the command transitions it to the target state.

The unless, onlyif, and creates properties check the initial state of the resource. If one or more of these properties is specified, the exec might not need to run. If the exec does not need to run, then the system is already in the target state. In such cases, the exec is considered successful without actually executing its command.

A caution: There's a widespread tendency to use collections of execs to manage resources that aren't covered by an existing resource type. This works fine for simple tasks, but once your exec pile gets complex enough that you really have to think to understand what's happening, you should consider developing a custom resource type instead, as it is much more predictable and maintainable.

Duplication: Even though command is the namevar, Puppet allows multiple exec resources with the same command value.

Refresh: exec resources can respond to refresh events (via notify, subscribe, or the ~> arrow). The refresh behavior of execs is non-standard, and can be affected by the refresh and refreshonly attributes:

  • If refreshonly is set to true, the exec runs only when it receives an event. This is the most reliable way to use refresh with execs.

  • If the exec has already run and then receives an event, it runs its command up to two times. If an onlyif, unless, or creates condition is no longer met after the first run, the second run does not occur.

  • If the exec has already run, has a refresh command, and receives an event, it runs its normal command. Then, if any onlyif, unless, or creates conditions are still met, the exec runs its refresh command.

  • If the exec has an onlyif, unless, or creates attribute that prevents it from running, and it then receives an event, it still will not run.

  • If the exec has noop => true, would otherwise have run, and receives an event from a non-noop resource, it runs once. However, if it has a refresh command, it runs that instead of its normal command.

In short: If there's a possibility of your exec receiving refresh events, it is extremely important to make sure the run conditions are restricted.

Autorequires: If Puppet is managing an exec's cwd or the executable file used in an exec's command, the exec resource autorequires those files. If Puppet is managing the user that an exec should run as, the exec resource autorequires that user.

Attributes 

exec { 'resource title':
  command     => # (namevar) The actual command to execute.  Must either be...
  creates     => # A file to look for before running the command...
  cwd         => # The directory from which to run the command.  If 
  environment => # An array of any additional environment variables 
  group       => # The group to run the command as.  This seems to...
  logoutput   => # Whether to log command output in addition to...
  onlyif      => # A test command that checks the state of the...
  path        => # The search path used for command execution...
  provider    => # The specific backend to use for this `exec...
  refresh     => # An alternate command to run when the `exec...
  refreshonly => # The command should only be run as a refresh...
  returns     => # The expected exit code(s).  An error will be...
  timeout     => # The maximum time the command should take.  If...
  tries       => # The number of times execution of the command...
  try_sleep   => # The time to sleep in seconds between 'tries'....
  umask       => # Sets the umask to be used while executing this...
  unless      => # A test command that checks the state of the...
  user        => # The user to run the command as.  > **Note:*...
  # ...plus any applicable metaparameters.
}

command

(Namevar: If omitted, this attribute's value defaults to the resource's title.)

The actual command to execute. Must either be fully qualified or a search path for the command must be provided. If the command succeeds, any output produced will be logged at the instance's normal log level (usually notice), but if the command fails (meaning its return code does not match the specified code) then any output is logged at the err log level.

Multiple exec resources can use the same command value; Puppet only uses the resource title to ensure execs are unique.

On *nix platforms, the command can be specified as an array of strings and Puppet will invoke it using the more secure method of parameterized system calls. For example, rather than executing the malicious injected code, this command will echo it out:

command => ['/bin/echo', 'hello world; rm -rf /']

(↑ Back to exec attributes)

creates

A file to look for before running the command. The command will only run if the file doesn't exist.

This parameter doesn't cause Puppet to create a file; it is only useful if the command itself creates a file.

exec { 'tar -xf /Volumes/nfs02/important.tar':
  cwd     => '/var/tmp',
  creates => '/var/tmp/myfile',
  path    => ['/usr/bin', '/usr/sbin',],
}

In this example, myfile is assumed to be a file inside important.tar. If it is ever deleted, the exec will bring it back by re-extracting the tarball. If important.tar does not actually contain myfile, the exec will keep running every time Puppet runs.

This parameter can also take an array of files, and the command will not run if any of these files exist. Consider this example:

creates => ['/tmp/file1', '/tmp/file2'],

The command is only run if both files don't exist.

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cwd

The directory from which to run the command. If this directory does not exist, the command will fail.

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environment

An array of any additional environment variables you want to set for a command, such as [ 'HOME=/root', 'MAIL=root@example.com']. Note that if you use this to set PATH, it will override the path attribute. Multiple environment variables should be specified as an array.

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group

The group to run the command as. This seems to work quite haphazardly on different platforms -- it is a platform issue not a Ruby or Puppet one, since the same variety exists when running commands as different users in the shell.

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logoutput

Whether to log command output in addition to logging the exit code. Defaults to on_failure, which only logs the output when the command has an exit code that does not match any value specified by the returns attribute. As with any resource type, the log level can be controlled with the loglevel metaparameter.

Default: on_failure

Allowed values:

  • true

  • false

  • on_failure

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onlyif

A test command that checks the state of the target system and restricts when the exec can run. If present, Puppet runs this test command first, and only runs the main command if the test has an exit code of 0 (success). For example:

exec { 'logrotate':
  path     => '/usr/bin:/usr/sbin:/bin',
  provider => shell,
  onlyif   => 'test `du /var/log/messages | cut -f1` -gt 100000',
}

This would run logrotate only if that test returns true.

Note that this test command runs with the same provider, path, user, cwd, and group as the main command. If the path isn't set, you must fully qualify the command's name.

Since this command is used in the process of determining whether the exec is already in sync, it must be run during a noop Puppet run.

This parameter can also take an array of commands. For example:

onlyif => ['test -f /tmp/file1', 'test -f /tmp/file2'],

or an array of arrays. For example:

onlyif => [['test', '-f', '/tmp/file1'], 'test -f /tmp/file2']

This exec would only run if every command in the array has an exit code of 0 (success).

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path

The search path used for command execution. Commands must be fully qualified if no path is specified. Paths can be specified as an array or as a '

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provider

The specific backend to use for this exec resource. You will seldom need to specify this --- Puppet will usually discover the appropriate provider for your platform.

Available providers are:

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refresh

An alternate command to run when the exec receives a refresh event from another resource. By default, Puppet runs the main command again. For more details, see the notes about refresh behavior above, in the description for this resource type.

Note that this alternate command runs with the same provider, path, user, and group as the main command. If the path isn't set, you must fully qualify the command's name.

(↑ Back to exec attributes)

refreshonly

The command should only be run as a refresh mechanism for when a dependent object is changed. It only makes sense to use this option when this command depends on some other object; it is useful for triggering an action:

# Pull down the main aliases file
file { '/etc/aliases':
  source => 'puppet://server/module/aliases',
}

# Rebuild the database, but only when the file changes
exec { newaliases:
  path        => ['/usr/bin', '/usr/sbin'],
  subscribe   => File['/etc/aliases'],
  refreshonly => true,
}

Note that only subscribe and notify can trigger actions, not require, so it only makes sense to use refreshonly with subscribe or notify.

Allowed values:

  • true

  • false

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returns

(Property: This attribute represents concrete state on the target system.)

The expected exit code(s). An error will be returned if the executed command has some other exit code. Can be specified as an array of acceptable exit codes or a single value.

On POSIX systems, exit codes are always integers between 0 and 255.

On Windows, most exit codes should be integers between 0 and 2147483647.

Larger exit codes on Windows can behave inconsistently across different tools. The Win32 APIs define exit codes as 32-bit unsigned integers, but both the cmd.exe shell and the .NET runtime cast them to signed integers. This means some tools will report negative numbers for exit codes above 2147483647. (For example, cmd.exe reports 4294967295 as -1.) Since Puppet uses the plain Win32 APIs, it will report the very large number instead of the negative number, which might not be what you expect if you got the exit code from a cmd.exe session.

Microsoft recommends against using negative/very large exit codes, and you should avoid them when possible. To convert a negative exit code to the positive one Puppet will use, add it to 4294967296.

Default: 0

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timeout

The maximum time the command should take. If the command takes longer than the timeout, the command is considered to have failed and will be stopped. The timeout is specified in seconds. The default timeout is 300 seconds and you can set it to 0 to disable the timeout.

Default: 300

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tries

The number of times execution of the command should be tried. This many attempts will be made to execute the command until an acceptable return code is returned. Note that the timeout parameter applies to each try rather than to the complete set of tries.

Default: 1

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unless

A test command that checks the state of the target system and restricts when the exec can run. If present, Puppet runs this test command first, then runs the main command unless the test has an exit code of 0 (success). For example:

exec { '/bin/echo root >> /usr/lib/cron/cron.allow':
  path   => '/usr/bin:/usr/sbin:/bin',
  unless => 'grep ^root$ /usr/lib/cron/cron.allow 2>/dev/null',
}

This would add root to the cron.allow file (on Solaris) unless grep determines it's already there.

Note that this test command runs with the same provider, path, user, cwd, and group as the main command. If the path isn't set, you must fully qualify the command's name.

Since this command is used in the process of determining whether the exec is already in sync, it must be run during a noop Puppet run.

This parameter can also take an array of commands. For example:

unless => ['test -f /tmp/file1', 'test -f /tmp/file2'],

or an array of arrays. For example:

unless => [['test', '-f', '/tmp/file1'], 'test -f /tmp/file2']

This exec would only run if every command in the array has a non-zero exit code.

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user

The user to run the command as.

Note: Puppet cannot execute commands as other users on Windows.

Note that if you use this attribute, any error output is not captured due to a bug within Ruby. If you use Puppet to create this user, the exec automatically requires the user, as long as it is specified by name.

The $HOME environment variable is not automatically set when using this attribute.

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Providers

posix

Executes external binaries by invoking Ruby's Kernel.exec. When the command is a string, it will be executed directly, without a shell, if it follows these rules:

  • no meta characters

  • no shell reserved word and no special built-in

When the command is an Array of Strings, passed as [cmdname, arg1, ...] it will be executed directly(the first element is taken as a command name and the rest are passed as parameters to command with no shell expansion) This is a safer and more predictable way to execute most commands, but prevents the use of globbing and shell built-ins (including control logic like "for" and "if" statements).

If the use of globbing and shell built-ins is desired, please check the shell provider

  • Confined to: feature == posix

  • Default for: ["feature", "posix"] ==

  • Supported features: umask

shell

Passes the provided command through /bin/sh; only available on POSIX systems. This allows the use of shell globbing and built-ins, and does not require that the path to a command be fully-qualified. Although this can be more convenient than the posix provider, it also means that you need to be more careful with escaping; as ever, with great power comes etc. etc.

This provider closely resembles the behavior of the exec type in Puppet 0.25.x.

  • Confined to: feature == posix

windows

Execute external binaries on Windows systems. As with the posix provider, this provider directly calls the command with the arguments given, without passing it through a shell or performing any interpolation. To use shell built-ins --- that is, to emulate the shell provider on Windows --- a command must explicitly invoke the shell:

exec {'echo foo':
  command => 'cmd.exe /c echo "foo"',
}

If no extension is specified for a command, Windows will use the PATHEXT environment variable to locate the executable.

Note on PowerShell scripts: PowerShell's default restricted execution policy doesn't allow it to run saved scripts. To run PowerShell scripts, specify the remotesigned execution policy as part of the command:

exec { 'test':
  path    => 'C:/Windows/System32/WindowsPowerShell/v1.0',
  command => 'powershell -executionpolicy remotesigned -file C:/test.ps1',
}

  • Confined to: os.name == windows

  • Default for: ["os.name", "windows"] ==