Proc::Govern - Run child process and govern its various aspects


This document describes version 0.200 of Proc::Govern (from Perl distribution Proc-Govern), released on 2018-01-31.


To use via command-line (in most cases):

 % govproc \
       --timeout 3600 \
       --log-stderr-dir        /var/log/myapp/ \
       --log-stderr-size       16M \
       --log-stderr-histories  12 \

To use directly as Perl module:

 use Proc::Govern qw(govern_process);
     name       => 'myapp',
     command    => ['/path/to/myapp', 'some', 'args'],
     timeout    => 3600,
     log_stderr => {
         dir       => '/var/log/myapp',
         size      => '16M',
         histories => 12,


Proc::Govern is a child process manager. It is meant to be a convenient bundle (a single parent/monitoring process) for functionalities commonly needed when managing a child process. It comes with a command-line interface, govproc.

Background story: I first created this module to record STDERR output of scripts that I run from cron. The scripts already log debugging information using Log::Any to an autorotated log file (using Log::Dispatch::FileRotate, via Log::Any::Adapter::Log4perl, via Log::Any::App). However, when the scripts warn/die, or when the programs that the scripts execute emit messages to STDERR, they do not get recorded. Thus, every script is then run through govproc. From there, govproc naturally gets additional features like timeout, preventing running multiple instances, and so on.

Currently the following governing functionalities are available:

  • logging of STDOUT & STDERR output to an autorotated file

  • execution time limit

  • preventing multiple instances from running simultaneously

  • load watch

  • autorestart

In the future the following features are also planned or contemplated:

  • CPU time limit

  • memory limit

    With an option to autorestart if process' memory size grow out of limit.

  • other resource usage limit

  • fork/start multiple processes

  • set (CPU) nice level

  • set I/O nice level (scheduling priority/class)

  • limit STDIN input, STDOUT/STDERR output?

  • trap/handle some signals for the child process?

  • set UID/GID?

  • provide daemon functionality?

  • provide network server functionality?

    Inspiration: djb's tcpserver.

  • set/clean environment variables


Below is the list of exit codes that Proc::Govern uses:

  • 124

    Timeout. The exit code is also used by timeout.

  • 202

    Another instance is already running (when single_instance option is true).


Not yet tested on Win32.




 govern_process(%args) -> int

Run child process and govern its various aspects.

It basically uses IPC::Run and a loop to check various conditions during the lifetime of the child process.

TODO: restart_delay, check_alive.

This function is not exported by default, but exportable.

Arguments ('*' denotes required arguments):

  • command* => array[str]

    Command to run.

    Passed to IPC::Run's start().

  • killfam => bool

    Instead of kill, use killfam (kill family of process).

    This can be useful e.g. to control load more successfully, if the load-generating processes are the subchildren of the one we're governing.

    This requires Proc::Killfam CPAN module, which is installed separately.

  • load_check_every => duration (default: 10)

    Frequency of load checking.

  • load_high_limit => int|code

    Limit above which program should be suspended, if load watching is enabled. If integer, will be compared against Unix::Uptime->load's $load1 value. Alternatively, you can provide a custom routine here, code should return true if load is considered too high.

  • load_low_limit => int|code

    Limit below which program should resume, if load watching is enabled. If integer, will be compared against Unix::Uptime->load's $load1 value. Alternatively, you can provide a custom routine here, code should return true if load is considered low.

  • load_watch => bool (default: 0)

    If set to 1, enable load watching. Program will be suspended when system load is too high and resumed if system load returns to a lower limit.

  • log_stderr => hash

    Will be passed as arguments to `File::Write::Rotate`.

    Specify logging for STDERR. Logging will be done using File::Write::Rotate. Known hash keys: dir (STR, defaults to /var/log, directory, preferably absolute, where the log file(s) will reside, should already exist and be writable, will be passed to File::Write::Rotate's constructor), size (int, also passed to File::Write::Rotate's constructor), histories (int, also passed to File::Write::Rotate's constructor), period (str, also passed to File::Write::Rotate's constructor).

  • log_stdout => hash

    Will be passed as arguments to `File::Write::Rotate`.

  • name => str

    Should match regex \A\w+\z. Used in several places, e.g. passed as prefix in File::Write::Rotate's constructor as well as used as name of PID file.

    If not given, will be taken from command.

  • no_screensaver => bool

    Prevent screensaver from being activated.

  • on_multiple_instance => str

    Can be set to exit to silently exit when there is already a running instance. Otherwise, will print an error message Program <NAME> already running.

  • pid_dir => str

    Directory to put PID file in.

  • restart => bool (default: 1)

    If set to true, do restart.

  • show_stderr => bool (default: 1)

    Can be used to turn off STDERR output. If you turn this off and set log_stderr, STDERR output will still be logged but not displayed to screen.

  • show_stdout => bool (default: 1)

    Just like `show_stderr`, but for STDOUT.

  • single_instance => bool (default: 0)

    If set to true, will prevent running multiple instances simultaneously. Implemented using Proc::PID::File. You will also normally have to set pid_dir, unless your script runs as root, in which case you can use the default /var/run.

  • timeout => int

    Apply execution time limit, in seconds.

    After this time is reached, process (and all its descendants) are first sent the TERM signal. If after 30 seconds pass some processes still survive, they are sent the KILL signal.

    The killing is implemented using IPC::Run's kill_kill().

    Upon timeout, exit code is set to 124.

Return value: Child's exit code (int)


Why use Proc::Govern?

The main feature this module offers is convenience: it creates a single parent process to monitor child process. This fact is more pronounced when you need to monitor lots of child processes. If you use, on the other hand, separate parent/monitoring process for timeout and then a separate one for CPU watching, and so on, there will potentially be a lot more processes running on the system. Compare for example:

 % govproc --timeout 10 --load-watch CMD

which only creates one monitoring process, versus:

 % timeout 10s loadwatch CMD

which will create two parent processes (three actually, loadwatch apparently forks first).


DEBUG => bool

If set to true, will display debugging output to STDERR, e.g. when stopping/starting a process.


Please visit the project's homepage at


Source repository is at


Please report any bugs or feature requests on the bugtracker website

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.


Proc::Govern uses IPC::Run at its core.

IPC::Cmd also uses IPC::Run (as well as IPC::Open3 on systems that do not have IPC::Run installed or on some archaic systems that do not support IPC::Run) and its run_forked() routine also has some of Proc::Govern's functionalities like capturing stdout and stderr, timeout, hiding (discarding) output. If you only need those functionalities, you can use IPC::Cmd as it is a core module.

Proc::Govern attempts (or will attempt, some day) to provide the functionality (or some of the functionality) of the builtins/modules/programs listed below:

  • Starting/autorestarting

    djb's supervise,

  • Pausing under high system load

    loadwatch. This program also has the ability to run N copies of program and interactively control stopping/resuming via Unix socket.

    cPanel also includes a program called cpuwatch.

  • Preventing multiple instances of program running simultaneously

    Proc::PID::File, Sys::RunAlone

  • Execution time limit


    alarm() (but alarm() cannot be used to timeout external programs started by system()/backtick).


  • Logging

    djb's multilog,

Although not really related, Perinci::Sub::Wrapper. This module also bundles functionalities like timeout, retries, argument validation, etc into a single function wrapper.


perlancar <>


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This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.