NAME

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

VERSION
This document describes version 0.211 of Proc::Govern (from Perl
distribution Proc-Govern), released on 2020-08-18.

SYNOPSIS
To use as Perl module:

use Proc::Govern qw(govern_process);
my $exit_code = govern_process(
command => ['/path/to/myapp', 'some', 'args'], # required

name => 'myapp', # optional, default will be taken from command. must be alphanum only.

# options to control number of instances
single_instance => 1, # optional. if set to 1 will fail if another instance is already running.
# implemented with pid files.
pid_dir => "/var/run", # optional. defaults to /var/run. pid filename is '<name>.pid'
on_multiple_instance => "exit", # optional. can be set to 'exit' to silently exit when another instance
# is already running. otherwise prints an error msg.

# timeout options
timeout => 3600, # optional, default is no timeout
killfam => 1, # optional. can be set to 1 to kill using killfam.

# output logging options
log_stderr => { # optional, passed to File::Write::Rotate
dir => '/var/log/myapp',
size => '16M',
histories => 12,
},
log_stdout => { # optional, passed to File::Write::Rotate
dir => '/var/log/myapp.out',
size => '16M',
histories => 12,
},
show_stdout => 0, # optional. can be set to 0 to suppress stdout output. note:
# stdout can still be logged even if not shown.
show_stderr => 0, # optional. can be set to 0 to suppress stderr output. note:
# stderr can still be logged even if not shown.

# load control options
load_watch => 1, # optional. can be set to 1 to enable load control.
load_high_limit => 5, # optional, default 1.25. at what load command should be paused? can also be set
# to a coderef that returns 1 when load is considered too high.
# note: just setting load_high_limit or load_low_limit won't automatically
# enable load control.
load_low_limit => 2, # optional, default 0.25. at what load paused command should be resumed? can also
# be set to a coderef that returns 1 when load is considered low already.
load_check_every => 20, # optional, default 10. frequency of load checking (in seconds).

# restart options
restart_if_failed => 1, # optional. if set to 1, will restart command if exit code is not zero.
restart_if_no_output_after => 60, # optional. if set to a positive number, will restart command after no
# stdout output after this many seconds

# screensaver control options
no_screensaver => 1, # optional. if set to 1, will prevent screensaver from being activated while command
# is running.

# power management options
no_sleep => 1, # optional. if set to 1, will prevent system from sleeping while command is running.
# this includes hybrid sleep, suspend, and hibernate.

# setuid options
euid => 1000, # optional. sets euid of command process. note: need to be root to be able to setuid.
egid => 1000, # optional. sets egid(s) of command process.
);

To use via command-line:

% govproc [options] <command>...

Example:

% govproc --timeout 86400 --load-watch --load-high 4 --load-low 0.75 backup-db

DESCRIPTION
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

* set (CPU) nice level (priority)

* preventing multiple instances from running simultaneously

* load watch

* autorestart

* preventing system from sleeping while process is running

* preventing screensaver from activating while process is running

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 I/O nice level (scheduling priority/class)

* limit STDIN input, STDOUT/STDERR output?

* trap/handle some signals for the child process?

* provide daemon functionality?

* provide network server functionality?

Inspiration: djb's tcpserver.

* set/clean environment variables

EXIT CODES
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).

FUNCTIONS
govern_process
Usage:

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()".

* egid => *str*

Set EGID(s) of command process.

Need to be root to be able to setuid.

* euid => *unix::local_uid*

Set EUID of command process.

Need to be root to be able to setuid.

* 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.

Note: "load_watch" needs to be set to true first for this to be
effective.

* 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.

Note: "load_watch" needs to be set to true first for this to be
effective.

* 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.

* nice => *int*

Set nice/priority level.

* no_screensaver => *true*

Prevent screensaver from being activated.

* no_sleep => *true*

Prevent system from sleeping.

* 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 => *dirname*

Directory to put PID file in.

* restart_if_failed => *bool*

If set to true, do restart.

* restart_if_no_output_after => *uint*

If set to positive number, restart when there is no output after
this many seconds.

* 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 => *duration*

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)

FAQ
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).

ENVIRONMENT
HOMEPAGE
Please visit the project's homepage at
<https://metacpan.org/release/Proc-Govern>.

SOURCE
Source repository is at <https://github.com/perlancar/perl-Proc-Govern>.

BUGS
Please report any bugs or feature requests on the bugtracker website
<https://rt.cpan.org/Public/Dist/Display.html?Name=Proc-Govern>

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.

CAVEATS
Not yet tested on Win32.

SEE ALSO
Forks::Super (since 2009) extends the fork(), wait(), and waitpid()
functions with some process/job management features, e.g. set timeout,
retries, chdir, environment, umask, delay before start, control
STDIN/STDOUT/STDERR, load control, priority/nice level, daemon, and a
lot more. Had I known about this module, I probably wouldn't start
Proc::Govern.

Proc::Govern uses IPC::Run at its core; you might want to use it
directly. It already has some features, e.g. controlling
STDIN/STDOUT/STDERR and timeout. But the main selling point of IPC::Run
is its redirection and piping features.

IPC::Cmd is a core module, but can also use 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). Its "run_forked()"
routine 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, http://cr.yp.to/daemontools/supervise.html

* 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

timeout.

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

Sys::RunUntil

* Logging

djb's multilog, http://cr.yp.to/daemontools/multilog.html

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

AUTHOR
perlancar <[email protected]>

COPYRIGHT AND LICENSE
This software is copyright (c) 2020, 2019, 2018, 2017, 2016, 2015, 2014,
2013, 2012 by [email protected].

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