No::Worries::PidFile - pid file handling without worries


  use No::Worries::PidFile qw(*);

  # idiomatic daemon code
  while (1) {
      $action = pf_check($pidfile);
      last if $action eq "quit";

  # idiomatic daemon code with sleeping
  while (1) {
      pf_sleep($pidfile, time => 5) or last;

  # here is how to handle a --status option
  if ($Option{status}) {
      ($status, $message, $code) = pf_status($pidfile, freshness => 10);
      printf("myprog %s\n", $message);

  # here is how to handle a --quit option
  if ($Option{quit}) {
          linger   => 10,
          callback => sub { printf("myprog %s\n", $_[0]) },


This module eases pid file handling by providing high level functions to set, check, touch and unset pid files. All the functions die() on error.

The pid file usually contains the process id on a single line, followed by a newline. However, it can also be followed by an optional action, also followed by a newline. This allows some kind of inter-process communication: a process using pf_quit() will append the quit action to the pid file and the owning process will detect this via pf_check().

All the functions properly handle concurrency. For instance, when two processes start at the exact same time and call pf_set(), only one will succeed and the other one will get an error.

Since an existing pid file will make pf_set() fail, it is very important to remove the pid file in all situations, including errors. The recommended way to do so is to use an END block:

  # we need to know about transient processes
  use No::Worries::Proc qw();
  # we need to record what needs to be cleaned up
  # we set the pid file here and remember to clean it up
  $NeedsCleanup{pidfile} = 1;
  # ... anything can happen here ...
  # cleanup code in an END block
  END {
      # transient processes do not need cleanup
      return if $No::Worries::Proc::Transient;
      # cleanup the pid file if needed
      pf_unset($pidfile) if $NeedsCleanup{pidfile};


This module provides the following functions (none of them being exported by default):

pf_set(PATH[, OPTIONS])

set the pid file by writing the given pid at the given path; supported options:

  • pid: the pid to use (default: $$)

pf_check(PATH[, OPTIONS])

check the pid file and make sure the given pid is present, also return the action in the pid file or the empty string; supported options:

  • pid: the pid to use (default: $$)


unset the pid file by removing the given path


touch the pid file (i.e. update the file modification time) to show that the owning process is alive

pf_sleep(PATH[, OPTIONS])

check and touch the pid file and eventually sleep for the givent amount of time, returning true if the program should continue or false if it has been told to stop via pf_quit(); supported options:

  • time: the time to sleep (default: 1, can be fractional)

pf_status(PATH[, OPTIONS])

use information from the pid file (including its last modification time) to guess the status of the corresponding process, return the status (true means that the process seems to be running); in list context, also return an informative message and an LSB compatible exit code; supported options:

  • freshness: maximum age allowed for an active pid file

  • timeout: check multiple times until success or timeout

pf_quit(PATH[, OPTIONS])

tell the process corresponding to the pid file to quit (setting its action to quit), wait a bit to check that it indeed stopped and kill it using No::Worries::Proc's proc_terminate() is everything else fails; supported options:

  • callback: code that will be called with information to report

  • linger: maximum time to wait after having told the process to quit (default: 5)

  • kill: kill specification to use when killing the process

SEE ALSO, No::Worries, No::Worries::Proc.


Lionel Cons

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