07-17-2019
I don't know of any OS that randomly picks the next PID to use when creating a new process. But, it is theoretically possible to do it that way.
Most of the systems I have worked on have a maximum PID value that is a configuration parameter. They start out assigning PIDs from 1 and increment the PID they want to assign by one every time a new process is created (e.g., by fork()), but before assigning that value, they check to see if that PID is currently in use. If it is in use, the OS tries again with the next possible PID until it finds one that is not in use. Using this method, you won't run into problems with PID recycling unless there are so many processes running on your system that you don't have many possible PIDs available that aren't in use.
Furthermore, if you have a ps utility that conforms to POSIX requirements, you can ask ps to just print the fields you want to see and not have to worry about some unexpected value in a field you aren't interested in containing what looks like a PID. (Look at your man page for the ps -o format option.)
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LEARN ABOUT DEBIAN
file::pid
File::Pid(3pm) User Contributed Perl Documentation File::Pid(3pm)
NAME
File::Pid - Pid File Manipulation
SYNOPSIS
use File::Pid;
my $pidfile = File::Pid->new({
file => '/some/file.pid',
});
$pidfile->write;
if ( my $num = $pidfile->running ) {
die "Already running: $num
";
}
$pidfile->remove;
DESCRIPTION
This software manages a pid file for you. It will create a pid file, query the process within to discover if it's still running, and remove
the pid file.
new
my $pidfile = File::Pid->new;
my $thisfile = File::Pid->new({
file => '/var/run/daemon.pid',
});
my $thisfileandpid = File::Pid->new({
file => '/var/run/daemon.pid',
pid => '145',
});
This constructor takes two optional paramters.
"file" - The name of the pid file to work on. If not specified, a pid file located in "File::Spec->tmpdir()" will be created that matches
"(File::Basename::basename($0))[0] . '.pid'". So, for example, if $0 is ~/bin/sig.pl, the pid file will be /tmp/sig.pl.pid.
"pid" - The pid to write to a new pidfile. If not specified, $$ is used when the pid file doesn't exist. When the pid file does exist, the
pid inside it is used.
file
my $pidfile = $pidfile->file;
Accessor/mutator for the filename used as the pid file.
pid
my $pid = $pidfile->pid;
Accessor/mutator for the pid being saved to the pid file.
write
my $pid = $pidfile->write;
Writes the pid file to disk, inserting the pid inside the file. On success, the pid written is returned. On failure, "undef" is returned.
running
my $pid = $pidfile->running;
die "Service already running: $pid
" if $pid;
Checks to see if the pricess identified in the pid file is still running. If the process is still running, the pid is returned. Otherwise
"undef" is returned.
remove
$pidfile->remove or warn "Couldn't unlink pid file
";
Removes the pid file from disk. Returns true on success, false on failure.
program_name
This is a utility method that allows you to determine what "File::Pid" thinks the program name is. Internally this is used when no pid file
is specified.
SEE ALSO
perl.
AUTHOR
Casey West, <casey@geeknest.com>.
COPYRIGHT
Copyright (c) 2005 Casey West. All rights reserved.
This module is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
perl v5.8.8 2008-04-05 File::Pid(3pm)