\cfg{man-identity}{pid}{1}{2012-11-30}{Simon Tatham}{Simon Tatham}

\define{dash} \u2013{-}

\title Man page for \c{pid}

\U NAME

\c{pid} \dash find the pid of a running program or script

\U SYNOPSIS

\c pid [ options ] command [ arg... ]
\e bbbb  iiiiiii   iiiiiii   iii

\U DESCRIPTION

\cw{pid} is a program for finding the PID (process ID) of a currently
running program. This is useful if you need to send a signal to a
program you're running, or attach \cw{strace}(\e{1}) or a debugger to
it, or look in its \cw{/proc} entry.

\cw{pid} tries to \q{do what you meant}. If you run \cw{pid emacs}, it
will find processes whose first command-line word is either \cw{emacs}
or ends in \cw{/emacs} (so it will match things like
\cw{/usr/local/bin/emacs} too). But if you run \cw{pid scriptname},
where \cw{scriptname} is the name of a shell script or Perl script, it
will find processes whose command line looks like \cw{sh scriptname}
or \cw{perl -w scriptname}. If the script has forked into multiple
processes (as shell scripts sometimes do while executing complex
pipelines), \cw{pid} will go further and automatically narrow down to
the parent process of the whole lot. (That's done on a \q{best guess}
basis \dash there's no genuinely reliable way to tell if one process
has forked from another without \cw{exec}-ing anything afterwards.)

By default, \cw{pid} outputs exactly one process ID, or the word
\cq{NONE} or \cq{MULTIPLE} if it finds no matching process or more
than one. This is a mode suitable for use as an argument to
\cw{strace} (which expects exactly one process ID after its \cw{-p}
argument) or \cw{gdb} or \cw{after} (which expect a single pid as an
argument); the \cq{NONE} or \cq{MULTIPLE} answers will provoke a
command-line parsing error rather than trying to trace the wrong
process or expanding to a less obviously wrong command line. Use the
\cw{-a} option to instead make \cw{pid} output a full list of pids
that match (e.g. if you want to pass them all to \cw{kill}(\e{1}).

You can also provide arguments to the command you're searching for, to
narrow your search further. For example, if you have several
\cw{emacs} processes editing different files, \cw{pid emacs foo.c}
will find just the one that was invoked with a particular filename on
its command line.

\U OPTIONS

\dt \cw{-a}

\dd Report all pids that match the search, instead of printing
\cq{MULTIPLE} if there is more than one. This also disables the
behaviour of filtering out apparent forks of the same script.

\dt \cw{-U}

\dd Report pids belonging to any user. By default, \cw{pid} will only
report processes owned by the same user as the one running it (except
when root, when it defaults to reporting everybody's).

\U BUGS

\cw{pid} is currently completely specific to the Linux kernel, since
it depends on a Linux-style \cw{/proc}. It could be enhanced to deal
with other process-finding mechanisms, but so far this has not been
done.

The whole idea of \cw{pid} is non-rigorous, so there will undoubtedly
be strange behaviour in corner cases of various kinds. The aim is to
do the right thing in most common cases.

The current list of programs that \cw{pid} recognises as interpreters
for scripting languages is hardwired and there is no way to override
it.

\U LICENCE

\cw{pid} is free software, distributed under the MIT licence. Type
\cw{pid --licence} to see the full licence text.

\versionid $Id$