2016년 8월 27일 토요일

Finding PID for programs - Why 'pidof foo' is less trustworthy than 'ps -eF | grep foo'

I often use pidof to find the PID of a running program. It works well with dhclient, dnsmasq and other executable binaries. But pidof runs into problems when trying to find the PID of script files that in turn invoke other programs. Take, for example, the Python 2 program deluge-gtk BitTorrent client.

[archjun@pinkS310 bin]$ pidof deluge-gtk
[archjun@pinkS310 bin]$ ps -eF | grep "deluge*" | grep -v grep
archjun  25862     1  3 289160 89272  1 16:47 ?        00:01:30 /usr/bin/python2 /usr/bin/deluge-gtk /MULTIMEDIA/Torrents/CentOS-5.5-x86_64-bin-DVD.torrent

In the first case, pidof fails to return any PID for the deluge-gtk executable file. In the second case, grepping for deluge-gtk in the output of ps -eF (all processes, extra full format) correctly returns the PID of the BitTorrent client which is executed by Python 2.

Let's take a look at the contents of the deluge-gtk executable file:

[archjun@pinkS310 bin]$ cat /usr/bin/deluge-gtk
#!/usr/bin/python2
# EASY-INSTALL-ENTRY-SCRIPT: 'deluge==1.3.13.dev0','gui_scripts','deluge-gtk'
__requires__ = 'deluge==1.3.13.dev0'
import sys
from pkg_resources import load_entry_point

if __name__ == '__main__':
    sys.exit(
        load_entry_point('deluge==1.3.13.dev0', 'gui_scripts', 'deluge-gtk')()
    )

ps -eF is more useful because it can follow an execution chain to the final PID.