Why pidof and pgrep are behaving differently

grepinit-scriptpidofprocess

I have a init script in /etc/init.d/myservice for initialize a service like this:

...
start() {
  ...
  daemon /usr/sbin/myservice
  ...
}

stop() {
  ...
  pgrep myservice
  pidof myservice
  ps -ef | grep myservice
  ...
}

And when I try to stop the service, this is the output:

10000 10001
10000
root      10000     1  0 09:52 ?        00:00:02 /usr/sbin/myservice
root      9791   9788  0 10:06 pts/1    00:00:00 /bin/sh /sbin/service myservice stop
root      10001  9791  1 10:06 pts/1    00:00:00 /bin/sh /etc/init.d/myservice stop 
root      9805   9796  0 10:06 pts/1    00:00:00 grep myservice

Is this expected? Why pidof is returning only the correct PID of the service that I want to stop and pgrep is returning the service PID and the PID of the init script? Can I rely on that pidof will always ignore the PID from the init script?

Best Answer

pidof = find the process ID of a running program

Pidof finds the process id's (pids) of the named programs. It prints those id's on the standard output. This program is on some systems used in run-level change scripts, especially when the system has a System-V like rc structure.

sysadmin@codewarden:~$ pidof apache2
5098 5095 5094 5092

pgrep = look up or signal processes based on name and other attributes, pgrep looks through the currently running processes and lists the process IDs which matches the selection criteria. 

sysadmin@codewarden:~$ pgrep apache2
5092
5094
5095
5098

pgrep, (p) = process, grep = grep prints the matching lines

Want to know more about pgrep & pidof ? Just run in terminal as

# man pidof
# man pgrep
Related Question