Today I was trying to send a usr2 signal to a process using pkill and it did not work:

pkill -signal usr2 someprocess
pkill: invalid session id: ignal

Has anyone seen this and have a solution?

From the output the command is unable to interpret -signal, actually the command should look something like:

Am not sure if USR2 signal is available, you can check that by running the following command:

If it show that as available then you can use it.

Let me give you an example:

1. dd if=/dev/zero of=/dev/null & (it will start the DD process in background)
2. To kill it using pkill you can run: pkill -SIGKILL dd , where -SIGKILL is the signal, you don't have to use -signal to mention the signal, just use "-" with kill signal.

EDIT: I misunderstand usr2, Gazl is right it should be SIGUSR2

You're misunderstanding its options. By -signal, it means
pkill -USR2 someprocess

or
pkill -SIGUSR2 someprocess

or even
pkill -12 someprocess

(though it's probably best to avoid using the numeric signal number (which can be subject to change from one UNIX arch to the the next).

1 members found this post helpful.

Thank you all for pointing my error. As GazL says I was misunderstanding the man page.

Once more thank you all for a prompt help.

Either -USR2 or -SIGUSR2 will work, it just depends on how verbose you like to be.

It's unfortunate that the authors of pkill decided to use '-s' for session-id, where as the 'kill' command uses -s for specifying the signal. The UNIX/linux command line would be much nicer if we didn't have to remember these little inconsistencies all the time.