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I have cobbled together a command to return the process ID of a running daemon:

ps aux | grep daemon_name | awk "{ print \$2 }"

It works perfectly and returns the PID, but it also returns a second PID which is presumably the process I'm running now. Is there a way I can exclude my command from the list of returned PIDs?

I've tested it a few times and it appears my command is always the second PID in the list, but I don't want to grab just the first PID in case it's inaccurate.

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5 Answers 5

up vote 18 down vote accepted

grep's -v switch reverses the result, excluding it from the queue. So make it like:

ps aux | grep daemon_name | grep -v grep | awk "{ print \$2 }"

Upd. You can also use -C switch to specify command name like so:

ps -C daemon_name -o pid=

The latter -o determines which columns of the information you want in the listing. pid lists only the process id column. And the equal sign = after pid means there will be no column title for that one, so you get only the clear numbers - PID's.

Hope this helps.

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Perfect, thank you! –  tak Apr 7 '12 at 12:24

You can use a character class trick. "[d]" does not match "[d]" only "d".

 ps aux | grep [d]aemon_name | awk "{ print \$2 }"

I prefer this to using | grep -v grep.

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Heh that's a clever trick, I like it. I'm keeping things simple at the moment though while I'm learning, and | grep -v grep will be easier to understand when I revisit my code. –  tak Apr 7 '12 at 12:29
    
I am trying to understand how this [h]ack works. Could you please explain what you mean with "[d]" does not match "[d]" only "d"? –  Nowaker Sep 28 '13 at 21:13
    
@Damian: The square brackets are metacharacters (delimiting a set of characters) in the search expression so the grep command won't match the ps output line for the grep command itself (what tak called "a second PID" in the original question). expression a[xy]d does not match text a[xy]d but it does match text axd or text ayd. Hence expression [f]oo matches text foo but not text [f]oo. I hope that is clear. –  RedGrittyBrick Sep 28 '13 at 21:34
    
Okay, I was wrong about ARGV. This is just a regexp. Thanks. –  Nowaker Sep 29 '13 at 1:29
    
Devilishly clever! Had to think about it for a moment -- thanks! –  Subfuzion Oct 23 '13 at 18:46

Avoid parsing ps's output if there are more reliable alternatives.

pgrep daemon_name
pidof daemon_name
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The ps -C option is not universal on all Unix based systems but if it works on your systems. Instead I would avoid grep altogether:

ps aux | awk '/daemon_name/ && !/awk/ { print $2 }'

No need to escape anything in single quotation marks. ps aux will give you the full list of processes on most Unix based systems and awk is typically installed by default.

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Use pgrep to look for the pid of a process by name:

pgrep proc_name

With extra process name in the result (-l):

pgrep -l proc_name

Look for and display the process name (-l) and arguments (-f):

pgrep -lf proc_name_or_argument

The good thing about pgrep is that it will never report itself as a match. But you don't need to get the pid by pgrep and then kill the corresponding process by kill. Use pkill instead:

pkill proc_name

Specify the SIGKILL signal (-9 or -KILL) instead of SIGTERM (by default):

pkill -9 proc_name

Look for the process name (-l) and arguments (-f), ask for confirmation (-I) before killing it by SIGKILL signal (-9 or -KILL):

pkill -KILL -Ilf proc_name_or_argument

Notice that the -I option is only available on some versions of pkill, e.g. the one on the OS X Mavericks.

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