Looking for a one liner to filter PID so I can kill it

ericcarlson · 08-18-2011, 11:42 AM

I'm on a virtual server which is subject to random spikes in load, such that I need a cron job firing every minute to ensure swap isn't exhausted. This sort of works but is a little drastic in that it restarts apache when the free level gets below x. I'm looking to refine that.

Right now if I do ps -A | grep apache2 I get
4575 ? 00:00:00 apache2
7162 ? 00:00:09 apache2
7346 ? 00:00:07 apache2
7357 ? 00:00:05 apache2
7409 ? 00:00:04 apache2
7434 ? 00:00:04 apache2
...

My goal is to kill -9 the pid on the first line. I'm certain this can be done as a one liner, something like ps -A | grep apache2 | take 1st val in 1st line > kill -9 or whatever, but they syntax of this is beyond me and I really don't want to faff about piping to files and parsing that. Any takers please? Thanks.

repo · 08-18-2011, 11:55 AM

You can use pidof

Code:

kill -9 $(pidof apache2)

Kind regards

ericcarlson · 08-18-2011, 12:06 PM

Quote:

Originally Posted by repo

You can use pidof

Code:

kill -9 $(pidof apache2)

Kind regards

Cheers, but I just tried that and it killed them all! I just want the oldest, which is the one in the first line in the command I gave.
I did see:

#pidof apache2
7513 7490 7489 7482 7481 7477 7469 7460 7448 7434 7409 7357 7346 7162 4575

So just getting the last pid from that line would do it.

chrism01 · 08-18-2011, 08:59 PM

You could use awk or cut to get the last value & pipe to kill.
This is only addressing the symptoms though; you should really try to fix the root cause.

Nominal Animal · 08-18-2011, 10:40 PM

This will send a KILL signal to the oldest (earliest started) apache2:

Code:

env LANG=C LC_ALL=C ps -C apache2 -o pid=,lstart= | bash -c '
    OLD=""
    CMD=(true)
    while read PID DATE ; do
        SEC=$[ $(env LANG=C LC_ALL=C date +%s -d "$DATE" 2>/dev/null) -0 ] || continue
        if [ -z "$OLD" ] || [ $OLD -gt $SEC ]; then
           OLD=$SEC
           CMD=(kill -KILL $PID)
        fi
    done
    "${CMD[@]}"
'

It uses Bash, and the date -d command to parse the date string ps provides. (It seems to be irrespective of locale, but I set the locale anyway.)

If you have runaway apache2 processes, consuming excess amounts of memory, you really should be killing based on that (or better yet, set a RAM limit for apache2 processes). To kill any apache2 that consumes (resident set, in RAM) more than X kilobytes, you can use

Code:

ps -C apache2 -o rss=,pid= | awk -v limit=X '($1 > limit) { system("kill -KILL " $2) }'

Diantre · 08-18-2011, 11:42 PM

You can try with the -s option. From the pidof manpage:

Code:

-s     Single shot - this instructs the program to only return one pid.

So maybe this will work:

Code:

kill -9 $(pidof -s apache2)