Prevent Process from Killing Itself Using Pkill

Prevent process from killing itself using pkill

You can explicitly filter out the current PID from the results:

kill $(pgrep -f $DAEMON | grep -v ^$$\$)

To correctly use the -f flag, be sure to supply the whole path to the daemon rather than just a substring. That will prevent you from killing the script (and eliminate the need for the above grep) and also from killing all other system processes that happen to share the daemon's name.

Find and kill a process in one line using bash and regex

In bash, you should be able to do:

kill $(ps aux | grep '[p]ython csp_build.py' | awk '{print $2}')

Details on its workings are as follows:

• The ps gives you the list of all the processes.
• The grep filters that based on your search string, [p] is a trick to stop you picking up the actual grep process itself.
• The awk just gives you the second field of each line, which is the PID.
• The $(x) construct means to execute x then take its output and put it on the command line. The output of that ps pipeline inside that construct above is the list of process IDs so you end up with a command like kill 1234 1122 7654.

Here's a transcript showing it in action:

pax> sleep 3600 &
[1] 2225
pax> sleep 3600 &
[2] 2226
pax> sleep 3600 &
[3] 2227
pax> sleep 3600 &
[4] 2228
pax> sleep 3600 &
[5] 2229
pax> kill $(ps aux | grep '[s]leep' | awk '{print $2}')
[5]+  Terminated              sleep 3600
[1]   Terminated              sleep 3600
[2]   Terminated              sleep 3600
[3]-  Terminated              sleep 3600
[4]+  Terminated              sleep 3600

and you can see it terminating all the sleepers.

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Explaining the grep '[p]ython csp_build.py' bit in a bit more detail:

When you do sleep 3600 & followed by ps -ef | grep sleep, you tend to get two processes with sleep in it, the sleep 3600 and the grep sleep (because they both have sleep in them, that's not rocket science).

However, ps -ef | grep '[s]leep' won't create a process with sleep in it, it instead creates grep '[s]leep' and here's the tricky bit: the grep doesn't find it because it's looking for the regular expression "any character from the character class [s] (which is s) followed by leep.

In other words, it's looking for sleep but the grep process is grep '[s]leep' which doesn't have sleep in it.

When I was shown this (by someone here on SO), I immediately started using it because

• it's one less process than adding | grep -v grep; and
• it's elegant and sneaky, a rare combination :-)

How to kill all processes with a given partial name?

Use pkill -f, which matches the pattern for any part of the command line

pkill -f my_pattern

Just in case it doesn't work, try to use this one as well:

pkill -9 -f my_pattern

My shell cannot prevent ctrl+c from killing itself

I wonder why ash or other bash could work, so dig into ash's source code. I try this snippets.

It works.

    int ofd;
    ofd = fd = open(_PATH_TTY, O_RDWR);
    if (fd < 0) {
/* BTW, bash will try to open(ttyname(0)) if open("/dev/tty") fails.
 * That sometimes helps to acquire controlling tty.
 * Obviously, a workaround for bugs when someone
 * failed to provide a controlling tty to bash! :) */
        fd = 2;
        while (!isatty(fd))
            if (--fd < 0)
                goto out;
    }
    /* fd is a tty at this point */
    fd = fcntl(fd, F_DUPFD, 10);
    if (ofd >= 0) /* if it is "/dev/tty", close. If 0/1/2, dont */
        close(ofd);
    if (fd < 0)
        goto out; /* F_DUPFD failed */
    close_on_exec_on(fd);
    while (1) { /* while we are in the background */
        pgrp = tcgetpgrp(fd);
        if (pgrp < 0) {
out:
            ash_msg("can't access tty; job control turned off");
            mflag = on = 0;
            goto close;
        }
        if (pgrp == getpgrp())
            break;
        killpg(0, SIGTTIN);
    }
    initialpgrp = pgrp;

    setsignal(SIGTSTP);
    setsignal(SIGTTOU);
    setsignal(SIGTTIN);
    pgrp = rootpid;
    setpgid(0, pgrp);
    xtcsetpgrp(fd, pgrp);

Why does running pkill -f anything over ssh fail only when branching on its result?

The problem appears to be that pkill is killing itself. Or rather, it is killing the shell that owns it.

First of all, it appears that ssh uses the remote user's shell to execute certain "complicated" commands:

$ ssh user@remote 'ps -F --pid $$'
UID        PID  PPID  C    SZ   RSS PSR STIME TTY          TIME CMD
user      9531  9526  0 11862  1616   6 14:36 ?        00:00:00 ps -F --pid 9531

$ ssh user@remote 'ps -F --pid $$ && echo hi'
UID        PID  PPID  C    SZ   RSS PSR STIME TTY          TIME CMD
user      9581  9577  0 28316  1588   5 14:36 ?        00:00:00 bash -c ps -F --pid $$ && echo hi
hi

Second, it appears that pkill -f normally knows not to kill itself (otherwise all pkill -f commands would suicide). But if run from a subshell, that logic fails:

$ pkill -f fake_process; echo $?
1

$ sh -c 'pkill -f fake_process'; echo $?
[1]    14031 terminated  sh -c 'pkill -f fake_process'
143

In my case, to fix this I just re-worked some of the code around my ssh/pkill so that I could avoid having a "complicated" remote command. Theoretically I think you could also do something like pgrep -f <cmd> | grep -v $$ | xargs kill.

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