How to find the PID of nginx process

I am trying to fix a problem with nginx and think that there is an nginx process running on my machine. When I run this command I get this output.

$ ps aux -P | grep nginx
1000      3947  0.0  0.0  13596   932 pts/0    S+   14:05   0:00 grep --color=auto nginx

But if I try to kill processes 1000, 3947, 13596 or 932 I get errors like:

bash: kill: (1000) - No such process

What's going on? How do I find and kill the nginx process?

Best Answer

I usually find pgrep more convenient than ps | grep. You might also want to look at killall if the end goal is blasting a bunch of processes by name.

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How to get the pid to the last background app

To background itself, that application forks a child process and exits the parent. The shell knows of the parent process as that's the one it has forked itself before executing the command itself, but it has no visibility on the children or grand-children that that process may have spawned.

A simpler example of such a backgrounding command would be:

$ sh -c 'ps -j; sleep 10 &'
  PID  PGID   SID TTY          TIME CMD
 6562  6562 14469 pts/13   00:00:00 sh
 6563  6562 14469 pts/13   00:00:00 ps
14469 14469 14469 pts/13   00:00:00 zsh

My zsh knows about that sh process and its process group.

However, all it sees is that 6562 process exiting. It has no way to know that 6562 process has spawned a 6563 one.

$ ps -j
  PID  PGID   SID TTY          TIME CMD
 6564  6562 14469 pts/13   00:00:00 sleep
 6565  6565 14469 pts/13   00:00:00 ps
14469 14469 14469 pts/13   00:00:00 zsh

However, you can see the process running sleep is also in that 6562 process group (though, there's nothing stopping commands start new process groups, or even sessions (as daemons typically do)).

Those process groups are only created when the shell is interactive though.

Another thing you could do is:

cmd | cat &
wait

If the processes that cmd spawns don't close their stdout, then cat won't die until they have all died.

Shell – How to find the PID of a particular program

Pidof command returns the PID and introduced by a given process name.

According entiend, you want to get a list of PIDs separated by commas, corresponding to potential PIDs as a process name. Pidof command to get that but in a list of PIDs separated by spaces. With the help of the tr command can truncate the characters corresponding to the space delimited by said output pidof another character, in this case the comma command. It could do so:

pidof <process_name> | tr '\ ' ','

Best Answer

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How to get the pid to the last background app

Shell – How to find the PID of a particular program

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