How to run a program and know its PID in Linux?
If I have several shells running each other, will they all have separate PIDs?
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3 Answers
Greg's wiki to the rescue:
$!is the PID of the last backgrounded process.kill -0 $PIDchecks whether$PIDis still running. Only use this for processes started by the current process or its descendants, otherwise the PID could have been recycled.waitwaits for all children to exit before continuing.
Actually, just read the link - It's all there (and more).
$$ is the PID of the current shell.
And yes, each shell will have its own PID (unless it's some homebrewed shell which doesn't fork to create a "new" shell).
Comments
1) There is a variable for that, often $$:
edd@max:~$ echo $$ # shell itself
20559
edd@max:~$ bash -c 'echo $$' # new shell with different PID
19284
edd@max:~$ bash -c 'echo $$' # dito
19382
edd@max:~$
2) Yes they do, the OS / kernel does that for you.
answered Mar 27, 2012 at 13:04
Dirk is no longer here
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7 Comments
Suzan Cioc
How to use
$$ variable? Does it contain PID of last runned program or what?
Dirk is no longer here
Look at the example I gave. For the shell, it is its own PID.
dldnh
in
bash $! is the PID of the last background process.Suzan Cioc
@dldnh is this possible to receive the same in
sh?Suzan Cioc
@Dirk but is it possible to know not the PID or the script, but the PID of the program runned by this script?
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the top command in linux(Ubuntu) shows the memory usage of all running programs in linux with their pid. Kill pid can kill the process.
