Linux

Process Id

,

1. ps

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# all process
> ps -ef
UID        PID  PPID  C STIME TTY          TIME CMD

> ps -aux
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND

## PID: column 9-15
## get speacial process PID
> ps -ef | grep CMD-NAME | grep -v grep | cut -c 9-15
> ps -aux | grep CMD-NAME | grep -v grep | cut -c 9-15
 
## ignore grep --color=auto,  
## If the pattern had been written without the square brackets, it would have matched not only the ps output line for cron, but also the ps output line for grep.
## https://www.gnu.org/software/grep/manual/grep.html
> ps -ef | grep  [i]nit

2. pidof

find the process ID of a running program

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> > ps -ef | grep /i
root         1     0  0 Jul16 ?        00:00:00 /init
root         6     1  0 Jul16 ?        00:00:00 /init
root         7     6  0 Jul16 ?        00:00:01 /init
root      2496     1  0 00:17 ?        00:00:00 /init
root      2497  2496  0 00:17 ?        00:00:00 /init
yang      2813  2498  0 00:51 pts/1    00:00:00 grep --color=auto /i

> pidof /init
2497 2496 7 6 1

# select one
> pidof /init | awk '{print $1}'
2497

3. pgrep/pkill

It searches for all the named processes that can be specified as extended regular expression patterns, and—by default—returns their process ID.

The running pgrep or pkill process will never report itself as a match.

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$ pgrep -u root sshd

   will only list the processes called sshd AND owned by root.  On the other hand,

$ pgrep -u root,daemon

   will list the processes owned by root OR daemon.
   
# a little bug, pattern don't  using '/' at the beginning. It auto append '*' at the begin/end of pattern string
$ pgrep pattern


> ps -ef | grep init
root         1     0  0 Jul16 ?        00:00:00 /init
root         6     1  0 Jul16 ?        00:00:00 /init
root         7     6  0 Jul16 ?        00:00:01 /init
root      2496     1  0 00:17 ?        00:00:00 /init
root      2497  2496  0 00:17 ?        00:00:00 /init
yang      2813  2498  0 00:51 pts/1    00:00:00 grep --color=auto /i
> pgrep  init
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2496
2497

please use -f option

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# -f, --full                use full process name to match
> pgrep -f process-name

the difference between pidof and pgrep

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# he equivalence is actually:
$ pidof 'program'
$ pgrep '^program$'
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