How to always cut the PID from `ps aux` command?

Question

I'd like to get the pid from my processes. I do ps aux | cut -d ' ' -f 2 but I notice that sometimes it gets the pid and sometimes it does not:

[user@ip ~]$ ps aux 
user  2049  0.5 10.4 6059216 1623520 ?     Sl   date   8:48 process 
user 12290  0.3  6.9 5881568 1086244 ?     Sl   date  2:30 
[user@ip ~]$ ps aux | cut -d ' ' -f 2 

12290
[user@ip ~]$ ps aux |  cut -d ' ' -f 3
2049

notice that the first cut command is piping it to 2 whereas the second one is piping it to 3. How do I pick out the PID from these without having to know which number to use (2 or 3)?

Can someone please tell me the difference between these and why it picks up one and not the other?

CtheSky · Accepted Answer · 2017-09-02T07:59:43.877

65

-d ' ' means using a single space as delimiter. Since there're 1 space before 2049 and 2 spaces before 12290, your command get them by -f 2 and -f 3.

I recommend using ps aux | awk '{print $2}' to get those pids.

Or you can use tr to squeeze those spaces first ps aux | tr -s ' ' | cut -d ' ' -f 2

edited Sep 02 '17 at 07:59

answered Sep 02 '17 at 07:51

CtheSky

2,484
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score 10 · Answer 2 · answered Oct 15 '20 at 06:19

10

You can always use pgrep to get process's PID

E.g PIDs with PS AUX

wix@wsys:~$ ps aux | grep sshd
root      1101  0.0  0.0  72304  3188 ?        Ss   Oct14   0:00 /usr/sbin/sshd -D
root      6372  0.0  0.1 105692  7064 ?        Ss   06:01   0:00 sshd: wix [priv]
wix       6481  0.0  0.1 107988  5748 ?        S    06:01   0:00 sshd: wix@pts/1
root      6497  0.0  0.1 105692  7092 ?        Ss   06:01   0:00 sshd: wix [priv]
wix       6580  0.0  0.1 107988  5484 ?        S    06:01   0:00 sshd: wix@pts/2
wix       6726  0.0  0.0  13136  1044 pts/1    S+   06:12   0:00 grep --color=auto sshd

Now just pgrep to get PIDs

wix@wsys:~$ pgrep sshd
1101
6372
6481
6497
6580
wix@wsys:~$

answered Oct 15 '20 at 06:19

Waqar Afridi

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How does this relate to the OP's question ? – Nicolas Melay Oct 15 '20 at 08:54
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I figure the goal is to get the PIDs so why not use a tool at hand rather then using complex chain of commands. – Waqar Afridi Oct 16 '20 at 06:07
He did not specify what his final intent is, but since collecting the PIDs of ALL your processes seems pointless, I guess you might be right. – Nicolas Melay Oct 20 '20 at 14:54
Even if you want all processes you can do pgrep "" – Ted Brownlow Nov 17 '20 at 23:15
how to do for `/sbin/lvmetad -f` pgrep will not be showing the PID's – Kishore Feb 17 '21 at 07:26
`pgrep --full` worked great for me. I was looking for particular python script invocations, and regular pgrep wasn't cutting it. – matt Mar 29 '22 at 01:47

score 7 · Answer 3 · answered Sep 02 '17 at 09:05

7

You can use the option -o to print only the pid:

ps -u user -o pid

answered Sep 02 '17 at 09:05

Minh Tuan Nguyen

1,026
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How to always cut the PID from `ps aux` command?

3 Answers3