Solved What does the process with [] shown in ps mean?

[sdf]

Hello,

What does the process with [] shown in ps mean? And why are some processes without directories?

Thanks.

 

[Bobi B.]

Kernel processes are printed in brackets.

If by "processes without directories" you mean entries, where full executable path is not visible, that might be due to: 1) change of a process' name with setproctitle(3) (more likely), or 2) omitted/incorrect path when executable were started with execl(3).

 

[sdf]

Thank you. Is there an internal command without a directory? Such as ps.
And why is there a - prefix in front of the shell's process? Such as -csh.

 

[Bobi B.]

There are builtin(1)s, meaning commands, integrated in the shell, for example cd and echo. But I cannot tell if shell will create a sub-process when executing a built-in command or not; most likely not (apart from the case, where you execute such command in background, like ls / &).

I believe a leading dash means that this is a login shell.

 

[sdf]

Thank you very much.
And is sendmail also a kernel process? But it has neither [] nor a display path.

 

[kpa]

Sendmail is a 100% user space program, all it does is listen for incoming mail and handles it by either delivering it locally or forwarding it to an outside address.

 

[Bobi B.]

As kpa said, sendmail(8) is a user-space program. The reason ps lists no path is that sendmail uses setproctitle(3) to label its processes; in this case process' name is appended at the end, in brackets; ps daxww | grep sendmail:

 1592  -  SsJ       1:16.86 |-- sendmail: accepting connections (sendmail)
 1595  -  IsJ       0:00.96 |-- sendmail: Queue runner@00:30:00 for /var/spool/clientmqueue (sendmail)
 2528  -  Ss        1:08.24 |-- sendmail: accepting connections (sendmail)
 2531  -  Is        0:00.95 |-- sendmail: Queue runner@00:30:00 for /var/spool/clientmqueue (sendmail)

Another example, ps daxww | grep \(:

 1751  -  SsJ       2:29.27 |-- php-fpm: master process (/usr/local/etc/php-fpm.conf) (php-fpm)
 1752  -  IJ       23:47.79 | |-- php-fpm: pool www (php-fpm)
 1753  -  IJ       23:24.40 | |-- php-fpm: pool www (php-fpm)
16680  -  IJ       22:58.74 | `-- php-fpm: pool www (php-fpm)[/cmd]

 

[sdf]

As kpa said, sendmail(8) is a user-space program. The reason ps lists no path is that sendmail uses setproctitle(3) to label its processes;

Thank you.
So in which directory is the sendmail daemon located?

 

[kpa]

It's located at:

% ls -l /usr/libexec/sendmail/sendmail
-r-xr-sr-x  1 root  smmsp  733896 Aug 20 16:55 /usr/libexec/sendmail/sendmail

Do read the following manual pages:
mailwrapper(8)
mailer.conf(5)
rc.sendmail(8)

 

[sdf]

Thank you very much.

 

[SirDice]

So in which directory is the sendmail daemon located?

whereis(1), locate(1).