Auto-changing process ID: E.g. vsftp

fanoflq · 11-08-2016, 03:24 PM

I am able to start vsftpd manually here:

Code:

[student@localhost etc]$ sudo /usr/sbin/vsftpd /etc/vsftpd/vsftpd.conf &
[1] 8105
[student@localhost etc]$ sudo ps aux | grep vsftpd
root       8110  0.0  0.0  52796   564 ?        Ss   13:42   0:00 /usr/sbin/vsftpd /etc/vsftpd/vsftpd.conf
student    8121  4.0  0.0 112644   920 pts/2    S+   13:43   0:00 grep --color=auto vsftpd
[1]+  Done                    sudo /usr/sbin/vsftpd /etc/vsftpd/vsftpd.conf

Q1: But when it got executed, it got a process ID of 8105.
Then when I use command: ps aux, its process ID is 8110.
This change in process IDs is repeatable!
Why?

Thank you.

jpollard · 11-08-2016, 04:31 PM

vsftpd is a daemon.

It listens for connections, then spawns a process to support it; then goes back to listen for more.

fanoflq · 11-08-2016, 04:38 PM

Quote:

Originally Posted by jpollard

vsftpd is a daemon.

It listens for connections, then spawns a process to support it; then goes back to listen for more.

Then why is its OWN process ID disappeared?
After it spawn another process, vsftpd should still be alive, correct?
What did I missed?

jpollard · 11-08-2016, 05:11 PM

Unless there has been a configuration failure I would expect it to still be there. Sometimes debug options are used to force that.

It looks like it terminated - otherwise the sudo command would not have terminated. I would have expected the daemon to detatch and run in the background (though the default appears to disable this).

There ought to be log entries if it failed.

You might try not putting it in the background to see if it operates differently.

fanoflq · 11-08-2016, 05:33 PM

Quote:

Originally Posted by jpollard

You might try not putting it in the background to see if it operates differently.

What do you mean?
vsftpd is already in background mode since it is a daemon, correct?

jpollard · 11-08-2016, 05:49 PM

Quote:

Originally Posted by fanoflq

What do you mean?
vsftpd is already in background mode since it is a daemon, correct?

Not according to the default options. It doesn't put itself in the background.

According to your own command "sudo /usr/sbin/vsftpd /etc/vsftpd/vsftpd.conf &" you put the sudo command into the background.

Now if sudo lost access to the terminal for some reason, it could get aborted. But I don't think that is what happened as you got a "[1]+ Done sudo /usr/sbin/vsftpd /etc/vsftpd/vsftpd.conf", which is a normal termination.

chrism01 · 11-08-2016, 09:45 PM

The 'sudo' process is 8105, vsftpd daemonizes itself so it gets a new pid 8110

fanoflq · 11-08-2016, 10:12 PM

Quote:

Originally Posted by chrism01

The 'sudo' process is 8105, vsftpd daemonizes itself so it gets a new pid 8110

Two commands should have two processes.
Thus two process IDs.
That makes more sense.
Thanks.

Side question/observation:
Why are you staying away from CentOS7?