view running deamon ps -p

fick_manning · 10-07-2018, 10:37 AM

hay guys
i am in a red hat course and in need to check if deamons that belongs to a service (chronyd)are running.
in the book they do it by ps -p PID
but when i do this i get this output:

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as you can see i dont get nothing.
why is that and how i can verifay that the deamon is running?

average_user · 10-07-2018, 11:10 AM

The last line 'ps -p 675' shows chronyd, what's the problem?

fick_manning · 10-07-2018, 11:27 AM

the assigment is that i need to verifay that that those deamons are running
but i dont understand the output - it is just headlines...
it dosent tell me if it is running or not

average_user · 10-07-2018, 11:45 AM

It does. Read 'man ps':

Code:

-p pidlist
   Select by PID.  This selects the processes whose process ID numbers appear in pidlist.  Identical to p and --pid.

When you pass a wrong PID process name is not shown and $? is set to non-zero. Try this:

Code:

$ ps -p 9999
  PID TTY          TIME CMD
$ echo $?
1
$ ps -p 1
  PID TTY          TIME CMD
    1 ?        00:00:21 init
$ echo $?
0

fick_manning · 10-07-2018, 12:06 PM

first of all tnx for the help!!
so.. in my example under all of them theres is nothing excpet for the main PID and even then theres is a "?" under tty.
unlike youre example that there is time and in my example the time is 00:00 and in yours there is time that have past...
i am passing the pid's from the the command "systemctl status chronyd" whic are:
728
661
and the main PID: 675

average_user · 10-07-2018, 01:49 PM

In your screenshot you use incorrect PIDs 728 and 661 - there are no processes that have such PIDs on your system. In my example above I've used 9999 as a fake PID to represent the situation. Notice that my version of ps acts identically to yours and only prints header when non-existent PID is given and sets $? to non-zero.

fick_manning · 10-07-2018, 02:35 PM

Quote:

Originally Posted by average_user

In your screenshot you use incorrect PIDs 728 and 661 - there are no processes that have such PIDs on your system. In my example above I've used 9999 as a fake PID to represent the situation. Notice that my version of ps acts identically to yours and only prints header when non-existent PID is given and sets $? to non-zero.

tnx man!

fick_manning · 10-07-2018, 04:46 PM

but than why are "728","661" cant be procces number? this is what i dont understand...
like in these blue box in i draw in the pic below (which you talked about erliar)

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i mean - 728 661 - why cant it be a processes if that's what the command return (again in the blue box i draw)
i can use the 675 like on "ps -p 675" then why not "ps -p 661/728" ?
the systemctl command show those numbers as proccess

scasey · 10-07-2018, 04:57 PM

Quote:

Originally Posted by fick_manning

but than why are "728","661" cant be procces number? this is what i dont understand...
like in these blue box in i draw in the pic below (which you talked about erliar)
Attachment 28752
i mean - 728 661 - why cant it be a processes if that's what the command return (again in the blue box i draw)
i can use the 675 like on "ps -p 675" then why not "ps -p 661/728" ?
the systemctl command show those numbers as proccess

Those processes have already ended. The only one continuing to run (the daemon) is 675

MadeInGermany · 10-09-2018, 08:57 PM

Perhaps 728 661 are threads (LWPs)?
Check the main PID for its threads

Code:

ps -fLp 675

Linux takes both processes and threads from the PID pool.

average_user · 10-10-2018, 08:12 AM

I don't think so. Notice ExecStart - these processes probably died after doing exec(). It looks like 661 change to 675.