I've googled this question, but never found anything useful for my particular case.
So, what I'm trying to figure out is the PID of a certain command that is running so I can kill it if necessary. I know it's possible to get the PID of a command by typing echo $! So supposedly
my_command & echo $!
should give me the PID. But this isn't the case, and I think I know why:
My command is as follows:
screen -d -m -S Radio /path/to/folder -f frequency -r path/to/song
which opens a detached screen first and then types the command so that it gets executed and keeps on running in the background. This way the PID that echo shows me is the wrong one. I'm guessing it shows me PID of screen -d -m -S Radio /path/to/folder -f frequency -r path/to/song instead of the PID of the command run in the new terminal created by screen.
But there's another problem to it: when I run screen -ls in the terminal, the command that is running in the background doesn't show up! I'm fairly certain it's running because the Pi is constantly at 25% CPU usage (instead of the 0% or 1% usually) and when I type ps au I can actually see the command and the PID.
So now I'm calling the community: any idea on how I could find the PID of that certain command in the new terminal? I'm writing a bash script, so it has to be possible to obtain the PID through code. Perfect would be a command that stores the PID in a variable!
Thanks to #glennjackman I managed to get the PID I wanted with a simple pgrep search_word. At first it wasn't working, but somehow I made it work after some trial and error. For those wanting the PID on a variable, just type
pid=$(pgrep search_word)
Regarding the problem with screen -ls not showing my detached session, it's still not solved, but I'm not bothered with it. Thanks again for solving my problem #glennjackman !
EDIT:
Second problem solved, check the comments on berends answer.
You can easily find out all the running process and their PID by writing (for example):
ps aux
The process is run by screen so you can probably find it easier by writing:
ps aux | grep screen
For more info about ps and the parameters I used check (quick google) -> https://www.lifewire.com/g00/uses-of-linux-ps-command-4058715?i10c
EDIT: You can use this command with bash scripting as well.
Related
Let's say I have a silly script:
while true;do
touch ~/test_file
sleep 3
done
And I start the script into the background and leave the terminal:
chmod u+x silly_script.sh
./silly_script.sh &
exit
Is there a way for me to identify and stop that script now? The way I see it is, that every command is started in it's own process and I might be able to catch and kill one command like the 'sleep 3' but not the execution of the entire script, am I mistaken? I expected a process to appear with the scripts name, but it does not. If I start the script with 'source silly_script.sh' I can't find a process by the name of 'source'. Do I need to identify the instance of bash, that is executing the script? How would I do that?
EDIT: There have been a few creative solutions, but so far they require the PID of the script execution to be stored right away, or the bash session to not be left with ^D or exit. I understand, that this way of running scripts should maybe be avoided, but I find it hard to believe, that any low privilege user could, even by accident, start an annoying script into the background, that is for instance filling the drive with garbage files or repeatedly starting new instances of some software and even the admin has no other option, than to restart the server, because a simple script can hide it's identifier without even trying.
With the help of the fine people here I was able to derive the answer I needed:
It is true, that the script runs every command in it's own process, so for instance killing the sleep 3 command won't do anything to the script being run, but through a command like the sleep 3 you can find the bash instance running the script, by looking for the parent process:
So after doing the above, you can run ps axf to show all processes in a tree form. You will then find this section:
18660 ? S 0:00 /bin/bash
18696 ? S 0:00 \_ sleep 3
Now you have found the bash instance, that is running the script and can stop it: kill 18660
(Of course your PID will be different from mine)
The jobs command will show you all running background jobs.
You can kill background jobs by id using kill, e.g.:
$ sleep 9999 &
[1] 58730
$ jobs
[1]+ Running sleep 9999 &
$ kill %1
[1]+ Terminated sleep 9999
$ jobs
$
58730 is the PID of the backgrounded task, and 1 is the task id of it. In this case kill 58730 and kill %1` would have the same effect.
See the JOB CONTROL section of man bash for more info.
When you exit, the backgrounded job will get a kill signal and die (assuming that's how it handles the signal - in your simple example it is), unless you disown it first.
That kill will propogate to the sleep process, which may well ignore it and continue sleeping. If this is the case you'll still see it in ps -e output, but with a parent pid of 1 indicating its original parent no longer exists.
You can use ps -o ppid= <pid> to find the parent of a process, or pstree -ap to visualise the job hierarchy and find the parent visually.
I have a nohup process running on my FreeBSD 8.4 box. Initially I was looking at nohup console messages output through
tail -f nohup.out
But I accidentally deleted nohup.out file. How can I access the console messages now ?
Its pretty easy actually.
First go back in your command history to find the command you used to start the process. For example, nohup my-long-process.sh & Or if you remember it (very likely), just go to the next step.
Now find the process ID of your process. In this example ps -ef|grep my-long-process
You will see the PID (process ID) and the PPID (parent process ID) right after the name of the user you started the process as. The PID you want is the number on the left. Let's say it is 2919 in this example.
Since the process is still running, you will find a directory called /proc/2919/fd. Here 2919 is the PID you got from the ps command above.
If you list that directory, with ls -l /proc/2919/fd, you will see a link (or two) called 1, 2 etc that point to your deleted file. In fact, the name of the destination file will be /path/to/your/nohup.out (deleted).
You can now tail -f tail -f /proc/2919/fd/1.
Oh, and if you want to see what you missed, you can less that file with less /proc/2919/fd/1
I have a bash script running on Ubuntu.
Is it possible to see the line/command executed now without script restart.
The issue is that script sometimes never exits. This is really hard to reproduce (now I caught it), so I can't just stop the script and start the debugging.
Any help would be really appreciated
P.S. Script logic is hard to understand, so I can't to figure out why it's frozen by power of thoughts.
Try to find the process id (pid) of the shell, you may use ps -ef | grep <script_name>
Let's set this pid in the shell variable $PID.
Find all the child processes of this $PID by:
ps --ppid $PID
You might find one or more (if for example it's stuck in a pipelined series of commands). Repeat this command couple of times. If it doesn't change this means the script is stuck in certain command. In this case, you may attach trace command to the running child process:
sudo strace -p $PID
This will show you what is being executed, either indefinite loop (like reading from a pipe) or waiting on some event that never happens.
In case you find ps --ppid $PID changes, this indicates that your script is advancing but it's stuck somewhere, e.g. local loop in the script. From the changing commands, it can give you a hint where in the script it's looping.
Using jobs I know the process is running.
bash-4.2$ jobs
[1]+ Running test.sh &
I wanted it to be set NOHUP so that it won't be killed when I exit. I used
disown
and
bash-4.2$ jobs
shows nothing. I'm not sure if the process is set NOHUP or not. I'm curious about this because after I read the manual it says
disown -h
should be used to set NOHUP.
Edit
I don't think the link Find the Process run by nohup command helps. The question is different than that one.
I'm gonna restate my problem. I run a program without nohup, and later I wanted it to be set NOHUP so that it won't be killed when I exit the system. So I used disown, but later I found the manual says I should have used disown -h to set NOHUP. I want to check if my process is set NOHUP or not successfully. If not, what can I do to set it to be NOHUP?
UPDATE
I know two ways my be helpful:
1) Whenever a process is running over nohup It writes output on ~/nohup.out . So you can check this file by running command find -cmin 2. It shows you if nohup.out is changing each 2 seconds or not.
If it is changing you would understand that sth is running by nohup command, after that you can check it with lsof and continue your checking...
2) If you logout from specific user andgo to tty then do ps aux | grep <user> or ps aux | grep ? then you can understand that is running with nohup command... because there is no pts then it shows you ? instead...
useful command:
ps aux | grep <program> | awk -F" " '{print $7}'
Hope to be helpful
Given a pid, for example 29264， how to get to know whether the process is running ?
Is there any easy way to do that ?
thx
Process status (ps) provides the information you're looking for:
ps -p 29264
Output in case the process is running (quick example on my Mac, works the same on Linux):
PID TIME CMD
127 4:54.03 /System/Library/CoreServices/Finder.app/Contents/MacOS/Finder
Otherwhise:
PID TIME CMD
kill -0 29264 ,and inspect the error (if any)
link to online linux (man 2) manual
link to online linux (man 1) manual
To get process status:
ps -p 29264 > /dev/null; echo $?