if I launch a bash script as a child, I can pass its own pid to the parent by using $$.
Is there any way to find the pid of a program that I launch from a script in background
like:
ping x.x.x.x &
what's the pid of that ping ?
(I just hope I expressed my self correctly ... my English is not the best)
PS. I'm looking for a simple and clean solution, I can imagine something like:
ping -t10000 -W10 x.x.x.x &
then
ps ax | grep 'ping -t10000 -W10 x.x.x.x'$
but is too complicated, also even that I used switches to personalize it is not clean, it may catch another processes in the system
The variable $! has the PID of the last background process you started.
Use this: $! right after executing the command whose PID you want. It means, though that you need to use an ampersand (&) after the command, to start it in background. E.g.:
my_command & CMDPID=$!
echo "$CMDPID"
Related
I am looking for an alternative to something like ssh user#node1 uptime && ssh user#node2 uptime, where both of the SSH-commands are run simultaneosly. As they are both blocking until the command returns, && and ; between them don't work.
My goal is to run infinite while loops on both nodes via SSH. So the first one would never return, and the second one would never be run. I would then like to save the output after terminating the loops with Ctrl+C to a log-file and read that one via Python.
Is there an easy solution to this?
Thanks in advance!
Capturing SSH output
On the one hand, you need to capture the ssh output/error and store it into a file so that you can process it afterwards with Python. To this purpose you can:
1- Store output and error directly into a file
ssh user#node cmd 2>&1 > session.log
2- Show output/error in the console while storing it into a file (I would recommend this one)
ssh user#node cmd 2>&1 | tee session.log
Check this for further information about the tee command.
Running commands in parallel
On the other hand, you want to run both commands in parallel and block the current bash process. You can achieve this by:
1- Blocking the current bash process until their childs are done.
cmd1 & ; cmd2 & ; wait
Check this for further information about the wait command.
2- Spawning the child processes and freeing the current bash process. Notice that the processes will be kept alive although the main process ends.
nohup cmd & ; nohup cmd &
The whole thing
I would recommend combining both approaches using tee (so you can still see the ssh outputs on your terminal) and blocking the current process until everything is done (so that when you kill the main process all the processes are killed too).
ssh user#node1 uptime 2>&1 | tee session1.log & ; ssh user#node2 uptime 2>&1 | tee session2.log & ; wait
What I usually do is pause my script, run it in the background and then disown it like
./script
^Z
bg
disown
However, I would like to be able to cancel my script at any time. If I have a script that runs indefinitely, I would like to be able to cancel it after a few hours or a day or whenever I feel like cancelling it.
Since you are having a bit of trouble following along, let's see if we can keep it simple for you. (this presumes you can write to /tmp, change as required). Let's start your script in the background and create a PID file containing the PID of its process.
$ ./script & echo $! > /tmp/scriptPID
You can check the contents of /tmp/scriptPID
$ cat /tmp/scriptPID
######
Where ###### is the PID number of the running ./script process. You can further confirm with pidof script (which will return the same ######). You can use ps aux | grep script to view the number as well.
When you are ready to kill the ./script process, you simply pass the number (e.g. ######) to kill. You can do that directly with:
$ kill $(</tmp/scriptPID)
(or with the other methods listed in my comment)
You can add rm /tmp/scriptPID to remove the pid file after killing the process.
Look things over and let me know if you have any further questions.
I am working with a Raspberry Pi running linux, and have modified the .bash_profile file in order to a run a program I've made automatically upon login. This works great, but I was wondering how to turn the program off, since for ctrl+c I would need to be running the program in the terminal.
You can use Kill to terminate program by its process Id, Top command will list all the processes, You can also use Pkill, which will Terminate the process by its name.
-9 option forces process to shut down, so its very commonly used.
Example:
kill -9 "Process ID without Quotation marks"
pkill -9 "Name with Quotation marks (Case Sensitive)"
Check this.
I always use
pkill - f processname
On a linux box, I have at most 3 java jars files running. How do I quickly kill all 3 with one command?
Usually I would:
ps ex - get the processes running
then find the process ids then do:
kill -9 #### #### ####
Any way to shorten this process? My eyes hurts from squinting to find the process ids.
My script does the following:
nohup ./start-gossip &
nohup ./start &
nohup ./start-admin &
Is there a way to get the process ids of each without looking it up?
Short answer:
pkill java
This looks up a process (or processes) to kill by name. This will find any other java processes too, so be careful. It also accepts -9, but you should avoid using -9 unless something is really broken.
EDIT:
Based on updates, you may be able to specify the script names to pkill as well (I'm not positive). But, the more traditional way to handle this issue is to leave pid files around. After you start a new process and background it, its pid is available in $!. If you write that pid to a file, then it's easy to check if the process is still running and kill just the processes you mean to. There is some chance that the pid will be reused, however.
You can save the PIDs when you start the processes so you can use them later:
nohup ./start-gossip &
START_GOSSIP_PID=$!
nohup ./start &
START_PID=$!
nohup ./start-admin &
START_ADMIN_PID=$!
...
kill -9 $START_GOSSIP_PID
kill -9 $START_PID
kill -9 $START_ADMIN_PID
This has the advantage (over pkill) of not killing off any other processes that coincidentally have similar names. If you don't want to perform the kill operation from the script itself, but just want to have the PIDs handy, write them to a file (from the script):
echo $START_GOSSIP_PID > /some/path/start_gossip.pid
Or even just do this when you launch the process, rather than saving the PID to a variable:
nohup ./start-gossip &
echo $! > /some/path/start_gossip.pid
To get the process id of that java process run
netstat -tuplen
Process ID (PID) of that process whom you want to kill and run
kill -9 PID
I know I can start the process with cron, but how would I go about stopping it? I thought about starting a new process1 everyday at 00:00, then at 23:59 I'd start a process2 doing ps -aux | grep process1, getting the pid from the line and then killing it, but I was wondering if there's be a better way to do it.
I could use Python or Java too if it's easier with either language.
Record its PID:
nohup my_service &
echo $! > /var/run/my_service.pid
and then kill by that PID.
You might want to check both PID and process name to make sure that during the day the process did not crash and some other process did not get that PID. (And even better idea would be to set up supervisor.) But if you are sure that there are no other process with that name you can simply use pkill or killall.