On running nohup with & on command line, it is returning the process id,
while the same command I am running in perl script within backticks and trying to read output is not returning any output.
Can anyone please guide?
nohup rm -rf ragh &
[1] 10029
The job number and PID are printed by the shell when starting a background process in a terminal. nohup is irrelevant. If you don't start the job from a terminal (i.e. you use backticks in Perl on shell, or you use a plain subshell) the information isn't shown. Why do you need it, anyway? See perlipc - Perl interprocess communication for details.
If you need the process ID of the background job then use the $! variable, for example:
nohup start_long_running_job &
echo $! > jobid.txt
And then if you need to kill the job:
kill $(cat jobid.txt)
It applies equally with or without nohup.
nohup means that you spawn a new process and execute the script in that context.
If your command there takes longer than your starting script it will survive the closing of your shell. If you need the output you should pipe it somewhere else
nohup rm -rf ragh > log.txt &
choroba correctly stated when the PID isn't shown ("If you don't start the job from a terminal").
Richard RP correctly stated that $! can be used. But for running in a Perl script within backticks, in addition we need to close the command's standard output, otherwise the backtick invocation would return only after the process has finished, because perl waits for the output's EOF.
$pid = `nohup rm -rf ragh >&-& echo \$!`
gets us rm's PID in $pid.
Related
I'm trying to make a function in my bashrc that would allow me to launch any command and automatically disown it.
e.g. launch ./myprogram or launch xdg-open myfolder
I've been used to do that many times command ; Ctrl+Z ; bg ; disown and would like to simply create a shortcut of these steps.
However I don't know how to embed the action of Ctrl+Z in a bash script. I've seen that its action is SIGTSTP, but I'm really lost as to how incorporate that in a bash function.
You can run the command in background directly instead of stopping it and then running it in the background. Use the &:
$ cat > launch
#! /bin/bash
"$#" & disown
Ctrl + d
$ chmod u+x ./launch
For posterity and othe people passing by, here is the bash function I made :
launch()
{
"$#" > /dev/null 2>&1 & disown
}
"$#" takes every arguments given in the prompt as one
> /dev/null 2>&1 redirects every output (stout and stderr) to dev/null which effectively delete them automatically, so that it doesn't appear on the shell
& runs the command in background, meaning it will let you input other commands in the shell
disown , as the name implies will lake it so that the process is no longer bound to the shell and you cans safely close the shell without it closing the process at the same time.
I have a well working bash script to create some random files. It runs a loop which create random bin files and then recreate them after a sleep time.
I would like to give an option so that I can run the script like a daemon. So the script would go in the background, detach stdin, stdout and stderr, maybe even attach itself to init instead of the current bash.
How should I do that?
The script is on github:
https://github.com/momeunier/randombin/blob/master/randombin.sh
Simply run a subshell:
function do_something {
<stuffs>
}
( do_something; ) &>/dev/null &
disown
Hmm, how about:
./randombin.sh >/dev/null 2>&1 &
disown
First redirects stdout and stderr to /dev/null and launches the script in the background.
Next command sets init as parent so you can close your terminal without the process exiting.
I am trying to write a script that starts rtmpsrv and waits for some output from it. rtmpsrv gives the desirable output and continues running, but the script is waiting for a termination of rtmpsrv. How do I gain access to the output of rtmpsrv without stopping it?
Well, I'm not familiar with rtmpsrv, but unless necessary you should wait for it to finish. However, you can probably redirect its output to a file, and then grep the file to see if it contains the string you are looking for.
(fictional code... you can expect syntax hell, just want to give you an idea)
nohup rtmpsrv >log.rtmpsrv 2>&1 &
...
while :; do
if ! result=$(grep "your desired line" log.rtmpsrv); then
echo "success: found $result"
break
fi
done
Note: the if constructs should work as per http://www.tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_01.html - just to have nicer code, as #Charles Duffy suggested.
The most simple way is this:
rtmpsrv > logfile &
Then you can search logfile for the text that you're looking for. Meanwhile, rtmpsrv will do it's thing, completely unaware of your script.
This question contains examples how to wait in your script for a certain pattern to appear in the logfile (so you don't have to search it again and again): Do a tail -F until matching a pattern
Note: If you start the rtmpsrv process in the script and the script terminates, it will probably kill the rtmpsrv process. To avoid that use nohup.
Just attach to the process using gdb -p <pid> where the pid is the process id of your script.
You can find the pid of your running script by doing smth like this ps ax | grep <My Script's Name>
http://etbe.coker.com.au/2008/02/27/redirecting-output-from-a-running-process/
I call a script in my .bashrc to print number of new messages I have when I open the terminal, I want the call to be non blocking as it accesses the network and sometimes takes a few seconds which means I can't use the terminal until it completes.
However if I put:
mailcheck &
in my bashrc, it works fine. but then prints an empty line and I have when I press enter and it prints
[1]+ Done ~/bin/mailcheck
This is very messy is there a way around this?
That message isn't coming from mailcheck, it's from bash's job control telling you about your backgrounded job. The way to avoid it is to tell bash you don't want it managed by job control:
mailcheck &
disown $!
This seems to work:
(mailcheck &)
You can call your script like this:
(exec mailcheck & )
try piping stderr to /dev/null
mailcheck & 2>/dev/null
Thinking about it for a few mins, another way might be to use write.
Pipe the output of the background task to yourself, that way it can complete at any time and you can bin any additional output from stdout as well as stderr.
mailcheck | write $(whoami) & > /dev/null
This was the last page I checked before I fixed an issue I was having so I figured I would leave my finished script that had the same issue as OP:
nohup bash -c '{anycommand};echo "CommandFinished"' 1> "output$(date +"%Y%m%d%H%M").out" 2> /dev/null & disown
This runs {anycommand} with nohup and sends the stdout to a unique file, the stderr to /dev/null, and the rest to console (the PID) for scraping. The stdout file is monitored by another process looking for the CommandFinished or whatever unique string.
Bash would later print this:
[1]+ Done nohup bash -c ....
Adding disown to the end stopped bash jobs from printing that to console.
I need to invoke a bash script by itself with a different set of arguments that would make it run as a background process, so I am using something like:
if [[ $a == $b ]]
then
$0 -v &> /dev/null
fi
The issue is that though I am invoking the same script as a background process using '&' as suffix and redirecting all outputs to /dev/null, the terminal that I invoke the script is not released, I am assuming that is because of the script which initially was invoked has a process which is running as a foreground process, so the query is, how to call a bash script by itself such that when it calls itself the process which is responsible for running the script for the first time is killed and the console released and the second call to itself runs as a background process?
You're not running it as a background process using &. &> is a completely separate token that redirects stdout and stderr at the same time. If you wanted to put that command in the background it would be $0 -v &>/dev/null &.
Try something like this:
nohup $0 -v &
The nohup command does the job of detaching the background job and ignoring signals, see the man page.