I am trying to automatically check if a process is running or not and have to perform next steps accordingly. I had written a bash script but it doesn't seem to work.
if ps aux | grep [M]yProcessName > /dev/null
then
echo "Running"
else
echo "Not running"
fi
Is my if statement wrongly used?
You don't want to know if a particular process (of known pid) is running (this can be done by testing if /proc/1234/ exists for pid 1234) but if some process is running a given command (or a given executable).
Notice that the kill(2) syscall can be portably used to check if a given process is running (with a 0 signal, e.g. kill(pid,0)). From inside a program, this is a common way to check that a process of known pid is still existing and running (or waiting).
You could use the pidof command to find the processes running some executable, e.g. pidof zsh to find all the zsh processes. You could also use killall -s 0 zsh
And you might be interested by the pgrep utility and the /proc filesystem.
ps aux | grep [M]yProcessName | grep -v grep
grep -v grep filters out the line(s) that contain "grep". This is necessary because ps aux | grep foo will capture lines listing all the processes currently running that contain the string "foo", which includes the command itself! In other words, you will always have a line in your results, whether a foo process is running or not. Using grep -v grep, you will have 0 lines when no foo process is running, and you will only get the line(s) pertaining to actual foo processes, not your command.
[M] already takes care of filtering out the grep process, a second grep is NOT needed in this case. Pattern [M]yProcessName only matches string MyProcessName, whereas grep shows up as grep [M]yProcessName in the process list, thus it does not match and does not get included.Using -z to check if a string is empty or not, something like this could work:
line=$(ps aux | grep [M]yProcessName)
if [ -z "$line" ]
then
echo "Not Running"
else
echo $line > /dev/null
echo "Rinnung"
fi
grep returns non-zero when it doesn't match, so test is not needed. The [] around the M eliminates the need for the grep -v grep.There is a solution:
if [ "$(ps aux | grep "what you need" | awk '{print $11}')" == "grep" ]; then ... elif [ ... ]; then ... else ... fi
This works fine in Debian 6. '{print $11}' is needed, because the sytem treats grep as a process as well
processid =$(ps aux | grep 'ProcessName' | grep -v grep| awk '{print $2}')
The above command will give you the process id. Assign that process id to a variable and do this -->
if cat /proc/$processid/status | grep "State: R (running)" > /dev/null
then
echo "Running"
else
echo "Not running"
fi
Just to explicitly mention a way this answer alluded to, pgrep is the best way to do this by process name:
pgrep [M]yProcessName
If a process whose name matches "[M]yProcessName" is running, pgrep will print its PID to stdout and will exit with code 0. Otherwise, it will print nothing and exit with code 1.
SMBD=$(pidof smbd)
if [ "$SMBD" == "" ];
then
/etc/init.d/samba start;
else
/etc/init.d/samba restart;
fi
return 0 means success while others failed
kill -0 `pid`; echo $?
On my system, ps aux | grep ProcessName always get a line of that grep process like:
edw4rd 9653 0.0 0.0 4388 832 pts/1 S+ 21:09 0:00 grep --color=auto ProcessName
So, the exit status is always 0. Maybe that's why your script doesn't work.
grep uses a regex which doesn't match itself.try this
ps aux | grep [M]yProcessName | grep -v grep
iflooks fine. Why don't you run it and find out yourself? It took me a minute to copy the if into a file and start it.