shell start / stop for python script

Question

I have a simple python script i need to start and stop and i need to use a start.sh and stop.sh script to do it.

I have start.sh:

#!/bin/sh script='/path/to/my/script.py' echo 'starting $script with nohup' nohup /usr/bin/python $script &

and stop.sh

#!/bin/sh PID=$(ps aux | grep "/path/to/my/script.py" | awk '{print $2}') echo "killing $PID" kill -15 $PID

I'm mainly concerned with the stop.sh script. I think that's an appropriate way to find the pid but i wouldn't bet much on it. start.sh successfully starts it. when i run stop.sh, i can no longer find the process by "ps aux | grep 'myscript.py'" but the console outputs:

killing 25052 25058 ./stop.sh: 5: kill: No such process

so it seems like it works AND gives an error of sorts with "No such process".

Is this actually an error? Am I approaching this in a sane way? Are there other things I should be paying attention to?

EDIT - I actually ended up with something like this: start.sh

#!/bin/bash ENVT=$1 COMPONENTS=$2 TARGETS=("/home/user/project/modules/script1.py" "/home/user/project/modules/script2.py") for target in "${TARGETS[@]}" do PID=$(ps aux | grep -v grep | grep $target | awk '{print $2}') echo $PID if [[ -z "$PID" ]] then echo "starting $target with nohup for env't: $ENVT" nohup python $target $ENVT $COMPONENTS & fi done

stop.sh

#!/bin/bash ENVT=$1 TARGETS=("/home/user/project/modules/script1.py" "/home/user/project/modules/script2.py") for target in "${TARGETS[@]}" do pkill -f $target echo "killing process $target" done

You can get the PID of the previous command with $!. Then you can use this in the stop.sh file. You also have nothing in there to deal with starting multiple times and such. — will
– will, Commented Jul 16, 2013 at 20:30

kojiro · Accepted Answer · 2013-07-17 19:49:23Z

It is because ps aux |grep SOMETHING also finds the grep SOMETHING process, because SOMETHING matches. After the execution the grep is finished, so it cannot find it.

Add a line: ps aux | grep -v grep | grep YOURSCRIPT

Where -v means exclude. More in man grep.

kojiro · Accepted Answer · 2013-07-16 20:38:53Z

The "correct" approach would probably be to have your script write its pid to a file in /var/run, and clear it out when you kill the script. If changing the script is not an option, have a look at start-stop-daemon.

If you want to continue with the grep-like approach, have a look at proctools. They're built in on most GNU/Linux machines and readily available on BSD including OS X:

pkill -f /path/to/my/script.py

glenn jackman · Accepted Answer · 2013-07-16 21:06:47Z

init-type scripts are useful for this. This is very similar to one I use. You store the pid in a file, and when you want to check if it's running, look into the /proc filesystem.

#!/bin/bash script_home=/path/to/my script_name="$script_home/script.py" pid_file="$script_home/script.pid" # returns a boolean and optionally the pid running() { local status=false if [[ -f $pid_file ]]; then # check to see it corresponds to the running script local pid=$(< "$pid_file") local cmdline=/proc/$pid/cmdline # you may need to adjust the regexp in the grep command if [[ -f $cmdline ]] && grep -q "$script_name" $cmdline; then status="true $pid" fi fi echo $status } start() { echo "starting $script_name" nohup "$script_name" & echo $! > "$pid_file" } stop() { # `kill -0 pid` returns successfully if the pid is running, but does not # actually kill it. kill -0 $1 && kill $1 rm "$pid_file" echo "stopped" } read running pid < <(running) case $1 in start) if $running; then echo "$script_name is already running with PID $pid" else start fi ;; stop) stop $pid ;; restart) stop $pid start ;; status) if $running; then echo "$script_name is running with PID $pid" else echo "$script_name is not running" fi ;; *) echo "usage: $0 <start|stop|restart|status>" exit ;; esac

Jon Kiparsky · Accepted Answer · 2013-07-16 20:33:35Z

ps aux | grep "/path/to/my/script.py"

will return both the pid for the instance of script.py and also for this instance of grep. That'll probably be why you're getting a no such process: by the time you get around to killing the grep, it's already dead.

will · Accepted Answer · 2013-07-16 20:41:26Z

I don't have a unix box on at the moment, so i can't test this, but it should be fairly simple to get the idea.

start.sh:

if [ -e ./temp ] then pid=`cat temp` echo "Process already exists; $pid" else script='/path/to/my/script.py' echo 'starting $script with nohup' nohup /usr/bin/python $script & echo $! > temp fi

stop.sh:

if [ -e ./temp ] then pid=`cat temp` echo "killing $pid" kill -15 $PID rm temp else echo "Process not started" fi

Try this out.

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