How to check if another instance of my shell script is running

Question

GNU bash, version 1.14.7(1)

I have a script is called \"abc.sh\" I have to check this from abc.sh script only... inside it I have written f

Answer 1

Someone please shoot me down if I'm wrong here

I understand that the mkdir operation is atomic, so you could create a lock directory

#!/bin/sh
lockdir=/tmp/AXgqg0lsoeykp9L9NZjIuaqvu7ANILL4foeqzpJcTs3YkwtiJ0
mkdir $lockdir  || {
    echo "lock directory exists. exiting"
    exit 1
}
# take pains to remove lock directory when script terminates
trap "rmdir $lockdir" EXIT INT KILL TERM

# rest of script here

Answer 2

This is compact and universal

# exit if another instance of this script is running
for pid in $(pidof -x `basename $0`); do
   [ $pid != $$ ] && { exit 1; }
done

Answer 3

Use the PS command in a little different way to ignore child process as well:

ps -eaf | grep -v grep | grep $PROCESS | grep -v $$

Answer 4

An easier way to check for a process already executing is the pidof command.

if pidof -x "abc.sh" >/dev/null; then
    echo "Process already running"
fi

Alternatively, have your script create a PID file when it executes. It's then a simple exercise of checking for the presence of the PID file to determine if the process is already running.

#!/bin/bash
# abc.sh

mypidfile=/var/run/abc.sh.pid

# Could add check for existence of mypidfile here if interlock is
# needed in the shell script itself.

# Ensure PID file is removed on program exit.
trap "rm -f -- '$mypidfile'" EXIT

# Create a file with current PID to indicate that process is running.
echo $$ > "$mypidfile"

...

Update: The question has now changed to check from the script itself. In this case, we would expect to always see at least one abc.sh running. If there is more than one abc.sh, then we know that process is still running. I'd still suggest use of the pidof command which would return 2 PIDs if the process was already running. You could use grep to filter out the current PID, loop in the shell or even revert to just counting PIDs with wc to detect multiple processes.

Here's an example:

#!/bin/bash

for pid in $(pidof -x abc.sh); do
    if [ $pid != $$ ]; then
        echo "[$(date)] : abc.sh : Process is already running with PID $pid"
        exit 1
    fi
done

Answer 5

I didn't want to hardcode abc.sh in the check, so I used the following:

MY_SCRIPT_NAME=`basename "$0"`
if pidof -o %PPID -x $MY_SCRIPT_NAME > /dev/null; then
    echo "$MY_SCRIPT_NAME already running; exiting"
    exit 1
fi

Answer 6

Here's how I do it in a bash script:

if ps ax | grep $0 | grep -v $$ | grep bash | grep -v grep
then
    echo "The script is already running."
    exit 1
fi

This allows me to use this snippet for any bash script. I needed to grep bash because when using with cron, it creates another process that executes it using /bin/sh.