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 following statement  status  ps -efww   grep -w  abc sh    grep -v grep   grep -v      awk    print  2     if     -z   status     then         echo    date     abc sh   Process is already running          exit 1  fi   I know it s wrong because every time it exits as it found its own process in  ps  how to solve it  how can I check that script is already running or not from that script only

User · Answer

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

User · Answer

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

User · Answer

The cleanest fastest way  processAlreadyRunning          process  quot   basename  quot   0  quot   quot      pidof -x  quot   process  quot  -o     amp  gt  dev null

User · Answer

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

User · Answer

pidof wasn t working for me so I searched some more and came across pgrep  for pid in   pgrep -f my script sh   do     if    pid          then         echo     date     my script sh   Process is already running with PID  pid          exit 1     else       echo  Running with PID  pid      fi   done   Taken in part from answers above and https   askubuntu com a 803106 802276

User · Answer

I you want the  pidof  method  here is the trick        if pidof -o  PPID -x  abc sh  gt  dev null  then         echo  Process already running      fi   Where the -o  PPID parameter tells to omit the pid of the calling shell or shell script  More info in the pidof man page

User · Answer

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  gt   dev null  then     echo   MY SCRIPT NAME already running  exiting      exit 1 fi

User · Answer

Here s one trick you ll see in various places   status  ps -efww   grep -w   a bc sh    awk -vpid      2    pid   print  2     if     -z   status     then     echo    date     abc sh   Process is already running      exit 1  fi   The brackets around the  a   or pick a different letter  prevent grep from finding itself  This makes the grep -v grep bit unnecessary  I also removed the grep -v    and fixed the awk part to accomplish the same thing

User · Answer

Use the PS command in a little different way to ignore child process as well   ps -eaf   grep -v grep   grep  PROCESS   grep -v

User · Answer

I find the answer from  Austin Phillips is spot on  One small improvement I d do is to add -o  to ignore the pid of the script itself  and match for the script with basename  ie same code can be put into any script    if pidof -x   basename  0   -o     gt  dev null  then     echo  Process already running  fi

User · Answer

I have found that using backticks to capture command output into a variable  adversly  yeilds one too many ps aux results  e g  for a single running instance of abc sh   ps aux   grep -w  abc sh    grep -v grep   wc -l   returns  1   However   count  ps aux   grep -w  abc sh    grep -v grep   wc -l  echo  count   returns  2   Seems like using the backtick construction somehow temporarily creates another process  Could be the reason why the topicstarter could not make this work  Just need to decrement the  count var

User · Answer

I create a temporary file during execution   This is how I do it      bin sh   check if lock file exists if   -e  tmp script lock    then   echo  script is already running  else   create a lock file   touch  tmp script lock   echo  run script      remove lock file  rm  tmp script lock fi

User · Answer

Definitely works  if     pgrep -f  0      quot    quot      then         echo  quot Exiting   Exist quot          exit fi

User · Answer

This is compact and universal    exit if another instance of this script is running for pid in   pidof -x  basename  0    do       pid          amp  amp    exit 1    done

User · Answer

pidof -x   basename  0             amp  amp  exit  https   github com x-zhao exit-if-bash-script-already-running blob master script sh

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

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