Shell Script to Check If Process Is Running

Linux/Unix command to determine if process is running?

While pidof and pgrep are great tools for determining what's running, they are both, unfortunately, unavailable on some operating systems. A definite fail safe would be to use the following: ps cax | grep command

The output on Gentoo Linux:

14484 ?        S      0:00 apache2
14667 ?        S      0:00 apache2
19620 ?        Sl     0:00 apache2
21132 ?        Ss     0:04 apache2

The output on OS X:

42582   ??  Z      0:00.00 (smbclient)
46529   ??  Z      0:00.00 (smbclient)
46539   ??  Z      0:00.00 (smbclient)
46547   ??  Z      0:00.00 (smbclient)
46586   ??  Z      0:00.00 (smbclient)
46594   ??  Z      0:00.00 (smbclient)

On both Linux and OS X, grep returns an exit code so it's easy to check if the process was found or not:

#!/bin/bash
ps cax | grep httpd > /dev/null
if [ $? -eq 0 ]; then
  echo "Process is running."
else
  echo "Process is not running."
fi

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Furthermore, if you would like the list of PIDs, you could easily grep for those as well:

ps cax | grep httpd | grep -o '^[ ]*[0-9]*'

Whose output is the same on Linux and OS X:

3519 3521 3523 3524

The output of the following is an empty string, making this approach safe for processes that are not running:

echo ps cax | grep aasdfasdf | grep -o '^[ ]*[0-9]*'

This approach is suitable for writing a simple empty string test, then even iterating through the discovered PIDs.

#!/bin/bash
PROCESS=$1
PIDS=`ps cax | grep $PROCESS | grep -o '^[ ]*[0-9]*'`
if [ -z "$PIDS" ]; then
  echo "Process not running." 1>&2
  exit 1
else
  for PID in $PIDS; do
    echo $PID
  done
fi

You can test it by saving it to a file (named "running") with execute permissions (chmod +x running) and executing it with a parameter: ./running "httpd"

#!/bin/bash
ps cax | grep httpd
if [ $? -eq 0 ]; then
  echo "Process is running."
else
  echo "Process is not running."
fi

---

WARNING!!!

Please keep in mind that you're simply parsing the output of ps ax which means that, as seen in the Linux output, it is not simply matching on processes, but also the arguments passed to that program. I highly recommend being as specific as possible when using this method (e.g. ./running "mysql" will also match 'mysqld' processes). I highly recommend using which to check against a full path where possible.

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References:

http://linux.about.com/od/commands/l/blcmdl1_ps.htm

http://linux.about.com/od/commands/l/blcmdl1_grep.htm

Linux Script to check if process is running and act on the result

Programs to monitor if a process on a system is running.

Script is stored in crontab and runs once every minute.

This works with if process is not running or process is running multiple times:

#! /bin/bash

case "$(pidof amadeus.x86 | wc -w)" in

0)  echo "Restarting Amadeus:     $(date)" >> /var/log/amadeus.txt
    /etc/amadeus/amadeus.x86 &
    ;;
1)  # all ok
    ;;
*)  echo "Removed double Amadeus: $(date)" >> /var/log/amadeus.txt
    kill $(pidof amadeus.x86 | awk '{print $1}')
    ;;
esac

0 If process is not found, restart it.

1 If process is found, all ok.

* If process running 2 or more, kill the last.

---

A simpler version. This just test if process is running, and if not restart it.

It just tests the exit flag $? from the pidof program. It will be 0 of process is running and 1 if not.

#!/bin/bash
pidof  amadeus.x86 >/dev/null
if [[ $? -ne 0 ]] ; then
        echo "Restarting Amadeus:     $(date)" >> /var/log/amadeus.txt
        /etc/amadeus/amadeus.x86 &
fi

---

And at last, a one liner

pidof amadeus.x86 >/dev/null ; [[ $? -ne 0 ]] && echo "Restarting Amadeus:     $(date)" >> /var/log/amadeus.txt && /etc/amadeus/amadeus.x86 &

This can then be used in crontab to run every minute like this:

* * * * * pidof amadeus.x86 >/dev/null ; [[ $? -ne 0 ]] && echo "Restarting Amadeus:     $(date)" >> /var/log/amadeus.txt && /etc/amadeus/amadeus.x86 &

cccam oscam

How can I check if a program exists from a Bash script?

Answer

POSIX compatible:

command -v <the_command>

Example use:

if ! command -v <the_command> &> /dev/null
then
    echo "<the_command> could not be found"
    exit
fi

For Bash specific environments:

hash <the_command> # For regular commands. Or...
type <the_command> # To check built-ins and keywords

Explanation

Avoid which. Not only is it an external process you're launching for doing very little (meaning builtins like hash, type or command are way cheaper), you can also rely on the builtins to actually do what you want, while the effects of external commands can easily vary from system to system.

Why care?

• Many operating systems have a which that doesn't even set an exit status, meaning the if which foo won't even work there and will always report that foo exists, even if it doesn't (note that some POSIX shells appear to do this for hash too).
• Many operating systems make which do custom and evil stuff like change the output or even hook into the package manager.

So, don't use which. Instead use one of these:

command -v foo >/dev/null 2>&1 || { echo >&2 "I require foo but it's not installed.  Aborting."; exit 1; }

type foo >/dev/null 2>&1 || { echo >&2 "I require foo but it's not installed.  Aborting."; exit 1; }

hash foo 2>/dev/null || { echo >&2 "I require foo but it's not installed.  Aborting."; exit 1; }

(Minor side-note: some will suggest 2>&- is the same 2>/dev/null but shorter – this is untrue. 2>&- closes FD 2 which causes an error in the program when it tries to write to stderr, which is very different from successfully writing to it and discarding the output (and dangerous!))

If your hash bang is /bin/sh then you should care about what POSIX says. type and hash's exit codes aren't terribly well defined by POSIX, and hash is seen to exit successfully when the command doesn't exist (haven't seen this with type yet). command's exit status is well defined by POSIX, so that one is probably the safest to use.

If your script uses bash though, POSIX rules don't really matter anymore and both type and hash become perfectly safe to use. type now has a -P to search just the PATH and hash has the side-effect that the command's location will be hashed (for faster lookup next time you use it), which is usually a good thing since you probably check for its existence in order to actually use it.

As a simple example, here's a function that runs gdate if it exists, otherwise date:

gnudate() {
    if hash gdate 2>/dev/null; then
        gdate "$@"
    else
        date "$@"
    fi
}

Alternative with a complete feature set

You can use scripts-common to reach your need.

To check if something is installed, you can do:

checkBin <the_command> || errorMessage "This tool requires <the_command>. Install it please, and then run this tool again."

Check if program is running with bash shell script?

If you want to execute that command, you should probably change:

PROCESS_NUM='ps -ef | grep "$1" | grep -v "grep" | wc -l'

to:

PROCESS_NUM=$(ps -ef | grep "$1" | grep -v "grep" | wc -l)

Shell script to check if process is running

Unless you're running BSD ps, you should be able to use a -C flag or pgrep

-C cmdlist      Select by command name. This selects the processes whose executable 
                name is given in cmdlist.

For example,

if ps -C node > /dev/null
then
        date > /etc/nodeCheck.log 
else
        date > /dev/null 
fi

or

if pgrep node > /dev/null
then
        date > /etc/nodeCheck.log 
else
        date > /dev/null 
fi

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