A Bash Process Controller to Start, Stop and Restart an Daemon Program

In Linux, we have service process controller which can be used to start, stop and restart a particular registered service. For example:

$ sudo service mysql stop
$ sudo service mysql start
$ sudo service mysql restart

We can use BASH script to customize a process controller, where we can pass the third paramter any long-running process e.g. yes which keeps printing the “y” to the console.

We use “nohup” to start the daemon program and put it in background. Output the process ID to $PID_FILE_PATH so that we can control it later with stop. The “restart” is an alias of “stop” and “start”.

If the PID_FILE_PATH is found, we search the process in memory using “ps” command, and exit the BASH if the process is found running.

#!/bin/bash

# Function: to start, stop and restart the application.
# Usage: $0 start|stop|restart application

if [[ "$#" -lt 2 ]]; then
    echo "Usage: $0 start|stop|restart command"
    echo "$# parameters given."
    exit 1
fi

PID_FILE_PATH="runner.pid"

case "${1}" in
    start)
        # Already running
        if [ -f ${PID_FILE_PATH} ]; then
            pid=$(cat ${PID_FILE_PATH})
            if $(ps -p ${pid} > /dev/null); then
                echo "Already running [PID: ${pid}], you can stop it and retry."
                exit 1
            fi
        fi

        nohup "$2" 2>&1 \
            & echo $! > ${PID_FILE_PATH}

        if [ $? -eq 0 ]; then
            echo "Succeeded to start $2."
        else
            echo "Failed to start $2."
            exit 1
        fi
    ;;
    stop)
        kill $(cat ${PID_FILE_PATH})

        if [ $? -eq 0 ]; then
            rm ${PID_FILE_PATH}
            echo "Succeeded to stop $2."
        else
            echo "Failed to stop $2."
            exit 1
        fi
    ;;
    restart)
        ${0} stop "$2" && sleep 1 && ${0} start "$2"
    ;;
esac

Example:

$ ./runner.sh stop yes
cat: runner.pid: No such file or directory
kill: usage: kill [-s sigspec | -n signum | -sigspec] pid | jobspec ... or kill -l [sigspec]
Failed to stop yes.
$ ./runner.sh start yes
Succeeded to start yes.
nohup: appending output to 'nohup.out'
$ ./runner.sh restart yes
Succeeded to stop yes.
Succeeded to start yes.
nohup: appending output to 'nohup.out'
$./runner.sh stop yes
Succeeded to stop yes
.

BASH Programming/Shell

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• Three Interesting/Fun BASH Commands
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• Simple Bash Function to Repeat a Command N times with Retries
• How to Extract a Domain Name from a Full URL in BASH?
• BASH Function to Compute the Greatest Common Divisor and Least Common Multiples
• BASH Function to Get Memory Information via AWK
• BASH Function to Escape Parameters Argument
• BASH Function to Check if sudo Available
• Full Permutation Algorithm Implementation in BASH
• BASH Function to Install Docker
• A Simple BASH Function/Script to Run a Command in Background
• BASH Script to Compute the Average Ping to a Domain
• A Bash Process Controller to Start, Stop and Restart an Daemon Program
• Linux BASH shell - Echo This if you get angry
• Bash SHELL, Chess Board Printing

–EOF (The Ultimate Computing & Technology Blog) —