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determine if an apache process is still running via bash to prevent multiple instances running

Given is the fact that you have some processes (like cronjobs) executed via an webserver like apache. Furthermore you have installed and enables apache server status. To add some re usability benefits, we should divide and conquer the problems into either shell scripts or shell functions. Side note, if I am writing about shell, I am in the bash environment. What are the problems we want to tackle down?:

  • find the correct environment
  • check all available webservers if a process is not running
  • specify which process should not run and start it if possible

We can put the first two problems into shell functions like the following ones. I am referencing to some self written shell functions. The reference is indicated by the "net_bazzline_" prefix.

#!/bin/bash
#find the correct environment

if net_bazzline_string_contains $HOSTNAME 'production';
    NET_BAZZLINE_IS_PRODUCTION_ENVIRONMENT=1
else
    NET_BAZZLINE_IS_PRODUCTION_ENVIRONMENT=0
fi

And the mighty check.

#!/bin/bash
#check all available webservers if a process is not running
####
# @param string <process name>
# @return int (0 if at least one process was found)
####
function local_is_there_at_least_one_apache_process_running()
{
    if [[ $# -lt 1 ]]; then
       echo 'invalid number of arguments'
       echo '    local_is_there_at_least_one_apache_process_running <process name>'

       return 1
    fi

    if [[ $NET_BAZZLINE_IS_PRODUCTION_ENVIRONMENT -eq 1 ]]; then
        LOCAL_ENVIRONMENT='production'
    else
        LOCAL_ENVIRONMENT='staging'
    fi

    #variables are prefixed with LOCAL_ to prevent overwriting system variables
    LOCAL_PROCESS_NAME="$1"

    #declare the array with all available host names
    declare -a LOCAL_HOSTNAMES=("webserver01" "webserver02" "webserver03");

    for LOCAL_HOSTNAME in ${LOCAL_HOSTNAMES[@]}; do
        APACHE_STATUS_URL="http://$LOCAL_HOSTNAME.my.domain/server-status"

        OUTPUT=$(curl -s $APACHE_STATUS_URL | grep -i $LOCAL_PROCESS_NAME)
        EXIT_CODE_OF_LAST_PROCESS="$?"

        if [[ $EXIT_CODE_OF_LAST_PROCESS == "0" ]]; then
            echo "$LOCAL_PROCESS_NAME found on $LOCAL_HOSTNAME"
            return 0
        fi
    done;

    return 1
}

And here is an example how to use it.

#!/bin/bash
#specify which process should not run and start it if possible

source /path/to/your/bash/functions

LOCAL_PROCESS_NAME="my_process"

local_is_there_at_least_one_apache_process_running $LOCAL_PROCESS_NAME

EXIT_CODE_OF_LAST_PROCESS="$?"

if [[ $EXIT_CODE_OF_LAST_PROCESS == "0" ]]; then
    echo "$LOCAL_PROCESS_NAME still running"
    exit 0;
else
    #execute your process
    echo 'started at: '$(date +'%Y-%m-%d %H:%M:%S');
    curl "my.domain/$LOCAL_PROCESS_NAME"
    echo 'started at: '$(date +'%Y-%m-%d %H:%M:%S');
fi

You can put this into a loop by calling it via the cronjob environment or use watch if you only need it from time to time:

watch -n 60 'bash /path/to/your/shell/script'

Enjoy your day :-).

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