Check if a process is not running and then run it

There are several ways to do this. One of them is using pgrep :

pgrep gedit

If gedit is running, a number will be returned.

17805

This number is the process ID (PID). This number obviously changes.

Combining this into a Shell Script :

#!/bin/bash

# Verifica se o gedit está sendo executado
if pgrep "gedit" > /dev/null
then
    echo "Executando"
else
    echo "Parado"
fi

Retrieved from How to determine if a process is running or not and make use of it to make a conditional shell script?

Important Note:

To ensure that the search is by the exact process name, use the -x option, for example:

pgrep ged

Would return any process that has ged in the name.

In turn:

pgrep -x gedit

I would only return processes that are exactly gedit .

You can create a shell script that returns how many processes are running. Of course the else can be deleted.

#!/bin/sh
# Verificacao se servico esta online

qtde=$(ps aux | grep "mysqld" | wc -l)

if test "$qtde" = "1"
then
  echo "MySQL is offline";
  echo "Starting...";
  /etc/init.d/mysql stop;
  /etc/init.d/mysql start;
else
  echo "MySQLd is online." ;
  echo "Nothing to do.";
fi

Starting a process only once when opening a session on the terminal. Place at the end of the ~ / .bashrc file:

pid=$(pgrep -x redshift)

if [ "$pid" = "" ]
then
  redshift &
fi