How To Write a Bash Script To Restart Server Programs

Yes, you’re correct! Before you can run a script from the command line or through a cron job, it needs to have the appropriate executable permissions. You can do this with the chmod command. Here’s how to ensure your script is executable:

1. Make the Script Executable: Use the following command:

chmod +x /path/to/your/script/relaunch.sh

Replace /path/to/your/script/relaunch.sh with the actual path to your script.

2. Verify Permissions: You can verify the permissions by running:

ls -l /path/to/your/script/relaunch.sh

The output should show something like -rwxr-xr-x, indicating that the script is executable.

Regards

The error message you’re encountering (unexpected operator) typically arises from using [ for conditional tests in a shell script where the syntax is not correctly followed. In this case, it might be due to the way you’re checking the exit status of the previous command. In shell scripts, the correct syntax for string comparison is = or != rather than using == as you might in other programming languages.

Here’s a revised version of your script that includes proper syntax and adds some logging for troubleshooting:

#!/bin/sh

LOGFILE="/var/log/mysql-check.log"

# Check if MySQL is running
if ps aux | grep mysql | grep -v grep > /dev/null; then
    echo "$(date): MySQL is running." >> $LOGFILE
else
    echo "$(date): MySQL is not running, attempting to restart." >> $LOGFILE
    service mysql restart >> $LOGFILE 2>&1
    if [ $? -eq 0 ]; then
        echo "$(date): MySQL restarted successfully." >> $LOGFILE
    else
        echo "$(date): Failed to restart MySQL." >> $LOGFILE
    fi
fi

If the script does not work as expected, check the log file at /var/log/mysql-check.log for any output that may indicate what went wrong.

Regards

It sounds like you’re on the right track with your script, but let’s clarify how the logic should work and how the exit status $? is used.

1. Exit Status $?: This special variable captures the exit status of the last command executed. In your case:

   • If ps auxw | grep mysql | grep -v grep finds a running MySQL process, it will exit with status 0.
   • If it does not find a running MySQL process (meaning MySQL is down), it will exit with a status 1 (or another non-zero value).

2. Condition Logic:

   • You want to check if MySQL is not running to restart it. Therefore, your condition should check for a non-zero exit status (!= 0).
   • If the exit status is 0, it means MySQL is running, and you should not restart it.
   • If the exit status is 1, it means MySQL is not running, and you want to restart it.

Here’s the script with comments explaining each part:

#!/bin/sh

# Check if MySQL is running
ps auxw | grep mysql | grep -v grep > /dev/null

# Check the exit status of the previous command
if [ $? != 0 ]; then
    # If MySQL is not running (exit status != 0), restart it
    echo "MySQL is down, restarting..." >> /var/log/mysql-check.log
    service mysql restart >> /var/log/mysql-check.log 2>&1
else
    # If MySQL is running (exit status = 0), do nothing
    echo "MySQL is running." >> /var/log/mysql-check.log
fi

• ps auxw | grep mysql | grep -v grep: This command lists all running processes and checks for “mysql”, filtering out the grep process itself.
• > /dev/null: Suppresses output.
• if [ $? != 0 ]: This checks if the exit status is not 0, indicating MySQL is not running.
• The script appends logs to /var/log/mysql-check.log so you can track when it checks the status and any actions taken.

To set this script to run periodically (e.g., every minute), you can add it to your crontab:

1. Open the crontab file:

crontab -e

2. Add the following line to run your script every minute:

* * * * * /path/to/your/script/relaunch.sh

• Log File: Make sure the log file exists and is writable by the user executing the cron job. If necessary, you can create it with:

sudo touch /var/log/mysql-check.log sudo chmod 664 /var/log/mysql-check.log

• Script Permissions: Ensure the script has executable permissions:

chmod +x /path/to/your/script/relaunch.sh

• Test Manually: You can test the script manually to see if it behaves as expected by running:

/path/to/your/script/relaunch.sh

Your original logic is correct. Keep the != 0 condition to restart MySQL when it’s not running. The added logging will help you diagnose what the script is doing when it runs via cron. If you still face issues, check the log file for entries and errors to help pinpoint the problem.

Regards

@savage above had some good stuff and I modified it for systemd based Debian and to my liking as follows - this works, and no, I also could not get the original syntax to work.

#!/bin/sh

#functions

RESTART=“/bin/systemctl restart apache2.service” SERVICE=“apache2.service” LOGFILE=“/home/username/Desktop/apache.log”

#check for the word dead in the service output from systemctl

if

    systemctl status apache2.service | grep dead

then

    echo "User, apache2 failed at $(date), so I restarted it for you." >> $LOGFILE
    $RESTART >> $LOGFILE

else echo “User, apache2 was running as of $(date)” >> $LOGFILE

fi

You can simplify your cron job by using a one-liner directly in the crontab. This approach checks the status of the Apache service and starts it if it’s not running, all in one command.

* * * * * service apache2 status || service apache2 start

Regards

The error you’re encountering is due to how you’re trying to add the cron job. When you add a cron job, the timing syntax should be specified without any leading characters like */1. Also, ~ (the home directory shortcut) may not resolve properly in the cron environment.

Here’s how to properly set up your cron job:

1. Specify the Full Path: Instead of using ~/launch.sh, specify the full path to your script. For example, if your script is located in /home/yourusername/launch.sh, you would use that full path.

2. Cron Timing Syntax: If you want to run the script every minute, you can simply use * * * * * instead of */1 * * * *. They both serve the same purpose, but the former is more commonly used.

Regards

You can double check the syntax in your commands and also examine the command output and also service logs to see if there is anything wrong with the services itself before automating the process to restart them.

Regards

The issue you’re encountering is likely due to the environment in which the cron job runs, which is more limited than your normal shell environment. When cron executes a script, it doesn’t inherit the same environment variables, which may affect how commands like /etc/init.d/apache2 restart work.

Here are a few things to check and modify to improve the functionality of your script when run from cron:

Modifications to the Script

1. Use Absolute Paths: Ensure that all commands used in the script have absolute paths. While you’ve done that for apache2, it’s good practice to specify the full path for ps and grep as well.
2. Check for Errors: Capture the output and error of the restart command to the log file.
3. Use a Shell Shebang: Instead of #!/bin/sh, you might want to use #!/bin/bash for better compatibility, especially if you’re using features specific to bash.

#!/bin/bash

LOGFILE="/var/log/uwe-crontab/crons.log"
TIMESTAMP=$(date "+%Y-%m-%d %H:%M:%S")

# Function to log messages with a timestamp
log_message() {
    echo "$TIMESTAMP - $1" >> $LOGFILE
}

# Log that the script is running
log_message "Running apache2 relaunch."

# Check if Apache is running
/usr/bin/ps auxw | /bin/grep apache2 | /bin/grep -v grep > /dev/null
STATUS_CODE=$?

if [ $STATUS_CODE -ne 0 ]; then
    # Apache is not running, attempt to restart
    /etc/init.d/apache2 restart >> $LOGFILE 2>&1
    log_message "Apache relaunched."
else
    log_message "Apache is running."
fi

Explanation of Changes

• Absolute Paths: The paths to ps and grep are specified to ensure that cron can find them.
• Logging: The output and errors from the restart command are captured in the log for easier debugging.
• Timestamp Function: A logging function is added to maintain a consistent log format.

Cron Entry

Ensure the cron job is set correctly:

* * * * * /bin/bash /etc/apache2/relaunch.sh

Permissions

Make sure the script is executable:

chmod +x /etc/apache2/relaunch.sh

Testing

After making these changes, monitor the log file to see if it behaves correctly when Apache is stopped. If it still doesn’t restart Apache, check the log file for any errors reported by the restart command. If issues persist, you can also check /var/log/syslog for cron-specific logs that may provide additional insights.