why the mysqld is located in 4 places in linux system?

Question

I have confusion while I'm execute the command "# find / -name mysqld". Because the mysqld is located in four places which are:

1. /usr/libexec/mysqld
2. /etc/rc.d/init.d/mysqld
3. /var/lock/subsys/mysqld
4. /var/run/mysqld

What is the purpose of another three mysql daemons?

Answer 1

Here is the following explanations

• /usr/libexec/mysqld : The actual binary executable
• /etc/rc.d/init.d/mysqld : The service startup file (text file)
• /var/run/mysqld : PID/run file folder (mysqld writes a run file in this folder)
• /var/lock/subsys/mysqld : not sure

If you run which mysqld you should see the first one

You never run that directly

When you run service mysqld start, it calls /etc/rc.d/init.d/mysqld to kickoff a program called mysqld_safe (Run which mysqld_safe). mysqld_safe and mysqld work together to be the server daemon.

In turn, mysqld_safe will kickoff mysqld and then checks for an exit code. You can run less /etc/rc.d/init.d/mysqld and see this. If mysqld did not end due to system shutdown or a normal service mysql stop, mysqld_safe will attempt to restart mysqld.