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Fixing MySQL "PID file could not be found" Error

When MySQL reports the following error:

ERROR! MySQL is running but PID file could not be found

it usually means that the server is running, but the PID file (which stores the process ID of the MySQL server) is missing or has been deleted. Without this file, MySQL cannot track or manage its own process correctly.

This issue often occurs on macOS systems where MySQL was installed via Homebrew or other package managers.

Steps to Resolve

1. Check MySQL Status

Run the following command to verify the issue:

mysql.server status

If you see:

ERROR! MySQL is running but PID file could not be found

then proceed to the next steps.

2. List All Running MySQL Processes

Find out which MySQL processes are currently running:

ps aux | grep mysql

This will list all processes related to MySQL (including the grep command itself).

3. Kill MySQL Processes

Stop all MySQL processes by killing them manually:

sudo kill <pid1> <pid2> <pid3> ...

Replace <pid1>, <pid2>, etc., with the process IDs you found in the previous step.

4. Restart MySQL

Now try starting MySQL again:

mysql.server start

If successful, you should see:

Starting MySQL . SUCCESS!

Permanent Fix (Optional)

If you frequently encounter this problem, you may need to define a PID file location in your MySQL configuration.

  • Locate your PID file (if it exists):
/usr/local/var/mysql/{username}.pid
  • Locate your MySQL configuration file (installed with Homebrew):
/usr/local/Cellar/mysql/<version>/my.cnf
  • Edit the configuration file:
subl ~/.my.cnf
  • Add the following line to the bottom of the file (replace {username} with your macOS username):
pid-file = /usr/local/var/mysql/{username}.pid
  • Save the file and restart MySQL.

Summary

  • The error occurs because the PID file is missing.
  • Kill all existing MySQL processes.
  • Restart the MySQL server.
  • (Optional) Configure a fixed PID file path in my.cnf to prevent the issue from reoccurring.

References