MySQL (Percona Server) PID file could not be found! [FAILED]

All of a sudden (i.e. no recent server changes), when we try to start mysqld:

/etc/init.d/mysql restartMySQL (Percona Server) PID file could not be found! [FAILED]Starting MySQL (Percona Server).The server quit without upd[FAILED]D file (/var/lib/mysql/servername.pid).

In the logs:

InnoDB: The first specified data file ./ibdata1 did not exist:InnoDB: a new database to be created!110905 23:40:00 InnoDB: Setting file ./ibdata1 size to 10 MBInnoDB: Database physically writes the file full: wait…110905 23:40:00 InnoDB: Log file ./ib_logfile0 did not exist: new to be createdInnoDB: Setting log file ./ib_logfile0 size to 5 MBInnoDB: Database physically writes the file full: wait…110905 23:40:00 InnoDB: Log file ./ib_logfile1 did not exist: new to be createdInnoDB: Setting log file ./ib_logfile1 size to 5 MBInnoDB: Database physically writes the file full: wait…InnoDB: Doublewrite buffer not found: creating newInnoDB: Doublewrite buffer createdInnoDB: 127 rollback segment(s) active.InnoDB: Creating foreign key constraint system tablesInnoDB: Foreign key constraint system tables created110905 23:40:00 InnoDB: Waiting for the background threads to start110905 23:40:01 Percona XtraDB (http://www.percona.com) 1.1.8-20.1 started; log sequence number 0110905 23:40:01 [Note] Event Scheduler: Loaded 0 events110905 23:40:01 [Note] /usr/sbin/mysqld: ready for connections.Version: ‘5.5.15-55’ socket: ‘/var/lib/mysql/mysql.sock’ port: 3306 Percona Server (GPL), Release rel21.0, Revision 158110905 23:40:02 [Note] /usr/sbin/mysqld: Normal shutdown

Permissions fine, no PIDs to remove, server rebooted, tried increasing log file size, no avail. We can’t identify anything that has changed between the server stopping and starting again.

Any ideas on what to look into?

Check to make sure that your configuration file (i.e. my.cnf) is still there and readable my MySQL. Your error log shows the server creating new InnoDB files, meaning it is not seeing your old ones. This could be due to it not finding your configuration file, and using the default directories instead.