Several referred to "Google Hell" on this subject, so let me add my own 2 cents worth in case you've arrived here from Google Hell!
It appears that what's happened is that the My SQL daemon has stopped catastrophically for some reason.
some new scripts to - handling user input - (2015-11-27)  Commenting out an echo killed my bash backup script - (2015-01-19)  Ruby, Perl, Linux, My SQL - some training notes - (2008-11-23)  Selecting file names in a shell - one word or another - (2008-02-02)  Lexical v Arithemetic testing, Bash and Perl - (2007-12-11)  Perl and Shell coding standards / costs of an IT project - (2007-09-11)  Work and play at Well House Manor - Football and Shell Shortcuts - (2007-08-02)  No news is good news with Unix and Linux - (2006-08-10)  Cottage industry or production line data handling methods - (2006-06-07)  Shell Script for CGI on the web - (2004-09-26)  Almost like old times - (2004-09-26) Web Server Admin - some of those things that happen, and solutions What and where are the Azores? The server quit without updating PID file - how we fixed it.
Election results - what if we had a party list system? Newark to New York - the PATH suburban railway Misusing statistics?
- (2009-05-15)  Using the internet to remotely check for power failure at home (PHP) - (2009-04-29)  daemons - what is running on my Linux server?It's confused into thinkig it should be referring to a PID file which didn't exist, and because it's crashed, it's refusing to restart. Ensure that /etc/contains: And restart the server as this will overstep the problem above, and also recover the databases; error recovery levels of 1 or 2 are likely to let you recover (almost) everything we're told, and I have the previous good backup anyway, so I can restore if I need to.And it's not got any process to tidy us if I try to run server stop scripts. Then stop the server once it's forced the recovery, remove the innodb_force_recovery assignment, and restart it. I'm monitoring carefully, and posting this to my blog partly as a test and partly in the hope it may provide a helpful clue to others in the future.At one point I had to restart My SQL (which up to this point was running fine), and received this error: After a good 20 minutes spent on Google trying various things (hunting down the mysql.plugin file to verify its permissions, removing my file, verifying my file was getting erased, etc), I finally stumbled upon the answer: My SQL was still running under a different hostname.
$ ls -l /opt/local/var/db/mysql5 total 41128 -rw-rw---- 1 _mysql _mysql 15566 Aug 14 Gabriels-Mac Book.-rw-rw---- 1 _mysql _mysql 771 Aug 15 SDF1.-rw-rw---- 1 _mysql _mysql 5 Aug 15 SDF1.... -rw-rw---- 1 _mysql _mysql 53778 Aug 16 laptop-134....Description: severals day ago, Cent OS is power off unexpectedly.