Recently we shifted our site to our own server with a better configuration. We did almost everything right and it worked for weeks without problem but then came a problem.
“mysqld dead but subsys locked”
I searched web and found some unrelated discussions. In such cases the true friend of a programmer is the log file. It explained everything, “no disk space available”. This happened as we were logging few queries to check the query speed. Once corrected it started working with all grace.