Web server configuration fails to rebuild from Parallels Plesk Panel. Running a configuration update from the command line produces the following error:
~# /usr/local/psa/admin/bin/httpdmng --reconfigure-all
SQLSTATE[HY000]: General error: 2006 MySQL server has gone away
PHP Warning: Releasing semaphore 1 in request cleanup; File: Unknown, Line: 0
Exception: PHP Warning: Releasing semaphore 1 in request cleanup; File: Unknown, Line: 0
trace: #0 [internal function]: Smb_Exception_Syntax::handleError(2, 'Releasing semap...', 'Unknown', 0, NULL)
The problem may happen on servers with a substantial number of domains and services or that are under an increased workload, which causes
httpdmng to leave the database connection idle for periods of time. If MySQL server is set up to have a short timeout for idle connections, the connection is closed and
httpdmng fails without further attempts to re-connect to the database.
The problem has been fixed in Parallels Plesk Panel 11.0.9 MU#19
wait_timeout value in the MySQL server configuration file,
/etc/mysql/my.cnf on Debian/Ubuntu.