Mediawiki returns “Call to a member function selectField() on a non-object”. Solution: clean disk & restart Mysql.

I had problems with my Mediawiki install: when changing a page, I got a session data related problem and the page asked me to log out & back in again. Same problem. After rebooting the complete server I got “Call to a member function selectField() on a non-object in …” on any page of my Mediawiki install and couldn’t find too much information (not to mention a solution) on the Internet.

It turned out Mysql ran out of disk space and hence didn’t want to display a page, although the disk didn’t seem full: Usage of /:  98.6% of 27.50GB (only using one partition for everything on this system).

The Apache logs didn’t reveal anything (default config). Restarting Apache went fine, too.

root@ubuntu:/var/log/apache2# /etc/init.d/apache2 restart
* Restarting web server apache2                                                                                                                                                                       … waiting                                                                                                                                                                                   [ OK ]
root@ubuntu:/var/log/apache2#

Mysql however didn’t want to start:

root@ubuntu:/# /etc/init.d/mysql restart
* Stopping MySQL database server mysqld                                                                                                                                                       [ OK ]
* /etc/init.d/mysql: ERROR: The partition with /var/lib/mysql is too full!
root@ubuntu:/#

root@ubuntu:/# rm (a big file)
root@ubuntu:/# /etc/init.d/mysql restart
* Stopping MySQL database server mysqld                                                                                                                                                       [ OK ]
* Starting MySQL database server mysqld                                                                                                                                                       [ OK ]
* Checking for corrupt, not cleanly closed and upgrade needing tables.
root@ubuntu:/# ERROR 126 (HY000) at line 1: Incorrect key file for table ‘/tmp/#sql_13fc_0.MYI’; try to repair it

It seems the MYI file got repaired since I was able to fully use Mediawiki on my server again.