Just updated to Kernel 3.12.5, and quickly reverted to 3.12.4..

Update:   the problem turned out to be a badly-timed coincidental update to MariaDB (5.5.34)..   Reverting to the previous version (5.5.33a) fixed the problem..    Now running 3.12.5..

With 3.12.5, Avahi mDNS failed, and – more importantly – MariaDB would not start:

mariadb.service - MariaDB database server
   Loaded: loaded (/usr/lib/systemd/system/mariadb.service; disabled)
   Active: failed (Result: exit-code) since Thu 2013-12-12 10:36:47 GMT; 58s ago
  Process: 3589 ExecStartPost=/usr/libexec/mariadb-wait-ready $MAINPID (code=exited, status=1/FAILURE)
  Process: 3588 ExecStart=/usr/bin/mysqld_safe --basedir=/usr (code=exited, status=0/SUCCESS)
  Process: 3564 ExecStartPre=/usr/libexec/mariadb-prepare-db-dir %n (code=exited, status=0/SUCCESS)
 Main PID: 3588 (code=exited, status=0/SUCCESS)

Dec 12 10:36:19 rglinux mariadb-prepare-db-dir[3564]: Failed to issue method call: Activation of org.freedesktop.systemd1 timed out
Dec 12 10:36:44 rglinux mariadb-prepare-db-dir[3564]: Failed to issue method call: Activation of org.freedesktop.systemd1 timed out
Dec 12 10:36:44 rglinux mysqld_safe[3588]: 131212 10:36:44 mysqld_safe Logging to '/var/log/mariadb/mariadb.log'.
Dec 12 10:36:44 rglinux mysqld_safe[3588]: 131212 10:36:44 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
Dec 12 10:36:46 rglinux systemd[1]: mariadb.service: control process exited, code=exited status=1
Dec 12 10:36:47 rglinux mysqld_safe[3588]: 131212 10:36:47 mysqld_safe mysqld from pid file /var/run/mariadb/mariadb.pid ended
Dec 12 10:36:47 rglinux systemd[1]: Failed to start MariaDB database server.
Dec 12 10:36:47 rglinux systemd[1]: Unit mariadb.service entered failed state.

I need to check the kernel config etc..  but for the time being, I am staying with 3.12.4..

Robert Gadsdon.   December 12, 2013