Description of problem:
[root@localhost log]# service mysqld start
Redirecting to /bin/systemctl start  mysqld.service
Job for mariadb.service failed. See 'systemctl status mariadb.service' and 'journalctl -xn' for details.
[root@localhost log]# systemctl status mariadb.service
mariadb.service - MariaDB database server
   Loaded: loaded (/usr/lib/systemd/system/mariadb.service; disabled)
   Active: failed (Result: exit-code) since Fri 2013-11-29 01:33:38 YEKT; 3s ago
  Process: 6541 ExecStartPost=/usr/libexec/mariadb-wait-ready $MAINPID (code=exited, status=1/FAILURE)
  Process: 6540 ExecStart=/usr/bin/mysqld_safe --basedir=/usr (code=exited, status=0/SUCCESS)
  Process: 6517 ExecStartPre=/usr/libexec/mariadb-prepare-db-dir %n (code=exited, status=0/SUCCESS)
 Main PID: 6540 (code=exited, status=0/SUCCESS)

Nov 29 01:33:35 localhost.localdomain systemd[1]: Starting MariaDB database server...
Nov 29 01:33:35 localhost.localdomain mysqld_safe[6540]: 131129 01:33:35 mysqld_safe Logging to '/var/log/mariadb/mariadb.log'.
Nov 29 01:33:35 localhost.localdomain mysqld_safe[6540]: 131129 01:33:35 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
Nov 29 01:33:37 localhost.localdomain systemd[1]: mariadb.service: control process exited, code=exited status=1
Nov 29 01:33:38 localhost.localdomain mysqld_safe[6540]: 131129 01:33:38 mysqld_safe mysqld from pid file /var/run/mariadb/mariadb.pid ended
Nov 29 01:33:38 localhost.localdomain systemd[1]: Failed to start MariaDB database server.
Nov 29 01:33:38 localhost.localdomain systemd[1]: Unit mariadb.service entered failed state.
[root@localhost log]# cat /var/log/mariadb/mariadb.log
131129 01:33:35 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
131129  1:33:35 InnoDB: The InnoDB memory heap is disabled
131129  1:33:35 InnoDB: Mutexes and rw_locks use GCC atomic builtins
131129  1:33:35 InnoDB: Compressed tables use zlib 1.2.8
131129  1:33:35 InnoDB: Using Linux native AIO
131129  1:33:35 InnoDB: Initializing buffer pool, size = 128.0M
131129  1:33:35 InnoDB: Completed initialization of buffer pool
131129  1:33:35 InnoDB: highest supported file format is Barracuda.
131129  1:33:35  InnoDB: Waiting for the background threads to start
131129  1:33:36 Percona XtraDB (http://www.percona.com) 5.5.34-MariaDB-31.1 started; log sequence number 35722578764
131129  1:33:36 [Note] Plugin 'FEEDBACK' is disabled.
131129  1:33:36 [Note] Server socket created on IP: '0.0.0.0'.
131129  1:33:36 [Note] Event Scheduler: Loaded 0 events
131129  1:33:36 [Note] /usr/libexec/mysqld: ready for connections.
Version: '5.5.34-MariaDB'  socket: '/var/lib/mysql/mysql.sock'  port: 3306  MariaDB Server
131129  1:33:37 [Note] /usr/libexec/mysqld: Normal shutdown

131129  1:33:37 [Note] Event Scheduler: Purging the queue. 0 events
131129  1:33:37  InnoDB: Starting shutdown...
131129  1:33:38  InnoDB: Shutdown completed; log sequence number 35722578764
131129  1:33:38 [Note] /usr/libexec/mysqld: Shutdown complete

131129 01:33:38 mysqld_safe mysqld from pid file /var/run/mariadb/mariadb.pid ended
[root@localhost log]# mysqld_safe
131129 01:34:21 mysqld_safe Logging to '/var/log/mariadb/mariadb.log'.
131129 01:34:21 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql