Mariadb won't start - Failed at step EXEC spawning

Symptoms

Can not start MariaDB, the following error appears in status:

~]# systemctl status mariadb.service -l
mariadb.service - MariaDB database server
   Loaded: loaded (/usr/lib/systemd/system/mariadb.service; enabled)
   Active: failed (Result: exit-code) since Sat 2015-05-30 12:37:44 CEST; 24min ago
  Process: 2674 ExecStartPre=/usr/libexec/mariadb-prepare-db-dir %n (code=exited, status=203/EXEC)

May 30 10:38:42 domain.tld mariadb-prepare-db-dir[3468]: Failed at step EXEC spawning /usr/libexec/mariadb-prepare-db-dir: Permission denied

The following errors can be found in /var/log/mariadb/mariadb.log :

150530 11:05:37 [ERROR] mysqld: Can't create/write to file '/tmp/ibH5045r' (Errcode: 13)
150530 11:05:37  InnoDB: Error: unable to create temporary file; errno: 13
150530 11:05:37 [ERROR] mysqld: Can't create/write to file '/var/lib/mysql/aria_log_control' (Errcode: 13)
150530 11:05:37 [ERROR] mysqld: Got error 'Can't create file' when trying to use aria control file '/var/lib/mysql/aria_log_control'

However, /usr/libexec/mariadb-prepare-db-dir have a proper permissions.

 ~]# stat /usr/libexec/mariadb-prepare-db-dir
  File: '/usr/libexec/mariadb-prepare-db-dir'
  Size: 3015            Blocks: 8          IO Block: 4096   regular file
Device: 3820b611h/941667857d    Inode: 410510      Links: 1
Access: (0755/-rwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)

Permissions on / is set as follows:

~]# ls -la /
total 120
drwxrwx--- 19 root root  4096 May 30 11:59 .
drwxrwx--- 19 root root  4096 May 30 11:59 ..

Cause

Invalid permissions on / , as a result only root user can execute.

Resolution

Set permission on /

~]# chmod a+x /