fix mariadb service timeout

现象: sudo systemctl status mariadb

mariadb.service - MariaDB 10.3.32 database server
     Loaded: loaded (/lib/systemd/system/mariadb.service; enabled; vendor preset: enabled)
     Active: failed (Result: timeout) since Wed 2022-01-19 03:26:04 UTC; 2min 30s ago
       Docs: man:mysqld(8)
             https://mariadb.com/kb/en/library/systemd/
    Process: 35373 ExecStartPre=/usr/bin/install -m 755 -o mysql -g root -d /var/run/mysqld (code=exited, status=0/SUCCESS)
    Process: 35374 ExecStartPre=/bin/sh -c systemctl unset-environment _WSREP_START_POSITION (code=exited, status=0/SUCCESS)
    Process: 35376 ExecStartPre=/bin/sh -c [ ! -e /usr/bin/galera_recovery ] && VAR= ||   VAR=`cd /usr/bin/..; /usr/bin/galera_recovery`; [ $? -eq 0 ]   && systemctl set-environment _WSREP_START_POSITION=$VAR>
    Process: 35427 ExecStart=/usr/sbin/mysqld $MYSQLD_OPTS $_WSREP_NEW_CLUSTER $_WSREP_START_POSITION (code=exited, status=0/SUCCESS)
   Main PID: 35427 (code=exited, status=0/SUCCESS)

Jan 19 03:11:02 ip-10-0-0-78 systemd[1]: Starting MariaDB 10.3.32 database server...
Jan 19 03:11:02 ip-10-0-0-78 mysqld[35427]: 2022-01-19  3:11:02 0 [Note] /usr/sbin/mysqld (mysqld 10.3.32-MariaDB-0ubuntu0.20.04.1) starting as process 35427 ...
Jan 19 03:26:03 ip-10-0-0-78 systemd[1]: mariadb.service: start operation timed out. Terminating.
Jan 19 03:26:04 ip-10-0-0-78 systemd[1]: mariadb.service: Failed with result 'timeout'.
Jan 19 03:26:04 ip-10-0-0-78 systemd[1]: Failed to start MariaDB 10.3.32 database server.

fix

$ echo "/usr/sbin/mysqld { }" > /etc/apparmor.d/usr.sbin.mysqld
$ apparmor_parser -v -R /etc/apparmor.d/usr.sbin.mysqld
$ systemctl restart mariadb