using "systemctl start <email address hidden>" doesn't help here neither

root@pxc:~# systemctl stop mysql
root@pxc:~# systemctl status mysql
● mysql.service - Percona XtraDB Cluster daemon
   Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: enabled)
   Active: inactive (dead) since Tue 2018-06-12 22:19:46 UTC; 2s ago
  Process: 2025 ExecStop=/etc/init.d/mysql stop (code=exited, status=0/SUCCESS)
 Main PID: 1505 (code=exited, status=0/SUCCESS)

Jun 12 22:06:36 pxc mysql[1467]:  * Starting MySQL (Percona XtraDB Cluster) database server mysqld
Jun 12 22:06:36 pxc /etc/init.d/mysql[1504]: MySQL PID not found, pid_file detected/guessed: /var/run/mysqld/mysqld.pid
Jun 12 22:06:38 pxc mysql[1467]:    ...done.
Jun 12 22:06:38 pxc systemd[1]: Started Percona XtraDB Cluster daemon.
Jun 12 22:06:38 pxc systemd[1]: mysql.service: Failed to reset devices.list: Operation not permitted
Jun 12 22:19:31 pxc systemd[1]: Stopping Percona XtraDB Cluster daemon...
Jun 12 22:19:31 pxc mysql[2025]:  * Stopping MySQL (Percona XtraDB Cluster) mysqld
Jun 12 22:19:46 pxc /etc/init.d/mysql[2128]: MySQL PID not found, pid_file detected/guessed: /var/run/mysqld/mysqld.pid
Jun 12 22:19:46 pxc mysql[2025]:    ...done.
Jun 12 22:19:46 pxc systemd[1]: Stopped Percona XtraDB Cluster daemon.
root@pxc:~# systemctl status <email address hidden>
● <email address hidden> - Percona XtraDB Cluster daemon with config /etc/default/mysql.bootstrap
   Loaded: loaded (/lib/systemd/system/mysql@.service; disabled; vendor preset: enabled)
   Active: inactive (dead)
root@pxc:~# systemctl start <email address hidden>
root@pxc:~# systemctl status <email address hidden>
● <email address hidden> - Percona XtraDB Cluster daemon with config /etc/default/mysql.bootstrap
   Loaded: loaded (/lib/systemd/system/mysql@.service; disabled; vendor preset: enabled)
   Active: active (running) since Tue 2018-06-12 22:20:17 UTC; 3s ago
  Process: 2209 ExecStart=/etc/init.d/mysql start ${EXTRA_ARGS} (code=exited, status=0/SUCCESS)
  Process: 2135 ExecStartPre=/usr/share/mysql/mysql-systemd-start pre (code=exited, status=0/SUCCESS)
 Main PID: 2247 (mysqld_safe)
    Tasks: 42 (limit: 4915)
   CGroup: /<email address hidden>
           ├─2247 /bin/sh /usr/bin/mysqld_safe --wsrep-new-cluster
           └─2635 /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/percona-xtradb-cluster --plugin-dir=/usr/lib/mysql/plugin --wsrep-provider=/usr/lib/galera3/libgalera_smm.so --wsrep-new-c

Jun 12 22:20:12 pxc systemd[1]: Starting Percona XtraDB Cluster daemon with config /etc/default/mysql.bootstrap...
Jun 12 22:20:15 pxc mysql[2209]:  * Starting MySQL (Percona XtraDB Cluster) database server mysqld
Jun 12 22:20:17 pxc mysql[2209]:    ...done.
Jun 12 22:20:17 pxc systemd[1]: Started Percona XtraDB Cluster daemon with config /etc/default/mysql.bootstrap.
root@pxc:~# systemctl status mysql
● mysql.service - Percona XtraDB Cluster daemon
   Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: enabled)
   Active: inactive (dead) since Tue 2018-06-12 22:19:46 UTC; 46s ago
  Process: 2025 ExecStop=/etc/init.d/mysql stop (code=exited, status=0/SUCCESS)
 Main PID: 1505 (code=exited, status=0/SUCCESS)

Jun 12 22:06:36 pxc mysql[1467]:  * Starting MySQL (Percona XtraDB Cluster) database server mysqld
Jun 12 22:06:36 pxc /etc/init.d/mysql[1504]: MySQL PID not found, pid_file detected/guessed: /var/run/mysqld/mysqld.pid
Jun 12 22:06:38 pxc mysql[1467]:    ...done.
Jun 12 22:06:38 pxc systemd[1]: Started Percona XtraDB Cluster daemon.
Jun 12 22:06:38 pxc systemd[1]: mysql.service: Failed to reset devices.list: Operation not permitted
Jun 12 22:19:31 pxc systemd[1]: Stopping Percona XtraDB Cluster daemon...
Jun 12 22:19:31 pxc mysql[2025]:  * Stopping MySQL (Percona XtraDB Cluster) mysqld
Jun 12 22:19:46 pxc /etc/init.d/mysql[2128]: MySQL PID not found, pid_file detected/guessed: /var/run/mysqld/mysqld.pid
Jun 12 22:19:46 pxc mysql[2025]:    ...done.
Jun 12 22:19:46 pxc systemd[1]: Stopped Percona XtraDB Cluster daemon.
root@pxc:~# cat /var/run/mysqld/mysqld.pid
2635