How to solve MYSQL startup error on Ubuntu?

Question

linux

Hey!
I decided to try adding a couple of lines to the mysql config to display query logs, added it, restarted it and got an error, returned everything to the default state, but mysql still does not work.
Error code for journalctl -xe command :

-- The result is failed.
июл 17 23:18:13 example.com systemd[1]: mysql.service: Unit entered failed state.
июл 17 23:18:13 example.com systemd[1]: mysql.service: Failed with result 'exit-code'.
июл 17 23:18:13 example.com systemd[1]: mysql.service: Service hold-off time over, scheduling restart.
июл 17 23:18:13 example.com systemd[1]: Stopped MySQL Community Server.
-- Subject: Unit mysql.service has finished shutting down
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit mysql.service has finished shutting down.
июл 17 23:18:13 example.com systemd[1]: Starting MySQL Community Server...
-- Subject: Unit mysql.service has begun start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit mysql.service has begun starting up.
июл 17 23:18:13 example.com audit[31180]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/31180/status" pid=31180 comm="mysqld" requested_mask="r" deni
июл 17 23:18:13 example.com audit[31180]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/sys/devices/system/node/" pid=31180 comm="mysqld" requested_mask="
июл 17 23:18:13 example.com kernel: audit: type=1400 audit(1500322693.284:321): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/31180/status" pid=31180 com
июл 17 23:18:13 example.com kernel: audit: type=1400 audit(1500322693.284:322): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/sys/devices/system/node/" pid=31
июл 17 23:18:13 example.com kernel: audit: type=1400 audit(1500322693.284:323): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/31180/status" pid=31180 com
июл 17 23:18:13 example.com audit[31180]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/31180/status" pid=31180 comm="mysqld" requested_mask="r" deni
июл 17 23:18:13 example.com systemd[1]: mysql.service: Main process exited, code=exited, status=1/FAILURE

by command systemctl status mysql.service

● mysql.service - MySQL Community Server
   Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: enabled)
   Active: activating (start-post) (Result: exit-code) since Пн 2017-07-17 23:39:03 MSK; 900ms ago
  Process: 3030 ExecStart=/usr/sbin/mysqld (code=exited, status=1/FAILURE)
  Process: 3022 ExecStartPre=/usr/share/mysql/mysql-systemd-start pre (code=exited, status=0/SUCCESS)
 Main PID: 3030 (code=exited, status=1/FAILURE);         : 3031 (mysql-systemd-s)
   CGroup: /system.slice/mysql.service
           └─control
             ├─3031 /bin/bash /usr/share/mysql/mysql-systemd-start post
             └─3034 sleep 1

июл 17 23:39:03 example.com systemd[1]: Starting MySQL Community Server...
июл 17 23:39:03 example.com systemd[1]: mysql.service: Main process exited, code=exited, status=1/FAILURE

And one more thing, I wanted to check the mysql recall with the mysql -v command and got this error

ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)

In this directory (the one in the error above) I did not find the mysqld.sock file.
What should I do?