MySQL installation fails - mysql

Question

I was having problems starting the MySQL service so I removed the packages like this:
sudo dpkg -P mysql-server mysql-server-5.7
sudo apt autoremove
sudo apt clean
sudo rm -rvf /var/lib/mysql
sudo apt install mysql-server
During installation, I was asked for the password for root and after that, the following happened:
Setting up mysql-server-5.7 (5.7.21-0ubuntu0.16.04.1) ...
Renaming removed key_buffer and myisam-recover options (if present)
Job for mysql.service failed because the control process exited with error code. See "systemctl status mysql.service" and "journalctl -xe" for details.
invoke-rc.d: initscript mysql, action "start" failed.
● mysql.service - MySQL Community Server
Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: enabled)
Active: activating (auto-restart) (Result: exit-code) since Mo 2018-04-23 17:22:42 CEST; 6ms ago
Process: 27860 ExecStartPost=/usr/share/mysql/mysql-systemd-start post (code=exited, status=0/SUCCESS)
Process: 27859 ExecStart=/usr/sbin/mysqld (code=exited, status=1/FAILURE)
Process: 27851 ExecStartPre=/usr/share/mysql/mysql-systemd-start pre (code=exited, status=0/SUCCESS)
Main PID: 27859 (code=exited, status=1/FAILURE)
Apr 23 17:22:42 mari systemd[1]: Failed to start MySQL Community Server.
Apr 23 17:22:42 mari systemd[1]: mysql.service: Unit entered failed state.
Apr 23 17:22:42 mari systemd[1]: mysql.service: Failed with result 'exit-code'.
dpkg: error processing package mysql-server-5.7 (--configure):
subprocess installed post-installation script returned error exit status 1
dpkg: dependency problems prevent configuration of mysql-server:
mysql-server depends on mysql-server-5.7; however:
Package mysql-server-5.7 is not configured yet.
dpkg: error processing package mysql-server (--configure):
dependency problems - leaving unconfigured
Errors were encountered while processing:
mysql-server-5.7
mysql-server
Running dpkg --configure -a results in the same errors. Here's journalctl -xe:
-- 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.
Apr 23 17:25:20 mari audit[28913]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/28913/status" pid=28913 comm="mysqld
Apr 23 17:25:20 mari audit[28913]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/sys/devices/system/node/" pid=28913 comm=
Apr 23 17:25:20 mari audit[28913]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/28913/status" pid=28913 comm="mysqld
Apr 23 17:25:20 mari kernel: audit: type=1400 audit(1524497120.211:209): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/28
Apr 23 17:25:22 mari systemd[1]: mysql.service: Main process exited, code=exited, status=1/FAILURE
Apr 23 17:25:50 mari systemd[1]: Failed to start MySQL Community Server.
-- Subject: Unit mysql.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit mysql.service has failed.
--
-- The result is failed.
Apr 23 17:25:50 mari systemd[1]: mysql.service: Unit entered failed state.
Apr 23 17:25:50 mari systemd[1]: mysql.service: Failed with result 'exit-code'.
Apr 23 17:25:50 mari sudo[28755]: pam_unix(sudo:session): session closed for user root
Apr 23 17:25:50 mari systemd[1]: mysql.service: Service hold-off time over, scheduling restart.
Apr 23 17:25:50 mari 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.
Apr 23 17:25:50 mari 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.
Apr 23 17:25:50 mari audit[29041]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/29041/status" pid=29041 comm="mysqld
Apr 23 17:25:50 mari audit[29041]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/sys/devices/system/node/" pid=29041 comm=
Apr 23 17:25:50 mari audit[29041]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/29041/status" pid=29041 comm="mysqld
Apr 23 17:25:50 mari kernel: kauditd_printk_skb: 2 callbacks suppressed
Apr 23 17:25:50 mari kernel: audit: type=1400 audit(1524497150.668:212): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/29
Apr 23 17:25:50 mari kernel: audit: type=1400 audit(1524497150.668:213): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/sys/dev
Apr 23 17:25:50 mari kernel: audit: type=1400 audit(1524497150.668:214): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/29
Apr 23 17:25:52 mari systemd[1]: mysql.service: Main process exited, code=exited, status=1/FAILURE
Others seem to have the same problem but none of the solutions I found so far worked. For example, someone said that their problem was being caused by a missing log file which is not missing for me.

Answer 1

Thank you to Michael O. for the comment, it helped me out tremendously. The answer to the question he linked by itself didn't solve my problem as, after whitelisting MySQL to access the files it needed, apparmor started to block MySQL from acquiring capabilities.
While searching I came across this blog post from Oracle that suggests using apparmor-utils's utility called aa-complain. This utility sets a profile to complain mode, basically letting you off with a warning.
So I installed apparmor-utils:
sudo apt install apparmor-utils
Checked where the MySQL service was located:
which mysql
And used the output to put the service on complain mode:
aa-complain /usr/bin/mysql
After restarting the computer the service started without errors.