Unable to start MySql service

Question

When I run command

mysql -u root -p

I got an error

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

When I try to run mysql service

service mysql start

it gets timed out with message

Job for mysql.service failed because a timeout was exceeded. See "systemctl status mysql.service" and "journalctl -xe" for details.

Logs

Jan 08 23:44:48 monal-Lenovo-IdeaPad-Z510 audit[30814]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/sys/devices/system/node/" pid=30814 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=123 ouid=0
Jan 08 23:44:48 monal-Lenovo-IdeaPad-Z510 audit[30814]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/30814/status" pid=30814 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=123 ouid=123
Jan 08 23:44:48 monal-Lenovo-IdeaPad-Z510 audit[30814]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/usr/my.cnf" pid=30814 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=123 ouid=0
Jan 08 23:44:48 monal-Lenovo-IdeaPad-Z510 kernel: audit: type=1400 audit(1483899288.523:210): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/30814/status" pid=30814 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=123 ouid=123
Jan 08 23:44:48 monal-Lenovo-IdeaPad-Z510 kernel: audit: type=1400 audit(1483899288.523:211): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/sys/devices/system/node/" pid=30814 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=123 ouid=0
Jan 08 23:44:48 monal-Lenovo-IdeaPad-Z510 kernel: audit: type=1400 audit(1483899288.523:212): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/30814/status" pid=30814 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=123 ouid=123
Jan 08 23:44:48 monal-Lenovo-IdeaPad-Z510 kernel: audit: type=1400 audit(1483899288.523:213): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/usr/my.cnf" pid=30814 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=123 ouid=0
Jan 08 23:44:48 monal-Lenovo-IdeaPad-Z510 mysqld_safe[30539]: 170108 23:44:48 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
Jan 08 23:45:01 monal-Lenovo-IdeaPad-Z510 CRON[30867]: pam_unix(cron:session): session opened for user root by (uid=0)
Jan 08 23:45:01 monal-Lenovo-IdeaPad-Z510 CRON[30868]: (root) CMD (command -v debian-sa1 > /dev/null && debian-sa1 1 1)
Jan 08 23:45:01 monal-Lenovo-IdeaPad-Z510 CRON[30867]: pam_unix(cron:session): session closed for user root

Answer 1

First stop the mysql instance. You will need to copy the exact /var/lib/mysql directory to your new data directory, preserving its permission. So use rsync with -a option

sudo rsync -av /var/lib/mysql /db/data/

Also change the data dir path in mysql.cnf file

You will need to add alias to apparmor so that it allows mysql to write to the new directory

To add alias:

sudo nano /etc/apparmor.d/tunables/alias

and then add this line to bottom

alias /var/lib/mysql/ -> /db/data/mysql

Restart the apparmor

sudo systemctl restart apparmor

and now start mysql. It should work