MySQL fails to start after editing my.cnf

I am trying to optimize memory usage (eating up more than 500MB by default) of MySQL using my.cnf, but I am having some trouble. The service is not starting after placing my custom my.cnf. It goes back to working state if I fallback to default my.cnf. MySQL version: > mysql Ver 14.14 Distrib 5.7.19, for Linux (x86_64) using EditLine > wrapper OS Version: > DISTRIB_ID=Ubuntu DISTRIB_RELEASE=17.04 DISTRIB_CODENAME=zesty > DISTRIB_DESCRIPTION="Ubuntu 17.04" > > Linux 4.10.0-32-generic #36-Ubuntu SMP Tue Aug 8 12:10:06 > UTC 2017 x86_64 x86_64 x86_64 GNU/Linux Here is my /etc/mysql/my.cnf ( generated using myconfgen with memory size parameter 0.25): [mysql] # CLIENT # port = 3306 socket = /var/lib/mysql/mysql.sock [mysqld] # GENERAL # user = mysql default-storage-engine = InnoDB socket = /var/lib/mysql/mysql.sock pid-file = /var/run/mysqld/mysqld.pid # MyISAM # # key-buffer-size = 32M # myisam-recover = FORCE,BACKUP # SAFETY # max-allowed-packet = 16M max-connect-errors = 1000000 skip-name-resolve sql-mode = NO_ENGINE_SUBSTITUTION,NO_AUTO_CREATE_USER sysdate-is-now = 1 innodb-strict-mode = 1 # DATA STORAGE # datadir = /var/lib/mysql # SERVER ID # server-id = 968898 # BINARY LOGGING # log-bin # CACHES AND LIMITS # max-connections = 500 tmp-table-size = 32M max-heap-table-size = 32M query-cache-type = 0 query-cache-size = 0 thread-cache-size = 50 open-files-limit = 65535 table-definition-cache = 1024 table-open-cache = 2048 # INNODB # innodb-flush-method = O_DIRECT innodb-log-files-in-group = 2 innodb-log-file-size = 768M innodb-flush-log-at-trx-commit = 1 innodb-file-per-table = 1 innodb-buffer-pool-size = 192M # LOGGING # log-error = /var/log/mysqld.log slow-query-log = 1 slow-query-log-file = /var/log/mysqld-slow.log log-queries-not-using-indexes = OFF long_query_time = 30 [mysqldump] max-allowed-packet = 16M When I try to start MySQL, this is what I get: ● mysql.service - MySQL Community Server Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: enabled) Active: activating (start-post) (Result: exit-code) since Mon 2017-08-21 12:09:51 UTC; 1s ago Process: 14659 ExecStart=/usr/sbin/mysqld (code=exited, status=1/FAILURE) Process: 14643 ExecStartPre=/usr/share/mysql/mysql-systemd-start pre (code=exited, status=0/SUCCESS) Main PID: 14659 (code=exited, status=1/FAILURE); Control PID: 14660 (mysql-systemd-s) Tasks: 2 (limit: 4915) Memory: 760.0K CPU: 223ms CGroup: /system.slice/mysql.service └─control ├─14660 /bin/bash /usr/share/mysql/mysql-systemd-start post └─14669 sleep 1 **There is nothing in /var/log/mysql.log**. I don't know where else to look for error log. Can you please help? Edit: I ran journalcl and found more error logs: -- Unit mysql.service has begun starting up. Aug 21 13:04:46 www.####.com kernel: audit: type=1400 audit(1503320686.962:1051): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/18169/status" pid=18169 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=112 ouid=112 Aug 21 13:04:46 www.####.com audit: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/18169/status" pid=18169 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=112 ouid=112 Aug 21 13:04:46 www.####.com audit: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/sys/devices/system/node/" pid=18169 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=112 ouid=0 Aug 21 13:04:46 www.####.com kernel: audit: type=1400 audit(1503320686.974:1052): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/sys/devices/system/node/" pid=18169 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=112 ouid=0 Aug 21 13:04:46 www.####.com audit: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/18169/status" pid=18169 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=112 ouid=112 Aug 21 13:04:46 www.####.com kernel: audit: type=1400 audit(1503320686.978:1053): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/18169/status" pid=18169 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=112 ouid=112 Aug 21 13:04:47 www.####.com audit: AVC apparmor="DENIED" operation="mknod" profile="/usr/sbin/mysqld" name="/var/log/mysqld.log" pid=18169 comm="mysqld" requested_mask="c" denied_mask="c" fsuid=112 ouid=112 Aug 21 13:04:47 www.####.com audit: AVC apparmor="DENIED" operation="mknod" profile="/usr/sbin/mysqld" name="/var/log/mysqld.log" pid=18169 comm="mysqld" requested_mask="c" denied_mask="c" fsuid=112 ouid=112 Aug 21 13:04:47 www.####.com audit: AVC apparmor="DENIED" operation="mknod" profile="/usr/sbin/mysqld" name="/var/log/mysqld.log" pid=18169 comm="mysqld" requested_mask="c" denied_mask="c" fsuid=112 ouid=112 Aug 21 13:04:47 www.####.com audit: AVC apparmor="DENIED" operation="mknod" profile="/usr/sbin/mysqld" name="/var/log/mysqld.log" pid=18169 comm="mysqld" requested_mask="c" denied_mask="c" fsuid=112 ouid=112 Aug 21 13:04:47 www.####.com audit: AVC apparmor="DENIED" operation="mknod" profile="/usr/sbin/mysqld" name="/var/log/mysqld.log" pid=18169 comm="mysqld" requested_mask="c" denied_mask="c" fsuid=112 ouid=112 Aug 21 13:04:47 www.####.com audit: AVC apparmor="DENIED" operation="mknod" profile="/usr/sbin/mysqld" name="/var/log/mysqld.log" pid=18169 comm="mysqld" requested_mask="c" denied_mask="c" fsuid=112 ouid=112 Aug 21 13:04:47 www.####.com kernel: audit: type=1400 audit(1503320687.182:1054): apparmor="DENIED" operation="mknod" profile="/usr/sbin/mysqld" name="/var/log/mysqld.log" pid=18169 comm="mysqld" requested_mask="c" denied_mask="c" fsuid=112 ouid=112 Aug 21 13:04:47 www.####.com kernel: audit: type=1400 audit(1503320687.182:1055): apparmor="DENIED" operation="mknod" profile="/usr/sbin/mysqld" name="/var/log/mysqld.log" pid=18169 comm="mysqld" requested_mask="c" denied_mask="c" fsuid=112 ouid=112 Aug 21 13:04:47 www.####.com kernel: audit: type=1400 audit(1503320687.182:1056): apparmor="DENIED" operation="mknod" profile="/usr/sbin/mysqld" name="/var/log/mysqld.log" pid=18169 comm="mysqld" requested_mask="c" denied_mask="c" fsuid=112 ouid=112 Aug 21 13:04:47 www.####.com kernel: audit: type=1400 audit(1503320687.182:1057): apparmor="DENIED" operation="mknod" profile="/usr/sbin/mysqld" name="/var/log/mysqld.log" pid=18169 comm="mysqld" requested_mask="c" denied_mask="c" fsuid=112 ouid=112 Aug 21 13:04:47 www.####.com kernel: audit: type=1400 audit(1503320687.182:1058): apparmor="DENIED" operation="mknod" profile="/usr/sbin/mysqld" name="/var/log/mysqld.log" pid=18169 comm="mysqld" requested_mask="c" denied_mask="c" fsuid=112 ouid=112 Aug 21 13:04:47 www.####.com kernel: audit: type=1400 audit(1503320687.182:1059): apparmor="DENIED" operation="mknod" profile="/usr/sbin/mysqld" name="/var/log/mysqld.log" pid=18169 comm="mysqld" requested_mask="c" denied_mask="c" fsuid=112 ouid=112 Aug 21 13:04:47 www.####.com systemd[1] : mysql.service: Main process exited, code=exited, status=1/FAILUREl.service: Main process exited, code=exited, status=1/FAILURE