What is the reason for the failure to start MySQL after the ubuntu server restarts? - Codes Helper

it was fine before rebooting, but after rebooting, it will never be able to start again
root@iZuf6acp86oa3jizjzwaqdZ:~-sharp service mysql start
Job for mysql.service failed because the control process exited with error code. See "systemctl status mysql.service" and "journalctl -xe" for details.
root@iZuf6acp86oa3jizjzwaqdZ:~-sharp 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 Wed 2018-12-19 14:13:09 CST; 22s ago
  Process: 5124 ExecStart=/usr/sbin/mysqld (code=exited, status=1/FAILURE)
  Process: 5116 ExecStartPre=/usr/share/mysql/mysql-systemd-start pre (code=exited, status=0/SUCCESS)
 Main PID: 5124 (code=exited, status=1/FAILURE);         : 5125 (mysql-systemd-s)
   CGroup: /system.slice/mysql.service
           control
             5125 /bin/bash /usr/share/mysql/mysql-systemd-start post
             5194 sleep 1

Dec 19 14:13:09 iZuf6acp86oa3jizjzwaqdZ systemd[1]: Starting MySQL Community Server...
Dec 19 14:13:11 iZuf6acp86oa3jizjzwaqdZ systemd[1]: mysql.service: Main process exited, code=exited, status=1/FAILURE

root@iZuf6acp86oa3jizjzwaqdZ:~-sharp journalctl -xe
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit mysql.service has begun starting up.
Dec 19 14:31:27 iZuf6acp86oa3jizjzwaqdZ audit[1938]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/1938/status" pid=1938 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=111 ouid=111
Dec 19 14:31:27 iZuf6acp86oa3jizjzwaqdZ kernel: audit: type=1400 audit(1545201087.234:39): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/1938/status" pid=1938 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=111 ouid=111
Dec 19 14:31:27 iZuf6acp86oa3jizjzwaqdZ audit[1938]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/sys/devices/system/node/" pid=1938 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=111 ouid=0
Dec 19 14:31:27 iZuf6acp86oa3jizjzwaqdZ audit[1938]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/1938/status" pid=1938 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=111 ouid=111
Dec 19 14:31:27 iZuf6acp86oa3jizjzwaqdZ kernel: audit: type=1400 audit(1545201087.238:40): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/sys/devices/system/node/" pid=1938 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=111 ouid=0
Dec 19 14:31:27 iZuf6acp86oa3jizjzwaqdZ kernel: audit: type=1400 audit(1545201087.238:41): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/1938/status" pid=1938 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=111 ouid=111
Dec 19 14:31:29 iZuf6acp86oa3jizjzwaqdZ systemd[1]: mysql.service: Main process exited, code=exited, status=1/FAILURE
Dec 19 14:31:58 iZuf6acp86oa3jizjzwaqdZ 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.
Dec 19 14:31:58 iZuf6acp86oa3jizjzwaqdZ systemd[1]: mysql.service: Unit entered failed state.
Dec 19 14:31:58 iZuf6acp86oa3jizjzwaqdZ systemd[1]: mysql.service: Failed with result "exit-code".
Dec 19 14:31:58 iZuf6acp86oa3jizjzwaqdZ systemd[1]: mysql.service: Service hold-off time over, scheduling restart.
Dec 19 14:31:58 iZuf6acp86oa3jizjzwaqdZ 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.
Dec 19 14:31:58 iZuf6acp86oa3jizjzwaqdZ 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.
Dec 19 14:31:58 iZuf6acp86oa3jizjzwaqdZ audit[2036]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/2036/status" pid=2036 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=111 ouid=111
Dec 19 14:31:58 iZuf6acp86oa3jizjzwaqdZ audit[2036]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/sys/devices/system/node/" pid=2036 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=111 ouid=0
Dec 19 14:31:58 iZuf6acp86oa3jizjzwaqdZ audit[2036]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/2036/status" pid=2036 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=111 ouid=111
Dec 19 14:31:58 iZuf6acp86oa3jizjzwaqdZ kernel: audit: type=1400 audit(1545201118.491:42): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/2036/status" pid=2036 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=111 ouid=111
Dec 19 14:31:58 iZuf6acp86oa3jizjzwaqdZ kernel: audit: type=1400 audit(1545201118.491:43): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/sys/devices/system/node/" pid=2036 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=111 ouid=0
Dec 19 14:31:58 iZuf6acp86oa3jizjzwaqdZ kernel: audit: type=1400 audit(1545201118.491:44): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/2036/status" pid=2036 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=111 ouid=111
Dec 19 14:32:00 iZuf6acp86oa3jizjzwaqdZ systemd[1]: mysql.service: Main process exited, code=exited, status=1/FAILURE
Dec 19 14:32:01 iZuf6acp86oa3jizjzwaqdZ CRON[2068]: pam_unix(cron:session): session opened for user root by (uid=0)
Dec 19 14:32:01 iZuf6acp86oa3jizjzwaqdZ CRON[2067]: pam_unix(cron:session): session opened for user root by (uid=0)
Dec 19 14:32:01 iZuf6acp86oa3jizjzwaqdZ CRON[2069]: (root) CMD (php /var/www/html/tiebasign/do.php)
Dec 19 14:32:01 iZuf6acp86oa3jizjzwaqdZ CRON[2071]: (root) CMD (php /var/www/html/tiebaid/test_only_cli_run_cw123456.php)
Dec 19 14:32:01 iZuf6acp86oa3jizjzwaqdZ cron[649]: Please install an MTA on this system if you want to use sendmail!
Dec 19 14:32:01 iZuf6acp86oa3jizjzwaqdZ CRON[2067]: (root) MAIL (mailed 378 bytes of output but got status 0x00ff from MTA
                                                    )
Dec 19 14:32:01 iZuf6acp86oa3jizjzwaqdZ CRON[2067]: pam_unix(cron:session): session closed for user root
Dec 19 14:32:01 iZuf6acp86oa3jizjzwaqdZ cron[649]: Please install an MTA on this system if you want to use sendmail!
Dec 19 14:32:01 iZuf6acp86oa3jizjzwaqdZ CRON[2068]: (root) MAIL (mailed 180 bytes of output but got status 0x00ff from MTA
                                                    )
Dec 19 14:32:01 iZuf6acp86oa3jizjzwaqdZ CRON[2068]: pam_unix(cron:session): session closed for user root
Dec 19 14:32:29 iZuf6acp86oa3jizjzwaqdZ 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.
Dec 19 14:32:29 iZuf6acp86oa3jizjzwaqdZ systemd[1]: mysql.service: Unit entered failed state.
Dec 19 14:32:29 iZuf6acp86oa3jizjzwaqdZ systemd[1]: mysql.service: Failed with result "exit-code".
Dec 19 14:32:29 iZuf6acp86oa3jizjzwaqdZ systemd[1]: mysql.service: Service hold-off time over, scheduling restart.
Dec 19 14:32:29 iZuf6acp86oa3jizjzwaqdZ 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.
Dec 19 14:32:29 iZuf6acp86oa3jizjzwaqdZ 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.
Dec 19 14:32:29 iZuf6acp86oa3jizjzwaqdZ audit[2141]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/2141/status" pid=2141 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=111 ouid=111
Dec 19 14:32:29 iZuf6acp86oa3jizjzwaqdZ kernel: audit: type=1400 audit(1545201149.732:45): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/2141/status" pid=2141 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=111 ouid=111
Dec 19 14:32:29 iZuf6acp86oa3jizjzwaqdZ audit[2141]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/sys/devices/system/node/" pid=2141 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=111 ouid=0
Dec 19 14:32:29 iZuf6acp86oa3jizjzwaqdZ kernel: audit: type=1400 audit(1545201149.736:46): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/sys/devices/system/node/" pid=2141 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=111 ouid=0
Dec 19 14:32:29 iZuf6acp86oa3jizjzwaqdZ audit[2141]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/2141/status" pid=2141 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=111 ouid=111
Dec 19 14:32:29 iZuf6acp86oa3jizjzwaqdZ kernel: audit: type=1400 audit(1545201149.740:47): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/2141/status" pid=2141 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=111 ouid=111
Dec 19 14:32:31 iZuf6acp86oa3jizjzwaqdZ systemd[1]: mysql.service: Main process exited, code=exited, status=1/FAILURE
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