mysql.user table damaged suddenly I didn't do an upgrade or anything but suddenly MySQL (MariaDB) stopped working after a restart. This is the log:

2018-02-11 14:10:02 140193631740480 [Note] Using unique option prefix 'innodb_buffer_pool_instance' is error-prone and can break in the future. Please use the full name 'innodb-buffer-pool-instances' instead.
2018-02-11 14:10:03 140193631740480 [Note] InnoDB: Using mutexes to ref count buffer pool pages
2018-02-11 14:10:03 140193631740480 [Note] InnoDB: The InnoDB memory heap is disabled
2018-02-11 14:10:03 140193631740480 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2018-02-11 14:10:03 140193631740480 [Note] InnoDB: GCC builtin __atomic_thread_fence() is used for memory barrier
2018-02-11 14:10:03 140193631740480 [Note] InnoDB: Compressed tables use zlib 1.2.8
2018-02-11 14:10:03 140193631740480 [Note] InnoDB: Using Linux native AIO
2018-02-11 14:10:03 140193631740480 [Note] InnoDB: Using SSE crc32 instructions
2018-02-11 14:10:03 140193631740480 [Note] InnoDB: Initializing buffer pool, size = 2.0G
2018-02-11 14:10:03 140193631740480 [Note] InnoDB: Completed initialization of buffer pool
2018-02-11 14:10:03 140193631740480 [Note] InnoDB: Highest supported file format is Barracuda.
2018-02-11 14:10:03 140193631740480 [Note] InnoDB: The log sequence number 1445306045 in ibdata file do not match the log sequence number 1445306065 in the ib_logfiles!
2018-02-11 14:10:03 140193631740480 [Note] InnoDB: Restoring possible half-written data pages from the doublewrite buffer...
2018-02-11 14:10:03 140193631740480 [Note] InnoDB: 128 rollback segment(s) are active.
2018-02-11 14:10:03 140193631740480 [Note] InnoDB: Waiting for purge to start
2018-02-11 14:10:03 140193631740480 [Note] InnoDB:  Percona XtraDB (http://www.percona.com) 5.6.36-82.1 started; log sequence number 1445306065
2018-02-11 14:10:03 140190647551744 [Note] InnoDB: Dumping buffer pool(s) not yet started
2018-02-11 14:10:03 140193631740480 [Note] Plugin 'FEEDBACK' is disabled.
2018-02-11 14:10:03 140193631740480 [Note] Recovering after a crash using tc.log
2018-02-11 14:10:03 140193631740480 [Note] Starting crash recovery...
2018-02-11 14:10:03 140193631740480 [Note] Crash recovery finished.
2018-02-11 14:10:03 140193631740480 [Note] Server socket created on IP: '127.0.0.1'.
2018-02-11 14:10:03 140193631740480 [ERROR] Fatal error: mysql.user table is damaged or in unsupported 3.20 format.


I tried looking around but can't quite see how to fix it.
Try mysqlcheck --all-databases.  That will probably say that mysql.user needs repair.  Then do

mysqlcheck --all-databases --repair


Ref: https://dev.mysql.com/doc/refman/5.7/en/mysqlcheck.html