Error in MySQL upgrade from 5.6 to 5.7

I tried to upgrade from mysql 5.6 to mysql 5.7 per a recommendation. It failed. When trying to start it, the error logs give me this: 2019-02-23T02:38:10.687444Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details). 2019-02-23T02:38:10.687879Z 0 [Note] /usr/sbin/mysqld (mysqld 5.7.25) starting as process 9550 ... 2019-02-23T02:38:10.699726Z 0 [Warning] InnoDB: Using innodb_support_xa is deprecated and the parameter may be removed in future releases. Only innodb_support_xa=ON is allowed. 2019-02-23T02:38:10.699834Z 0 [Note] InnoDB: PUNCH HOLE support available 2019-02-23T02:38:10.699882Z 0 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins 2019-02-23T02:38:10.699894Z 0 [Note] InnoDB: Uses event mutexes 2019-02-23T02:38:10.699904Z 0 [Note] InnoDB: GCC builtin __sync_synchronize() is used for memory barrier 2019-02-23T02:38:10.699918Z 0 [Note] InnoDB: Compressed tables use zlib 1.2.11 2019-02-23T02:38:10.699942Z 0 [Note] InnoDB: Using Linux native AIO 2019-02-23T02:38:10.700499Z 0 [Note] InnoDB: Number of pools: 1 2019-02-23T02:38:10.700793Z 0 [Note] InnoDB: Using CPU crc32 instructions 2019-02-23T02:38:10.704355Z 0 [Note] InnoDB: Initializing buffer pool, total size = 128M, instances = 1, chunk size = 128M 2019-02-23T02:38:10.721659Z 0 [Note] InnoDB: Completed initialization of buffer pool 2019-02-23T02:38:10.727002Z 0 [Note] InnoDB: If the mysqld execution user is authorized, page cleaner thread priority can be changed. See the man page of setpriority(). 2019-02-23T02:38:10.743571Z 0 [Note] InnoDB: Highest supported file format is Barracuda. 2019-02-23T02:38:10.743731Z 0 [ERROR] InnoDB: Operating system error number 40 in a file operation. 2019-02-23T02:38:10.743763Z 0 [ERROR] InnoDB: Error number 40 means 'Too many levels of symbolic links' 2019-02-23T02:38:10.743776Z 0 [Note] InnoDB: Some operating system error numbers are described at http://dev.mysql.com/doc/refman/5.7/en/operating-system-error-codes.html 2019-02-23T02:38:10.743794Z 0 [ERROR] InnoDB: File .//mysql.sock: 'stat' returned OS error 140. 2019-02-23T02:38:10.743821Z 0 [ERROR] InnoDB: os_file_readdir_next_file() returned -1 in directory ./, crash recovery may have failed for some .ibd files! 2019-02-23T02:38:10.743896Z 0 [ERROR] InnoDB: Plugin initialization aborted with error Generic error 2019-02-23T02:38:11.344488Z 0 [ERROR] Plugin 'InnoDB' init function returned error. 2019-02-23T02:38:11.344571Z 0 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed. 2019-02-23T02:38:11.344600Z 0 [ERROR] Failed to initialize builtin plugins. 2019-02-23T02:38:11.344609Z 0 [ERROR] Aborting 2019-02-23T02:38:11.344624Z 0 [Note] Binlog end 2019-02-23T02:38:11.345357Z 0 [Note] /usr/sbin/mysqld: Shutdown complete
How do I fix this and restore the mysql service?