We ran into some issues when upgrading to MySQL 5.6.38. There were no error logs, nothing. The only thing it returned was:

Starting MySQL. ERROR! The server quit without updating PID file (/var/lib/mysql/server.pid).
I tried starting it with
sh -x /etc/init.d/mysqld start
which gave me the full command it used:

[root@server mysql]# /usr/bin/mysqld_safe --datadir=/var/lib/mysql --pid-file=/var/lib/mysql/server.pid
171114 08:53:48 mysqld_safe Logging to '/var/log/mysql.log'.
171114 08:53:48 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
171114 08:53:48 mysqld_safe mysqld from pid file /var/lib/mysql/server.pid ended
It never returned an error until I tried 'mysqld':

[root@server mysql]# mysqld
mysqld: error while loading shared libraries: libnuma.so.1: cannot open shared object file: No such file or directory
Installing 'numactl' solved it on CentOS 6.9.