MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6 Error Logging on Unix and Unix-Like Systems

On Unix and Unix-like systems, mysqld uses the --log-error option to determine whether mysqld writes the error log to the console or a file, and, if to a file, the file name:


It is common for Yum or APT package installations to configure an error log file location under /var/log with an option like log-error=/var/log/mysqld.log in a server configuration file. Removing the file name from the option causes the host_name.err file in the data directory to be used.

If the server writes the error log to the console, it sets the log_error system variable to stderr. Otherwise, the server writes the error log to a file and sets log_error to the file name.