phpMyAdmin does not open from the cPanel interface

Introduction

When accessing PHPMyAdmin from cPanel, the interface never loads.

Procedure

From the command line, you will need to review the MySQL error log and the cPanel error log to gather more details on why this is happening. 

1. First, access the WHM interface as the root user.
2. Navigate to the Terminal interface at "WHM / Server Configuration / Terminal".

3. Run the following:

   grep "Failed to setup the temp session" /usr/local/cpanel/logs/error_log

   grep "Incorrect definition" /var/log/mysql.log

   Please note, your MySQL log may be in another location or named differently. Please refer to the additional resource section to determine the MySQL error log location.
    

   If you see the log entries like this:

   [2023-10-14 15:51:38 -0300] warn [cpwrapd] Unexpected error from cpses_tool: The subprocess reported error number 255 when it ended.
   Cpanel::Exception/(XID 7bnpuy) Failed to setup the temp session user at /usr/local/cpanel/Cpanel/Admin/Modules/Cpanel/session_call.pm line 287.
   	...propagated at /usr/local/cpanel/Cpanel/Admin/Base.pm line 769.

   [ERROR] Incorrect definition of table mysql.proc: expected column 'sql_mode' at position 14 to have type set('REAL_AS_FLOAT','PIPES_AS_CONCAT','ANSI_QUOTES','IGNORE_SPACE','IGNORE_BAD_TABLE_OPTIONS','ONLY_FULL_GROUP_BY','NO_UNSIGNED_SUBTRACTION','NO_DIR_IN_CREATE','POSTGRESQL','ORACLE','MSSQL','DB2','MAXDB','NO_KEY_OPTIONS','NO_TABLE_OPTIONS','NO_FIELD_OPTIONS','MYSQL323','MYSQL40','ANSI','NO_AUTO_VALUE_ON_ZERO','NO_BACKSLASH_ESCAPES','STRICT_TRANS_TABLES','STRICT_ALL_TABLES','NO_ZERO_IN_DATE','NO_ZERO_DATE','INVA
   [ERROR] Incorrect definition of table mysql.proc: expected column 'definer' at position 11 to have type char(, found type varchar(384).

   You will need to run the mysql_upgrade command. 

4. # mysql_upgrade -sf

Additional Resources

How to locate the MySQL or MariaDB log