The job of MMON( Manageability Monitor) background process is to perform tasks like taking AWR snapshots and automatic diagnostic analysis.

Sometime, MMON process crashes or get suspended .

Follow below steps to restart the MMON process:

1. Grant restricted session to public:

This grant is required to avoid any impact on the sessions connecting to database.

grant restricted session to public;

2. Enable and disable restricted sessions

Enabling and disabling will start the MMON process.

alter system enable restricted session;

alter system disable restricted session;

3. Revoke the restricted session:

revoke restricted session from  public;

4. Check MMON process;

ps -ef | grep mmon