From MEPIS Documentation Wiki
Autologin refers to bypassing the login screen so that no user password is required. Despite its convenience for the user, it is not recommended because it undermines the first level of security.
MEPIS 8.5 and 11
1. Press Alt+F2 to open the Run Command window
2. Enter the command 'kdesu systemsettings' and press <Enter>
3. When the System Settings window opens, go to Advanced > Login Manager > Convenience (in M11 Login Manager > Convenience)
4. Tick the "Enable Auto-Login" box and select your User
5. Click Apply