MS-DOS 6.22 Clean Boot Using the F5 Key

This article explains how clean boot mode functions in MS-DOS 6.22, how to use the F5 key during startup, and the specific configuration setting in CONFIG.SYS that controls whether this bypass feature is enabled or disabled.

The Default F5 Clean Boot Behavior

In MS-DOS 6.22, clean boot mode is enabled by default natively. When the operating system initializes, the screen displays the message:

Starting MS-DOS...

Pressing the F5 key (or holding down the Left Shift key) during the brief pause after this message bypasses the execution of both CONFIG.SYS and AUTOEXEC.BAT. This loads a minimal DOS environment without device drivers, memory managers, or TSR programs.

The Configuration Option: The SWITCHES Command

The specific CONFIG.SYS configuration directive that controls the availability of the F5 clean boot key is the SWITCHES command.

While MS-DOS enables F5 by default, administrators can disable this feature by adding the /N parameter:

SWITCHES=/N

When SWITCHES=/N is present in CONFIG.SYS, the user is prevented from bypassing startup files using F5 or stepping through them using F8.

To enable or restore clean boot functionality via F5, open your CONFIG.SYS file in a text editor (such as the MS-DOS Editor) and modify the line:

  1. Remove /N: If your file contains SWITCHES=/N, delete the /N switch or remove the entire line.
  2. Avoid /F: Ensure SWITCHES=/F is not present, as the /F switch skips the standard two-second delay after displaying "Starting MS-DOS...", making it significantly harder to press F5 in time.

Saving CONFIG.SYS without the /N flag ensures that the F5 clean boot key is active and ready to use during the boot sequence.