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Lessons · IT support · safe mode and drivers

Safe mode: the operating system with nothing extra loaded

A driver is the small program the operating system uses to talk to one piece of hardware. Safe mode starts the operating system with only the drivers it cannot run without, and no third-party programs. If the fault is gone in safe mode, the cause is something safe mode left out: a driver or a program, not the OS itself.

Hone is a place to practise a career, one idea a day. This is one of its lessons, written out in full and free to read without an account.

What it is for

After an update, a laptop shows a scrambled screen and cannot be used long enough to undo anything. In safe mode the screen is plain and fine. That single fact has done the diagnosis: the display driver the update brought. Roll it back from inside safe mode, restart, done. Without safe mode it would have been a reinstall and a lost afternoon.

How to think about it

Use safe mode as a test, not as a fix. Boot into it and try the failing thing. Works in safe mode: a driver or a start-up program is the cause, and the most recently changed one is the first suspect; roll it back or disable it from inside safe mode. Still fails in safe mode: the cause is the OS or the hardware, and the driver list is not where to look.

Worked example

Normal boot: scrambled screen within a minute of sign-in
The fault, reproduced.
Safe mode: plain screen, stable for ten minutes
The fault is gone. Whatever causes it is something safe mode does not load.
Device list: display driver updated yesterday 23:10
The most recent change, in the class safe mode leaves out. Prime suspect.
Roll back the display driver, normal boot: stable
One change, verified. The note names the driver and the date, and the update gets held until the vendor fixes it.

Your turn

A machine crashes on a normal boot and also crashes in safe mode. Write what that rules out.

Crashes in safe mode too → not a third-party

The trap

Reinstalling every driver on the machine because one is bad. Safe mode told you which class of thing it was; the update history tells you which one. Six changes where one would do is five new faults waiting.

Practise safe mode and drivers on HoneA question on it now, a coding challenge where there is one, and it is remembered for review. Free, no email needed.