Essential classic Mac boot key combos
Press this together with Power button
Cmd-Option-Shift-Delete-(#)Boot from a SCSI device on the SCSI bus other than the disk selected in the Startup Disk control panel. The Optionional number allows for booting from a specific SCSI ID.
RForce PowerBook to reset screen.
CBoot from Apple-brand CD-ROM drive. Works with a few third-party drives too. For drives that can't boot using the C key, try Cmd-Option-Shift-delete as explained above.
Hold mouse buttonEject floppy and optical drive.
Press this after startup chime plays
CommandBoot with virtual memory off (System 7 - Mac OS 9.x only).
ShiftBoot with Extensions, Control Panels, and Startup Items disabled (including VM, if on).
SpaceOpen Extensions Manager (System 7.5.x and higher only) on boot.
othersCheck documentation for third-party extensions and control panels; there are often keys to disable these individually.
Press this before Finder starts, after Mac OS logo dissapears
Cmd-OptionRebuild the desktop file.
ShiftDisable Startup Items only.
OptionStart Finder with no open windows.
The following are some other useful shortcuts/undocumented combos
Cmd-Optionwhile opening Memory control panel: allow startup RAM tests to be turned off (Mac OS 8.5 - 9.x only).
Cmd-PowerEnter NMI, or Macsbug (if installed).
Cmd-Optionwhile opening Chooser: rebuild Chooser's cache.
Updated on 22.04.2017