Some hotkeys to hold when powering on the Mac:
- ⌘+V — Verbose mode
- ⌘+S — Single-user mode
- ⇧ — Safe mode
- ⌥ — Startup manager (select boot medium)
- C — Boot from CD-/DVD-ROM or USB
- D — Boot to diagnostics
- ⌥+D — Boot to diagnostics over the Internet
- N — Netboot
- ⌥+N — Netboot using default image
- ⌘+R — Boot to recovery
- ⌥+⌘+R — Boot to recovery over the Internet
- ⌥+⌘+P+R — Reset NVRAM
- T — Startup in target disk mode (to receive files from another Mac)
- X — Force boot to MacOS