boot —
system bootstrapping procedures
Normally, the system will reboot itself at power-up or after crashes. An
  automatic consistency check of the file systems will be performed as described
  in fsck(8). and unless this
  fails, the system will resume multi-user operations.
The disk-boot program (/usr/mdec/bootsd) will attempt to
  load netbsd from partition A of the boot device, which
  must currently be an “sd” disk.
The tape-boot program (/usr/mdec/bootst) will attempt to
  load netbsd from a SCSI tape drive.
The network boot program (/usr/mdec/netboot) will load
  netbsd from the NFS root as determined by the
  procedure described in
  diskless(8). Note that the
  MVME147 is unable to boot directly from the network without the help of a
  small bootloader program (/usr/mdec/sboot).
  - -a
- Prompt for the root file system device, the system crash dump device, and
      the path to init(8).
- -d
- Bring the system up in debug mode. Here it waits for a kernel debugger
      connect; see ddb(4).
- -q
- Boot the system in quiet mode.
- -s
- Bring the system up in single-user mode.
- -v
- Boot the system in verbose mode.
Any extra flags or arguments, or the <boot
    string> after the -- separator are passed to the boot PROM. Other
    flags are currently ignored.
At any time you can break to the kernel debugger
    ddb(4) (assuming
    options DDB was specified in the kernel configuration
    file) by sending a serial line BREAK character. If you do this accidentally
    you can continue whatever was in progress by typing ‘c’
    followed by the return key.
  - /netbsd
- system code
- /usr/mdec/bootxx
- first-level boot block for disks
- /usr/mdec/stboot
- first-level boot block for tapes
- /usr/mdec/bootsd
- second-level boot block for UFS disks
- /usr/mdec/bootst
- second-level boot block for tapes
- /usr/mdec/netboot
- boot program for NFS (diskless) boot
- /usr/mdec/sboot
- network bootstrap program for MVME147
- /usr/mdec/installboot
- program to install bootxx on a disk