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System starts

When powered on, after a panic, or if the system is rebooted via reboot(8) or shutdown(8), the PROM will proceed to its initialization, and will boot an operating system if autoboot is enabled.

Boot process description

System boot blocks are installed near the start of the boot disk using the procedure described in installboot(8). The boot program attempts to load the kernel from the selected boot device, which must currently be an “sd”, “xd” or “xy” disk, or an SCSI CD-ROM (“cd”) or tape drive (“st”).

The SPARC boot ROM comes in two flavours: an “old-style” ROM is used in sun4 machines, while a “new-style” ROM can be found on sun4c and sun4m models. The “new-style” SPARC boot ROM is a full-featured Forth system with emacs key bindings. It can be put in “old-style” user-interface compatibility mode (in which case it shows a simple “>” prompt), but this is essentially useless. However, by default the ROM runs in old-mode; to enter new-mode type “n”. The ROM then shows a Forth-style “ok” prompt. It is recommended to have the ROM always start in its native “new-style” mode. Utter the following incantation in new-mode to force the ROM to always start in new-mode:

ok setenv sunmon-compat? false

Old-style PROM operation

By default, the old ROM will poll for boot devices, unless the eeprom settings are set to specify a particular boot device. The OpenBSD bootloader will then look for a kernel named bsd by default, unless a different filename has been specified in the boot command.

Refer to the “PROM User's Manual” for more information.

OpenBoot PROM version 1 operation

Older OpenBOOT PROM, as well as hybrid (dual-mode) versions operating in compatibility mode (with the variable version2? set to false) will look for a bootloader and kernel filename as specified by the boot-from variable. To change the default so that OpenBSD will be loaded, type the following:

ok setenv boot-from sd(0,0,0)bsd

Replace “sd(0,0,0)” with the appropriate boot device if necessary.

Autoboot is enabled by setting the auto-boot? variable to “true”, and is the factory default.

OpenBoot PROM version 2 operation

Version 2 OpenBOOT PROM will look for a bootloader on the device specified by the boot-device variable. The OpenBSD bootloader will then look for a kernel named bsd by default, unless the boot-file variable is set, or a different filename has been specified in the boot command. To reset this variable to its default, empty, value, type the following:

ok set-default boot-file

Autoboot is enabled by setting the auto-boot? variable to “true”, and is the factory default.

Boot process options

The following options are recognized:

Abnormal system termination

If the system crashes, it will enter the kernel debugger, ddb(4), if it is configured in the kernel. If the crash occurred during initialization and the debugger is not present or is exited, the kernel will halt the system. If the crash occurred during normal operation and the debugger is not present or is exited, the system will attempt a dump to the configured dump device (which will be automatically recovered with savecore(8) during the next multi-user boot cycle), and after the dump is complete (successful or not) the kernel will attempt a reboot.

Accessing the PROM during runtime

If the sysctl(8) variable ddb.console is enabled, at any time you can break back to the ROM by pressing the “L1” (also known as the “stop key”) and “a” keys at the same time (if the console is a serial port the same is achieved by sending a “break”), and entering machine prom at the prompt. If you do this accidentally you can continue whatever was in progress by typing go on an OpenBOOT PROM, or c on an old-style PROM to return to ddb, and then cont to return to the system.