SUNLABEL(8) System Manager's Manual SUNLABEL(8)

sunlabel — read or modify a SunOS disk label

sunlabel [-mnqs] device

sunlabel reads or modifies a SunOS disk label on device, which is used by the PROM on NetBSD/sparc hardware to find partitions to boot from. sunlabel only reads/writes the first 512 bytes of device.

The supported options are:

Ignore an incorrect magic number in the disk label.
Synthesize a new label rather than reading what is there.
Quiet mode - don't print unnecessary babble (currently this suppresses the “sunlabel>” prompt).
Ignore checksum errors when reading the label.

Note that -m is dangerous, especially when combined with -s, since it will then happily believe whatever garbage it may find in the label. When using these flags, all values should be checked carefully, both those printed by L and the partition table printed by P.

sunlabel prints a prompt “sunlabel>” and expects commands. The following commands are understood:

?
Show a short help message.
<cylno> <size>
Change partition (see below).
Print label, except for the partition table.
Print the partition table.

In addition, a simple textual map of the partition layout is printed. The map is scaled to the current terminal width; each character column represents a span of the disk and is labeled with the corresponding partition letter (a through p). Unallocated regions are shown as spaces. Overlapping partitions may appear on multiple map lines.

Quit program (error if no write since last change).
Quit program (unconditionally) [EOF also quits].
Set label in the kernel (orthogonal to W).
<name> <value>
Change a non-partition label value.
Write (possibly modified) label out.

The a through p commands will accept, for the <size> parameter, the nnn/nnn/nnn syntax used by SunOS 4.x format. (For those not familiar with this syntax, a/b/c means a cylinders + b tracks + c sectors. For example, if the disk has 16 tracks of 32 sectors, 3/4/5 means (3*16*32)+(4*32)+5=1669. This calculation always uses the nsect and ntrack values as printed by the L command; in particular, if they are zero (which they will initially be if -n is used), this syntax is not very useful. Some additional strings are accepted. For the <cylno> parameter, “end-X” (where X is a partition letter) indicates that the partition should start with the first free cylinder after partition X; “start-X” indicates that the partition should start at the same place as partition X. For the <size> parameter, “end-X” indicates that the partition should end at the same place as partition X (even if partition X ends partway through a cylinder); “start-X” indicates that the partition should end with the last cylinder before partition X; and “size-X” means that the partition's size should exactly match partition X's size.

Note that sunlabel supports 16 partitions. SunOS supports only 8. Labels written by sunlabel, when partitions i through p are all set offset=0 size=0, are identical to Sun labels. If any of the “extended” partitions are nontrivial, information about them is tucked into some otherwise unused space in the Sun label format.

The V command changes fields printed by the L command. For example, if the L command prints

ascii: ST15230N cyl 5657 alt 2 hd 19 sec 78
rpm: 0          pcyl: 0         apc: 0          obs1: 0
obs2: 0         intrlv: 1       ncyl: 5657      acyl: 0
nhead: 19       nsect: 78       obs3: 0         obs4: 0

then V ncyl 6204 would set the ncyl value to 6204, or V ascii Seagate ST15230N cyl 5657 hd 19 sec varying would set the ascii-label string to that string. sunlabel performs very few consistency checks on the values you supply, and the ones it does perform never generate errors, only warnings.

der Mouse <mouse@rodents.montreal.qc.ca>

It may be that the space in the label where the information for the extended partitions is saved is used by SunOS.

Not very many consistency checks are done on the V arguments, and those only produce warnings.

NetBSD doesn't support 16 partitions in a Sun disk label yet.

January 11, 2026 NetBSD 11.0