DISKLABEL(8)

NAME
disklabel - read and write disk pack label

SYNOPSIS
disklabel [-r] disk
disklabel -w [-r] disk disktype [packid]
disklabel -e [-r] disk
disklabel -R [-r] disk protofile
disklabel [-NW] disk

disklabel -B [ -b boot1 [-s boot2]] disk [disktype]
disklabel -w -B [ -b boot1 [-s boot2]] disk disktype [packid]
disklabel -R -B [ -b boot1 [-s boot2]] disk protofile [disktype]

DESCRIPTION
Disklabel can be used to install, examine or modify the label on a disk drive or pack. When writing the label, it can be used to change the drive identification, the disk partitions on the drive, or to replace a damaged label. On some systems, disklabel can be used to install bootstrap code as well. There are several forms of the command that read (display), install or edit the label on a disk. Each form has an additional option, -r, which causes the label to be read from or written to the disk directly, rather than going through the system's in-core copy of the label. This option may allow a label to be installed on a disk without kernel support for a label, such as when labels are first installed on a system; it must be used when first installing a label on a disk. The specific effect of -r is described under each command. The read and install forms also support the -B option to install bootstrap code. These variants are described later.

The first form of the command (read) is used to examine the label on the named disk drive (e.g. sd0 or /dev/rsd0c). It will display all of the parameters associated with the drive and its partition layout. Unless the -r flag is given, the kernel's in-core copy of the label is displayed; if the disk has no label, or the partition types on the disk are incorrect, the kernel may have constructed or modified the label. If the -r flag is given, the label from the raw disk will be displayed rather than the in-core label.

The second form of the command, with the -w flag, is used to write a standard label on the designated drive. The required arguments to disklabel are the drive to be labelled (e.g. sd0), and the drive type as described in the disktab(5) file. The drive parameters and partitions are taken from that file. If different disks of the same physical type are to have different partitions, it will be necessary to have separate disktab entries describing each, or to edit the label after installation as described below. The optional argument is a pack identification string, up to 16 characters long. The pack id must be quoted if it contains blanks. If the -r flag is given, the disk sectors containing the label and bootstrap will be written directly. A side-effect of this is that any existing bootstrap code will be overwritten and the disk rendered unbootable. If -r is not specified, the existing label will be updated via the in-core copy and any bootstrap code will be unaffected. If the disk does not already have a label, the -r flag must be used. In either case, the kernel's in-core label is replaced.

For a virgin disk that is not known to disktab(5), disktype can be specified as “auto”. In this case, the driver is requested to produce a virgin label for the disk. This might or might not be successful, depending on whether the driver for the disk is able to get the required data without reading anything from the disk at all. It will likely succeed for all SCSI disks, most IDE disks, and vnode devices. Writing a label to the disk is the only supported operation, and the disk itself must be provided as the canonical name, i.e. not as a full path name.

An existing disk label may be edited by using the -e flag. The label is read from the in-core kernel copy, or directly from the disk if the -r flag is also given. The label is formatted and then supplied to an editor for changes. If no editor is specified in an EDITOR environment variable, vi(1) is used. When the editor terminates, the formatted label is reread and used to rewrite the disk label. Existing bootstrap code is unchanged regardless of whether -r was specified.

With the -R flag, disklabel is capable of restoring a disk label that was formatted in a prior operation and saved in an ascii file. The prototype file used to create the label should be in the same format as that produced when reading or editing a label. Comments are delimited by # and newline. As with -w, any existing bootstrap code will be clobbered if -r is specified and will be unaffected otherwise.

The -NW flags for disklabel explicitly disallow and allow, respectively, writing of the pack label area on the selected disk.

The final three forms of disklabel are used to install boostrap code on machines where the bootstrap is part of the label. The bootstrap code is comprised of one or two boot programs depending on the machine. The -B option is used to denote that bootstrap code is to be installed. The -r flag is implied by -B and never needs to be specified. The name of the boot program(s) to be installed can be selected in a variety of ways. First, the names can be specified explicitly via the -b and -s flags. On machines with only a single level of boot program, -b is the name of that program. For machines with a two-level bootstrap, -b indicates the primary boot program and -s the secondary boot program. If the names are not explicitly given, standard boot programs will be used. The boot programs are located in /usr/mdec. The names of the programs are taken from the ``b0'' and ``b1'' parameters of the disktab(5) entry for the disk if disktype was given and its disktab entry exists and includes those parameters. Otherwise, boot program names are derived from the name of the disk. These names are of the form basenameboot for the primary (or only) bootstrap, and bootbasename for the secondary bootstrap; for example, /usr/mdec/sdboot and /usr/mdec/bootsd if the disk device is sd0.

The first of the three boot-installation forms is used to install bootstrap code without changing the existing label. It is essentially a read command with respect to the disk label itself and all options are related to the specification of the boot program as described previously. The final two forms are analogous to the basic write and restore versions except that they will install bootstrap code in addition to a new label.

FILES
/etc/disktab
/usr/mdec/xxboot
/usr/mdec/bootxx

EXAMPLES
    disklabel sd0

Display the in-core label for sd0 as obtained via /dev/rsd0c.

    disklabel -w -r /dev/rsd0c sd2212 foo

Create a label for sd0 based on information for ``sd2212'' found in /etc/disktab. Any existing bootstrap code will be clobbered.

    disklabel -e -r sd0

Read the on-disk label for sd0, edit it and reinstall in-core as well as on-disk. Existing bootstrap code is unaffected.

    disklabel -r -w sd0 auto

Try to auto-detect the required information from sd0, and write a new label to the disk. Use another disklabel -e command to edit the partitioning and file system information.

    disklabel -R sd0 mylabel

Restore the on-disk and in-core label for sd0 from information in mylabel. Existing bootstrap code is unaffected.

    disklabel -B sd0

Install a new bootstrap on sd0. The boot code comes from /usr/mdec/sdboot and possibly /usr/mdec/bootsd. On-disk and in-core labels are unchanged.

    disklabel -w -B /dev/rsd0c -b newboot sd2212

Install a new label and bootstrap. The label is derived from disktab information for ``sd2212'' and installed both in-core and on-disk. The bootstrap code comes from the file /usr/mdec/newboot.

SEE ALSO
disktab(5), disklabel(5)

DIAGNOSTICS
The kernel device drivers will not allow the size of a disk partition to be decreased or the offset of a partition to be changed while it is open. Some device drivers create a label containing only a single large partition if a disk is unlabeled; thus, the label must be written to the ``a'' partition of the disk while it is open. This sometimes requires the desired label to be set in two steps, the first one creating at least one other partition, and the second setting the label on the new partition while shrinking the ``a'' partition.

On some machines the bootstrap code may not fit entirely in the area allocated for it by some filesystems. As a result, it may not be possible to have filesystems on some partitions of a ``bootable'' disk. When installing bootstrap code, disklabel checks for these cases. If the installed boot code would overlap a partition of type FS_UNUSED it is marked as type FS_BOOT. The newfs(8) utility will disallow creation of filesystems on FS_BOOT partitions. Conversely, if a partition has a type other than FS_UNUSED or FS_BOOT, disklabel will not install bootstrap code that overlaps it.

BUGS
When a disk name is given without a full pathname, the constructed device name uses the ``a'' partition on the tahoe, the ``c'' partition on all others.

For the i386 architecture, the primary bootstrap sector contains an embedded fdisk table. Disklabel takes care to not clobber it when installing a bootstrap only (-B), or when editing an existing label (-e), but it unconditionally writes the primary bootstrap program onto the disk for -w or -R, thus replacing the fdisk table by the dummy one in the bootstrap program. This is only of concern if the disk is fully dedicated, so that the BSD disklabel starts at absolute block 0 on the disk.