freebsd-src/lib/geom/label/glabel.8

.\" Copyright (c) 2004-2005 Pawel Jakub Dawidek <pjd@FreeBSD.org>
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.Dd April 19, 2024
.Dt GLABEL 8
.Os
.Sh NAME
.Nm glabel
.Nd "disk labelization control utility"
.Sh SYNOPSIS
.Nm
.Cm create
.Op Fl v
.Ar name
.Ar dev
.Nm
.Cm destroy
.Op Fl fv
.Ar name ...
.Nm
.Cm label
.Op Fl v
.Ar name
.Ar dev
.Nm
.Cm stop
.Op Fl fv
.Ar name ...
.Nm
.Cm clear
.Op Fl v
.Ar dev ...
.Nm
.Cm dump
.Ar dev ...
.Nm
.Cm refresh
.Ar dev ...
.Nm
.Cm list
.Nm
.Cm status
.Nm
.Cm load
.Nm
.Cm unload
.Sh DESCRIPTION
The
.Nm
utility is used for GEOM provider labelization.
A label can be set up on a GEOM provider in two ways:
.Dq manual
or
.Dq automatic .
When using the
.Dq manual
method, no metadata are stored on the devices, so a label has to be configured
by hand every time it is needed.
The
.Dq automatic
method uses on-disk metadata to store the label and detect it automatically in
the future.
.Pp
This GEOM class also provides volume label detection for file systems.
Those labels cannot be set with
.Nm ,
but must be set with the appropriate file system utility, e.g.\& for UFS
the file system label is set with
.Xr tunefs 8 .
Currently supported file systems are:
.Pp
.Bl -bullet -offset indent -compact
.It
UFS1 volume names (directory
.Pa /dev/ufs/ ) .
.It
UFS2 volume names (directory
.Pa /dev/ufs/ ) .
.It
UFS1 file system IDs (directory
.Pa /dev/ufsid/ ) .
.It
UFS2 file system IDs (directory
.Pa /dev/ufsid/ ) .
.It
MSDOSFS (FAT12, FAT16, FAT32) (directory
.Pa /dev/msdosfs/ ) .
.It
CD ISO9660 (directory
.Pa /dev/iso9660/ ) .
.It
EXT2FS (directory
.Pa /dev/ext2fs/ ) .
.It
NTFS (directory
.Pa /dev/ntfs/ ) .
.It
Swap Linux (directory
.Pa /dev/swaplinux/ ) .
.El
.Pp
Support for partition metadata is implemented for:
.Pp
.Bl -bullet -offset indent -compact
.It
GPT labels (directory
.Pa /dev/gpt/ ) .
.It
GPT UUIDs (directory
.Pa /dev/gptid/ ) .
.El
.Pp
Generic disk ID strings are exported as labels in the format
.Pa /dev/diskid/GEOM_CLASS-ident
e.g.
.Pa /dev/diskid/DISK-6QG3Z026  .
.Pp
Generic labels created and managed solely by
.Nm
are created in the
.Pa /dev/label/
directory.
Note that generic, automatic labels occupy some space on the device
and thus should not be added to a device already containing a file system.
In particular,
.Nm
reserves the last sector of the device to store the label information.
If the device already contains a file system,
.Nm
will overwrite the last sector, possibly damaging the file system, and the
file system may later overwrite the label sector.
Instead, create a label before initializing the file system, and initialize
that file system on the device created by
.Nm
under the
.Pa /dev/label/
directory.
Then the file system will correctly account for the space occupied by the
generic label,
since the
.Nm
device will be one sector smaller than the device from which it was created.
.Pp
Note that for all label types, nested GEOM classes will cause additional
device nodes to be created, with context-specific data appended to their
names.
E.g. for every node like
.Pa /dev/label/bigdisk
there will be additional entries for any partitions which the device
contains, like
.Pa /dev/label/bigdiskp1
and
.Pa /dev/label/bigdiskp1a .
.Pp
.Nm
requires write access to a device to create, modify, and destroy
"automatic" labels.
It will fail to persist changes if they are applied while a file
system on the device is currently mounted.
To ensure that modifications are stored across a reboot, the file system
needs to be unmounted first.
If the device holds the system's root file system, entering into
single user mode and mounting in read-only mode is required to persist
the change.
.Pp
The first argument to
.Nm
indicates an action to be performed:
.Bl -tag -width ".Cm destroy"
.It Cm create
Create temporary label
.Ar name
for the given provider.
This is the
.Dq manual
method.
The kernel module
.Pa geom_label.ko
will be loaded if it is not loaded already.
.It Cm label
Set up a label
.Ar name
for the given provider.
This is the
.Dq automatic
method, where metadata is stored in a provider's last sector.
The kernel module
.Pa geom_label.ko
will be loaded if it is not loaded already.
.It Cm stop
Turn off the given label by its
.Ar name .
This command does not touch on-disk metadata!
.It Cm destroy
Same as
.Cm stop .
.It Cm clear
Clear metadata on the given devices.
.It Cm dump
Dump metadata stored on the given devices.
.It Cm refresh
Refresh / rediscover metadata from the given devices.
.It Cm list
See
.Xr geom 8 .
.It Cm status
See
.Xr geom 8 .
.It Cm load
See
.Xr geom 8 .
.It Cm unload
See
.Xr geom 8 .
.El
.Pp
Additional options:
.Bl -tag -width indent
.It Fl f
Force the removal of the specified labels.
.It Fl v
Be more verbose.
.El
.Sh SYSCTL VARIABLES
The following
.Xr sysctl 8
variables can be used to control the behavior of the
.Nm LABEL
GEOM class.
The default value is shown next to each variable.
.Bl -tag -width indent
.It Va kern.geom.label.debug : No 0
Debug level of the
.Nm LABEL
GEOM class.
This can be set to a number between 0 and 2 inclusive.
If set to 0 minimal debug information is printed, and if set to 2 the
maximum amount of debug information is printed.
.El
.Bl -tag -width indent
.It Va kern.geom.label.*.enable : No 1
Most
.Nm LABEL
providers implement a
.Xr sysctl 8
flag and a tunable variable named in the above format.
This flag controls if the label provider will be active, tasting devices
and creating label nodes in the
.Xr devfs 4
tree.
It is sometimes desirable to disable certain label types if they
conflict with other classes in complex GEOM topologies.
.El
.Sh EXIT STATUS
Exit status is 0 on success, and 1 if the command fails.
.Sh EXAMPLES
The following example shows how to set up a label for disk
.Dq Li da2 ,
create a file system on it, and mount it:
.Bd -literal -offset indent
glabel label -v usr /dev/da2
newfs /dev/label/usr
mount /dev/label/usr /usr
[...]
umount /usr
glabel stop usr
glabel unload
.Ed
.Pp
The next example shows how to set up a label for a UFS file system:
.Bd -literal -offset indent
tunefs -L data /dev/da4s1a
mount /dev/ufs/data /mnt/data
.Ed
.Sh SEE ALSO
.Xr geom 4 ,
.Xr loader.conf 5 ,
.Xr geom 8 ,
.Xr mount 8 ,
.Xr newfs 8 ,
.Xr sysctl 8 ,
.Xr tunefs 8 ,
.Xr umount 8
.Sh HISTORY
The
.Nm
utility appeared in
.Fx 5.3 .
.Sh AUTHORS
.An Pawel Jakub Dawidek Aq Mt pjd@FreeBSD.org