devlabel
DEVLABEL(8) DEVLABEL(8)
NAME
devlabel - Consistent/persistent storage device access through symlink-
ing
SYNOPSIS
devlabel [action] [options]
DESCRIPTION
devlabel is a script which manages symlinks to storage devices on your
system. This is accomplished by utilizing the inherent unique identi-
fiers (UUID) that each device *should* have in order to maintain a cor-
rectly pointing symlink in the event that the device name changes (eg.
/dev/sdc1 becomes /dev/sdd1). By adding entries using devlabel its
users can instead reference all devices by their symlink and no longer
care what the true name of their device is. Similary, consistent raw
device access can also be guaranteed through use of devlabel as it
treats entries in the format of /dev/raw/raw# as a special form of sym-
link so that each raw device can consistently be bound to the correct
storage device.
devlabel works with both IDE and SCSI storage and has been integrated
into the hotplug system to allow USB, IEEE1394 (firewire) and PCI
detection and consistency.
ACTIONS
reload Affirms the mappings of symlinks to storage devices. If a
device cannot be found by its UUID, the existing symlink will be
deleted. If the device name has changed, it will update the
symlink. Both start and restart are synonyms for this command.
add [-d device] [-s symlink]
Adds the entry symlink -> device and determines the UUID.
Alternatively, you can add by UUID if the correct UUID of the
device is known. For this type of add you specify the [-s sym-
link] and the [-u UUID] Note that you must use the option
[--partnum partition#] to specify which partition of the device
with that UUID should have a symlink pointed to it. If no part-
num is specified, the symlink is pointed just to the name of the
disk itself.
remove [-s symlink]
Removes the entry symlink
status Returns the current status of all symlinks that are set to be
configured. If the symlink is a raw device, it will return what
major/minor combination it is bound to.
printid [-d device]
Returns the identifier that devlabel finds for the device in
question.
OPTIONS
-d <device>
The name of the device to be used for the specified action.
-s <symlink>
The name of the symlink to be used.
-u <uuid>
The UUID of the device to be used. The -u option is currently
only recognized during an add command.
--partnum <partition#>
The partition number parameter is only supported in conjunction
with the -u <uuid> option while doing an add command. Since
UUIDs are currently disk specific and not partition specific,
devlabel must be told through this parameter which partition of
the disk to have the symlink pointed at. If no value is given,
the symlink will be pointed at just the disk (e.g. /dev/sdc
instead of /dev/sdc5).
--automount
This option is only available during an add. If specified, it
will cause this device to be automatically mounted every time
devlabel is restarted if, within /etc/fstab , a corresponding
entry is found for that symlink. If no entry is found, nothing
will happen. Automount is stored as an option in the 4th field
of the /etc/sysconfig/devlabel configuration file.
-q Quiet.
FILES
/etc/sysconfig/devlabel
The file containing all symlinks/rawdevices bindings to be made.
This file should not be edited by hand. Instead, the devlabel
program should be used to manipulate it.
METHODOLOGY
To determine the unique identifier associated with a SCSI device,
devlabel uses the program /usr/bin/scsi_unique_id. If this program
cannot determine a unique identifier for your block device then the
device cannot be used with devlabel.
Unique identifiers for SCSI devices are read from Page83 and Page80 of
your SCSI block device as based on the SCSI standard. This program
will look for identifiers in the order of: page 83 type 3, page 83 type
2, page 83 type 1, page 80, and then lastly page 83 type 0.
Unique identifiers for IDE devices are taken from /proc/ide/hd#/iden-
tify.
Both IDE and SCSI identifiers will be prefaced with their identifier
type and concluded with the model name of the storage device. This
entire string constitutes the device's UUID.
Note that all partitions from the same device will have the same unique
identifier but will be distinguishable from each other by their parti-
tion number.
If two or more storage devices on your system return the same UUID,
none of them may be used with devlabel
USAGE
Hotpluggable storage devices which show themselves as SCSI devices
internally (eg. USB, firewire, but not PCMCIA) should have carefully
chosen symlink names (eg. /dev/smartcardreader) as the UUIDs pulled
from these devices are most likely being supplied by the connection
hardware and not by the actual storage media itself.
If symlinks setup by devlabel are to be used within /etc/fstab , these
symlinks must be located on the root partition so that they are access-
able by /etc/rc.d/rc.sysinit during the boot-up process.
LIMITATIONS
Devlabel does not currently handle interdisk renaming events. These
events occur when one partition within a disk gets deleted and all of
the partitions after it shift down a number (e.g. when /dev/sda6 is
deleted, /dev/sda7 becomes /dev/sda6). Currently IA-64 systems utilize
the Intel Extensible Firmware Interface (EFI) Spec for partition spe-
cific identifiers which would make this functionality possible, but
until the spec becomes more widely used, its usage will not be adopted
(or worthwhile) within devlabel.
UUID NAMING CONVENTION
UUIDs are prefaced with a tag to alert devlabel as to where the identi-
fier came from. Currently, devlabel supports SCSI firware identifiers
and IDE identifiers.
S83.3 SCSI Page 83, Type 3 identifier
S83.2 SCSI Page 83, Type 2 identifier
S83.1 SCSI Page 83, Type 1 identifier
S80 SCSI Page 80 identifier (Serial Number)
S83.0 SCSI Page 83, Type 0 identifier
I IDE identifier as found in words 11-20 of
/proc/ide/<device>/identify
AUTHOR
Gary Lerhaupt (gary_lerhaupt@dell.com)
Version 0.4 January 2003 DEVLABEL(8)
