SCSIDEV(8) System Manager's Manual SCSIDEV(8)
# # $Id: scsidev.8,v 126.96.36.199 2004/02/18 10:08:59 garloff Exp $ #
scsidev - populate /dev/scsi with device names that are persistent
against SCSI configuration changes.
scsidev [ -f ] [ -n ] [ -d ] [ -l ] [ -L ] [ -m mode ] [ -c mxms ] [ -A
aliasfile ] [ -r ] [ -M ] [ -e ] [ -o ] [ -s ] [ -v ] [ -q ] [ -h ]
scsidev is a utility that is used to guarantee that the same device
node can be used for the same scsi device, no matter what other scsi
devices are added or removed from the scsi chain. The need for this
tool arose because device numbers are assigned dynamicly at boot time,
and if a new disk were added to the system (or if some disk didn't spin
up), then fixed device nodes would cause the wrong filesystems to be
mounted, checked, etc. This can also result in security holes, as some
device nodes may have permissions that allow general users access to
the raw device, and if the mappings were to change, users would be able
to access different devices.
scsidev is designed to be used once each time the system boots. It
will scan all of the detected devices on the system, and determine a
immutable name that will represent the device. It first checks to see
if a node by this name already exists - if this is the case, then it
checks to see if the major/minor numbers are correct. If a change in
the minor number is required, then a new device is created with the
correct major/minor numbers, and in addition, any ownership and permis-
sions for the old device are applied to the new device.
Once this process is complete, then scsidev will scan all of the
entries in the /dev/scsi directory, and see if any of them are for
devices nodes which were added for devices that are not active. The
permissions of inactive devices are stored in a .shadow. file and the
device node is removed as a security precaution, since these might have
permissions that would allow people to access devices that they should
not be able to access. This is the default behaviour and is considered
ideal for most cases, as it preserves the ownership and permissions of
the files and is secure.
The so called sanitizing can be influenced by the options -f -d -n.
When you rescan the bus by using the rescan-scsi-bus.sh script or manu-
ally by using commands like
echo "scsi add-single-device C B T U" >/proc/scsi/scsi
(C = Controller (host) no., B = Bus (Channel), T = Target (SCSI ID), U
= Unit (SCSI LUN)) after the system is booted, then you will have to
rerun scsidev so that the device nodes for the newly detected devices
are properly updated.
The device nodes that scsidev creates look something like
"sdh4-334c0i0l0p1". In this case, the various components of the name
represent physical attributes about the device or the host adapter to
which it is connected. To begin with, the "h4" indicates that it is
connected to an Adaptec 1542. The "-334" is a means of identifying
which 1542 the device is attached to (since linux supports more than
one 1542 in the system at the same time) and (in this case) corresponds
to the IO Port number (hex) of the controller (this is the host adapter
id number). The "c0" represents the channel number (since some host
adapters can drive multiple scsi busses). The "i0l0" indicates that
this device is scsi ID 0, with lun 0. Finally the "p1" indicated par-
tition number 1.
-f Flush everything from /dev/scsi prior to scanning the detected
devices. This means that new device nodes will be created even
if the old ones were OK.
-d Sanitize by deletion. The .shadow. backup files will not be cre-
ated, so you loose all non-default ownership/permissions that
may have been set.
-n Don't touch device nodes for non-existing SCSI devices. This
might have security implications and is therefore not recom-
-l Symbolic link mode. Instead of creating nodes, symbolic links
are created which point to the older /dev/sda1 types of device
nodes. When using this option, the permissions of the /dev/XXX
device nodes will be changed to match the ones stored in
/dev/scsi/YYY file, if present.
-L Use symbolic names for the aliases assigned through the
/etc/scsi.alias settings (see below).
Specifies the mode (permissions) for new entries that need to be
Normally, if scsidev fails to open a generic scsi device, it
finishes its scan for devices. With this option, it goes on
until maxmiss missing devices were found. This is only used, if
you don't have the /proc/scsi/scsi extensions for large disks.
Use an alternative file instead of the default /etc/scsi.alias
-r scsidev does first probe the generic and then -- if appropriate
-- the other highlevel devices (st, sd, sr). For removable
devices (sd, sr, osst), this will fail, if no medium is
inserted, so scsidev can not ensure, that the device actually
corresponds to the one reported by the sg interface. After the
first device scan, the situation is clear and scsidev will do
the right guesses. So using -r in bootup scripts is safe. After
you removed devices from your SCSI config, it isn't safe any
longer. This is only needed, if you don't have the
/proc/scsi/scsi extensions for large disks.
-M Multipath support. scsidev normally does complain if a line in
scsi.alias matches more than one device and does not create an
alias then. With multipatch support on, it just creates the
alias for the first device found matching the description in the
-e Instructs scsidev to use devfs like names, i.e. using the cbtu
(controller, bus, target unit) chraracters instead of hcil
(host, channel, scsi Id, scsi Lun) to build the device name.
-o Instructs scsidev to use scd instead of sr for the old names of
CD-ROM devices (relevant for symlink mode).
-s Tells scsidev
to print out the device serial numbers of all detected devices
on the system. This string can be useful for forming aliases.
If supported, also the WWID is printed.
-v Verbosity. Mainly used for debugging purposes. Use multiple
times for more verbosity.
-q Be Quiet. Only produce output, if there are errors.
-h Output short usage summary and copyright info and exit.
It was intended that scsidev be useful without any configuration at
all. There are times when it is much more convenient to have symbolic
names for various devices. These symbolic names should track devices
as they get moved from controller to another, or even if the SCSI id
number is changed.
The general idea is that there is a configuration file /etc/scsi.alias
which lists the aliases that scsidev will attempt to create. Each line
represents a separate alias, and consists of a series of tokens. Here
are a couple of example entries:
serial_number="DX908FK", devtype=disk, alias=fourgig
manufacturer=WANGTEK, devtype=tape, alias=qictape
id=2, devtype=generic, alias=cdwriter
The minimum requirements are that each line have a alias and a devtype
field. The alias will be used to build the pathnames, and the devtype
must be one of disk, tape, osst, cdrom or generic.
The additional qualifiers are optional, and you must specify a suffi-
cient number of them such that the alias will match only one device.
The allowable qualifiers are:
Specifies the name of the manufacturer. This is the same string
that is printed at boot time, and is also available through
model= Specifies the model number of the device. This is the same
string that is printed at boot time, and is also available
rev= Specifies the revision string of the device. This is the same
string that is printed at boot time, and is also available
Specifies the serial number of the device. Not all devices
implement this, but for those that do it provides a convenient
mechanism to uniquely identify a device no matter where it is
found on the scsi chain. The serial number is the one reported
in INQUIRY page 0x80 with EVPD=1. It is displayed by scsidev -s
wwid= Specifies the WWID number of a device. This is a 64bit world
wide unique number, which is supported by SCSI-3 devices and
reported via INQUIRY page 0x83 with EVPD=1. If supported, it's
displayed by scsidev -s .
id= Specifies the scsi id number for the device.
lun= Specifies the lun for the device. Most devices have a lun of 0,
and it is only special devices such as cd changers that imple-
ment multiple lun devices.
chan= Specifies which channel (i.e. which bus) for host adapters that
drive multiple channels.
Specifies the partition number for disk drives. If unspecified,
the alias will match all partitions on the disk.
Specifies the host adapter id number (0x334 part of
sdh4-334c0i0l0p1 for example).
Specifies the unique number that each host adpater driver
returns. Generally this number is always 0 except for cases
where the driver supports more than one device of a given type
on the system.
Specifies the host adapter driver name. (Only the given chars
need to match, so you may omit the version number.)
Note that the specifiers which take string arguments can be quoted if
the string contains whitespace.
For disks, aliases for all partitions will be created (unless parti-
tion= is specified). The names get a -pN suffix (N indicating the num-
ber of the partition. For tapes (st and osst type), the non-rewinding
variant with an n prepended will be created automatically.
... was written by Eric Youngdale <ericATaib.com>
... was enhanced by Kurt Garloff <garloffATsuse.de>
Probably there are ...
The BIOS and LILO do not have the knowledge about the SCSI devices at
boot time, so you still have to ensure, your kernel can be loaded when
you insert a new disk.
This program is free software. You can use it under the terms of the
GNU GPL (General Public License) Version 2 (or any later version, at
your option). Note, that the GNU GPL implies, that there is NO WAR-
RANTY at all. Full text of the GPL can be found in /usr/share/common-
scsidev is available from
and will also be put on standard anonymous ftp servers.
The old version is available from
Version 2.29 June 2003 SCSIDEV(8)