sg_map man page on Alpinelinux
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SG_MAP(8) SG3_UTILS SG_MAP(8)
NAME
sg_map - displays mapping between Linux sg and other SCSI devices
SYNOPSIS
sg_map [-a] [-h] [-i] [-n] [-scd] [-sd] [-sr] [-st] [-V] [-x]
DESCRIPTION
Sometimes it is difficult to determine which SCSI device a sg device
name (e.g. /dev/sg0) refers to. This command loops through the sg
devices and finds the corresponding SCSI disk, cdrom or tape device
name (if any). Scanners are an example of SCSI devices that have no
alternate SCSI device name apart from their sg device name.
This utility is deprecated and has not been updated for years, only
very obvious bugs will be fixed. Unless a very old version of Linux is
being used (e.g. 2.4 series or earlier), then please use a utility
like lsscsi(8) or the facilities offered by udev(8).
OPTIONS
-a assume the sg devices have alphabetical device names and loop
through /dev/sga, /dev/sgb, etc. Default is numeric scan. Note
that sg device nodes with an alphabetical index have been depre‐
cated since the Linux kernel 2.2 series.
-h print usage message then exit.
-i in addition do a standard INQUIRY and output vendor, product and
revision strings for devices that are found.
-n assume the sg devices have numeric device names and loop through
/dev/sg0, /dev/sg1, etc. Default is numeric scan
-scd display mappings to SCSI cdrom device names of the form
/dev/scd0, /dev/scd1 etc
-sd display mappings to SCSI disk device names
-sr display mappings to SCSI cdrom device names of the form
/dev/sr0, /dev/sr1 etc
-st display mappings to SCSI tape device names
-V print out version string then exit (without further ado).
-x after each active sg device name is displayed there are five
digits: <host_number> <bus> <scsi_id> <lun> <scsi_type>
NOTES
If no options starting with "-s" are given then the mapping to all SCSI
disk, cdrom and tape device names is shown.
If the device file system (devfs) is present a line noting this is out‐
put. The "native" devfs scsi hierarchy makes the relationship between a
sg device name and any corresponding disk, cdrom or tape device name
easy to establish. This replaces the need for this command. However
many applications will continue to look for Linux SCSI device names in
their traditional places. [Devfs supplies a compatibility daemon called
devfsd whose default configuration adds back the Linux device names in
their traditional positions.
Quite often the mapping information can be derived by observing the
output of the command: "cat /proc/scsi/scsi". However if devices have
been added since boot this can be deceptive.
In the Linux kernel 2.6 series something close to the mapping shown by
this utility can be found by analysing sysfs. The main difference is
that sysfs analysis will show the mapping between sg nodes and other
SCSI device nodes in terms of major and minor numbers. While major 8,
minor 16 will usually be /dev/sdb this is not necessarily so. Facili‐
ties associated with udev may assign major 8, minor 16 some other
device node name. This version of sg_map has been extended to cope with
sparse disk device node names of the form "/dev/sd<str>" where <str>
can be one of [a-z,aa-zz,aaa-zzz]. See the sg_map26 utility for a more
precise way (i.e. less directory scanning) for mapping between sg
device names and higher level names; including finding user defined
names.
This utility was written at a time when hotplugging of SCSI devices was
not supported in Linux. It used a simple algorithm to scan sg device
nodes in ascending numeric or alphabetical order, stopping after there
were 5 consecutive errors.
In the Linux kernel 2.6 series, this utility uses sysfs to find which
sg device nodes are active and only checks those. Hence there can be
large "holes" in the numbering of sg device nodes (e.g. after an
adapter has been removed) and still all active sg device nodes will be
listed. This utility assumes that sg device nodes are named using the
normal conventions and searches from /dev/sg0 to /dev/sg4095 inclusive.
EXAMPLES
My system has a SCSI disk, a cd writer and a dvd player:
$ sg_map
# Note: the devfs pseudo file system is present
/dev/sg0 /dev/sda
/dev/sg1 /dev/sr0
/dev/sg2 /dev/sr1
In order to find which sg device name corresponds to the disk:
$ sg_map -sd
# Note: the devfs pseudo file system is present
/dev/sg0 /dev/sda
/dev/sg1
/dev/sg2
The "-x" option gives the following output:
sg_map -x
# Note: the devfs pseudo file system is present
/dev/sg0 1 0 1 0 0 /dev/sda
/dev/sg1 2 0 4 0 5 /dev/sr0
/dev/sg2 2 0 6 0 5 /dev/sr1
When a SCSI scanner is added the output becomes:
$ sg_map
# Note: the devfs pseudo file system is present
/dev/sg0 /dev/sda
/dev/sg1 /dev/sr0
/dev/sg2 /dev/sr1
/dev/sg3
By process of elimination /dev/sg3 must be the scanner.
EXIT STATUS
The exit status of sg_map is 0 when it is successful. Otherwise see the
sg3_utils(8) man page.
AUTHOR
Written by Douglas Gilbert
REPORTING BUGS
Report bugs to <dgilbert at interlog dot com>.
COPYRIGHT
Copyright © 2000-2013 Douglas Gilbert
This software is distributed under the GPL version 2. There is NO war‐
ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
POSE.
SEE ALSO
sg_map26(8) , scsi_info(8) , scsidev(8) , devfsd(8) , lsscsi(8) ,
udev(7)
sg3_utils-1.36 May 2013 SG_MAP(8)
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