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SG_READ_ATTR(8) SG3_UTILS SG_READ_ATTR(8)
NAME
sg_read_attr - send SCSI READ ATTRIBUTE command
SYNOPSIS
sg_read_attr [--cache] [--enumerate] [--ea=EA] [--filter=FL] [--first=FAI] [--help]
[--hex] [--in=FN] [--lvn=LVN] [--maxlen=LEN] [--pn=PN] [--quiet] [--raw] [--readonly]
[--sa=SA] [--verbose] [--version] DEVICE
DESCRIPTION
Sends a SCSI READ ATTRIBUTE command to DEVICE and outputs the data returned. This command
was introduced in SPC-3 revision 1 and thus is applicable to all SCSI devices. In practice
it is used mainly for tape systems. This utility is based on the SPC-5 draft standard, re-
vision 17 (spc5r17.pdf).
OPTIONS
Arguments to long options are mandatory for short options as well.
-c, --cache
sets the CACHE bit in the READ ATTRIBUTE cdb. This instructs the device server to
return cached attributes. By default that bit is cleared which instructs the device
server not to return cached attributes.
-e, --enumerate
enumerates all known attributes and service actions. Attributes include an identi-
fier, length, format and a name as defined by T10. If DEVICE is given then it is
ignored.
-E, --ea=EA
where EA is an element address which is placed in the READ ATTRIBUTE cdb. This
field is only found in SMC-2 and SMC-3 drafts for medium changers usually associ-
ated with tape libraries. By default this field is set to zero.
-f, --filter=FL
where FL is an attribute identifier in the range 0 to 65535 or -1. Attribute iden-
tifiers are typically given in hexadecimal in which case the hex number should be
prefixed by "0x" or has a trailing "h". "-1" is the default value and means 'match
all'; for all other values of FL on the matching attribute is output.
-F, --first=FAI
where FAI is the "first attribute identifier" field in the cdb. It seems as though
the intent of this field is that only attributes whose identifiers are equal to or
greater than FAI are returned. The default value of FAI is zero. Attributes are re-
turned in ascending identifier order.
-h, --help
output the usage message then exit.
-H, --hex
output the response in hexadecimal to stdout. When used once the whole response is
output in ASCII hexadecimal with a leading address (starting at 0) on each line.
When used twice each attribute descriptor in the response is output separately in
hexadecimal. When used thrice the whole response is output in hexadecimal with no
leading address (on each line).
Output generated by '-HHH' (or --hex used three times) can be redirected to a file.
That file will be in suitable format for --in=FN to use in a later invocation.
-i, --in=FN
FN is treated as a file name (or '-' for stdin) which contains ASCII hexadecimal or
binary representing the response to a READ ATTRIBUTE command with service action
0x0 (i.e (fetch) attribute values). When this option is given then DEVICE (if also
given) is ignored.
By default FN is assumed to contain ASCII hexadecimal arranged as bytes which a
space, tab or comma delimited. All characters from (and including) "#" to the end
of line are ignored. If the --raw option is also given then FN is assumed to con-
tain binary data. When the --raw option is given then after processing the input
the internal raw variable is reset to 0 so it has no effect on the output.
Since the READ ATTRIBUTE response does not contain the service action number that
it is a response to, then the --sa=SA should be given (if not service action 0 (at-
tribute values) is assumed.
-l, --lvn=LVN
where LVN is placed in the "logical volume number" field of the cdb. The default
value is zero which is required to be the logical volume number if the device only
has one volume.
-m, --maxlen=LEN
where LEN is the (maximum) response length in bytes. It is placed in the cdb's "al-
location length" field. If not given (or LEN is zero) then 8192 is used. The maxi-
mum allowed value of LEN is 1048576.
-p, --pn=PN
where PN is placed in the "partition number" field of the cdb. If the DEVICE only
has one partition then its partition number must be zero. The default value of PN
is zero.
-q, --quiet
this option reduces the amount of information output. For example when used once
(SA=0), it suppresses the header line announcing the output of attributes; when
used twice it suppresses the name of each attribute, leaving only the associated
attribute values (or strings).
-r, --raw
output the SCSI response (i.e. the data-out buffer) in binary (to stdout).
-R, --readonly
open the DEVICE read-only (e.g. in Unix with the O_RDONLY flag). The default is to
open it read-write.
-s, --sa=SA
where SA is placed on the "service action" field of the cdb. Values of 0 to 63 are
accepted with a default of 0. spc5r08.pdf defines five service actions: 0 for at-
tributes values ; 1 for an attribute list (names, not values), 2 for the logical
volume list; 3 for the partition list; 4 is restricted for SMC-3; and 5 for the
supported attribute list.
Alternatively an acronym can be given for SA. The acronym should be one of "av",
"al", "lvl", "pn", "smc" or "sa" for service actions 0 to 5 respectively. The acro-
nyms can also be given in upper case.
-v, --verbose
increase the level of verbosity, (i.e. debug output).
-V, --version
print the version string and then exit.
NOTES
Only tape systems seem to implement the SCSI READ ATTRIBUTE command. The vast majority of
its definition is in the SPC standard so other device types could use it.
Much of the information provided by READ ATTRIBUTE can also be found in pages returned by
LOG SENSE (see the sg_logs utility) and in the VPD pages returned by the INQUIRY command.
EXAMPLES
To list the attributes of a tape drive whose DEVICE is /dev/sg1 , the following could be
used:
# sg_read_attr -s al /dev/sg1
Attribute list:
Remaining capacity in partition [MiB]
Maximum capacity in partition [MiB]
TapeAlert flags
Load count
MAM space remaining [B]
Assigning organization
Format density code
...
To check the number of partitions:
# sg_read_attr -s pl /dev/sg1
Partition number list:
First partition number: 0
Number of partitions available: 2
And to see the attribute values (which is the default service action):
# sg_read_attr /dev/sg1
Attribute values:
Remaining capacity in partition [MiB]: 1386103
Maximum capacity in partition [MiB]: 1386103
TapeAlert flags: 0
....
To redirect the attribute values response to a file for later decoding:
# sg_read_attr -HHH /dev/sg1 > av.hex
And later the response held in the av.hex file could be decoded with:
# sg_read_attr -s av --in=av.hex
Attribute values:
Remaining capacity in partition [MiB]: 1386103
Maximum capacity in partition [MiB]: 1386103
TapeAlert flags: 0
....
EXIT STATUS
The exit status of sg_read_attr is 0 when it is successful. Otherwise see the sg3_utils(8)
man page.
AUTHORS
Written by Douglas Gilbert.
REPORTING BUGS
Report bugs to <dgilbert at interlog dot com>.
COPYRIGHT
Copyright (C) 2016-2020 Douglas Gilbert
This software is distributed under a FreeBSD license. There is NO warranty; not even for
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
SEE ALSO
sg_vpd,sg_logs(sg3_utils)
sg3_utils-1.46 December 2020 SG_READ_ATTR(8)
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