sg_persist - sends a SCSI PERSISTENT RESERVE (IN or OUT) command
to manipulate registrations and reservations
sg_persist--help | --version
This utility allows Persistent reservations and registrations to be
queried and changed. Persistent reservations and registrations are
queried by sub-commands (called "service actions" in SPC-4) of the
SCSI PERSISTENT RESERVE IN (PRIN) command. Persistent reservations and
registrations are changed by sub-commands of the SCSI PERSISTENT RESERVE
OUT (PROUT) command.
There is a two stage process to obtain a persistent reservation. First an
application (an I_T nexus in standard's jargon) must register a reservation
key. If that is accepted (and it should be unless some other I_T nexus has
registered that key) then the application can try and reserve the device.
The reserve operation must specify the reservation key and a "type" (see
the --prout-type=TYPE option).
It is relatively safe to query the state of Persistent reservations and
registrations. With no options this utility defaults to the READ KEYS
sub-command of the PRIN command. Other PRIN sub-commands are
READ RESERVATION, REPORT CAPABILITIES and READ FULL STATUS.
Before trying to change Persistent reservations and registrations users
should be aware of what they are doing. The relevant sections of the
SCSI Primary Commands document (i.e. SPC-4 whose most recent draft is
revision 20 dated 22 May 2009) are sections 5.7 (titled "Reservations"),
6.13 (for the PRIN command) and 6.14 (for the PROUT command). To safeguard
against accidental use, the --out option must be given when a
PROUT sub-command (e.g. --register) is used.
The older SCSI RESERVE and RELEASE commands (both 6 and 10 byte variants)
are not supported by this utility. In SPC-3, RESERVE and RELEASE are
deprecated, replaced by Persistent Reservations. RESERVE and RELEASE
have been removed from SPC-4 and Annex B is provided showing how to
convert to persistent reservation commands. See a utility
called 'scsires' for support of the SCSI RESERVE and RELEASE commands.
The DEVICE is required by all variants of this utility apart
from --help. The DEVICE can be given either as an
argument (typically but not necessarily the last one) or via
the --device=DEVICE option.
SPC-4 does not use the term "sub-command". It uses the term "service action"
for this and for part of a field's name in the parameter block associated
with the PROUT command (i.e. "service action reservation key"). To lessen
the potential confusion the term "sub-command" has been introduced.
Arguments to long options are mandatory for short options as well.
The following options are sorted in alphabetical order, based on their
long option name.
specify the allocation length of the PRIN command. LEN is a hex value.
By default this value is set to the size of the data-in buffer (8192).
This parameter is of use for verification that response to PRIN commands
with various allocation lengths is per section 22.214.171.124 of SPC-4 revision 18.
Valid LEN values are 0-8192.
Clear is a sub-command of the PROUT command. It releases the
persistent reservation (if any) and clears all registrations from the
device. It is required to supply a reservation key that is registered
for this I_T_L nexus (identified by --param-rk=RK).
DEVICE to send SCSI commands to. The DEVICE can either be
provided via this option or via a freestanding argument. For example,
these two: 'sg_persist --device=/dev/sg2' and 'sg_persist /dev/sg2'
output a usage message.
the response to a valid PRIN sub-command will be output in hexadecimal.
By default (i.e. without this option) if the PRIN sub-command is recognised
then the response will be decoded as per SPC-4.
specify that a SCSI PERSISTENT RESERVE IN command is required. This
is the default.
the default action is to do a standard SCSI INQUIRY command and output
make, product and revision strings plus the peripheral device type
prior to executing a PRIN or PROUT command. With this option the
INQUIRY command is skipped.
specify that a SCSI PERSISTENT RESERVE OUT command is required.
set the 'all target ports' (ALL_TG_PT) flag in the parameter block of the
PROUT command. Only relevant for 'register' and 'register and ignore existing
set the 'activate persist through power loss' (APTPL) flag in the parameter
block of the PROUT command. Relevant for 'register', 'register and ignore
existing key' and 'register and move' sub-commands.
specify the reservation key found in the parameter block of the PROUT
command. RK is assumed to be hex (up to 8 bytes long). Default value
is 0. This option is needed by most PROUT sub-commands.
specify the service action reservation key found in the parameter block
of the PROUT command. SARK is assumed to be hex (up to 8 bytes long).
Default value is 0. This option is needed by some PROUT sub-commands.
Preempt is a sub-command of the PROUT command. Preempts the existing
persistent reservation (identified by --param-sark=SARK) with
the registration key that is registered for this I_T_L nexus (identified
by --param-rk=RK). The associated --prout-type=TYPE option
needs to match the type of the reservation.
Preempt and Abort is a sub-command of the PROUT command. Preempts
the existing persistent reservation (identified by --param-sark=SARK)
with the registration key that is registered for this I_T_L nexus (identified
by --param-rk=RK). The associated --prout-type=TYPE option
needs to match the type of the reservation. ACA and other pending tasks are
specify the PROUT command's 'type' argument. Required by
the 'register-move', 'reserve', 'release' and 'preempt (and abort)'
sub-commands. Valid TYPE values: 1-> write exclusive, 3->
exclusive access, 5-> write exclusive - registrants only, 6->
exclusive access - registrants only, 7-> write exclusive - all registrants,
8-> exclusive access - all registrants. Default value is 0 (which is
an invalid type). Each "persistent reservation type" is explained in more
detail in a subsection of that name in the read reservation section of
the PRIN command (section 126.96.36.199 of SPC-4 revision 9).
Read Full Status is a sub-command of the PRIN command. For each registration
with the given SCSI device, it lists the reservation key and associated
information. TransportIDs, if supplied in the response, are decoded.
Read Keys is a sub-command of the PRIN command. Lists all the reservation
keys registered (i.e. registrations) with the given SCSI device. This is
the default sub-command for the SCSI PRIN command.
Read Reservation is a sub-command of the PRIN command. List information
about the current holder of the reservation on the DEVICE. If there
is no current reservation this will be noted. Information about the current
holder of the reservation includes its reservation key, scope and type.
same as --read-full-status.
Register is a sub-command of the PROUT command. It has 3 different
actions depending on associated parameters. a) add a new registration
with '--param-rk=0' and '--param-sark=<new_rk>'; b) Change an existing
registration with '--param-rk=<old_rk>'
and '--param-sark=<new_rk>'; or c) Delete an existing registration
with '--param-rk=<old_rk>' and '--param-sark=0'.
Register and Ignore Existing Key is a sub-command of the PROUT command.
Similar to --register except that when changing a reservation key
the old key is not specified. The '--param-sark=<new_rk>' option should
also be given.
register (another initiator) and move (the reservation held by the current
initiator to that other initiator) is a sub-command of the PROUT command.
It requires the transportID of the other initiator. [The standard uses the
term I_T nexus but the point to stress is that there are two initiators
(the one sending this command and another one) but only one logical unit.]
The --prout-type=TYPE and --param-rk=RK options need to
match that of the existing reservation while --param-sark=SARK
option specifies the reservation key of the new (i.e. destination)
relative target port identifier that reservation is to be moved to by
PROUT 'register and move' sub-command. RTPI is assumed to be hex
in the range 0 to ffff inclusive. Defaults to 0 .
Release is a sub-command of the PROUT command. It releases the
current persistent reservation. The --prout-type=TYPE
and --param-rk=RK options, matching the reservation, must also be
Report Capabilities is a sub-command of the PRIN command. It lists
information about the aspects of persistent reservations that the
Reserve is a sub-command of the PROUT command. It creates a new
persistent reservation (if permitted). The --prout-type=TYPE
and --param-rk=RK options must also be specified.
The TIDS argument can take one of several forms. It can be a
comma (or single space) separated list of ASCII hex bytes representing
a single TransportID as defined in SPC-4. They are usually 24 bytes
long apart from in iSCSI. The TIDS argument may be a transport
specific form (e.g. "sas,5000c50005b32001"). The TIDS argument
may be "-" in which case one or more TransportIDs can be read from stdin.
The TIDS argument may be of the form "file=<name>" in which case
one or more TransportIDs can be read from a file called <name>. See
the "TRANSPORT IDs" section below for more information.
optional when the PROUT register and move sub-command is invoked. If given
it will unregister the current initiator (I_T nexus) after the other initiator
has been registered and the reservation moved to it. When not given the
initiator (I_T nexus) that sent the PROUT command remains registered.
print out cdb of issued commands prior to execution. If used twice
prints out the parameter block associated with the PROUT command prior
to its execution as well. If used thrice decodes given transportID(s)
as well. To see the response to a PRIN command in low level form use
the --hex option.
print out version string. Ignore all other parameters.
output usage message. Ignore all other parameters.
TransportIDs are used in persistent reservations to identify initiators.
The format of a TransportID differs depending on the type of transport
being used. Their format is described in SPC-4 (in draft revision
20 see section 7.5.4).
A TransportID is required for the PROUT 'register and move' sub-command and
the PROUT 'register' sub-command can have zero, one or more TransportIDs.
When the --transport-id=TIDS option is given then the TIDS
argument may be a comma (or single space) separated list of ASCII hex bytes
that represent a single TransportID as defined in SPC-4. Alternatively the
TIDS argument may be a transport specific string starting with
either "fcp,", "spi,", "sbp,", "srp,", "iqn", or "sas,". The "iqn" form is
an iSCSI qualified name. Apart from "iqn" the other transport specific
leadin string may be given in upper case (e.g. "FCP,").
The "fcp," form should be followed by 16 ASCII hex digits that represent an
initiator's N_PORT_NAME. The "spi," form should be followed
by "<scsi_address>,<relative_target_port_identifier>" (both decimal numbers).
The "sbp," form should be followed by 16 ASCII hex digits that represent an
initiator's EUI-64 name. The "srp," form should be followed by 32 ASCII hex
digits that represent an initiator port identifier. The "sas," form should be
followed by 16 ASCII hex digits that represent an initiator's port SAS
There are two iSCSI qualified name forms. The shorter form contains the
iSCSI name of the initiator
port (e.g. "iqn.5886.com.acme.diskarrays-sn-a8675309"). The longer form adds
the initiator session id (ISID in hex) separated by ",i,0x".
For example "iqn.5886.com.acme.diskarrays-sn-a8675309,i,0x1234567890ab".
On the command line to stop punctuation in an iSCSI name being (mis)-
interpreted by the shell, putting the option argument containing the iSCSI
name in double quotes is advised. iSCSI names are encoded in UTF-8 so if
non (7 bit) ASCII characters appear in the iSCSI name on the command line,
there will be difficulties if they are not encoded in UTF-8. The locale can
be changed temporarily by prefixing the command line invocation of
sg_persist with "LANG=en_US.utf-8" for example.
Alternatively the TIDS argument may specify a file (or pipe) from which
one or more TransportIDs may be read. If the TIDS argument is "-"
then stdin (standard input) is read. If the TIDS argument is of the
form "file=<name>" than a file called <name> is read.
A valid SPC-4 TransportID is built from the transport specific string
outlined in the previous paragraphs. The parsing of the data read is
realtively simple. Empty lines are ignored. Everything from and including
a "#" on a line is ignored. Leading spaces and tabs are ignored. There
can be one transportID per line. The transportID can either be a comma,
space or tab separated list of ASCII hex bytes that represent a
TransportID as defined in SPC-4. Padding with zero bytes to a minimum
length of 24 bytes is performed if necessary. The transportID may also
be transport specific string type discussed above.
In SPC-3 the SPEC_I_PT bit set to one and TransportIDs were allowed for
the PROUT register and ignore existing key sub-command. In SPC-4 that
is disallowed yielding a CHECK CONDITION status with and ILLEGAL REQUEST
sense key and an additional sense code set to INVALID FIELD IN PARAMETER
In the 2.4 series of Linux kernels the DEVICE must be
a SCSI generic (sg) device. In the 2.6 series any SCSI device
name (e.g. /dev/sdc, /dev/st1m or /dev/sg3) can be specified.
For example "sg_persist --read-keys /dev/sdb"
will work in the 2.6 series kernels.
The only scope for PROUT commands supported in the current draft of
SPC-4 is "LU_SCOPE". Hence there seems to be no point in offering an
option to set scope to another value.
Most errors with the PROUT sub-commands (e.g. missing or
mismatched --prout-type=TYPE) will result in a RESERVATION
CONFLICT status. This can be a bit confusing when you know there is
only one (active) initiator: the "conflict" is with the SPC standard, not
Some recent disks accept some PRIN and PROUT sub-commands when the
media is stopped. One exception was setting the APTPL flag (with
the --param-aptpl option) during a key register operation,
it complained if the disk one stopped. The error indicated it wanted
the disk spun up and when that happened, the registration was
These examples use Linux device names. For suitable device names in
other supported Operating Systems see the sg3_utils(8) man page.
Due to the various option defaults the simplest example executes
the 'read keys' sub-command of the PRIN command:
This is the same as the following (long-winded) command:
sg_persist --in --read-keys --device=/dev/sdb
To read the current reservation either the '--read-reservation' form or
the shorter '-r' can be used:
sg_persist -r /dev/sdb
the new reservation key 0x123abc the following could be used:
Now have a close look at the difference between the register and
unregister examples above.
An example file that is suitably formatted to pass transportIDs via
a '--transport-id=file=transport_ids.txt' option can be found in the
examples sub-directory of the sg3_utils package. There is also a
simple test script called sg_persist_tst.sh in the same directory.
The above sequence of commands was tested successfully on a Seagate Savvio
10K.3 disk which has a SAS interface.
The exit status of sg_persist is 0 when it is successful. Otherwise see
the sg3_utils(8) man page.