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SG_STREAM_CTL

Section: SG3_UTILS (8)
Updated: December 2023
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NAME

sg_stream_ctl - send SCSI GET STREAM STATUS or STREAM CONTROL command

SYNOPSIS

sg_stream_ctl [--brief] [--close] [--ctl=CTL] [--get] [--help] [--hex] [--id=SID] [--inhex=FN] [--json[=JO]] [--js-file=JFN] [--maxlen=LEN] [--open] [--raw] [--readonly] [--verbose] [--version] DEVICE

DESCRIPTION

Sends a SCSI GET STREAM STATUS or STREAM CONTROL command to the DEVICE. These commands, together with WRITE STREAM(16 and 32) and several fields in the Block Limits Extension VPD page [0xb7] support the streams concept. There is also the IO advice hints grouping mode page [0xa,0x4] . Amongst other things that mode page indicates whether a stream identifier do double duty as a group number found in most SCSI media access commands (e.g. READ, WRITE and VERIFY).

The stream commands were added in SBC-4 draft 8 (September 2015). The stream commands were extended in SBC-5 draft 5 (October 2023).

Both the GET STREAM STATUS and STREAM CONTROL commands expect data from the DEVICE (referred to as 'data-in'). In the case of STREAM CONTROL only the 'open' (STR_CTL<--0x1) actually needs the data-in as it contains the "Assigned stream id" if the open was successful. The assigned stream id should be used by subsequent WRITE STREAM commands and ultimately by the STREAM CONTROL close (STR_CTL<--0x2). Valid stream ids are between 1 and 65535 inclusive.

OPTIONS

Arguments to long options are mandatory for short options as well.

-b, --brief: this option reduces the output of the GET STREAM STATUS command to just one number (in decimal) per line sent to stdout. Those numbers are the currently open stream ids. If an error occurs then -1 is sent to stdout and error related messages are sent to stderr. The default is to print more words (and fields) from the GET STREAM STATUS response.
-c, --close: selects the STREAM CONTROL command and sets STR_CTL<--0x2 (i.e. 'close'). The --id=SID option should also be given because it defaults to 0 which is not a valid stream id.
-C, --ctl=CTL: CTL is the value placed in the STR_CTL field of the STREAM CONTROL command (cdb). It is a two bit field so has 4 variants: 0 and 3 are reserved; 1 opens are new stream and 2 closes the given stream id. '--ctl=1' is equivalent to '--open' while '--ctl=2' is equivalent to '--close'.
-g, --get: selects the GET STREAM STATUS command. If the --id=SID option is also given then the response starts listing open stream ids from and including SID. If the --id=SID option is not given (or SID is 0) then all open stream ids will be returned in the response (data-in) as long as the allocation length is long enough. The allocation length defaults to 248 bytes which can be overridden by the --maxlen=LEN option.
: This option usually does not need to be given as calling the GET STREAM STATUS command is the default action of this utility in the absence of any other "selecting" option.
-h, --help: output the usage message then exit.
-H, --hex
-H, --hex: output response to this command in ASCII hex. Each line of 16 bytes is preceded by an address or index, starting at 0 and the address is also in hex. If given twice then an ASCII rendering of each byte is appended to the line output. If given three or more times then only the ASCII hex of each byte is output, 16 bytes per line (i.e. so no leading address nor trailing ASCII rendering). This latter form is suitable for placing in a file and being used with the --inhex=FN option in a later invocation.
-i, --id=SID: SID is a stream id, a value between 1 and 65535. It is used by STREAM CONTROL (close) to identify the stream to close. It is used by the GET STREAM STATUS command as the starting stream id (from and including); so stream ids that are less than SID will not appear in the response.
-I, --inhex=FN: where FN is a file name whose contents are assumed to be ASCII hexadecimal. If DEVICE is also given then DEVICE is ignored, a warning is issued and the utility continues, decoding the file named FN. See the "HEX, BINARY AND JSON FORMATS" section in the sg3_utils manpage for more information. If the --raw option is also given then the contents of FN are treated as binary.
FN may either contain data representing the response to a SCSI GET STREAM STATUS or a STREAM CONTROL command. This utility defaults to expecting the former. When FN contains data from a STREAM CONTROL command response then an additional option (other than this option) needs to be given: either --close, --ctl=CTL, or --open.
-j[=JO], --json[=JO]: output is in JSON format instead of plain text form. Note that arguments to the short and long form are themselves optional and if present start with "=" and no whitespace is permitted around that "=".
See sg3_utils_json manpage or use '?' for JO to get a summary.
-J, --js-file=JFN: output is in JSON format and it is sent to a file named JFN. If that file exists then it is truncated. By default, the JSON output is sent to stdout.
When this option is given, the --json[=JO] option is implied and need not be given. The --json[=JO] option may still be needed to set the JO parameter to non-default values.
-m, --maxlen=LEN: LEN is the maximum length the response can be. It becomes the ALLOCATION LENGTH field in both commands. The default (in the absence of this option) is 8 bytes for STREAM CONTROL and 248 bytes for GET STREAM STATUS.
-o, --open: selects the STREAM CONTROL command and sets STR_CTL<--0x1 (i.e. 'open'). If the --id=SID option is given then it is ignored. The user should observe the response as the "Assigned stream id" is printed on stdout if the open is successful, if not '-1' is sent to stdout and error messages are sent to stderr. If the --brief option is also given then the only thing sent to stdout is a number of the assigned stream id (1 to 65535 inclusive) or '-1' if there is an error.
-r, --readonly: this option sets a 'read-only' flag when the underlying operating system opens the given DEVICE. This may not work since operating systems can not easily determine whether a pass-through command is a logical read or write operation on the media (or its metadata) so they take a risk averse stance and require read-write type permissions on the DEVICE open irrespective of what is performed by the pass-through.
-R, --raw: output response in binary (to stdout) unless the --inhex=FN option is also given. In that case the input file name (FN) is decoded as binary (and the output is _not_ in binary).
To relax that final restriction this option can be given multiple times. If this option is given once or three times, FN is assumed to be binary. If this option is given two or three times, the (undecoded) output is in binary. These actions only apply when the --inhex=FN option ia given.
-v, --verbose: increase the level of verbosity, (i.e. debug output).
-V, --version: print the version string and then exit.

NOTES

There are no special read commands for streams. This implies that "normal" READs (6, 10, 12, 16 or 32) can be used. Note that when a stream is closed, all resources associated with that stream id are removed, apart from the data in the written LBAs. To make sure the reading back data is not delayed too much by error recovery (in the presence of media errors) the user may set the RECOVERY TIME LIMIT field (RTL, units for non-zero values: milliseconds) in the 'Read-write error recovery' mode page. This can be done with the sdparm utility.

The SCSI WRITE STREAM (16 and 32) commands can be found in the sg_write_x utility in this package.

EXIT STATUS

The exit status of sg_stream_ctl 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

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Time: 01:03:14 GMT, July 22, 2026