.TH SG_PREVENT "8" "June 2006" "sg3_utils-1.21" SG3_UTILS
.SH NAME
sg_prevent \- invoke SCSI PREVENT ALLOW MEDIUM REMOVAL command on a device
.SH SYNOPSIS
.B sg_prevent
[\fI--allow\fR] [\fI--help\fR] [\fI--prevent=<n>\fR] [\fI--verbose\fR]
[\fI--version\fR] \fI<scsi_device>\fR
.SH DESCRIPTION
.\" Add any additional description here
.PP
Sends a SCSI PREVENT ALLOW MEDIUM REMOVAL command to the given Linux SCSI
device. The default action of this utility is to allow the user and the SCSI
command START STOP UNIT (see sg_start) to remove or eject
the medium from a drive. Typical examples are a removable disk, a tape
or a cd/dvd drive. The definition of the "prevent" codes for this command
differ between disks and tapes (covered by SPC-3) and cd/dvd drives (covered
by MMC-4). At the time of writing there are moves to remove these differences.
The "prevent codes" described here are from MMC-4 which seems to be close
to the proposed merged definition.
.TP
--allow | -a
allow medium removal. This is equivalent to setting the argument
to '--prevent' to 2. Cannot be used with '--prevent' option (i.e. use
no options (hence prevent removal), this option or '--prevent').
.TP
--help | -h
output the usage message then exit.
.TP
--prevent=<n> | -p <n>
prevent codes: 0 allows removal, 1 prevents removal (default), 2 allows
persistent removal while 3 prevents persistent removal. "Persistent" in this
context means that the initiator (port) that successfully uses code 3 blocks
other initiators (ports) from allowing removal. A "persistent prevent" state
can be cleared by owner allowing persistent removal (code 2) or a power
cycle (or anything that resets the device (lun)) or some special
commands (e.g. various service actions of Persistent Reserve Out, see SPC-3).
.TP
--verbose | -v
increase the level of verbosity, (i.e. debug output).
.TP
--version | -V
print the version string and then exit.
.PP
In some cases removable media can be ejected by an application (see
sg_start and its '-loej' option). Often a user with physical access
to the drive can attempt to eject the media by pressing a button on
the drive.
.SH EXIT STATUS
The exit status of sg_prevent is 0 when it is successful. Otherwise see
the sg3_utils(8) man page.
.SH AUTHORS
Written by Douglas Gilbert.
.SH "REPORTING BUGS"
Report bugs to <dgilbert at interlog dot com>.
.SH COPYRIGHT
Copyright \(co 2004-2006 Douglas Gilbert
.br
This software is distributed under a FreeBSD license. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
.SH "SEE ALSO"
.B sg_start(sg3_utils), sg_persist(sg3_utils)