sg_prevent - invoke SCSI PREVENT ALLOW MEDIUM REMOVAL command on a device

sg_prevent [--allow] [--help] [--prevent=<n>] [--verbose] [--version] <scsi_device>

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.

--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').

--help | -h

output the usage message then exit.

--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).

--verbose | -v

increase the level of verbosity, (i.e. debug output).

--version | -V

print the version string and then exit.

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.

Written by Douglas Gilbert.

Report bugs to <dgilbert at interlog dot com>.

Copyright © 2004 Douglas Gilbert

This software is distributed under a FreeBSD license. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

sg_start(sg3_utils), sg_persist(sg3_utils)