Podemos interrogar el estado de unidad de cinta mediante el comando mt, y mandando la opción status.

[root@srv-dlt ~]# mt -f /dev/nst0 status
SCSI 2 tape drive:
File number=0, block number=0, partition=0.
Tape block size 0 bytes. Density code 0x19 (DLT 10GB).
Soft error count since last status=0
General status bits on (45010000):
BOT WR_PROT ONLINE IM_REP_EN

Después de General status nos devuelve una cadena con el estado tal que:

Status Bit Description
BOT The tape is positioned at the beginning of the first file.
EOT A tape operation has reached the physical End Of Tape.
EOF The tape is positioned just after a filemark.
WR_PROT The tape (or drive) is write-protected. For some drives this can also mean that the drive does not support writing on the current medium type.
ONLINE The drive has a tape in place and ready for operation.
DR_OPEN Door is open. Depending on the type of drive, this usually means that the drive does not have a tape in place.
IM_REP_EN Immediate report mode. This bit is set if there are no guarantees that the data has been physically written to the tape when the write call returns. It is set to zero only when the driver does not buffer data and the drive is set not to buffer data.
SM The tape is currently positioned at a setmark. DDS specific.
EOD The tape is positioned at the end of recorded data. DDS specific.
D_6250
D_1600
D_800
This “generic” status information reports the current density setting for 9-track 1/2 inch tape drives only.

Las cadenas más típicas son:

BOT ONLINE IM_REP_EN – tape drive is online and ready
DR_OPEN IM_REP_EN – no tape is in the drive
IM_REP_EN – tape is being loaded

Para más información sobre comandos de mt y restauraciones con tar: