mt

Understanding mt

mt (magnetic tape) is a command-line utility that allows you to control magnetic tape drives. This includes operations like rewinding, writing, reading, and skipping forward or backward on the tape. Its functionality is essential for performing tape backups and restorations. Before you begin, ensure you have a tape drive connected and properly configured. You’ll likely need root privileges to execute most mt commands.

Essential mt Commands

The core functionality of mt revolves around a set of concise commands. These commands are usually preceded by the device name, often /dev/st0 (the first SCSI tape drive) but this can vary depending on your system’s configuration. Always check your /dev directory to determine the correct device path.

Rewinding the Tape

The most common operation is rewinding the tape to the beginning. This ensures you start from a known position:

sudo mt -f /dev/st0 rewind

This command rewinds the tape on the device /dev/st0. Replace /dev/st0 with your actual tape drive device name.

Forward Spacing (Skipping Blocks)

mt allows you to skip forward a specified number of blocks or files. This is useful when navigating through a multi-file tape backup:

sudo mt -f /dev/st0 fsf 5  #Skip 5 files forward
sudo mt -f /dev/st0 bfs 10 #Skip 10 blocks forward

fsf stands for “forward space file,” and bfs stands for “backward space file”. The number following the command specifies the quantity.

Backward Spacing

Similarly, you can skip backward using the following:

sudo mt -f /dev/st0 bsf 2 #Skip 2 files backward
sudo mt -f /dev/st0 bbs 5 #Skip 5 blocks backward

Ejecting the Tape

To safely remove the tape cartridge, use the eject command:

sudo mt -f /dev/st0 offl

offl stands for “offline” and effectively ejects the tape.

Checking Tape Status

It’s good practice to check the tape’s status before and after operations:

sudo mt -f /dev/st0 status

This command displays information about the tape, including its position, density, and block size.

Advanced Usage and Error Handling

mt offers more advanced options, such as setting block size and specifying tape density. Refer to the man mt page for a complete list of options. Handle potential errors. mt typically returns error codes that you can check using the $? variable in your scripts. For example, a simple script to rewind and check for errors:

#!/bin/bash

sudo mt -f /dev/st0 rewind
if [ $? -ne 0 ]; then
  echo "Error rewinding tape!"
  exit 1
fi
echo "Tape Rewound Successfully!"

This script rewinds the tape and checks the return code. A non-zero return code indicates an error.

Integrating mt into Backup Strategies

While mt directly handles tape interactions, it is rarely used independently for creating backups. It’s typically integrated with other backup utilities like tar (for creating archives) and dd (for copying raw data) to create and restore tape backups. A typical workflow would involve using tar to create an archive, then piping the output to dd which writes to the tape device controlled by mt. Restoring would be the reverse process. A more detailed explanation of this combined workflow is beyond the scope of this introduction to mt.