rmt Command in Linux

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The rmt (remote magtape) command in Linux is a utility used for remote magnetic tape operations. It is typically used in conjunction with other tape-related commands like tar, cpio, mt, and the remote dump and restore programs to manipulate a magnetic tape drive through an interprocess communication connection.

The rmt command accepts requests specific to the manipulation of magnetic tapes, performs the commands, and then responds with a status indication. These responses are in ASCII and can indicate either successful or unsuccessful commands. The protocol includes commands for opening and closing tape devices, performing seek operations, reading and writing data, and obtaining the status of the tape device.

Table of Contents

Let's understand more about the rmt command in Linux, which is used for remote magnetic tape operations. Here we will provide a detailed explanation along with examples to help you understand its usage.

• Understanding of rmt Command
• Installation of rmt Command
• Syntax of rmt Command
• rmt Command Options
• Examples of rmt Command in Linux
• Security Considerations

Understanding of rmt Command

One of the key features of the rmt command is its ability to facilitate remote tape operations, making it a valuable tool for system administrators who need to manage backups and data transfers across different systems.

For example, the rmt command can be used to open a tape device on a remote machine, write data to it, and then close the device, all from a local machine. This capability is particularly useful in environments where tape drives are not directly accessible from all systems.

However, it is important to note that the rmt command is often used in conjunction with other commands like rsh or rexec, which may have security implications. As such, administrators should consider using more secure alternatives like ssh for remote operations to ensure data security.

Installation of rmt Command

The rmt command is typically included in the rmt package. If it's not installed on your system, you can install it using your package manager. For example −

On Debian-based systems (like Ubuntu) −

sudo apt-get install rmt

On Red Hat-based systems (like Fedora) −

sudo yum install rmt

Syntax of rmt Command

The basic syntax of the rmt command is as follows −

rmt [options] command [arguments]

Here, command refers to the specific tape operation you want to perform, and arguments are the parameters required for that operation.

rmt Command Options

Here are some important commands and options you can use with rmt −

Examples of rmt Command in Linux

The rmt (remote magnetic tape) command is a utility in Unix-like operating systems that allows users to perform tape operations on a remote machine. It is typically used in conjunction with other tape-related commands like tar, dd, and dump to facilitate remote backups and data transfers.

• Opening a Tape Device
• Closing a Tape Device
• Writing Data to a Tape
• Reading Data from a Tape
• Performing an I/O Control Operation
• Getting the Status of a Tape Device

Opening a Tape Device

To open a tape device on a remote machine, use the following command −

rmt open /dev/nst0

This command will open the tape device /dev/nst0 on the remote machine.

Closing a Tape Device

To close a tape device on a remote machine, use the following command −

rmt close

This command will close the currently open tape device on the remote machine.

Writing Data to a Tape

To write data to a tape on a remote machine, use the following command −

rmt write 1024

This command will write 1024 bytes of data to the currently open tape device on the remote machine.

Reading Data from a Tape

To read data from a tape on a remote machine, use the following command −

rmt read 1024

This command will read 1024 bytes of data from the currently open tape device on the remote machine.

Performing an I/O Control Operation

To perform an I/O control operation on a tape device, use the following command −

rmt ioctl MTFSF 1

This command will perform the MTFSF (forward space file) operation on the currently open tape device, moving the tape forward by one file.

Getting the Status of a Tape Device

To get the status of a tape device on a remote machine, use the following command −

rmt status

This command will display the status of the currently open tape device on the remote machine.

Using rmt with tar

You can use the rmt command in conjunction with tar to perform remote backups. For example, to create a backup of a directory on a remote tape device, use the following command −

tar -cvf - /path/to/directory | rsh remotehost dd of=/dev/nst0

This command will create a tar archive of the specified directory and write it to the tape device /dev/nst0 on the remote host using rsh.

Using rmt with dd

You can use the rmt command in conjunction with dd to perform remote data transfers. For example, to copy data from a local file to a remote tape device, use the following command −

dd if=/path/to/localfile | rsh remotehost dd of=/dev/nst0

This command will read data from the specified local file and write it to the tape device /dev/nst0 on the remote host using rsh.

Using rmt with dump

You can use the rmt command in conjunction with dump to perform remote backups of file systems. For example, to create a backup of a file system on a remote tape device, use the following command −

dump 0f - /dev/sda1 | rsh remotehost dd of=/dev/nst0

This command will create a dump of the specified file system and write it to the tape device /dev/nst0 on the remote host using rsh.

Security Considerations

The rmt command is often used in conjunction with rsh, which is considered insecure because it transmits data, including passwords, in plain text over the network. It is recommended to use more secure alternatives like ssh (Secure Shell) for remote operations. ssh provides encrypted communication and better security features.

Conclusion

The rmt command is a powerful tool for performing remote magnetic tape operations in Unix-like operating systems. By understanding its commands and options, you can effectively manage tape devices on remote machines and perform tasks like backups and data transfers. However, due to security concerns, it is recommended to use more secure alternatives like ssh.