--- name: "rmt-dump" section: "8" platform: "linux" package: "dump" version: "0.4b49-2" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/rmt-dump" --- # rmt-dump(8) remote magtape protocol module ## NAME rmt - remote magtape protocol module ## SYNOPSIS **rmt** ## DESCRIPTION **Rmt** is a program used by the remote [**dump**(8)](/dump/8.md), [**restore**(8)](/restore/8.md) or [**tar**(1)](/tar/1.md) programs in manipulating a magnetic tape drive through an interprocess communication connection. **Rmt** is normally started up with an [**rexec**(3)](/rexec/3.md) or [**rcmd**(3)](/rcmd/3.md) call. The **rmt** program accepts requests specific to the manipulation of magnetic tapes, performs the commands, then responds with a status indication. All responses are in **ASCII** and in one of the following two forms. Successful commands have responses of: **A*number*\\n** where *number* is an **ASCII** representation of a decimal number. Unsuccessful commands are responded to with: **E*error-number*\\n*error-message*\\n** where *error-number* is one of the possible error numbers described in [**intro**(2)](/intro/2.md) and *error-message* is the corresponding error string as printed from a call to [**perror**(3)](/perror/3.md). The protocol is comprised of the following commands, which are sent as indicated - no spaces are supplied between the command and its arguments, or between its arguments, and \\n indicates that a newline should be supplied: - **O*device*\\n*mode*\\n** Open the specified *device* using the indicated *mode*. *Device* is a full pathname and *mode* is an **ASCII** representation of a decimal number suitable for passing to [**open**(2)](/open/2.md). If a device had already been opened, it is closed before a new open is performed. - **C*device*\\n** Close the currently open device. The *device* specified is ignored. - **L*whence*\\n*offset*\\n** Perform an [**lseek**(2)](/lseek/2.md) operation using the specified parameters. The response value is that returned from the **lseek** call. - **W*count*\\n** Write data onto the open device. **Rmt** reads *count* bytes from the connection, aborting if a premature end-of-file is encountered. The response value is that returned from the [**write**(2)](/write/2.md) call. - **R*count*\\n** Read *count* bytes of data from the open device. If *count* exceeds the size of the data buffer (10 kilobytes), it is truncated to the data buffer size. **Rmt** then performs the requested [**read**(2)](/read/2.md) and responds with **A*count-read*\\n** if the read was successful; otherwise an error in the standard format is returned. If the read was successful, the data read is then sent. - **I*operation*\\n*count*\\n** Perform a **MTIOCOP** [**ioctl**(2)](/ioctl/2.md) command using the specified parameters. The parameters are interpreted as the **ASCII** representations of the decimal values to place in the **mt\_op** and **mt\_count** fields of the structure used in the **ioctl** call. The return value is the *count* parameter when the operation is successful. - By issuing the **I-1\\n0\\n** command, a client will specify that he is using the VERSION 1 protocol. - For a VERSION 0 client, the *operation* parameter is the platform **mt\_op** value (could be different if the client and the **rmt** server are on two different platforms). For a VERSION 1 client, the *operation* parameter is standardized as below: - **0** Issue a **MTWEOF** command (write *count* end-of-file records). - **1** Issue a **MTFSF** command (forward space over *count* file marks). - **2** Issue a **MTBSF** command (backward space over *count* file marks). - **3** Issue a **MTFSR** command (forward space *count* inter-record gaps). - **4** Issue a **MTBSR** command (backward space *count* inter-record gaps). - **5** Issue a **MTREW** command (rewind). - **6** Issue a **MTOFFL** command (rewind and put the drive offline). - **7** Issue a **MTNOP** command (no operation, set status only). - **i*operation*\\n*count*\\n** Perform an extended **MTIOCOP** [**ioctl**(2)](/ioctl/2.md) command using the specified parameters. The parameters are interpreted as the **ASCII** representations of the decimal values to place in the **mt\_op** and **mt\_count** fields of the structure used in the **ioctl** call. The return value is the *count* parameter when the operation is successful. The possible operations are: - **0** Issue a **MTCACHE** command (switch cache on). - **1** Issue a **MTNOCACHE** command (switch cache off). - **2** Issue a **MTRETEN** command (retension the tape). - **3** Issue a **MTERASE** command (erase the entire tape). - **4** Issue a **MTEOM** command (position to end of media). - **5** Issue a **MTNBSF** command (backward space count files to BOF). - **S** Return the status of the open device, as obtained with a **MTIOCGET** **ioctl** call. If the operation was successful, an “ack” is sent with the size of the status buffer, then the status buffer is sent (in binary, which is non-portable between different platforms). - **s***sub-command* This is a replacement for the previous **S** command, portable across different platforms. If the open device is a magnetic tape, return members of the magnetic tape status structure, as obtained with a **MTIOCGET** ioctl call. If the open device is not a magnetic tape, an error is returned. If the **MTIOCGET** operation was successful, the numerical value of the structure member is returned in decimal. The following sub commands are supported: - **T** return the content of the structure member **mt\_type** which contains the type of the magnetic tape device. - **D** return the content of the structure member **mt\_dsreg** which contains the "drive status register". - **E** return the content of the structure member **mt\_erreg** which contains the "error register". This structure member must be retrieved first because it is cleared after each **MTIOCGET** ioctl call. - **R** return the content of the structure member **mt\_resid** which contains the residual count of the last I/O. - **F** return the content of the structure member **mt\_fileno** which contains the file number of the current tape position. - **B** return the content of the structure member **mt\_blkno** which contains the block number of the current tape position. - **f** return the content of the structure member **mt\_flags** which contains MTF\_ flags from the driver. - **b** return the content of the structure member **mt\_bf** which contains the optimum blocking factor. Any other command causes **rmt** to exit. ## DIAGNOSTICS All responses are of the form described above. ## SEE ALSO [**rcmd**(3)](/rcmd/3.md), [**rexec**(3)](/rexec/3.md), */usr/include/sys/mtio.h,* [**rdump**(8)](/rdump/8.md), [**rrestore**(8)](/rrestore/8.md) ## BUGS People should be discouraged from using this for a remote file access protocol. ## AUTHOR The **dump/restore** backup suit was ported to Linux's Second Extended File System by Remy Card \. He maintained the initial versions of **dump** (up and including 0.4b4, released in january 1997). Starting with 0.4b5, the new maintainer is Stelian Pop \. ## AVAILABILITY The **dump/restore** backup suit is available from \ ## HISTORY The **rmt** command appeared in 4.2BSD.