--- name: "rmt-star" section: "1" platform: "linux" package: "star" version: "1.4a17-3" release: "Debian 3.0 (Woody)" platforms: ["linux"] url: "https://new.carta.tech/rmt-star" --- # rmt-star(1) remote magnetic tape protocol server ## NAME rmt - remote magnetic tape protocol server ## SYNOPSIS **/opt/schily/sbin/rmt**\ **/etc/rmt** ## DESCRIPTION This is the description of the enhanced **Schily SING** version of the **rmt** remote tape server program. **rmt** is a program used by programs like **star** and **ufsdump** hat like to access remote magnetic tape drives and files 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 **open**, **close**, **read**, **write** and **seek** requests and requests that are specific to magnetic tapes. **rmt** performs the commands and then responds with a status indication. This **Schily SING** version of the rmt server gives full compatibility to the original BSD version, the enhanced Sun version and the enhanced GNU version. It supports best speed and best compliance even when server and client code are running on different platforms. It is prepared to be installed as a user shell in the passwd file to create remote tape specific logins and security checking. To use the enhanced compatibility features, you need to either use the remote tape client code from **star** or reimplement it's features. All responses are in ASCII and in one of the following two forms. Successful commands have responses of - **A***number\\n* where *number* is the 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 retrieved by [**strerror**(3)](/strerror/3.md). The protocol implements the following commands: - **O***device***\\n***mode***\\n** - **O***device***\\n***mode symbolic\_mode***\\n** Open the specified *device* or file using the indicated *mode*. *device* is a full path name, and *mode* is an ASCII representation of a decimal number suitable for passing to [**open**(2)](/open/2.md). If both, *mode* and *symbolic\_mode* are used, they are separated by a space character; *symbolic\_mode* appears on the same line as the numeric is in the same notation as it would appear in a C source (e.g. **O\_RDWR\|O\_CREAT**). If the *symbolic\_mode* is send to the server, the numeric **mode** is ignored. The symbolic notation allows to send the expected open mode over the wire using a system independent method. This is needed because different operating systems define all bits execpt the lowest two bits in a different way. If a device is already open, it is closed before a new open is performed. A VERSION 1 client that is aware of the official *mt\_op* codes should issue a\ **I***-1***\\n***0\\n*\ command just after opening a file or device. This is needed to tell the server that the client is aware of the official order of the *mt\_op* codes in the range 0..7 and maps differing values to the official ones.\ - **C***device***\\n** Close the currently open device or file. The argument *device* is ignored.\ - **R***count***\\n** Read *count* bytes of data from the open device or file. **rmt** performs the requested [**read**(2)](/read/2.md) operation and responds with **A***count-read\\n* if the read operation was successful; otherwise an error in standard format is returned. If the read operation was successful, the data read is sent directly after the response described above.\ - **W***count***\\n** Write data to the open device or file. After reading the command specification, **rmt** reads *count* bytes from the network connection and aborts if a premature EOF is encountered. The return value from the [**write**(2)](/write/2.md) operation is returned as reply.\ - **L***whence***\\n***offset***\\n** Perform an [**lseek**(2)](/lseek/2.md) operation on open the device or file using the specified parameters. The return value from the [**lseek**(2)](/lseek/2.md) operation is returned as reply.\ - **S** The old non-portable status call. If the open device is a magnetic tape, return the magnetic tape status, 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, an “ack” is sent with the size of the status buffer, then the status buffer is sent. As the status buffer is sent in binary, this command it considered outdated. Please use the extended status command instead. This command is not terminated with a new-line.\ - **s***sub-command* The new portable status call. 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 block 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. This command is not terminated with a new-line. - **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. When the operation is successful the return value is the *count* parameter. Only Opcodes 0..7 are unique across different architectures. But as in many cases **Linux** does not even follow this rule. If we know that we have been called by a VERSION 1 client, we may safely assume that the client is not using **Linux** mapping over the wire but the standard mapping described below: - \-1 Retrieve the version number of the **rmt** server and tell the server that the client is aware of the official order of the **MTIOCOP** [**ioctl**(2)](/ioctl/2.md) opcodes in the range 0..7. Local *mt\_op* codes must be remapped to the official values before sendig them over the wire. The answer of the current version of **rmt** is 1. Other **rmt** implementations send an error code back when this command is used. - 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 a **MTIOCOP** [**ioctl**(2)](/ioctl/2.md) command using the specified parameters. This command implements support for commands bejond MTWEOF..MTNOP (0..7). The parameters are interpreted as the ASCII representations of the decimal values described below. They are converted into the local values *mt\_op* and *mt\_count* fields of the structure used in the **ioctl** call according to the actual values found in \. When the operation is successful the return value is the *count* parameter. - 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). - **v***\\n* Return the version of the **rmt** server. This is currently the decimal number 1. Any other command causes **rmt** to exit. ## FILES - /etc/default/rmt Default values can be set for the following options in /etc/default/rmt. For example: USER=tape - DEBUG If you like to get debug information, set this to a file name where **rmt** puts debug information. - USER The name of a user (local to the magnetic tape server) that may use the services of the **rmt** server. A line **USER=**\* grants access to all users. - ACCESS The name of a user (local to the magnetic tape server) that may use the services of the **rmt** server followed by the name of a host from where operation is granted and a file specifier for a file or file sub tree that may be accessed. ## SEE ALSO [**star**(1)](/star/1.md), [**rcmd**(3)](/rcmd/3.md), [**rexec**(3)](/rexec/3.md), **mtio**(7), ## DIAGNOSTICS All responses are send to the network connection. They use the form described above. ## NOTES To use **rmt** as a remote file access protocol you need to use the symbolic open modes as e.g. the *O\_CREAT* flag is not unique between different architectures. This implementation of **rmt** adds some security features to the server that make it behave slightly different from older implementations. Read the documentation about the file /etc/default/rmt to make sure your local installation is configured for your needs. To grant the same permissions as with the old **rmt** servers, create a file /etc/default/rmt and add the following lines to this file: **USER=**\*\ **ACCESS=**\* \* \* Note that the three fields in the **ACCESS=** line need to be separated by a TAB character. ## BUGS None known. ## HISTORY The **rmt** command first appeared on BSD in march 1981. This **rmt** server is a new implementation that tries to be compatible to all existing implementations. It is the only known implementation that in addition tries to fix the data exchange problems between differen architectures. ## AUTHOR ``` Joerg Schilling Seestr. 110 D-13353 Berlin Germany ``` Mail bugs and suggestions to: **schilling@fokus.gmd.de** or **js@cs.tu-berlin.de** or **joerg@schily.isdn.cs.tu-berlin.de**