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BACKUP(8) AFS Command Reference BACKUP(8)


backup - Introduction to the backup command suite


The commands in the backup command suite are the administrative interface to the AFS Backup System. There are several categories of commands in the suite:

  • Commands to copy data from AFS volumes to tape or a backup data file, and to restore it to the file system: backup diskrestore, backup dump, backup volrestore, and backup volsetrestore.
  • Commands to administer the records in the Backup Database: backup adddump, backup addhost, backup addvolentry, backup addvolset, backup deldump, backup deletedump, backup delhost, backup delvolentry, backup delvolset, backup dumpinfo, backup listdumps, backup listhosts, backup listvolsets, backup scantape, backup setexp, and backup volinfo.
  • Commands to write and read tape labels: backup labeltape and backup readlabel.
  • Commands to list and change the status of backup operations and the machines performing them: backup jobs, backup kill, and backup status.
  • Commands to enter and leave interactive mode: backup interactive and backup quit.
  • Commands to check for and repair corruption in the Backup Database: backup dbverify, backup restoredb, and backup savedb.
  • Commands to obtain help: backup apropos and backup help.
  • A command to display the OpenAFS command suite version: backup version.

The backup command interpreter interacts with two other processes:

  • The Backup Server (buserver) process. It maintains the Backup Database, which stores most of the administrative information used by the Backup System. In the standard configuration, the Backup Server runs on each database server machine in the cell, and uses AFS's distributed database technology, Ubik, to synchronize its copy of the database with the copies on the other database server machines.
  • The Backup Tape Coordinator (butc) process. A separate instance of the process controls each tape device or backup data file used to dump or restore data. The Tape Coordinator runs on a Tape Coordinator machine, which is an AFS server or client machine that has one or more tape devices attached, or has sufficient disk space to accommodate one or more backup data files on its local disk.

    Each Tape Coordinator must be registered in the Backup Database and in the /var/lib/openafs/backup/tapeconfig configuration file on the Tape Coordinator machine's local disk, and information in the two places must be consistent for proper Backup System performance. The optional /var/lib/openafs/backup/CFG_device_name for each Tape Coordinator records information used to automate its operation.

In addition to the standard command line interface, the backup command suite provides an interactive interface, which has several useful features described in backup_interactive(8). Three of the commands in the suite are available only in interactive mode: backup jobs, backup kill, and backup quit


The following options are available on many commands in the backup suite. The reference page for each command also lists them, but they are described here in greater detail.

Names the cell in which to run the command. It is acceptable to abbreviate the cell name to the shortest form that distinguishes it from the other entries in the /etc/openafs/CellServDB file on the local machine. If the -cell argument is omitted, the command interpreter determines the name of the local cell by reading the following in order:
  • The value of the AFSCELL environment variable.
  • The local /etc/openafs/ThisCell file.

Do not combine the -cell and -localauth options. A command on which the -localauth flag is included always runs in the local cell (as defined in the server machine's local /etc/openafs/server/ThisCell file), whereas a command on which the -cell argument is included runs in the specified foreign cell.

The -cell argument is not available on commands issued in interactive mode. The cell defined when the backup command interpreter enters interactive mode applies to all commands issued during the interactive session.

Prints a command's online help message on the standard output stream. Do not combine this flag with any of the command's other options; when it is provided, the command interpreter ignores all other options, and only prints the help message.
Constructs a server ticket using the server encryption key with the highest key version number in the local /etc/openafs/server/KeyFile or /etc/openafs/server/KeyFileExt file. The backup command interpreter presents the ticket, which never expires, to the Backup Server, Volume Server and Volume Location (VL) Server during mutual authentication.

Use this flag only when issuing a command on a server machine; client machines do not usually have a /etc/openafs/server/KeyFile or /etc/openafs/server/KeyFileExt file. The issuer of a command that includes this flag must be logged on to the server machine as the local superuser "root". The flag is useful for commands invoked by an unattended application program, such as a process controlled by the UNIX cron utility or by a cron entry in the machine's /etc/openafs/BosConfig file. It is also useful if an administrator is unable to authenticate to AFS but is logged in as the local superuser "root".

Do not combine the -cell and -localauth options. A command on which the -localauth flag is included always runs in the local cell (as defined in the server machine's local /etc/openafs/server/ThisCell file), whereas a command on which the -cell argument is included runs in the specified foreign cell.

The -localauth argument is not available on commands issued in interactive mode. The local identity and AFS tokens with which the backup command interpreter enters interactive mode apply to all commands issued during the interactive session.

Prior to the fix for OPENAFS-SA-2018-001, butc did not allow incoming connections to be authenticated. As part of that fix, backup was modified to authenticate to the butc services when possible, but a backup utility with the security fix will not interoperate with a butc that lacks the fix unless this option is passed, which forces the use of unauthenticated connections to the butc. Use of this option is strongly disrecommended, and it is provided only for backwards compatibility in environments where backup and butc communicate over a secure network environment that denies access to untrusted parties.
Specifies the port offset number of the Tape Coordinator that is to execute the backup command. The port offset number uniquely identifies a pairing of a Tape Coordinator (butc) process and tape device or backup data file.

The backup command interpreter and Tape Coordinator process communicate via a UDP socket, or port. Before issuing a backup command that involves reading or writing a tape, the backup operator must start a butc process that controls the appropriate tape device and listens for requests sent to its port number. If a Backup System machine has multiple tape devices attached, they can perform backup operations simultaneously because each device has its own associated butc process and port offset number.

The Backup System associates a tape capacity and file mark size with each port offset (as defined in the tapeconfig file). For a compressing tape device, the capacity and file mark values differ for compression and non-compression modes, so the two modes have distinct port offset numbers.

The Backup Database can store up to 58,511 port offsets, so the legal values for this argument are the integers 0 through 58510. If the issuer omits the argument, it defaults to 0. (The limit of 58,511 port offsets results from the fact that UDP socket numbers are identified by a 16-bit integer, and the lowest socket number used by the Backup System is 7025. The largest number that a 16-bit integer can represent is 65,535. Subtracting 7,025 yields 58,510. The addition of port offset 0 (zero) increases the maximum to 58,511.)

Although it is possible to define up to 58,511 port offset numbers for a cell, it is not possible to run 58,511 tape devices simultaneously, due to the following limits:

  • The maximum number of dump or restore operations that can run simultaneously is 64.
  • The maximum number of tape devices that can work together on a restore operation is 128 (that is the maximum number of values that can be provided for the -portoffset argument to the backup diskrestore, backup volrestore, or backup volsetrestore command).

The Backup System does not reserve UDP sockets. If another application is already using the Tape Coordinator's socket when it tries to start, the butc process fails and the following error message appears at the shell prompt:

   bind: Address already in use
   rxi_GetUDPSocket: bind failed


To issue any backup command that accesses the Backup Database only, the issuer must be listed in the /etc/openafs/server/UserList file on every machine where the Backup Server is running. To issue any backup command that accesses volume data, the issuer must appear in the UserList file on every Backup Server machine, every Volume Location (VL) Server machine, and every file server machine that houses affected volumes. By convention, a common UserList file is distributed to all database server and file server machines in the cell. See the chapter on privileged users in the OpenAFS Administration Guide for more information on this type of privilege.

If the -localauth flag is included, the user must instead be logged on as the local superuser "root" on the server machine where the backup command is issued.


BosConfig(5), CellServDB(5), KeyFile(5), KeyFileExt(5), ThisCell(5), UserList(5), butc(5), tapeconfig(5), backup_adddump(8), backup_addhost(8), backup_addvolentry(8), backup_addvolset(8), backup_apropos(8), backup_dbverify(8), backup_deldump(8), backup_deletedump(8), backup_delhost(8), backup_delvolentry(8), backup_delvolset(8), backup_diskrestore(8), backup_dump(8), backup_dumpinfo(8), backup_help(8), backup_interactive(8), backup_jobs(8), backup_kill(8), backup_labeltape(8), backup_listdumps(8), backup_listhosts(8), backup_listvolsets(8), backup_quit(8), backup_readlabel(8), backup_restoredb(8), backup_savedb(8), backup_scantape(8), backup_setexp(8), backup_status(8), backup_volinfo(8), backup_volrestore(8), backup_volsetrestore(8), buserver(8), butc(8)


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2022-12-22 OpenAFS