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#### 5.4.3 User Hooks

User hooks are shell functions executed before and after each `tar` invocation. Thus, there are backup hooks, which are executed before and after dumping each file system, and restore hooks, executed before and after restoring a file system. Each user hook is a shell function taking four arguments:

User Hook Function: hook level host fs fsname

  Its arguments are:

  level

    Current backup or restore level.

  host

    Name or IP address of the host machine being dumped or restored.

  fs

    Full file name of the file system being dumped or restored.

  fsname

    File system name with directory separators replaced with colons. This is useful, e.g., for creating unique files.

Following variables keep the names of user hook functions:

Backup variable: DUMP_BEGIN

  Dump begin function. It is executed before dumping the file system.

Backup variable: DUMP_END

  Executed after dumping the file system.

Backup variable: RESTORE_BEGIN

  Executed before restoring the file system.

Backup variable: RESTORE_END

  Executed after restoring the file system.