one (GNU tar 1.35)

### 6.10 Crossing File System Boundaries

`tar` will normally automatically cross file system boundaries in order to archive files which are part of a directory tree. You can change this behavior by running `tar` and specifying `--one-file-system`. This option only affects files that are archived because they are in a directory that is being archived; `tar` will still archive files explicitly named on the command line or through `--files-from`, regardless of where they reside.

`--one-file-system`

  Prevents `tar` from crossing file system boundaries when archiving. Use in conjunction with any write operation.

The `--one-file-system` option causes `tar` to modify its normal behavior in archiving the contents of directories. If a file in a directory is not on the same file system as the directory itself, then `tar` will not archive that file. If the file is a directory itself, `tar` will not archive anything beneath it; in other words, `tar` will not cross mount points.

This option is useful for making full or incremental archival backups of a file system. If this option is used in conjunction with `--verbose` (`-v`), files that are excluded are mentioned by name on the standard error.