file-modification-time · shipping · also mtime, Modification time, Last modification time

File modification time

File modification time (mtime) is the filesystem timestamp associated with the latest change to a file's contents or a directory's entries.

Writes and truncation update mtime; changing ownership or permissions alone does not. The timestamp can also be set explicitly with utimensat(), subject to permissions, without changing file contents. Filesystem resolution limits the stored value. [1] [2]

The default rsync quick check compares file size and mtime, not content. Its default comparison ignores nanoseconds; --modify-window=-1 includes them when the receiver is version 3.1.3 or later. Equal size and mtime are not proof of identical data. [3]

Relations

related
Inode, Inode change time, File access time, File birth time, Rsync quick check

Advantages

  • Provides a low-cost signal for selecting files that may need synchronization.

Limitations

  • Can be preserved or reset independently of file contents.
  • Filesystem and comparison precision can hide distinct changes.

Citations

  1. Linux man-pages: inode(7) (accessed 2026-10-21)
  2. Linux man-pages: utimensat(2) (accessed 2026-10-21)
  3. rsync(1): file selection and modification-time comparison (accessed 2026-10-21)

Further reading

  1. Hesela: interpreting file timestamps during rsync selection (accessed 2026-10-21)

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Hesela team. File modification time. Hesela. 2026-10-21. https://hesela.dev/terms/file-modification-time/