μfilewatch

A microscopic file watch for Linux.

mfw watches a file for updates, and runs a command when one is detected.

This can be considered a minimal version of inotifywait. See LIMITATIONS.

example usage

# Run pdflatex on file change
mfw homework.tex pdflatex homework.tex

If the file disappears, the mfw process disappears as well.

installation

Build and install to the default $PREFIX.

make
sudo make install

If $PREFIX is unset, mfw installs to /usr/local.
You can also specify a prefix via environment variable:

# installs to ~/.local/bin/mfw
PREFIX=~/.local make install

features

• Watch for file change to run a shell command
• Kill process if file disappears
• Recursively watch a directory

limitations

use of inotify

This only watches a single file using the Linux kernel inotify library.

By using inotify, we inherit some limitations of inotify:

• Nonrecursive (to implement recursion, all of a directory's subdirectories need manual assignment of inotify descriptors)
• Requires support by the Linux kernel (reasonable; inotify was added in 2.6.13)
• May lose events due to race conditions, e.g. time-to-check-to-time-to-use (article)
• Has a maximum amount of simultaneous watches dictated by the kernel (see SUSE docs)

However, since mfw does not implement recursion (not included in inotify API), the issue of $O(n)$ memory scaling to the amount of directories watched does not apply. This also means buffer overflows are unlikely.

Note

Although inotify isn't very efficient, alternatives such as fanotify require root.

comparison of similar software

• swomf/mfw
  • 🟩 Implemented in a single source file in pure C.
  • 🟩 Minimal memory for the job (uses about 1MB)
  • 🟥 Only watches a single file in Linux via inotify.
• emcrisostomo/fswatch
  • 🟩 Written with minimal dependencies in C++11.
  • 🟩 Avoids inotify.
  • 🟩 Reasonably memory-efficient (starts at around 5MB; uses 42MB to watch my whole home directory)
  • Uses autoconf
• watchexec
  • 🟩 Written in Rust as both a library and a CLI (cargo install watchexec-cli)
  • 🟩 Avoids inotify
  • Somewhat memory-efficient (starts at around 10MB; uses 42MB to watch my whole home directory)
• inotify-tools: inotifywait
  • 🟥 Not as simple as the above three software
  • 🟥 Uses inotify for recursion
  • Uses autoconf
• inotify_dtree.c
  • 🟩 Implemented as a single (big) source file in pure C
  • 🟥 Written only as a literature example for inotify
  • 🟥 Incredibly memory-inefficient during recursion (uses 300MB+ to watch my whole home directory)