mastertraitorApr 30, 2025

pathway mtu discovery bash script

https://programming.dev/post/29474998

pathway mtu discovery bash script - programming.dev

I wrote pmtud.sh [https://gist.github.com/bneils/8f337bedebffbe3c1bf2c59def7029d2] this weekend to get the MTU of a link (or tunnel) quickly, reliably, and without sending a ton of pings. It can do so in about 11 pings per target. I had fun writing the entire thing in sh, tried making it “POSIX-compliant,” but probably failed somewhere since POSIX isn’t worded well. The script only needs dig and ping and uses shell built-ins for everything else. It performs a recursive binary search on the MTU search domain and asynchronously queues pings for later.

Show threadCrestwave

Some stylistic notes

  • The head -1 syntax is obsolete in POSIX, replaced by head -n 1.
  • for filename in $(ls) will break on whitespace and is inefficient. You can use shell globbing for this instead, e.g., for filename in *.
  • A lot of the variables seem to be inconsistently quoted. I recommend running ShellCheck on it, as this can be dangerous (if you set TMPDIR to /tmp/ dir, I believe it will remove /tmp and dir)
Apr 30, 2025 at 9:03amWeb
Show threadmastertraitorMay 1, 2025
Saved my bacon with this comment. Fixed a ton of (seemingly) innocuous errors.
Show threadIanTwentyMay 24, 2025
100% use shellcheck! Saves so much time. Even better: github.com/bash-lsp/bash-language-server