DWARFS-ENV(7)

📦
version 0.15.8 · 2 versions
, in nixpkgs unstable

🌸 DWARFS-ENV(7) — the env var glow-up

okay so bestie, welcome to dwarfs-env from the Miscellaneous Information Manual, aka the page where the DwarFS tools' environment variables live. literally just environment variables. that's the whole vibe. ✨

💜 NAME

dwarfs-env — DwarFS Environment Variables. yes that's it. that's the name. iconic of it honestly.

🦋 DESCRIPTION

bestie listen 👑 the DwarFS tools read the following environment variables to configure certain aspects of their behavior. like little knobs you can turn from outside the program. no cap.

🎀 DWARFS_IOLAYER_OPTS

okay so DWARFS_IOLAYER_OPTS is the main character here 💅 you can use it to configure certain aspects of the I/O layer that all DwarFS tools use. the value is a comma-separated list of key-value pairs (or just keys if it's a boolean option). here's what you can set:

  • max_eager_map_size=value — the maximum size of a file that'll get eagerly mapped into memory when it's opened. anything bigger gets accessed using on-demand mappings instead. this is mostly relevant for 32-bit systems, where the address space is limited (rip, tiny address space 😭). value can be unlimited, a size in bytes, or an integer with a suffix of k, m, or g for kibibytes, mebibytes, or gibibytes respectively. default is 1 TiB on 64-bit systems and 32 MiB on 32-bit systems. slay.
  • open_mode=mmap|read — picks between memory-mapped I/O (mmap) and using "standard" read calls (pread) to access file data. default is mmap because it's generally more efficient, periodt. but ⚠️ if you've got trouble with like unreliable hardware or unstable network filesystems, this can easily make a process accessing a memory-mapped file crash with a bus error (SIGBUS). scary, i know 💀 in those cases you can try switching to read mode, which should prevent such crashes and instead deliver proper I/O error messages that are genuinely useful for finding the root cause of the problem. a whole glow-up for debugging ngl.
fr fr: if your network filesystem is acting sus, open_mode=read might be your new bestie 🫶

🧚 AUTHOR

Written by Marcus Holland-Moritz. we stan. 💖

Copyright (C) Marcus Holland-Moritz. periodt.

⭐ SEE ALSO

go read these next, bestie, they're all linked:

filed under: Miscellaneous Information Manual, DWARFS-ENV(7), dated January 1980 (yes really, that date is giving time traveler energy 🕰️✨). mwah, go configure your I/O layer responsibly 💅

📦 where this page comes from