FUNIONFS(8)

🦋 NAME 🦋

funionfs — user-space directory concatenation. That's it, that's the vibe, and it's from the FUNIONFS(8) manual page, bestie. 🫶

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🌸 SYNOPSIS 🌸

funionfs upper_dir mountpoint [ option ] ...

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✨ OPTIONS ✨

• -o opt,[opt...] — mount options, the classic
• -h, --help — print help, aka the "what does this do again" button 🙈
• -V, --version — print version, for when you need receipts

💖 Mount options include:

• funionfs_debug — print some debugging information, slay for when things are acting up
• dirs=LIST — a colon separated list of directories 👑
  • /branch1=rw — a directory in a read-write mode
  • /branch1 — if no permission is specified, the branch is in a read-write mode
  • /branch2=ro — a directory in a read-only mode
• copyupuid=N — uid of the copied-up files (no default)
• copyupgid=N — gid of the copied-up files (no default)
• copyupmode=N — mode of the copied-up files (no default)
• del_string=N — string to mark a deleted file (default: _DELETED~)
• delete=TYPE — specifies how funionfs deletes and renames
  • all (default) — delete all objects in read-write branch (default) and add a whiteout file if objects exists in read-only branches.
  • whiteout — only add a whiteout file in upper (rw) branch or delete file in upper branch.
• copyup=TYPE — specifies how to manage attributes
  • preserve — preserve uid, gid and mode of object (default)
  • currentuser — the object owns to the user doing the operation
  • mounter — the object owns to the mounter

⚠️ Heads up bestie: there is no implementation of -o delete and -o copyup for now. Not me warning you before you go looking for a feature that isn't there 😭

You could use the mount command instead 🎀 :

mount -t fuse funionfs#/upper_dir mountpoint [ options ]

If you want to name all directories in -o dirs=, then pass "none" as upper_dir. iykyk

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🫶 DESCRIPTION 🫶

funionfs concatenates directories mentioned in options (and upper_dir) to mountpoint. Also, although some (but not all) of the directories are read-only, you still can write in resulting mounted directory. main character energy honestly

For example, if you have files a/a and b/b and mount mountpoint r with -o dirs=a=ro:b=ro:w=rw, then you will see files r/a and r/b. You will be able to write to them, and original files will remain intact (changes will go to w). 🦋

Note that it is impossible to have file with name ending by del_string value, if you create r/a_DELETED~ in mentioned example, it will dissapear together with a. literally gone, no cap 💀

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👀 SEE ALSO 👀

The source.. ✨

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💀 BUGS 💀

You cannot mount an overlay on / (the program that list the content of / will hang). This is probably due to a loop call of the fuse driver. There is no known solution for now. fr fr do NOT try this one 😭

Probably minor (or major) mistakes in not-so-frequent cases.

Not enough tested. 🙈

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Okay that's the whole page bestie, you're officially funionfs-literate, periodt. 💅

This cutie right here is from FUNIONFS(8), dated 15 June 2006 — that's the source, the version tag, and the date all in one, so you know exactly what era of Unix you're getting into. 🎀 ✨ 🦋