erofs(5)

💖 erofs — the Enhanced Read-Only File System 💖

okay bestie, gather round, because this is the page for erofs, aka the Enhanced Read-Only File System, and it is lowkey iconic. this is the erofs(5) page from the File Formats Manual, and we're gonna go through it together, no cap. 🦋

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✨ NAME ✨

erofs — the Enhanced Read-Only File System. that's it, that's the name, she's simple and she knows it 💅

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🌸 DESCRIPTION 🌸

so erofs is a create-once read-only filesystem, and she comes with two very cute party tricks: support for compression, and a multi-device backing store. obsessed. 🫶

there are two inode formats, and you will be hearing about both:

• 32-byte compact — with 16-bit UID/GID, 32-bit file size, and no file times (she lives in the moment, no timestamps, periodt)
• 64-byte extended — with 32-bit UID/GID, 64-bit file size, and a modification time (st_mtim). she remembers everything, main character energy honestly ✨

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🎀 Mount options 🎀

the way that mounting has OPTIONS, and every single one matters, so let's go one by one, no skipping, we're not doing that here:

• user_xattr, nouser_xattr — controls whether user extended attributes are exposed. defaults to yes. 🌈
• acl, noacl — controls whether POSIX acl(5)s are exposed. defaults to yes. literally the same vibe as the xattr one but for ACLs ✨
• cache_strategy=disabled|readahead|readaround — cache allocation for compressed files. the three values line up like this: never (disabled), if reading from start of file (readahead), regardless of position (readaround). defaults to readaround. she's generous with the cache by default, we love that for her 💖
• dax, dax=always|never — Direct Access control. if you go always and the source device supports DAX, then uncompressed non-inlined files will be read directly, without going through the page cache. spicy! 🔥 also: plain dax is a synonym for always. defaults to unset, which is equivalent to never. so by default she is NOT doing the DAX thing, noted 📝
• device=blobdev — add an extra device holding some of the data. okay this one is important bestie: it must be given as many times, and in the same order, as --blobdev was to mkfs.erofs(1). same count, same order, or it's not gonna vibe check correctly 😭
• domain_id=did, fsid=id — control CacheFiles on-demand read support. and then... "To be documented." yeah. that's the whole thing. the docs said we'll get to it, and they did NOT get to it 💀. we respect the honesty tho 🎀

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👑 VERSIONS 👑

erofs images are versioned through the use of feature flags; these are listed in the -E section of mkfs.erofs(1), 🦋

so if you wanna know what your image is actually capable of, that's where you look, iykyk ✨

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🧚 CONFIGURATION 🧚

Linux must be configured with the CONFIG_EROFS_FS option to mount EROFS filesystems. no config, no mount, that's the rule, bestie 💅

and heads up: there are sub-configuration items that restrict the availability of some of the parameters above. so yeah, some of those cute mount options might just not be available depending on how your kernel was built. rude, but that's the deal 🙈

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🌈 HISTORY 🌈

Stable since Linux 5.4. she's been thriving for a while now, an absolute icon ⭐

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🫶 SEE ALSO 🫶

• mkfs.erofs(1)
• fsck.erofs(1)
• dump.erofs(1)

and also, from the Linux source: Documentation/filesystems/erofs.rst 📚

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okay that's the whole page, you ate that reading it, go mount something read-only and be free 🦋💜

this was the Linux man-pages 6.20 version, dated 2026-09-09 — mwah, love u, bye 👑✨