[EROFS](https://www.kernel.org/doc/html/latest/filesystems/erofs.html), like Squashfs, is a read-only file system. It can be used to store airootfs in an image file. EROFS advantage is that it supports ACLs, unlike Squashfs. This can be seen when creating `airootfs.sfs` with `mksquashfs`: ``` Unrecognised xattr prefix system.posix_acl_access Unrecognised xattr prefix system.posix_acl_default Unrecognised xattr prefix system.posix_acl_access Unrecognised xattr prefix system.posix_acl_default ``` There have been attempts to add ACL support to squashfs, the latest patch ([[v5,0/2] squashfs/squashfs-tools: Add posix acl support](https://patchwork.kernel.org/cover/10780825/)) is from 2019, but there seems to be no progress in merging them. <details> <summary>For reference, the files with ACLs:</summary> ``` /var/log/journal/ /var/log/journal/remote/ ``` </details> The only downside is that EROFS currently only supports LZ4 compression, but according to [erofs-utils 1.1 release announcement](https://lore.kernel.org/linux-erofs/20200413164544.GA5578@hsiangkao-HP-ZHAN-66-Pro-G1/), support for LZMA compression is being worked on.