MKFS.EROFS(1) General Commands Manual MKFS.EROFS(1)

mkfs.erofs - tool to create an EROFS filesystem

mkfs.erofs [OPTIONS] DESTINATION SOURCE

EROFS is a new enhanced lightweight linux read-only filesystem with modern designs (eg. no buffer head, reduced metadata, inline xattrs/data, etc.) for scenarios which need high-performance read-only requirements, e.g. Android OS for smartphones and LIVECDs.

It also provides fixed-sized output compression support, which improves storage density, keeps relatively higher compression ratios, which is more useful to achieve high performance for embedded devices with limited memory since it has unnoticable memory overhead and page cache thrashing.

mkfs.erofs is used to create such EROFS filesystem DESTINATION image file from SOURCE directory or tarball.

Set a primary algorithm for data compression, which can be set with an optional compression level. Alternative algorithms could be specified and separated by colons. See the output of mkfs.erofs --help for a listing of the algorithms that mkfs.erofs is compiled with and what their respective level ranges are.
Set the fundamental block size of the filesystem in bytes. In other words, specify the smallest amount of data that can be accessed at a time. The default is the system page size. It cannot be less than 512 bytes.
Specify the maximum size of compress physical cluster in bytes. This may cause the big pcluster feature to be enabled (Linux v5.13+).
Specify the level of debugging messages. The default is 2, which shows basic warning messages.
Limit how many xattrs will be inlined. The default is 2. Disables storing xattrs if < 0.
Set extended options for the filesystem. Extended options are comma separated, and may take an extra argument using the equals ('=') sign. The following extended options are supported:
Forcely record the whole files into a special inode for better compression and it may take an argument as the pcluster size of the packed inode in bytes. (Linux v6.1+)
Enable global compressed data deduplication to minimize duplicated data in the filesystem. May further reduce image size when used with -E fragments. (Linux v6.1+)
Force generation of compact (32-byte) inodes.
Force generation of extended (64-byte) inodes.
Force generation of inode chunk format as a 4-byte block address array.
Forcely generate inode chunk format as an 8-byte chunk index (with device ID).
Pack the tail part (pcluster) of compressed files, or entire files, into a special inode for smaller image sizes, and it may take an argument as the pcluster size of the packed inode in bytes. (Linux v6.1+)
Disable "inplace decompression" and "compacted indexes", for compatibility with Linux pre-v5.4.
Don't inline regular files to enable FSDAX for these files (Linux v5.15+).
^xattr-name-filter
Turn off/on xattr name filter to optimize negative xattr lookups (Linux v6.6+).
Pack the tail part (pcluster) of compressed files into its metadata to save more space and the tail part I/O. (Linux v5.17+)
Set the volume label for the filesystem to volume-label. The maximum length of the volume label is 16 bytes.
Specify a UNIX timestamp for image creation time for reproducible builds. If --mkfs-time is not specified, it will behave as --all-time: setting all files to the specified UNIX timestamp instead of using the modification times of the source files.
Set the universally unique identifier (UUID) of the filesystem to UUID. The format of the UUID is a series of hex digits separated by hyphens, like this: "c1b9d5a2-f162-11cf-9ece-0020afc76f16". The UUID parameter may also be one of the following:
clear the file system UUID
generate a new randomly-generated UUID
Make all files owned by root.
(used together with -T) set all files to the fixed timestamp. This is the default.
Specify an extra blob device to store chunk-based data.
Generate chunk-based files with #-byte chunks.
Apply a per-file compression strategy. Each line in file is defined by tokens separated by spaces in the following form. Optionally, instead of the given primary algorithm, alternative algorithms can be specified with algorithm-index explicitly:
<pcluster-size-in-bytes> [algorithm-index] <match-pattern>

match-patterns are extended regular expressions, matched against absolute paths within the output filesystem, with no leading /.

Ignore file that matches the exact literal path. You may give multiple --exclude-path options.
Ignore files that match the given extended regular expression. You may give multiple --exclude-regex options.
Read SELinux label configuration/overrides from file in the selinux_file(5) format.
Set all file UIDs to UID.
Set all file GIDs to GID.
Add GIDOFFSET to all file GIDs. When this option is used together with --force-gid, the final file gids are set to GID + GID-OFFSET.
Print the version number and exit.
Display help string and exit.
Ignore the file modification time whenever it would cause mkfs.erofs to use extended inodes over compact inodes. When not using a fixed timestamp, this can reduce total metadata size. Implied by -E force-inode-compact.
Specify maximum decompressed extent size in bytes.
(used together with -T) the given timestamp is only applied to the build time.
Use extended inodes instead of compact inodes if the file modification time would overflow compact inodes. This is the default. Overrides --ignore-mtime.
Inode data sorting order for tarballs as input.

MODE may be one of none or path.

none: No particular data order is specified for the target image to avoid unnecessary overhead; Currently, it takes effect if `-E^inline_data` is specified and no compression is applied.

path: Data order strictly follows the tree generation order. (default)

Treat SOURCE as a tarball or tarball-like "headerball" rather than as a directory.

MODE may be one of f, i, or headerball.

f: Generate a full EROFS image from a regular tarball. (default)

i: Generate a meta-only EROFS image from a regular tarball. Only metadata such as dentries, inodes, and xattrs will be added to the image, without file data. Uses for such images include as a layer in an overlay filesystem with other data-only layers.

headerball: Generate a meta-only EROFS image from a stream identical to a tarball except that file data is not present after each file header. It can improve performance especially when SOURCE is not seekable.

Add UIDOFFSET to all file UIDs. When this option is used together with --force-uid, the final file uids are set to UID + UIDOFFSET.
Filter tarball streams through gzip. Optionally, raw streams can be dumped together.
Filter tarball streams through xz, lzma, or lzip. Optionally, raw streams can be dumped together.
Specify a customized extended attribute namespace prefix for space saving, e.g. "trusted.overlay.". You may give multiple --xattr-prefix options (Linux v6.4+).

This version of mkfs.erofs is written by Li Guifu <blucerlee@gmail.com>, Miao Xie <miaoxie@huawei.com> and Gao Xiang <xiang@kernel.org> with continuously improvements from others.

This manual page was written by Gao Xiang <xiang@kernel.org>.

mkfs.erofs is part of erofs-utils package and is available from git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs-utils.git.

mkfs(8).