mkfs.erofs - Man Page

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.

-z compression-algorithm[,#][:...]

Set a primary algorithm for data compression, which can be set with an optional compression level (1 to 12 for LZ4HC, 0 to 9 for LZMA and 100 to 109 for LZMA extreme compression) separated by a comma.  Alternative algorithms could be specified and separated by colons.

-b block-size

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.

-C max-pcluster-size

Specify the maximum size of compress physical cluster in bytes. This may cause the big pcluster feature to be enabled (Linux v5.13+).

-d #

Specify the level of debugging messages. The default is 2, which shows basic warning messages.

-x #

Limit how many xattrs will be inlined. The default is 2. Disables storing xattrs if < 0.

-E extended-option[,...]

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:

all-fragments

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+)

dedupe

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-inode-compact

Force generation of compact (32-byte) inodes.

force-inode-extended

Force generation of extended (64-byte) inodes.

force-inode-blockmap

Force generation of inode chunk format as a 4-byte block address array.

force-chunk-indexes

Forcely generate inode chunk format as an 8-byte chunk index (with device ID).

fragments[=size]

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+)

legacy-compress

Disable "inplace decompression" and "compacted indexes", for compatibility with Linux pre-v5.4.

noinline_data

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+).

ztailpacking

Pack the tail part (pcluster) of compressed files into its metadata to save more space and the tail part I/O. (Linux v5.17+)

-L volume-label

Set the volume label for the filesystem to volume-label. The maximum length of the volume label is 16 bytes.

-T #

Set all files to the given UNIX timestamp. Reproducible builds require setting all to a specific one. By default, the source file's modification time is used.

-U UUID

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".

--all-root

Make all files owned by root.

--blobdev file

Specify an extra blob device to store chunk-based data.

--chunksize #

Generate chunk-based files with #-byte chunks.

--compress-hints file

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 /.

--exclude-path=path

Ignore file that matches the exact literal path. You may give multiple --exclude-path options.

--exclude-regex=regex

Ignore files that match the given extended regular expression. You may give multiple --exclude-regex options.

--file-contexts=file

Read SELinux label configuration/overrides from file in the selinux_file(5) format.

--force-uid=UID

Set all file UIDs to UID.

--force-gid=GID

Set all file GIDs to GID.

--gid-offset=GIDOFFSET

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.

--gzip

Filter tarball streams through gzip.

--help

Display help string and exit.

--ignore-mtime

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.

--max-extent-bytes #

Specify maximum decompressed extent size in bytes.

--preserve-mtime

Use extended inodes instead of compact inodes if the file modification time would overflow compact inodes. This is the default. Overrides --ignore-mtime.

--tar=f

Generate a full EROFS image from a tarball.

--tar=i

Generate an meta-only EROFS image from a tarball.

--uid-offset=UIDOFFSET

Add UIDOFFSET to all file UIDs. When this option is used together with --force-uid, the final file uids are set to UID + UIDOFFSET.

--xattr-prefix=PREFIX

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).

dump.erofs(1), erofs(5).