Ubuntu Manpage: mkfs.erofs - tool to create an EROFS filesystem

NAME

       mkfs.erofs - tool to create an EROFS filesystem

SYNOPSIS

       mkfs.erofs [OPTIONS] DESTINATION SOURCE

DESCRIPTION

       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.

OPTIONS

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

-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. To disable a feature, usually prefix the extended
option name with a caret ('^') character. 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).

[^]fragdedupe[=<inode|full>]
Set the mode for fragment data deduplication. It's effective only when
-E(all)-fragments is used together. If a caret ('^') character is set, fragment data
deduplication is disabled.

inode Deduplicate fragment data only when the inode data is identical. This
option will result in faster image generation with the current codebase

full Always deduplicate fragment data if possible

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+)

^inline_data
Don't inline regular files. It's typically useful to enable FSDAX (Linux 5.15+) for
those images, however, there could be other use cases too.

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

xattr-name-filter
Enable a name filter for extended attributes to optimize negative 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 15 bytes.

-T # 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.

-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".
The UUID parameter may also be one of the following:

clear clear the file system UUID

random generate a new randomly-generated UUID

--all-root
Make all files owned by root.

--all-time
(used together with -T) set all files to the fixed timestamp. This is the default.

--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 /.

--dsunit=#
Align all data block addresses to multiples of #.

--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.

-V, --version
Print the version number and exit.

-h, --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.

--mkfs-time
(used together with -T) the given timestamp is only applied to the build time.

--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.

--sort=MODE
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)

--tar, --tar=MODE
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.

--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.

--ungzip[=file]
Filter tarball streams through gzip. Optionally, raw streams can be dumped together.

--unxz[=file]
Filter tarball streams through xz, lzma, or lzip. Optionally, raw streams can be dumped together.

--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+).

AUTHOR

       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>.

AVAILABILITY