genext2fs - ext2 filesystem generator for embedded systems
genext2fs [ options ] [ output-image ]
genext2fs generates an ext2 filesystem as a normal (non-root) user. It does not require you to mount the image file to copy files on it, nor does it require that you become the superuser to make device nodes.
The filesystem image is created in the file output-image. If not
specified, it is sent to stdout. The -d and -a options support reading
from stdin if a single hyphen is given as an argument. Thus, genext2fs
can be used as part of a pipeline without any temporary files.
By default, the maximum number of inodes in the filesystem is the minimum number required to accommodate the initial contents. In this way, a minimal filesystem (typically read-only) can be created with minimal free inodes. If required, free inodes can be added by passing the relevant options. The filesystem image size in blocks can be minimised by trial and error.
-x, --starting-image image
Use this image as a starting point.
-d, --root directory[:path]
Add the given directory and contents at a particular path (by default the root).
-D, --devtable spec-file[:path]
Use spec-file to specify inodes to be added, at the given path (by default the root), including files, directories and special files like devices. If the specified files are already present in the image, their ownership and permission modes will be adjusted accordingly (this can only occur when the -D option appears after the options that create the specified files). Furthermore, you can use a single table entry to create many devices with a range of minor numbers (see examples below). All specified inodes receive the mtime of spec-file itself.
-a, --tarball file[:path]
Add the given archive (tarball) contents at a particular path (by default
the root). If file is a hyphen, then the tarball will be read from
standard input.
Note: if not compiled with libarchive, genext2fs will use a builtin
tarball parser with very primitive capabilities (e.g. no sparse file
support, generally no support other than for modern GNU tar without
fancy options).
-b, --size-in-blocks blocks
Size of the image in blocks.
-B, --block-size bytes
Size of a filesystem block in bytes.
-N, --number-of-inodes inodes
Minimum number of inodes. The required inode number will be computed
automatically for all input that is not read from stdin. The number given
by this option sets the minimum number of inodes. If you add anything
from standard input, you should set this value because in that case the
required number of inodes cannot be precomputed. The value set by this
option will be overwritten by the value computed from the -i option,
if the resulting number of inodes is larger.
-L, --volume-label name
Set the volume label for the filesystem.
-i, --bytes-per-inode ratio
Used to calculate the minimum number of inodes from the available blocks.
Inodes are computed by multiplying the number of blocks (-b) by the blocksize
(1024) and dividing that by the ratio given in this option. If the result
is larger, then the number of required inodes counted from the input or the
minimum number of inodes from the -N option, then the value computed by
this option is used.
-m, --reserved-percentage N
Number of reserved blocks as a percentage of size. Reserving 0 blocks
will prevent creation of the lost+found directory.
-o, --creator-os name
Value for creator OS field in superblock.
-g, --block-map path
Generate a block map file for this path.
-e, --fill-value value
Fill unallocated blocks with value.
-z, --allow-holes
Make files with holes.
-f, --faketime
Use a timestamp of 0 for inode and filesystem creation, instead of the present. Useful for testing.
-q, --squash
Squash permissions and owners (same as -P -U).
-U, --squash-uids
Squash ownership of inodes added using the -d option, making them all owned by root:root.
-P, --squash-perms
Squash permissions of inodes added using the -d option. Analogous to
umask 077.
-v, --verbose
Print resulting filesystem structure.
-V, --version
Print genext2fs version.
-h, --help
Display help.
genext2fs -b 1440 -d src /dev/fd0
All files in the src directory will be written to /dev/fd0 as a new ext2 filesystem image. You can then mount the floppy as usual.
genext2fs -b 1024 -d src -D devicetable.txt flashdisk.img
This example builds a filesystem from all the files in src, then device nodes are created based on the contents of the file devicetable.txt. Entries in the device table take the form of:
<name> <type> <mode> <uid> <gid> <major> <minor> <start> <inc> <count>
where name is the file name and type can be one of:
f A regular file
d Directory
c Character special device file
b Block special device file
p Fifo (named pipe)
uid is the user id for the target file, gid is the group id for the target file. The rest of the entries (major, minor, etc) apply only to device special files.
An example device file follows:
# name type mode uid gid major minor start inc count
/dev d 755 0 0 - - - - -
/dev/mem c 640 0 0 1 1 0 0 -
/dev/tty c 666 0 0 5 0 0 0 -
/dev/tty c 666 0 0 4 0 0 1 6
/dev/loop b 640 0 0 7 0 0 1 2
/dev/hda b 640 0 0 3 0 0 0 -
/dev/hda b 640 0 0 3 1 1 1 16
/dev/log s 666 0 0 - - - - -
This device table creates the /dev directory, a character device node
/dev/mem (major 1, minor 1), and also creates /dev/tty, /dev/tty[0-5],
/dev/loop[0-1], /dev/hda, /dev/hda1 to /dev/hda15 and /dev/log socket.