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mksquashfs − Create or modify a Squash file system

SYNOPSIS

DESCRIPTION

A squashfs is a compressed read−only file system. Use the mksquashfs program to create a new squashed file system, and to append new data to an existing squashed file system.

If a single source directory is specified (i.e. mksquashfs source output_fs), the squashfs filesystem will consist of that directory, with the top−level root directory corresponding to the source directory.

If multiple source directories or files are specified, mksquashfs will merge the specified sources into a single filesystem, with the root directory containing each of the source files/directories. The name of each directory entry will be the basename of the source path. If more than one source entry maps to the same name, the conflicts are named xxx_1, xxx_2, etc. where xxx is the original name.

The dest argument can either be a conventional file or a block device. If the file doesn’t exist it will be created, if it does exist and a squashfs filesystem exists on it, mksquashfs will append. The −noappend option will write a new filesystem irrespective of whether an existing filesystem is present.

There are a large number of options that can be used to control the compression in mksquashfs. By and large the defaults are the most optimum settings and should only be changed in exceptional circumstances !

The −noI, −noD and −noF options (also −noInodeCompression, −noDataCompression and −noFragmentCompression) can be used to force mksquashfs to not compress inodes/directories, data and fragments respectively. Giving all options generates an uncompressed filesystem.

By default files in the generated filesystem inherit the UID and GID ownership of the original file. However, mksquashfs provides a number of options which can be used to override the ownership:

The −e and −ef options allow files/directories to be specified which are excluded from the output filesystem. The −e option takes the exclude files/directories from the command line, the −ef option takes the exlude files/directories from the specified exclude file, one file/directory per line. If an exclude file/directory is absolute (i.e. prefixed with /, ../, or ./) the entry is treated as absolute, however, if an exclude file/directory is relative, it is treated as being relative to each of the sources in turn, i.e. mksquashfs /tmp/source1 source2 output_fs −e ex1 /tmp/source1/ex2 out/ex3 Will generate exclude files /tmp/source1/ex2, /tmp/source1/ex1, source2/ex1, /tmp/source1/out/ex3 and source2/out/ex3.

The −e and −ef exclude options are usefully used in archiving the entire filesystem, where it is wished to avoid archiving /proc, and the filesystem being generated, i.e. mksquashfs / /tmp/root.sqsh −e proc /tmp/root.sqsh

Multiple −ef options can be specified on the command line, and the −ef option can be used in conjuction with the −e option.

The −info option displays the files/directories as they are compressed and added to the filesystem. The original uncompressed size of each file is printed, along with DUPLICATE if the file is a duplicate of a file in the filesystem.

The −le and −be options can be used to force mksquashfs to generate a little endian or big endian filesystem. Normally mksquashfs will generate a filesystem in the host byte order. Squashfs, for portability, will mount different ordered filesystems (i.e. it can mount big endian filesystems running on a little endian machine), but these options can be used for greater optimisation.

OPTIONS

−version

print version, licence and copyright message.

−info

print files written to filesystem

−b block_size

set data block to block_size. This can be either 4096, 8192, 16384, 32768 or 65536 bytes. Default is 65536 bytes

−2.0

create a 2.0 filesystem

−noI or −noInodeCompression

do not compress inode table

−noDor −noDataCompression

do not compress data blocks

−noF or −noFragmentCompression

do not compress fragment blocks

−no−fragments

do not use fragments: tells mksquashfs to not generate fragment blocks, and rather generate a filesystem similar to a Squashfs 1.x filesystem. It will of course still be a Squashfs 2.0 filesystem but without fragments, and so it won’t be mountable on a Squashfs 1.x system.

−always−use−fragments

use fragment blocks for files larger than block size: tells mksquashfs to always generate fragments for files irrespective of the file length. By default only small files less than the block size are packed into fragment blocks. The ends of files which do not fit fully into a block, are NOT by default packed into fragments. To illustrate this, a 100K file has an initial 64K block and a 36K remainder. This 36K remainder is not packed into a fragment by default. This is because to do so leads to a 10 − 20% drop in sequential I/O performance, as a disk head seek is needed to seek to the initial file data and another disk seek is need to seek to the fragment block. Specify this option if you want file remainders to be packed into fragment blocks. Doing so may increase the compression obtained BUT at the expense of I/O speed.

−no−duplicates

do not perform duplicate checking: tells mksquashfs to not check the files being added to the filesystem for duplicates. This can result in quicker filesystem generation and appending although obviously compression will suffer badly if there is a lot of duplicate files.

−noappend

do not append to existing filesystem

−keep−as−directory

if one source directory is specified, create a root directory containing that directory, rather than the contents of the directory

−root−becomes name

when appending source files/directories, make the original root become a subdirectory in the new root called name, rather than adding the new source items to the original root

−all−root or −root−owned

make all files owned by root

−force−uid uid

set all file uids to uid

−force−gid gid

set all file gids to gid

−le

create a little endian filesystem

−be

create a big endian filesystem

−nopad

do not pad filesystem to a multiple of 4Ko. This is performed by default to enable the output filesystem file to be mounted by loopback, which requires files to be a 4K multiple. If the filesystem is being written to a block device, or is to be stored in a bootimage, the extra pad bytes are not needed.

−check_data

add checkdata for greater filesystem checks

−sort sort_file

sort files according to priorities in sort_file. One file or dir with priority per line. Priority −32768 to 32767, default priority 0

−e list of exclude dirs/files

inline list of files / directories to exclude

−ef exclude_file

file containing a list of files / directories to exclude, one per line

EXAMPLES

For following examples, take two example directories:

Exemple 1. 

mksquashfs /home/phillip/test output_fs

This will generate a squashfs filesystem with root entries file1, file2 and dir1.

Exemple 2. 

mksquashfs /home/phillip/test goodies output_fs

This will create a squashfs filesystem with the root containing entries test and goodies corresponding to the source directories /home/phillip/test and goodies.

Exemple 3. 

mksquashfs /home/phillip/test goodies test output_fs

This is the same as the previous example, except a third source directory test has been specified. This conflicts with the first directory named test and will be renamed test_1.

Multiple sources allow filesystems to be generated without needing to copy all source files into a common directory. This simplifies creating filesystems.

Exemple 4. 

mksquashfs /home/phillip/test output_fs −keep−as−directory

This is the same as the first example, except for −keep−as−directory. This will generate a root directory containing directory test, rather than the test directory contents file1, file2 and dir1.

AUTHORS

Squashfs was written by Phillip Lougher <plougher [AT] users.net>, in Chepstow, Wales, UK. If you like the program, or have any problems, then please email me, as it’s nice to get feedback !

This manual page was written by Frédéric Boiteux <fboiteux [AT] calistel.com> for the Debian(TM) system (but may be used by others) using the SquashFS HOWTO from Artemiy I. Pavlov and squashfs’s README file. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU General Public License, Version 2 any later version published by the Free Software Foundation.

On Debian systems, the complete text of the GNU General Public License can be found in /usr/share/common−licenses/GPL.

COPYRIGHT

Copyright © 2005 Frédéric Boiteux