sqfstar

Create a squashfs filesystem (compressed using gzip by default) from an uncompressed tar archive

$ sqfstar [filesystem.squashfs] < [archive.tar]

$ zcat [archive.tar.gz] | sqfstar -comp [gzip|lzo|lz4|xz|zstd|lzma] [filesystem.squashfs]

$ xzcat [archive.tar.xz] | sqfstar [filesystem.squashfs] [file1 file2 ...]

$ zstdcat [archive.tar.zst] | sqfstar [filesystem.squashfs] "[*.gz]"

$ lz4cat [archive.tar.lz4] | sqfstar [filesystem.squashfs] -regex "[regular_expression]"

cat xxx.tar | sqfstar [OPTIONS] FILESYSTEM [exclude files] zcat xxx.tgz | sqfstar [OPTIONS] FILESYSTEM [exclude files] xzcat xxx.tar.xz | sqfstar [OPTIONS] FILESYSTEM [exclude files] zstdcat xxx.tar.zst | sqfstar [OPTIONS] FILESYSTEM [exclude files]

Squashfs is a highly compressed read-only filesystem for Linux. It uses either gzip/xz/lzo/lz4/zstd compression to compress both files, inodes and directories. Inodes in the system are very small and all blocks are packed to minimise data overhead. Block sizes greater than 4K are supported up to a maximum of 1Mbytes (default block size 128K).

Squashfs is intended for general read-only filesystem use, for archival use (i.e. in cases where a .tar.gz file may be used), and in constrained block device/memory systems (e.g. embedded systems) where low overhead is needed.

Filesystem compression options:

-b BLOCK_SIZE

set data block to BLOCK_SIZE. Default 128 Kbytes. Optionally a suffix of K or M can be given to specify Kbytes or Mbytes respectively.

-comp COMP

select COMP compression. Compressors available: gzip (default), lzo, lz4, xz, zstd, lzma.

-noI

do not compress inode table.

-noId

do not compress the uid/gid table (implied by -noI).

-noD

do not compress data blocks.

-noF

do not compress fragment blocks.

-noX

do not compress extended attributes.

-no-compression

do not compress any of the data or metadata. This is equivalent to specifying -noI -noD -noF and -noX.

Filesystem build options:

-reproducible

build filesystems that are reproducible (default).

-not-reproducible

build filesystems that are not reproducible.

-mkfs-time TIME

set filesystem creation timestamp to TIME. TIME can be an unsigned 32-bit int indicating seconds since the epoch (1970-01-01) or a string value which is passed to the "date" command to parse. Any string value which the date command recognises can be used such as "now", "last week", or "Wed Feb 15 21:02:39 GMT 2023".

-all-time TIME

set all file timestamps to TIME. TIME can be an unsigned 32-bit int indicating seconds since the epoch (1970-01-01) or a string value which is passed to the "date" command to parse. Any string value which the date command recognises can be used such as "now", "last week", or "Wed Feb 15 21:02:39 GMT 2023".

-root-time TIME

set root directory time to TIME. TIME can be an unsigned 32-bit int indicating seconds since the epoch (1970-01-01) or a string value which is passed to the "date" command to parse. Any string value which the date command recognises can be used such as "now", "last week", or "Wed Feb 15 21:02:39 GMT 2023".

-root-mode MODE

set root directory permissions to octal MODE.

-root-uid VALUE

set root directory owner to specified VALUE, VALUE can be either an integer uid or user name.

-root-gid VALUE

set root directory group to specified VALUE, VALUE can be either an integer gid or group name.

-all-root

make all files owned by root.

-force-uid VALUE

set all file uids to specified VALUE, VALUE can be either an integer uid or user name.

-force-gid VALUE

set all file gids to specified VALUE, VALUE can be either an integer gid or group name.

-default-mode MODE

tar files often do not store permissions for intermediate directories. This option sets the default directory permissions to octal MODE, rather than 0755. This also sets the root inode mode.

-default-uid UID

tar files often do not store uids for intermediate directories. This option sets the default directory owner to UID, rather than the user running Sqfstar. This also sets the root inode uid.

-default-gid GID

tar files often do not store gids for intermediate directories. This option sets the default directory group to GID, rather than the group of the user running Sqfstar. This also sets the root inode gid.

-pseudo-override

make pseudo file uids and gids override -all-root, -force-uid and -force-gid options.

-exports

make the filesystem exportable via NFS.

-no-sparse

do not detect sparse files.

-no-fragments

do not use fragments.

-no-tailends

do not pack tail ends into fragments.

-no-duplicates

do not perform duplicate checking.

-no-hardlinks

do not hardlink files, instead store duplicates.

Filesystem filter options:

-p PSEUDO-DEFINITION

add pseudo file definition. The definition should be quoted.

-pf PSEUDO-FILE

add list of pseudo file definitions. Pseudo file definitions in pseudo-files should not be quoted.

-ef EXCLUDE_FILE

list of exclude dirs/files. One per line.

-regex

allow POSIX regular expressions to be used in exclude dirs/files.

-ignore-zeros

allow tar files to be concatenated together and fed to Sqfstar. Normally a tarfile has two consecutive 512 byte blocks filled with zeros which means EOF and Sqfstar will stop reading after the first tar file on encountering them. This option makes Sqfstar ignore the zero filled blocks.

Filesystem extended attribute (xattrs) options:

-no-xattrs

do not store extended attributes.

-xattrs

store extended attributes (default).

-xattrs-exclude REGEX

exclude any xattr names matching REGEX. REGEX is a POSIX regular expression, e.g. -xattrs-exclude '^user.' excludes xattrs from the user namespace.

-xattrs-include REGEX

include any xattr names matching REGEX. REGEX is a POSIX regular expression, e.g. -xattrs-include '^user.' includes xattrs from the user namespace.

-xattrs-add NAME=VAL

add the xattr NAME with VAL to files. If an user xattr it will be added to regular files and directories (see man 7 xattr). Otherwise it will be added to all files. VAL by default will be treated as binary (i.e. an uninterpreted byte sequence), but it can be prefixed with 0s, where it will be treated as base64 encoded, or prefixed with 0x, where val will be treated as hexidecimal. Additionally it can be prefixed with 0t where this encoding is similar to binary encoding, except backslashes are specially treated, and a backslash followed by 3 octal digits can be used to encode any ASCII character, which obviously can be used to encode control codes. The option can be repeated multiple times to add multiple xattrs.

Sqfstar runtime options:

-version

print version, licence and copyright message.

-force

force Sqfstar to write to block device or file.

-exit-on-error

treat normally ignored errors as fatal.

-quiet

no verbose output.

-info

print files written to filesystem.

-no-progress

do not display the progress bar.

-progress

display progress bar when using the -info option.

-percentage

display a percentage rather than the full progress bar. Can be used with dialog --gauge etc.

-throttle PERCENTAGE

throttle the I/O input rate by the given percentage. This can be used to reduce the I/O and CPU consumption of Sqfstar.

-limit PERCENTAGE

limit the I/O input rate to the given percentage. This can be used to reduce the I/O and CPU consumption of Sqfstar (alternative to -throttle).

-processors NUMBER

use NUMBER processors. By default will use number of processors available.

-mem SIZE

use SIZE physical memory for caches. Use K, M or G to specify Kbytes, Mbytes or Gbytes respectively.

-mem-percent PERCENT

use PERCENT physical memory for caches. Default 25%.

-mem-default

print default memory usage in Mbytes.

Expert options (these may make the filesystem unmountable):

-nopad

do not pad filesystem to a multiple of 4K.

-offset OFFSET

skip OFFSET bytes at the beginning of FILESYSTEM. Optionally a suffix of K, M or G can be given to specify Kbytes, Mbytes or Gbytes respectively. Default 0 bytes.

-o OFFSET

synonym for -offset.

Miscellaneous options:

-fstime TIME

alternative name for mkfs-time.

-root-owned

alternative name for -all-root.

-noInodeCompression

alternative name for -noI.

-noIdTableCompression

alternative name for -noId.

-noDataCompression

alternative name for -noD.

-noFragmentCompression

alternative name for -noF.

-noXattrCompression

alternative name for -noX.

-help

output this options text to stdout.

-h

output this options text to stdout.

-Xhelp

print compressor options for selected compressor.

-p "filename d mode uid gid"

create a directory.

-p "filename m mode uid gid"

modify filename.

-p "filename b mode uid gid major minor"

create a block device.

-p "filename c mode uid gid major minor"

create a character device.

-p "filename f mode uid gid command"

create file from stdout of command.

-p "filename s mode uid gid symlink"

create a symbolic link.

-p "filename i mode uid gid [s|f]"

create a socket (s) or FIFO (f).

-p "filename x name=val"

create an extended attribute.

-p "filename l linkname"

create a hard-link to linkname.

-p "filename L pseudo_filename"

same, but link to pseudo file.

-p "filename D time mode uid gid"

create a directory with timestamp time.

-p "filename M time mode uid gid"

modify a file with timestamp time.

-p "filename B time mode uid gid major minor"

create block device with timestamp time.

-p "filename C time mode uid gid major minor"

create char device with timestamp time.

-p "filename F time mode uid gid command"

create file with timestamp time.

-p "filename S time mode uid gid symlink"

create symlink with timestamp time.

-p "filename I time mode uid gid [s|f]"

create socket/fifo with timestamp time.

gzip (default):

-Xcompression-level COMPRESSION-LEVEL

COMPRESSION-LEVEL should be 1 .. 9 (default 9).

-Xwindow-size WINDOW-SIZE

WINDOW-SIZE should be 8 .. 15 (default 15).

-Xstrategy strategy1,strategy2,...,strategyN

Compress using strategy1,strategy2,...,strategyN in turn and choose the best compression. Available strategies: default, filtered, huffman_only, run_length_encoded and fixed.

lzo:

-Xalgorithm ALGORITHM

Where ALGORITHM is one of: lzo1x_1, lzo1x_1_11, lzo1x_1_12, lzo1x_1_15, lzo1x_999 (default).

-Xcompression-level COMPRESSION-LEVEL

COMPRESSION-LEVEL should be 1 .. 9 (default 8) Only applies to lzo1x_999 algorithm.

lz4:

-Xhc

Compress using LZ4 High Compression.

xz:

-Xbcj filter1,filter2,...,filterN

Compress using filter1,filter2,...,filterN in turn (in addition to no filter), and choose the best compression. Available filters: x86, arm, armthumb, powerpc, sparc, ia64.

-Xdict-size DICT-SIZE

Use DICT-SIZE as the XZ dictionary size. The dictionary size can be specified as a percentage of the block size, or as an absolute value. The dictionary size must be less than or equal to the block size and 8192 bytes or larger. It must also be storable in the xz header as either 2^n or as 2^n+2^(n+1). Example dict-sizes are 75%, 50%, 37.5%, 25%, or 32K, 16K, 8K etc.

zstd:

-Xcompression-level COMPRESSION-LEVEL

COMPRESSION-LEVEL should be 1 .. 22 (default 15).

lzma:

(no options) (deprecated - no kernel support)

SOURCE_DATE_EPOCH

If set, this is used as the filesystem creation timestamp. Also any file timestamps which are after SOURCE_DATE_EPOCH will be clamped to SOURCE_DATE_EPOCH. See https://reproducible-builds.org/docs/source-date-epoch/ for more information.

sqfstar IMAGE.SQFS < archive.tar

Create a Squashfs filesystem from the uncompressed tar file "archive.tar". Sqfstar will use the default compressor (normally gzip), and block size of 128 Kbytes.

zcat archive.tgz | sqfstar IMAGE.SQFS

Create a Squashfs filesystem from the compressed tar file "archive.tgz". Sqfstar will use the default compressor (normally gzip), and block size of 128 Kbytes.

sqfstar -b 1M -comp zstd IMAGE.SQFS < archive.tar

Use a block size of 1 Mbyte and Zstandard compression to create the filesystem.

sqfstar -root-uid 0 -root-gid 0 IMAGE.SQFS < archive.tar

Tar files do not supply a definition for the root directory, and the default is to make the directory owned/group owned by the user running Sqfstar. The above command sets the ownership/group ownership to root.

sqfstar -root-mode 0755 IMAGE.SQFS < archive.tar

The default permissions for the root directory is 0777 (rwxrwxrwx). The above command sets the permissions to 0755 (rwxr-xr-x).

sqfstar IMAGE.SQFS file1 file2 < archive.tar

Exclude file1 and file2 from the tar file when creating filesystem.

sqfstar IMAGE.SQFS "*.gz" < archive.tar

Exclude any files in the top level directory which matches the wildcard pattern "*.gz".

sqfstar IMAGE.SQFS "... *.gz" < archive.tar

Exclude any file which matches the wildcard pattern "*.gz" anywhere within the tar file. The initial "..." indicates the wildcard pattern is "non-anchored" and will match anywhere.

Note: when passing wildcarded names to Sqfstar, they should be quoted (as in the above examples), to ensure that they are not processed by the shell.

Using pseudo file definitions

sqfstar -p "build_dir d 0644 0 0" IMAGE.SQFS < archive.tar

Create a directory called "build_dir" in the output filesystem.

sqfstar -p "version.txt l /tmp/build/version" IMAGE.SQFS < archive.tar

Create a reference called "version.txt" to a file not in the tar archive, which acts as if that file was in the tar archive.

sqfstar -p "date.txt f 0644 0 0 date" IMAGE.SQFS < archive.tar

Create a file called "date.txt" which holds the output (stdout) from running the "date" command.

sqfstar -p "\"hello world\" f 0644 0 0 date" IMAGE.SQFS < archive.tar

As above, but, showing that filenames can have spaces, if they are quoted. The quotes need to be blackslashed to protect them from the shell.

sqfstar -p "input f 0644 root root dd if=/dev/sda1 bs=1024" IMAGE.SQFS < archive.tar

Create a file containing the contents of partition /dev/sda1". The above allows input from these special files to be captured and placed in the Squashfs filesystem.

Note: pseudo file definitions should be quoted (as in the above examples), to ensure that they are passed to Mksquashfs as a single argument, and to ensure that they are not processed by the shell.

Copyright © 2023 Phillip Lougher <phillip@squashfs.org.uk>

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

mksquashfs(1), unsquashfs(1), sqfscat(1) The README for the Squashfs-tools 4.6.1 release, describing the new features can be read here https://github.com/plougher/squashfs-tools/blob/master/README-4.6.1 The Squashfs-tools USAGE guide can be read here https://github.com/plougher/squashfs-tools/blob/master/USAGE-4.6

Written by Phillip Lougher <phillip@squashfs.org.uk>