sqfstar(1)

Usage

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]}

Overview

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.

Options

Filesystem compression options:

-b BLOCK-SIZE: set data block to BLOCK-SIZE. Default 128 Kbytes. Optionally a suffix of K, KB, Kbytes or M, MB, Mbytes can be given to specify Kbytes or Mbytes respectively.

-comp COMP: select COMP compression. Run -help-comp COMP to get compressor options for COMP, or ALL for all the compressors. 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:

-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.

-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.

-ef EXCLUDE-FILE: list of exclude dirs/files. One per line.

Filesystem time options:

-mkfs-time TIME: set filesystem creation timestamp to TIME. TIME can be "inode", which means use the latest inode timestamp, 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".

-inode-time TIME: set all file and directory timestamps to TIME. TIME can be "inode", which means use the latest inode timestamp, 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 2025". This option sets and overrides the -root-time option.

-root-time TIME: set root directory time to TIME. TIME can be "inode", which means use the latest inode timestamp, 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 2025".

-repro: build a reproducible filesystem image. This is equivalent to -mkfs-time inode, which achieves reproducibility by setting the filesystem build time to the latest inode timestamp. Obviously the image won't be reproducible if the timestamps or content changes.

-repro-time TIME: build a reproducible filesystem image. This is equivalent to specifying -mkfs-time TIME and -inode-time TIME, which achieves reproducibility by setting all timestamps to TIME. This option can be used in cases where timestamps may change, and where -repro cannot be used for this reason.

Filesystem permissions options:

-all-root: make all files and directories owned by root.

-root-mode MODE: set root directory permissions to MODE. MODE can be symbolic or octal (see section Symbolic mode specification). Default root mode is ugo=rwx or 0777 octal.

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

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

-force-file-mode MODE: set all file (non-directory) permissions to MODE. MODE can be symbolic or octal (see section Symbolic mode specification).

-force-dir-mode MODE: set all directory permissions to MODE. MODE can be symbolic or octal (see section Symbolic mode specification).

-force-uid USER: set all file and directory uids to specified USER, USER can be either an integer uid or user name.

-force-gid GROUP: set all file and directory gids to specified GROUP, GROUP can be either an integer gid or group name.

-uid-gid-offset VALUE: offset all uid and gids by specified VALUE. VALUE should be a positive integer.

-default-mode MODE: tar files often do not store permissions for intermediate directories. This option sets the default directory permissions to MODE. MODE can be symbolic or octal (see section Symbolic mode specification). Default mode is u=rwx,go=rx or 0755 octal. This also sets the root directory mode.

-default-uid USER: tar files often do not store uids for intermediate directories. This option sets the default directory owner to USER, rather than the user running Sqfstar. USER can be either an integer uid or user name. This also sets the root directory uid.

-default-gid GROUP: tar files often do not store gids for intermediate directories. This option sets the default directory group to GROUP, rather than the group of the user running Sqfstar. GROUP can be either an integer gid or group name. This also sets the root directory gid.

-numeric-owner: Use the numeric uid and gid in the tarfile rather than the user name or group name. This is useful where the user name or group name maps to a different uid or gid on the system where Sqfstar is being run, and this remapping behaviour is not wanted.

Filesystem pseudo options:

-p PSEUDO-DEFINITION: add pseudo file definition. The definition should be quoted. See section "Pseudo file definition format" for format details.

-pd "d mode uid gid": specify a default pseudo directory which will be used in pseudo definitions if a directory in the pathname does not exist. This also allows pseudo definitions to be specified without specifying all the directories in the pathname. The definition should be quoted.

-pd "D time mode uid gid": specify a default pseudo directory which will be used in pseudo definitions if a directory in the pathname does not exist. The D type also allows a timestamp to be specified in addition to mode, uid and gid.

-pf PSEUDO-FILE: add list of pseudo file definitions. Pseudo file definitions in pseudo-files should not be quoted.

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

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 to stdout. This automatically disables the progress bar. See -info-file to output to file without disabling the progress bar.

-info-file FILE: print files written to filesystem to file FILE. This does not disable the progress bar.

-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.

-overcommit PERCENT: allow PERCENT more threads to run in parallel than available processors. Doing this may increase CPU utilisation. Default is 0%, because normally overcommiting reduces performance due to trashing. The percentage value is at the granularity of the number of processors, e.g. 4 processors have a percentage granularity of 25%, and 20 processors have a percentage granularity of 5%.

Expert options (these may make the filesystem unmountable):

-stream: output the filesystem to STDOUT rather than to a file. This allows the output to be piped to another program or elsewhere with ssh. The resultant streamed Squashfs filesystem will not be a normal Squashfs filesystem because the super block will be at the end of the filesystem. But it can be fixed up afterwards with the -fix option and Unsquashfs 4.7.3 and later can read streamed unfixed up filesystems directly. Duplicate detection is disabled using the -stream option.

-fix FILESYSTEM: fix FILESYSTEM generated using the -stream option.

-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.

Help options:

-help: print help summary information to pager (or stdout if not a terminal).

-help-option REGEX: print the help information for options matching REGEX to pager (or stdout if not a terminal).

-help-section SECTION: print the help information for section SECTION to pager (or stdout if not a terminal). If SECTION does not exactly match a section name, it is treated as a regular expression, and all section names that match are displayed. Use "list" as section name to get a list of sections and their names.

-help-comp COMP: print compressor options for compressor COMP. Use "list" to get a list of available compressors, and "all" to get the compressor options for all the compressors.

-help-all: print help information for all Sqfstar options and sections to pager (or stdout if not a terminal).

-Xhelp: print compressor options for selected compressor.

-h: shorthand alternative to -help.

-ho REGEX: shorthand alternative to -help-option.

-hs SECTION: shorthand alternative to -help-section.

-ha: shorthand alternative to -help-all.

-no-pager: do not use a pager to output help information.

-cols WIDTH: use WIDTH columns to output help information. Useful if output is not to a terminal.

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.

Pseudo file definition format

`-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 h linkname"`	create a hard-link to linkname, follows symlinks.
`-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.

Symbolic mode specification

The symbolic mode is of the format [ugoa]*[[+-=]PERMS]+. PERMS = [rwxXst]+ or [ugo], and the sequence can be repeated separated with commas.

A combination of the letters ugoa specify which permission bits will be affected, u means user, g means group, o means other, and a means all or ugo.

The next letter is +, - or =. The letter + means add to the existing permission bits, - means remove the bits from the existing permission bits, and = means set the permission bits.

The permission bits (PERMS) are a combination of [rwxXst] which sets/adds/removes those bits for the specified ugoa combination, r means read, w means write and x means execute for files or search for directories. X has a special meaning, if the file is a directory it is equivalent to x or search, but if it is a non-directory, it only takes effect if execute is already set for user, group or other. The s flag sets user or group ID on execution, and the t flag on a directory sets restricted deletion, or historically made the file sticky if a non-directory.

The permission bits can also be u, g or o, which takes the permission bits from the user, group or other of the file respectively.

Exit status

0: Sqfstar successfully generated a filesystem.

1: Fatal errors occurred, Sqfstar aborted and did not generate a filesystem.

Options

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, arm64, powerpc, sparc, ia64, riscv.

-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 -131072 .. -1 or 1 .. 22 (default 15). Negative compression levels correspond to the zstd --fast option.

lzma:

: (no options) (deprecated - no kernel support)

Environment

SQFS_CMDLINE: If set, this is used as the directory to write the file sqfs_cmdline which contains the command line arguments given to Sqfstar. Each command line argument is wrapped in quotes to ensure there is no ambiguity when arguments contain spaces. If the file already exists then the command line is appended to the file.

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.

PAGER: If set, this is used as the name of the program used to display the help text. The value can be a simple command or a pathname. The default is /usr/bin/pager.

Examples

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 -all-time now IMAGE.SQFS < archive.tar: Set all file and directory timestamps to "now" (current time) in the filesystem.

sqfstar -force-uid phillip -force-gid phillip IMAGE.SQFS < archive.tar: Make all files and directories in the filesystem owned by "phillip".

sqfstar -force-file-mode ugo+r,go-w IMAGE.SQFS < archive.tar: Make all files readable by everyone, but only writable by user, all other permission bits are unaffected.

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.

Releases

3 releases since Debian 12 (Bookworm); the text changed 2 times.

-cols since Arch Linux 2026-11-01; -default-gid since Debian 13 (Trixie); -default-mode since Debian 13 (Trixie); -default-uid since Debian 13 (Trixie); -fix since Arch Linux 2026-11-01; -force-dir-mode since Arch Linux 2026-11-01; -force-file-mode since Arch Linux 2026-11-01; -ha since Arch Linux 2026-11-01; -help-all since Arch Linux 2026-11-01; -help-comp since Arch Linux 2026-11-01; -help-option since Arch Linux 2026-11-01; -help-section since Arch Linux 2026-11-01; -ho since Arch Linux 2026-11-01; -hs since Arch Linux 2026-11-01; -ignore-zeros since Debian 13 (Trixie); -info-file since Arch Linux 2026-11-01; -inode-time since Arch Linux 2026-11-01; -mem-default since Debian 13 (Trixie); -mem-percent since Debian 13 (Trixie); -no-compression since Debian 13 (Trixie); -no-pager since Arch Linux 2026-11-01; -numeric-owner since Arch Linux 2026-11-01; -overcommit since Arch Linux 2026-11-01; -p since Debian 13 (Trixie); -percentage since Debian 13 (Trixie); -pf since Debian 13 (Trixie); -pseudo-override since Debian 13 (Trixie); -repro since Arch Linux 2026-11-01; -repro-time since Arch Linux 2026-11-01; -stream since Arch Linux 2026-11-01; -uid-gid-offset since Arch Linux 2026-11-01; -xattrs-add since Debian 13 (Trixie); -xattrs-exclude since Debian 13 (Trixie); -xattrs-include since Debian 13 (Trixie).

-all-time until Debian 13 (Trixie); -not-reproducible until Debian 13 (Trixie); -reproducible until Debian 13 (Trixie).

Referred to by

sqfscat(1) tool to cat files from a squashfs filesystem to stdout mksquashfs(1) tool to create and append to squashfs filesystems unsquashfs(1) tool to uncompress, extract and list squashfs filesystems

Usage

Overview

Options

Filesystem compression options:

Filesystem build options:

Filesystem time options:

Filesystem permissions options:

Filesystem pseudo options:

Filesystem extended attribute (xattrs) options:

Sqfstar runtime options:

Expert options (these may make the filesystem unmountable):

Help options:

Miscellaneous options:

Pseudo file definition format

Symbolic mode specification

Exit status

Options

gzip (default):

lzo:

lz4:

xz:

zstd:

lzma:

Environment

Examples

Using pseudo file definitions

Releases

See also

Referred to by