TAR2SQFS

Section: User Commands (1)
Updated: June 2019
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NAME

tar2sqfs - create a SquashFS image from a tar archive

SYNOPSIS

tar2sqfs [,OPTIONS/...] ,<sqfsfile>/

DESCRIPTION

Quickly and painlessly turn a tar ball into a SquashFS filesystem image.

By default, the program reads the archive from standard input. Compressed archives are supported.

Possible options:

--root-becomes, -r <dir>

If set, only pack entries that are underneath the specified directory. The prefix is stripped and the meta data for the directory itself is copied to the root inode (i.e. the ownership, permissions, extended attributes, modification time).

If this option is not set, tar2sqfs implicitly treats ./ or absolute paths this way, i.e. if the archive contains an entry for ./, it becomes the root node and the prefix is stripped from all paths (and similar for absolute paths and /).

--no-symlink-retarget, -S

If --root-becomes is used, link targets are adjusted if they are prefixed by the root path. By default, this is also done on symbolic links, that have a target that is prefixed by the root path and they are converted to aboluste paths with the prefix removed. However, because symlinks can point across mount points, this may actually be intended for some use cases.

This flag allows changing the default behaviour, so only hard links are retargeted.

--compressor, -c <name>

Select the compressor to use. Run tar2sqfs --help to get a list of all available compressors and the default selection.

--comp-extra, -X <options>

A comma separated list of extra options for the selected compressor. Specify help to get a list of available options.

--num-jobs, -j <count>

If libsquashfs was compiled with a thread pool based, parallel data compressor, this option can be used to set the number of compressor threads. If not set, the default is the number of available CPU cores.

--queue-backlog, -Q <count>

Maximum number of data blocks in the thread worker queue before the packer starts waiting for the block processors to catch up. Higher values result in higher memory consumption. Defaults to 10 times the number of workers.

--block-size, -b <size>

Block size to use for SquashFS image. Defaults to 131072.

--dev-block-size, -B <size>

Device block size to padd the image to. Defaults to 4096.

--defaults, -d <options>

A comma separated list of default values for implicitly created directories. The following values can be set:

Option	Default
uid=<value>	0
gid=<value>	0
mode=<value>	0755
mtime=<value>	$SOURCE_DATE_EPOCH if set, 0 otherwise

--no-keep-time, -k

Replace the time stamps from the tar archive with default time stamps for all entries.

The default behavior is to preserve the time stamps from the archive to the extent possible (SquashFS has second resolution and 32 bit time stamps; tar can use extensions to specify much larger timestamps with arbitrary precision). The root inode (unless --root-becomes is used) and the modification time on the SquashFS image itself will still be set to defaults.

--no-xattr, -x

Do not copy extended attributes from archive. Default behaviour is to copy all extended attributes and skip the ones that cannot be encoded in SquashFS.

--no-skip, -s

Abort if a tar record cannot be read instead of skipping it.

--exportable, -e

Generate an export table for NFS support.

--no-tail-packing, -T

Do not perform tail end packing on files that are larger than the specified block size.

--force, -f

Overwrite the output file if it exists.

--quiet, -q

Do not print out progress reports.

--help, -h

Print help text and exit.

--version, -V

Print version information and exit.

COMPATIBILITY

Currently the program can process v7 format, pre-POSIX ustar, POSIX tar and GNU tar archives. PAX extension headers are also supported. Global PAX headers are ignored.

The support for GNU tar is limited to a commonly used subset (i.e. some legacy extensions that GNU tar itself no longer generates are not supported; neither are multi volume archives).

The input tar file can either be uncompressed, or stream compressed using gzip, xz, zstd or bzip2. The program transparently auto-detects and unpacks any stream compressed archive. The exact list of supported compressors depends on the compile configuration.

Extended attributes are supported through the SCHILY.xattr extension (favoured by GNU tar and star) or through the LIBARCHIVE.xattr extension.

If any unsupported section or extended attribute key is encountered in an archive, a warning message is written to stderr. If the --no-skip option is set, processing aborts. By default, unknown sections and unsupported extended attributes are simply skipped after issuing a warning.

ENVIRONMENT

If the command line switch --defaults is not used or no default mtime is specified, the value of the environment variable SOURCE_DATE_EPOCH is used for all file and filesystem timestamps.

If SOURCE_DATE_EPOCH is not set, not a parsable number or it is out of range, the timestamps default to 0.

Environment variables are only used if no explicit command line switches are set. Explicit command line switches are always preferred over the environment variables.

EXAMPLES

Turn an uncompressed tar archive into a SquashFS image:
: tar2sqfs rootfs.sqfs < rootfs.tar.gz

AUTHOR

Written by David Oberhollenzer.

COPYRIGHT

Copyright © 2019 David Oberhollenzer License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.