.
package in debian stable (Stretch) is v4.3-3 ...but contains an outdated manpage, written in 2012
https://sources.debian.org/src/squashfs ... hfs.1/#L25
Debian's buster/sid mksquashfs package also contains that same (2012, outdated) manpage
https://sources.debian.org/src/squashfs ... quashfs.1/
^--- significant b/c the older manpage lacks mention of mksquashfs support for lz4, and ability to preserve extended attributes
In the absence of an up-do-date manpage, the following page at author's github repo stand as the definitive documentation:
https://github.com/plougher/squashfs-to ... ASE-README
==============
an undocumented mksquashfs feature:
ref:
https://github.com/plougher/squashfs-tools/issues/24 and
action.c
We can pass one or multiple
-action commandline options to mksquashfs,
to specify wildcard (or regex) patterns and instruct "don't waste effort attempting to re-compress files matching this pattern"
^--- significant regardless which compression algorithm is chosen (for instance, filesystem contains hundreds of .gz manpage files...)
==============
(mentioned for the sake of completeness)
another undocumented, or at least rarely mentioned, mksquashfs feature is ability to create/inject files "out of thin air":
https://github.com/plougher/squashfs-to ... le.example
==============
In addition to lz4, mksquashfs will
{now} soon provide ability to choose
zstd compression. (ref:
wikipedia and
here)
(FWIW, zstd -compressed images can be consumed by the 4.14 kernel and squashFUSE)
^--- the code now is in place, pending a new squashfs-tools version release
==============
anecdotal: Last year (I wasn't aware of lz4 availability at the time) I conducted experiments, varying the levels of compression and the various compressors. Applying lighter compression when creating an "antiX full" snapshot yielded 2sec (newer PC) to 4sec (older PC) shorter boot times.
Ubuntu may use yet another compression format now, zstd, that's supposed to make the install about 10% faster...and the ISOs about 6% larger: I can see that being a net loss...it adds more time to download and write the ISO to a medium than the few seconds you save when installing from a USB.
aw, I drafted this while offline & didn't notice that Stevo had already mentioned zstd.