Package: squashfs-tools
Version: 4.3
Version 4.2 also has this bug!
I use mksquashfs frequently for archiving purposes. No recent version
has failed me, and I usually verify the squashfs output against the
input. But one verification cycle recently failed. I'm pretty sure I've
found what appears to be a compressor-independent bug somewhere in
mksquashfs, versions 4.3 (2014/05/12) (built from source I just
downloaded from SourceForge) and 4.2-git (2013/04/07) which is installed
by default in Ubuntu 14.04.
To verify the bug (I have verified it several times now), you may
download the uncompressed original file (big!) from:
http://snewcomb.net/mksquashfs_discrepancy/mksqtest//Crawl-Anywhere-4.0.0-rc-Appliance-Ubuntu-Desktop-12.04-LTS/Crawl-Anywhere-4.0.0-rc-Appliance-Ubuntu-Desktop-12.04-LTS-disk1.vmdk
..and the same file in a v4.3 squashfs (xz compression) context at:
http://snewcomb.net/mksquashfs_discrepancy/mksqtest.sqfs
It doesn't matter whether I use gzip or xz compression. Either way, when
I compare the original to the unsquashed retrieved version, the same
discrepancy appears.
A report about the first 128K discrepant bytes can be seen at:
http://snewcomb.net/mksquashfs_discrepancy/diff_128K.txt
(The "cmp" tool verifies that there is a discrepancy, so the problem is
not in my verification program.) The discrepancies exist regardless of
whether I use unsquashfs or I mount the sqfs filesystem and use the
kernel to decompress.
The tests were made on a host machine whose uname -a command says:
Linux daat 3.13.0-46-generic #76-Ubuntu SMP Thu Feb 26 18:52:13 UTC 2015
x86_64 x86_64 x86_64 GNU/Linux
It is a fully up-to-date Ubuntu Server 14.04 installation. The hardware
is quite stable. It's an Intel i7-930 with 24 Gb RAM and not heavily
loaded. I have exactly reproduced the problem several times, and I'm
pretty sure you will be able to reproduce it faithfully, given the files
at the URLs given above.
Steve Newcomb
srn at coolheads.com
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