(tar)Checksumming Problems

Old V7 and POSIX

Portability

Checksumming Problems
---------------------

   SunOS and HP-UX `tar' fail to accept archives created using GNU
`tar' and containing non-ASCII file names, because they use signed
checksums, while GNU `tar' uses unsigned checksums while creating
archives, as per POSIX standards.  On reading, GNU `tar' computes both
checksums and accept any.  It is somewhat worrying that a lot of people
may go around doing backup of their files using faulty (or at least
non-standard) software, not learning about it until it's time to
restore their missing files with an incompatible file extractor, or vice
versa.

   GNU `tar' is supposed to compute both checksums, signed and
unsigned, and accept any.  However, 1.11.2 has a bug by which signed
checksums are incorrectly initialized, so they do not work.  This is
corrected in the subsequent GNU `tar' versions.  However, GNU `tar' has
not been modified to *produce* incorrect archives to be read by buggy
`tar''s.

   I've been told that when Sun first imported `tar' on their system,
they recompiled it without realizing that the checksums were computed
differently, because of a change in the default signing of `char''s in
their compiler.  So they started computing checksums wrongly, and
stayed compatible with themselves afterwards.  It now falls on the
shoulders of SunOS and HP-UX users to get a `tar' able to read the good
archives they receive.