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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.
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