The file is an
ar archive with a magic value of
!<arch>. Only the common ar archive format is supported, with no long file
name extensions, but with file names containing an optional trailing
slash, which limits their length to 15 characters (from the 16 allowed).
File sizes are limited to 10 ASCII decimal digits, allowing for up to
approximately 9536.74 MiB member files.
The tar archives currently allowed are, the old-style (v7) format,
the pre-POSIX ustar format, a subset of the GNU format (only the new
style long pathnames and long linknames, supported since dpkg 184.108.40.206),
and the POSIX ustar format (long names supported since dpkg 1.15.0).
Unrecognized tar typeflags are considered an error.
The first member is named
debian-binary and contains a series of lines, separated by newlines. Currently only
one line is present, the format version number,
2.0 at the time this manual page was written.
Programs which read new-format archives should be prepared for the
minor number to be increased and new lines to be present, and should
ignore these if this is the case.
If the major number has changed, an incompatible change has been made
and the program should stop. If it has not, then the program should
be able to safely continue, unless it encounters an unexpected member
in the archive (except at the end), as described below.
The second required member is named
control.tar. It is a tar archive containing the package control information, either
not compressed (supported since dpkg 1.17.6), or compressed with
gzip (with .gz extension) or
xz (with .xz extension, supported since 1.17.6),
as a series of plain files, of which the file
control is mandatory and contains the core control information. The control
tarball may optionally contain an entry for
., the current directory.
The third, last required member is named
data.tar. It contains the filesystem as a tar archive, either
not compressed (supported since dpkg 1.10.24), or compressed with
gzip (with .gz extension),
xz (with .xz extension, supported since dpkg 1.15.6),
bzip2 (with .bz2 extension, supported since dpkg 1.10.24) or
lzma (with .lzma extension, supported since dpkg 1.13.25).
These members must occur in this exact order. Current implementations
should ignore any additional members after
data.tar. Further members may be defined in the future, and (if possible) will be
placed after these three. Any additional members that may need to be
debian-binary and before
data.tar and which should be safely ignored by older programs, will have names
starting with an underscore,
Those new members which wont be able to be safely ignored will be
data.tar with names starting with something other than underscores, or will
(more likely) cause the major version number to be increased.