Version numbers as used for Debian binary and source packages consist
of three components. These are:
epoch This is a single (generally small) unsigned integer. It may be
omitted, in which case zero is assumed. If it is omitted then
the upstream-version may not contain any colons.
It is provided to allow mistakes in the version numbers of older
versions of a package, and also a package's previous version
numbering schemes, to be left behind.
This is the main part of the version number. It is usually the
version number of the original ("upstream") package from which
the .deb file has been made, if this is applicable. Usually
this will be in the same format as that specified by the
upstream author(s); however, it may need to be reformatted to
fit into the package management system's format and comparison
The comparison behavior of the package management system with
respect to the upstream-version is described below. The
upstream-version portion of the version number is mandatory.
The upstream-version may contain only alphanumerics ("A-Za-
z0-9") and the characters . + - : ~ (full stop, plus, hyphen,
colon, tilde) and should start with a digit. If there is no
debian-revision then hyphens are not allowed; if there is no
epoch then colons are not allowed.
This part of the version number specifies the version of the
Debian package based on the upstream version. It may contain
only alphanumerics and the characters + . ~ (plus, full stop,
tilde) and is compared in the same way as the upstream-version
It is optional; if it isn't present then the upstream-version
may not contain a hyphen. This format represents the case where
a piece of software was written specifically to be turned into a
Debian package, and so there is only one "debianisation" of it
and therefore no revision indication is required.
It is conventional to restart the debian-revision at '1' each
time time the upstream-version is increased.
Dpkg will break the version number apart at the last hyphen in
the string (if there is one) to determine the upstream-version
and debian-revision. The absence of a debian-revision compares
lexical comparison is a comparison of ASCII values modified so that all
the letters sort earlier than all the non-letters and so that a tilde
sorts before anything, even the end of a part. For example, the fol-
lowing parts are in sorted order: '~~', '~~a', '~', the empty part,
Then the initial part of the remainder of each string which consists
entirely of digit characters is determined. The numerical values of
these two parts are compared, and any difference found is returned as
the result of the comparison. For these purposes an empty string
(which can only occur at the end of one or both version strings being
compared) counts as zero.
These two steps (comparing and removing initial non-digit strings and
initial digit strings) are repeated until a difference is found or both
strings are exhausted.
Note that the purpose of epochs is to allow us to leave behind mistakes
in version numbering, and to cope with situations where the version
numbering scheme changes. It is not intended to cope with version num-
bers containing strings of letters which the package management system
cannot interpret (such as 'ALPHA' or 'pre-'), or with silly orderings.
The tilde character and its special sorting properties were introduced
in dpkg 1.10 and some parts of the dpkg build scripts only gained sup-
port for it later in the 1.10.x series.
deb-control(5), deb(5), dpkg(1)
Debian Project 2013-04-02 deb-version(5)
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