What is the meaning of the tilde in some debian openjdk package version string?

Question

Reading the changelog of the debian openjdk-8 source package we see that there is a version called openjdk-8 (8u45-b14-4) and the next one is openjdk-8 (8u60~b22-1).

What is the meaning of the tilde in this last version?

Answer 1

The official reference for the Debian package version format is in the Debian Policy Manual. The format is designed to allow “reasonable-looking” version numbers with a well-defined (if somewhat complex) comparison relation to decide when a version is more recent than another.

For the most part, the comparison is a lexicographic comparison of the string. For example, 1foo is sorted before 1ga. However, sequences of digits are compared in numerical order, so foo10bar is sorted after foo9bar.

With a lexicographic order, a string is always sorted before its prefix. The tilde character allows a deviation from that: foo~bar is always sorted before foo as well as before any version that begins with foo followed by a character other than ~. This is often used for beta versions: 8u60~b22 is sorted before 8u60. I don't know why the OpenJDK 8 packages seem to alternate between -b and ~b suffixes though.

Tilde suffixes are also used for backports of all kinds. For example, if the same version of a package is present in both Debian stable and testing, and a security fix needs to enter stable, then the package in stable will have a suffix like -2~deb1 while the version in testing (compiled against more recent libraries) will have -2; that way the package is an upgrade to the -1 version, but if a system is upgraded from stable to testing, the -2~deb1 stable version will be upgraded to the -2 testing version. Official backports use ~bpoNUMBER for the same purpose, this way a 4.2~bpo7 version will be upgraded to 4.2 if that ever appears in the main distribution.