When I type dpkg -l | grep xserver-xorg, I get list of installed packages and their versions:ii  xserver-xorg               1:7.7+3~deb7u1ii  xserver-xorg-core          2:1.12.4-6ii  xserver-xorg-input-evdev   1:2.7.0-1+b1ii  xserver-xorg-input-kbd     1:1.6.1-1+b1ii  xserver-xorg-input-mouse   1:1.7.2-3ii  xserver-xorg-video-radeon  1:6.14.4-8I am wondering what the number  infront of the colon means, ie the number 2 in 2:1.12.4-6
understanding Debian dpkg package version numbers
debian;dpkg
The version numbers in Debian are of the form [epoch:]upstream_version[-debian_revision] whereepoch is a single (generally small) unsigned integer, which is included to allow mistakes in the version numbers of older versions of a package. If omitted, the epoch is assumed to be zero.upstream_version  is usually the version number of the original source package from which the .deb file has been made. It is usually kept the same as the format used for the upstream source.debian_revision specifies the version of the Debian package based on the upstream version. It is optional and is omitted in cases where a piece of software was written specifically to be a Debian package.