For any given version or installation of Linux Mint, how would I find out which version of Ubuntu it is based on? I'm sure it must be in documentation somewhere right?
You'll find Ubuntu version in the
$ cat /etc/upstream-release/lsb-release DISTRIB_ID=Ubuntu DISTRIB_RELEASE=14.04 DISTRIB_CODENAME=trusty
To figure out which subrelease you are using, you need to know what kernel you are running, e.g. here kernel 3.19:
$ uname -r 3.19.0-32-generic
/etc/os-release. Here is the result with extended information:
NAME="Linux Mint" VERSION="18.3 (Sylvia)" ID=linuxmint ID_LIKE=ubuntu PRETTY_NAME="Linux Mint 18.3" VERSION_ID="18.3" HOME_URL="http://www.linuxmint.com/" SUPPORT_URL="http://forums.linuxmint.com/" BUG_REPORT_URL="http://bugs.launchpad.net/linuxmint/" VERSION_CODENAME=sylvia UBUNTU_CODENAME=xenial