os_version (3) - Linux Man Pages
os_version: Version of the OS currently running. Allegro game programming library.
os_version, os_revision - Version of the OS currently running. Allegro game programming library.
extern int os_version;
extern int os_revision;
The major and minor version of the Operating System currently running.
Set by allegro_init(). If Allegro for some reason was not able to
retrieve the version of the Operating System, os_version and
os_revision will be set to -1. For example: Under Win98 SE (v4.10.2222)
os_version will be set to 4 and os_revision to 10.