OS Conditional Defines
 

When compiling using any C compile for different OS's it is often necessary to use

#indef <os_tag>
<code>
#endif

The OS tag for SCO systems in _SCO_DS

Anyone know what the standard definitions are for various varieties of Linux are?

Specifically RedHat and Suse.

i dont think so, cause it depends only on the type of system.
distributions only differ in the amount of packages or the use of special kernels.

but as long as the kernel-architecture is mainly the same ( i think linux kernels are ) you couldn't make a difference between distributions but kernel-versions