There is a big difference: the *BSD systems have a tightly integrated base system, where kernel and libc are adapted to changes in lockstep, and there is no sta

There is a big difference: the *BSD systems have a tightly integrated base system, where kernel and libc are adapted to changes in lockstep, and there is no stable kernel ABI. FreeBSD ABI stability is not guaranteed between major releases (only between minor releases), while OpenBSD does not even guarantee ABI stability between minor releases. Linux and GNU libc are separate projects, and there are pretty strong compatibility guarantees for the Linux syscall ABI; the glibc ABI is also stable, and glibc uses ELF symbol versioning to provide older deprecated functions for compatibility. This means the system is more modular, but at the cost that interface changes like changing 32-bit time_t to 64-bit require a lot more effort and coordination. Of course the advantage of the Linux approach is that existing application binaries will continue to run, even ones that do syscalls directly or with statically linked libc. ---- Edited to add: actually it turns out you were wrong with your claim about 64-bit time_t in FreeBSD: Here is the current trunk header where it defines a 32-bit time_t for the i386 architecture. https://svnweb.freebsd.org/base/head/sys/x86/include/_types.h?view=markup#l115 https://svnweb.freebsd.org/base/head/sys/x86/include/_types....