On Wed, Nov 7, 2018 at 4:05 AM <arnold@skeeve.com> wrote:

When DNS came along, it became
a matter of editing /etc/nsswitch.conf to include dns as one of the
options along with files and yp/nis.  I think the average user didn't
see any big difference since all the apps (ftp, telnet) just went
through gethostbyname().

This doesn't mesh with my memory. I recall building BIND from source and having to rebuild network programs (e.g. on 4.3 on the RT or VAXen) to pick up the new version of libresolv.a, and hacking the resolver library into libc.so on Suns. I remember using resolv.conf fairly early on, but my memory is that nsswitch.conf came later (Solaris 2.x era?). Ultrix did have a configuration file for where to do host lookups, but I think the set of sources was fixed: files, NIS or DNS.