It's everywhere in large companies. I was a sysadmin in the internal managed services division of a healthcare company and we had AIX, Solaris, HP-UX, Linux (C

It's everywhere in large companies. I was a sysadmin in the internal managed services division of a healthcare company and we had AIX, Solaris, HP-UX, Linux (CentOS, Debian, RHEL), BSD, Open-VMS, and FreeBSD. We had about 150 Sysadmins to manage it all, a lot of the guys had been doing their respective OS's exclusively for 20+ years.