We use a wide variety of software and hardware to create the work we do, and we have the advantage of being able to use the best tool for the job. While our 2D department runs primarily on Windows and MacOS machines, our 3D pipeline is almost exclusively done on Linux machines. Linux has long been used in the VFX industry after the demise of IRIX and is the logical choice for our pipeline. However while Linux is the sane choice it is also my personal favourite choice and i have been using Linux since 2004 with the introduction of Fedora Core 2.
We have used various Linux distributions over the years, however we have standardized around CentOS. While CentOS lags behind in terms of its package selection is makes up for this with its rock solid stability and security. We have also used Ubuntu LTS with good success and the only reason we didn't use Ubuntu is due to Autodesk Maya being easier to install and manage under CentOS due to its rpm package format. In the past we have used a variety of other distributions including Debian and Arch Linux (shockingly Archlinux was used in production for over 2 years without issue!). But as we grow and expand standardizing on a single Linux distribution simplifies management and workflow.
Our internal infrastructure however doesn't run on Mac, Windows or Linux. Our Networking and Storage servers run BSD. More specifically OpnSense and FreeNAS, both of which are based upon FreeBSD. While Linux is an excellent Server distribution and my personal OS of choice BSD has certain advantages over Linux. Primarily down to ZFS and FreeBSD’s network stack.
While Linux has an excellent network stack FreeBSD's is better due to years of investment from ISP's who standardized around BSD earlyon. ZFS is arguably the best Filesystem in the world, and while it was originally developed for Solaris (one of the few OS we *don't* run at C&W) it was released under a BSD compatible license and included in BSD under the title of openZFS. Ports do exist for Linux but as the licenses aren't *compatible* it can't be included in the kernel.