A while ago somebody asked me what he could tell his boss to convince him to migrate to Linux, so I made him a small list.
Bosses know calculators, so this is the number one thing to tell your boss why you should migrate to Linux. The total cost of ownership(TCO) of linux is lower than windows. While linux administrators are a little more expensive, they are a lot more efficient so this gives a benefit. The licensing costs are lower, you don't have to migrate to a new OS every few years, you can use the same hardware twice as long.
Linux is more secure than windows, there are few computer viruses targeting Linux and it has been historically built as a network operating system this makes it much safer to use than windows. Windows is based on a standalone architecture and has a legacy it can't avoid. Linux is Open Source which is also more secure because everybody can look at the source and so holes in the security have a bigger chance of being discovered and fixed.
Linux is valued as a high performing operating system. Due to its modular nature - entire portions of the operating system can be easily added or removed, the operating system can be easily tuned for a specific purpose. Need a webserver? You can install a webserver only system, no gui, no nothing you don't really need.
Need a mailserver? You can run a dedicated mailserver without a problem, just doing mail and nothing else.
Linux is more stable than windows. Does your boss ever get frustrated with windows because of the instability? Tell him/her about Linux stability, and how it's almost always possible to recover if something "hangs" in Linux. In windows if something goes wrong the whole system freezes and you can only fix it by rebooting. This almost never happens in Linux, if something goes wrong a program may freeze and you can easily kill of that program.
5. Open Standards
Because Linux is open source and freely distributable, it includes open standards which protect you from the so called vendor-lock-in. Any smart boss can recognize being locked in by technology is great, for the owner of that technology. Competition is a good thing for users because it gives guarantees of quality and reasonable price. Being bound to technology and standards owned by companies eliminates competition.
With Linux it's very easy to communicate over a network with just about any other computer platform, with various protocols, such as for exchanging data files. Linux has samba which can make it even act as a windows fileserver and Active Directory domain member. Linux also has very good free office suites that read windows office files.
When you need something in windows software which is not available you'll need to have completely new software developed. In Linux there's a big chance you can just take an existing project and adapt it to your needs. This happens all the time and is one of the great benefits of open source.
8. Free software
It's not only the OS, when you use Linux you not only get a great operating system. You also get an incredible amount of free and open source programs to do almost everything you ever need. This is something which is overlooked often. When you compare Linux to windows TCO you might only look at operating system cost. But if you need anything in windows it's probably going to cost you money, there are open source projects available for windows, but nowhere near as many as for Linux. Almost everything in Linux is available free of cost, office suites, planning tools, development tools, administration tools, you name it.
Linux has very advanced virtualization solutions giving you the possibilities to run virtual servers with very little overhead. Here's another opportunity for stressing the cost saving possibilities. Free virtualization solutions available here! And as most bosses understand money much better than technology this is a very strong point.
10. Future proof
Linux won't disappear, it's shown a very steady growth and it's backed by some very big companies these days. If the only company owning and supporting your operating system software disappears you'll have a big problem. If all big company's backing Linux would disappear (which is nearly impossible) the code would still be available and any new player on the market can just pick it up and continue support.
11. Happy sysadmin
The most important reason, Linux makes system administrators happy.
Linux is so much easier and nicer to maintain, because it's built for users by users.
Nothing can compete when it comes to maintenance, linux is so transparent and every tool you can imagine is freely available.
Know some more?
Know more reasons? Help us convince this guys boss and the other bosses of the world, leave a comment!