Choosing an Operating System

Where I work, we run many varieties of Unix. When I first installed Squid it was on my desktop Linux machine - if I break it by mistake it's not going to cause users hassles, so I am free to do on it what I wish.

Once I had tested Squid, we decided to allow general access to the cache. I installed Squid on the fastest unused machine we had available at the time: a (then, at least) top of the range Pentium 133 with 128Mb of RAM running FreeBSD.

I was much more familiar with Linux at that stage, and eventually installed Linux on the public cache machine. Though running Linux caused some inconveniences (specifically with low per-process filehandle limits), it was the right choice, simply because I could maintain the machine better. Many times my experience with Linux has gotten me out of potentially sticky situations.

If your choice of operating system saves you time, and runs Squid, use it! Just as I didn't use Digital Unix (Squid is developed on funded Digital Unix machines at NLANR), you don't need to use Linux just because I do.

Most modern operating systems sport both similar performance and similar feature sets. If your system is commonly used and roughly Posix compliant at the source level, it will almost certainly be supported by Squid.

When was the last time you had an outage due to hardware failure? Unless you are particularly unlucky, the interval between hardware failures is low. While the quality of hardware has increased dramatically, software often does not keep pace. Many outages are caused by faulty application of operating system software. You must thus be able to pick up the pieces if your operating system crashes for some reason.


If you normally work on a specific operating system, you should probably not use your cache as a system to experiment with a new 'flavor' of Unix. If you have more experience in an operating system, you should use that system as the basis for your cache server. Customers rapidly turn off caching when a cache stops accepting requests (while you learn your way around some 'feature').

Your cache system will almost certainly form a core part of your network as soon as it is stable. You must be able to return the system to working order in minimal time in the event of a system failure, and this is where your existing experience becomes crucial. If the failure happens out of business hours you may not be able to get technical support from your vendor. A dialup ISP's hours of business differ dramatically to that of Operating System vendors.


Though most operating systems support similar features, there are often no standards for functions required for some of the less commonly used operating system features. One example is transparency: many operating systems can now support transparent redirection to a local program, but almost all of them function in a different way, since there is not a real standard for the way an operating system is supposed to function in this scenario.

If you are unable to find information about Squid on your operating system, you may want to organize a trial hardware installation (assuming that you are using a commercial operating system) as a test. Only when you have the system running can you be sure that your operating system supports the required features.

Squid works on the following systems: (? List ?)

If you are using Squid without extensions like transparency and ARP access control lists, you should not have problems. For your convenience a table of operating system support of specific features is included. Since Squid is constantly being developed, it's likely that this list will change.


Squid is written on Digital Unix (?version ?) machines running the GNU C compiler (GCC). GCC is included with free operating systems such as Linux and FreeBSD, and is easily available for many other operating systems and hardware platforms. The GNU compiler adheres as closely to the ANSI C standard as possible, so if a different compiler is included with your operating system, it may (or may not) have trouble interpreting Squid's source code, depending on it's level of ANSI compliance. In practice, most compilers work fine.

Some commercial compilers choose backward compatibility with older versions over ANSI compliance. These compilers generally support an option that turns on 'ANSI compliant mode'. If you have trouble compiling Squid you may have to turn this mode on. (? is this still valid? I remember things like this back in the Borland C days - though I seem to remember this on a Unix system too... ?) In the worst possible scenario you may have to compile GCC with your existing compiler and use GCC to compile Squid.

If you do not have a compiler, you may be able to find a precompiled version of GCC for your system on the Internet. Be very careful when installing software from untrusted sources. This is discussed shortly in the "precompiled binary" section.

If you cannot find versions of GCC for your platform, you may have to factor in the cost of the compiler when deciding on your operating system and hardware.