What are useful commands, tools, or tricks that one would find on Solaris or OpenSolaris that aren't available on a typical Linux distribution?
Hidden Features of Solaris/OpenSolaris
opensolarissolaris
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I'd go for Linux on the Desktop and run Solaris x86 in a Sun Virtual Box environment. Its basically VMWare Workstation, but its free and has good support for Linux/Solaris. In my experience, OpenSolaris has poor hardware support. I wasn't able to get it installed on my Dell P490 or T5400.
You can learn about Virtual Box at www.virtualbox.org.
Full disclaimer I'm currently working at Sun but I don't speak for them - all this info is freely available, but a bit difficult to find.
Solaris 10 while having been out a few years is now at update 7 - new features have gone into Solaris 10 from OpenSolaris and will almost certainly continue to do so, but at a slower pace than an OpenSolaris distribution.
The name OpenSolaris confusing refers to a few different things. There is the Solaris Express Community Edition (SXCE) - a binary distribution that comes out roughly every 2 weeks is created from the internal builds of a product called Nevada (aka Solaris 11). Shortly following the putbacks to Nevada/SXCE these then go back to the development build of OpenSolaris 2009.06 (aka Indiana) and that comes out every couple of weeks as well. If you want to run the latest and greatest bits you can do so by changing your OpenSolaris (indiana) repository.
The 2008.11 and 2009.06 6 monthly releases of OpenSolaris are almost entirely Open Source (nvidia graphics drivers being one of the notable exceptions) and are also supported, these are not BETA releases - you can buy a contract and will get any important fixes back ported to these releases through a paid for support repository. Security fixes will get back ported to OpenSolaris 2008.11 and 2009.06 (latest two releases) eventually and will be available without a contract to anybody.
Your choices are Solaris 10 update 7 or OpenSolaris 2009.06 the SXCE distribution has never been a supported OS and the only way to get fixes is to upgrade your entire OS. Personally I would recommend the 6 monthly releases of 2009.06 as a good starting point unless you have a need for very long term enterprise support (10+ years) for your environment. If your interested in scaling then it is worth noting that you can get OpenSolaris 2009.06 instances in Amazons EC2 cloud these days. All Sun Solaris distributions will run on most x86 and most SPARC hardware.
Check http://www.opensolaris.com/learn/faq/ if you haven't already.
Best Answer
Live Upgrade, which uses ZFS, creates writable snapshots of the operating system boot environment. With Live Upgrade, you can apply patches to a snapshot boot environment, then make that snapshot bootable. Upon the next reboot you get a patched OS environment. If you discover an issue with a patch, you can make the old snapshot bootable, reboot and you've backed out your changes. Its a pretty impressive solution to patching.
ZFS for the boot environment requires Solaris 10u6 or newer.
Also, Solaris Zones are pretty useful for application isolation. Obviously DTrace is very nice but RedHat is playing catchup with System Tap.