The request for an easy way to package Solaris kernel configuration (/etc/system basically) came up both via the Solaris Customer Advisory Board meetings and requests from customers with early access to Solaris 11.2 via the Platinum Customer Program. I also had another fix for the Solaris Cryptographic Framework that I needed to implement to stop cryptoadm(1M) from writing to /etc/system (some of the background to what that is needed is in my recent blog post about FIPS 140-2).
So /etc/system.d was born. My initial plan for the implementation was to read the "fragment" files directly from the kernel. However that is very complex to do at the time we need to read these; since it happens (in kernel boot time scales) eons before we have the root file system mounted. We can however read from a well known file name that is in the boot archive.
The way I ended up implementing this is that during boot archive creation (either manually running 'bootadm update-archive' or as a result of BE or packaging operations or just a system reboot) we assemble together the content of /etc/system.d into a single well known /etc/system.d/.self-assembly (but considered a Private interface) file. We read the files in /etc/system.d/ in C locale collation order and ignore all files that start with a "." character, this ensures that the assembly is predictable and consistent across all systems.
I then had too choose wither /etc/system.d or /etc/system "wins" if a variable happens to get set in both. The decision was that /etc/system is read second and thus wins, this preserves existing behaviours.
I also enhanced the diagnostic output from when the system file parser detects duplication so that we could indicate which file it was that caused the issue. When bootadm creates the .self-assembly file it includes START/END comment markers so that you will be able to easily determine which file from /etc/system.d delivered a given setting.
So now you can much more easily deliver any Solaris kernel customisations you need by using IPS to deliver fragments (one line or many) into /etc/system.d/ instead of attempting to modify /etc/system via first boot SMF services or other scripting. This also means they apply on first boot of the image after install as well.
So how do I pick which file name in /etc/system.d/ to use so that it doesn't clash with other people ? The recommendation (which will be documented in the man pages and in /etc/system itself) is to use the full name of the IPS package (with '/' replaced by ':' ) as the prefix or name of any files you deliver to /etc/system.
Information on how to get the Solaris 11.2 Beta is available from this OTN page.
Note that this particular change came in after the Solaris 11.2 Beta build was closed so you won't see this in Solaris 11.2 Beta (which is build 37).