Thoughts on Multi-Symlink Concept

[Robert Watson]

On Sat, 22 Feb 2014, Jordan Hubbard wrote:

>> Yes, please can we get these ....
>>
>> Apollo Domain systems had those, and they were great. Set SYSTYPE to BSD4 
>> and get the BSD tree and all that came with it, or SYSV to get the other 
>> stuff.
>
> Yep, I loved these things on Domain/OS!  We system admin types used them to 
> do all kinds of clever (and useful) things.
>
> Looks like FreeBSD has actually *had* an implementation for 6 years now.  I 
> don’t necessarily agree with the architectural decision to create a 
> different namespace and command (varsym) to manipulate it - it was really 
> nice just having it be a part of the standard environ(7) - but hey, any 
> implementation is better than no implementation.  Whatever happened to 
> https://wiki.freebsd.org/200808DevSummit?action=AttachFile&do=get&target=variant-symlinks-for-freebsd.pdf 
> ?

Some care is required here: at least one of the past implementations floating 
around had the neat property that user-defined symlink expansions occurred 
before system-defined ones, even for setuid binaries.  This allowed trivial 
replacement of libraries out from under a binary, making rooting boxes easy. 
I'm actually a fan of variant symlinks as well, having used them in AFS -- I'd 
just prefer we aim for a model that minimises inconvenient rooting of boxes. 
(I'm not passing judgement on this particular patch, mind you.)  I believe 
Brooks Davis did the last serious pass at variant symlinks and might opine 
further on the topic.

Robert