[roland at redhat.com: Re: More info on static binary/libnss* mystery]

Bruce Dubbs bdubbs at swbell.net
Mon Oct 7 19:04:56 PDT 2002


Gerard Beekmans wrote:

>On October 7, 2002 09:42 am, Bruce Dubbs wrote:
>  
>
>>problem a little better.
>>    
>>
>
>When you create a statically linked program, it's not 100% statically linked. 
>There's still a library part of Glibc called the NSS library (Name Server 
>Switch). They are rarely available as static libraries but don't show up when 
>running "ldd". These libraries are called by Glibc itself.
>
>So a static library might need functions from the NSS library. The NSS library 
>tells apps where the passwd database is (/etc/passwd), where to look for DNS 
>servers (/etc/resolv.conf), NIS(+) stuff and more of that. So an example in 
>our case is Bash - it needs to (or tries to) resolve usernames, and group 
>names. This needs the NSS library. Now, when we enter chroot, the Glibc 
>inside /static/bin/bash will try to load an NSS library to figure out how to 
>resolve a userid to a name. Without Glibc installed, there are no NSS 
>libraries in /lib so it says "I have no name!"
>
>When you do install Glibc, there are libnss* files in /lib, the static 
>/static/bin/bash all of the sudden has an NSS library it can load. But...this 
>NSS library is incompatible with the Glibc version that Bash was built 
>against. So it finds an NSS library, and seg. faults.
>
>One of the fixes was to sed bash and replace all NSS library names with 
>something invalid like FOOBAR. This way Bash will never find /lib/libnss* 
>files until you recompile Bash dynamically. We'd have to do the same with 
>"ls" and other apps that might need it.
>
>Is it clearer now?
>
Yes it is, thanks.  But now for follow up questions.  If we keep /bin, 
/lib, /usr/lib, /usr/bin out of the appropriate search paths during 
chapter 6, it would appear that they wouldn't find libnss* and the 
builds could proceed. Has that been tied?  Alternatively, would moving 
/lib/libnns* and /usr/lib/nss* somewhere else until we are ready work?

I'll be glad to try, but I don't have time until Friday.  I suspect 
someone else will try it before then if it hasn't been tried already.

  -- Bruce

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