uname(3) return being truncated

[Lowell Gilbert]

Daniel Bye <dan at slightlystrange.org> writes:

> Morning all,
> 
> I have just come across something that strikes me as a little peculiar.  I
> don't know if it's a FreeBSD peculiarity, or an Exim oddity.
> 
> My MTA is exim 4.20.  I had left the $primary_hostname unset in my config
> file, expecting exim to take the return value from uname(3), which is the
> stated default action.  However, looking through headers of test mails I
> sent myself (posts to the list were failing - without bounces...), I found
> the hostname was mangled slightly - the last character of the FQDN was
> truncated.
> 
> Received: from danielby by catflap.home.slightlystrange.or with local (Exim
>                                                         ^^^
> 
> I had a quick look in sys/utsname.h, and lib/libc/gen/uname.c, but don't
> know enough C to figure what's going on.  Is there a limit on the length of
> the nodename that is returned?  Or is exim chopping the last character?
> 
> Explicitly setting $primary_hostname in the exim config fixes the problem -
> my posts now get through to the list again.
> 
> Just wondered if anyone could shed any light?

According to /usr/include/sys/utsname.h, there is a 32-byte limit on
the string that holds the hostname.  It looks like it could be boosted
without much trouble, but *anything* that used the utsname structure
would need to be recompiled.  And you'd have to migrate the change
forward.  Doesn't sound worth it to me...