NIS problem (and proposal for solutions)

Raffaele Biscosi rbiscosi at
Thu Oct 5 13:59:02 BST 2006

I hope this is the right place for my concern. If not, please tell me. I also 
hope that my explanation is clear and not too long winded...

I have installed NIS recently and noticed that it is important that entries 
in /etc/hosts belonging to maintain a certain order. It is 
necessary that the first name for be the systems name (uname -n). 
Unfortuantely installation routines (namely netcfg) create a different order. 
The /etc/hosts of a fresh installed ubuntu will look something like this:	localhost nis-srv	nis-srv

This order makes it impossible to properly configure a NIS environment with 
slave servers. The point of failure is '/usr/lib/yp/yphelper'. This command 
is used by NIS initialization scripts to determine the machines name (among 
other things).
When 'yphelper' is called with parameter '--hostname' (like this is done in 
the NIS makefile /var/yp/Makefile) it first determines the machine's hostname 
using 'gethostname' (from libc) and passing the result to 'gethostbyname' 
which in turn returns a hostent structure. Finally the content of structure 
member 'h_name' is printed.
Thus if you call '/usr/lib/yp/yphelper --hostname' on a fresh installed ubuntu 
system (be it dapper or breezy, that's what I tested) the result will 
be 'localhost'.

The next step in NIS makefile consists of building the maps. These maps have a 
key (YP_MASTER_NAME) to tell which NIS server is master for a certain map. In 
our case YP_MASTER_NAME is set to 'localhost' instead of the master server's 
real name. Transfer scripts for NIS maps rely on this field and fail since it 
contains the wrong name.

I think there are two (and a half) ways to avoid this problem:

a) netcfg creates an /etc/hosts entry like " nis-srv localhost" 
instead of " localhost nis-srv"

b) change function print_hostname in yphelper.c: If called with 
parameter "--hostname" only, print the result of 'gethostname' and exit 
instead of calling 'gethostbyname'

( c) Mention the problem in NIS-package README and let administrators do the 
work )


  Raffaele Biscosi

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