I have a RHES4 as NIS master. Since my account is in the nis maps, I
thought to change its password, I would do:

[mauricio@moss ~]$ yppasswd
Changing NIS account information for mauricio on localhost.localdomain.
Please enter old password:
Changing NIS password for mauricio on localhost.localdomain.
Please enter new password:
The password must have at least 6 characters.
Please enter new password:
Please retype new password:
Error while changing the NIS password.
The NIS password has not been changed on localhost.localdomain.

[mauricio@moss ~]$

First of all, how can I get it to tell me what went wrong? Second, why
does it says I am changing the password in localhost.localdomain as
opposite to in my yp domain? I try to do a bit more investigating using
another of the yp-tools, ypwhich:

[mauricio@moss ~]$ ypwhich -m
group.bygid moss.somewhere.edu
ypservers moss.somewhere.edu
passwd.byuid localhost.localdomain
netgroup localhost.localdomain
hosts.byname moss.somewhere.edu
netgroup.byhost localhost.localdomain
passwd.byname localhost.localdomain
group.byname moss.somewhere.edu
auto.home localhost.localdomain
netgroup.byuser localhost.localdomain
hosts.byaddr moss.somewhere.edu
[mauricio@moss ~]$

Now I am quite confused: where is yp_master() defined, since it is used
in yp-tools to get the NIS master, and where does it get its info?