DESCRIPTION
 The 
ypcat(1), 
ypmatch(1), and 
ypwhich(1) commands reference NIS (YP) maps as specified by the user. Occasionally it is desirable to use a shorthand reference for a longer map name, hence the 
nicknames file, kept in “/var/yp/nicknames.”
The format of the file is
nickname map
one pair per line. The default installed nickname map is as follows:
- 
passwd
- 
passwd.byname
- 
group
- 
group.byname
- 
networks
- 
networks.byaddr
- 
hosts
- 
hosts.byname
- 
protocols
- 
protocols.bynumber
- 
services
- 
services.byname
- 
aliases
- 
aliases.byname
- 
ethers
- 
ethers.byname
- 
master.passwd
- 
master.passwd.byname
A blank or incomplete nicknames file will affect any scripts which use nicknames for map lookup, whereas if the file is simply missing, the default compiled-in list will be used.