HP-UX System Administrator's Guide: Routine Management Tasks

And, of course, users receiving e-mail through your system will not be able to do so
while your system is down.
Name Server
If your computer is a network name server (for example, a DNS name server), it is
responsible for translating computer alias names into IP addresses for its own users
and those who have configured their systems to use your computer as their name
server. Usually systems are configured to use multiple sources for name switch
information so if your system is down, they can use an alternate name server, a local
hosts file, or directly use IP addresses to access remote machines until your system is
back on line.
You can configure which systems (or other sources) a computer will use to map
computer names to IP addresses by editing the file /etc/resolv.conf.
Network Gateway
If your computer is serving as a network gateway computer: that is, it has several
network interface cards in it, and is a member of multiple networks (subnets), your
computer’s absence on the network can have a huge impact on network operations. An
example of this is the computer called flserver in the Sample Network. While such
a computer is down, computers on one of the subnets are unable to communicate with
computers on other subnets, unless other gateway computers exist that can handle the
traffic.
Plan very carefully for such shutdowns and make sure users of the network are notified
as far in advance as possible that they will be unable to communicate with computers
on the other subnets.
TIP: If you have multiple subnets in your network, try whenever possible to build
redundancy into the network so that you can freely take a computer off line without
prohibiting network traffic flow.
NFS File Server
If your computer is an NFS file server, other computers in the network may have
mounted one or more of your computer’s file systems to be a part of their own directory
trees. When your system goes down, attempts to access the files or directories of your
system by users on the other systems will result in those accesses hanging if the file
systems have been hard mounted, or returning an error if they have been soft mounted.
After your system reboots the client systems may operate normally or return a stale
file handle error. If a stale file handle error occurs, you can unmount then remount the
file system, the other systems will likely require a reboot once your system is back on
line before those systems will again be able to access your computer’s file systems.
Shutting Down Systems 91