I have accounts on a number of systems where the sysadmin doesn't
maintain a comprehensive `/etc/hosts` file.  In order to work around
this, I wanted to have a per-user `~/.hosts` to extend the system file
with my own aliases.  Then I could use my short nicknames for network
activity without spelling out the whole domain name (the `domain`
setting in `/etc/resolv.conf` is often not close enough for the
nicknames to work using [[DNS]]).

A common technique for translating host names into IP addresses is to
use either `getaddrinfo(3)` or the obsolete `gethostbyname(3)`.  As
mentioned in `hostname(7)`, you can set the `HOSTALIASES` environment
variable to point to an alias file, and you've got per-user aliases!

Well, mostly…

`HOSTALIASES` will work if your program (`ping`, `ssh`, etc.)
satisfies two conditions:

1. It has to actually use one of the two functions listed above to
   resolve the host name.  I haven't run across anything that doesn't,
   but you never know.
2. It cannot be setuid to another user.  If it is, [libc sanitizes the
   environment][sanitize], so your `HOSTALIASES` setting is lost.  See
   `sysdeps/generic/unsecvars.h` for a list of all environment
   variables that glibc removes for setuid programs.

`ping` is setuid `root` (because it needs to listen for ICMP packets),
so `HOSTALIASES` will not work with `ping` unless you're already
`root` before you call `ping`.

Here's an example:

    $ echo 'g www.google.com' >> ~/.hosts
    $ export HOSTALIASES=~/.hosts
    $ firefox g

Adjust your `~/.bashrc` appropriately, and you can forget about
`/etc/hosts` entirely :).

[sanitize]: http://en.wikipedia.org/wiki/Environment_variable#Security