Is it safe to add additional 127.0.0.1 entries to /etc/hosts?

Question

I want to add this entry:

127.0.0.1       api.localhost

To test the api of my web app.

However, the hosts file says:

##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
##

Is it safe to add the entry I want to add? Can things go wrong?

Answer 1

The "do not change" warning refers to changing the name "localhost". Many software packages expect "localhost" to resolve to 127.0.0.1.

Adding more entries is not a problem. You can add the entries after the host (as shown by Iain), or add additional lines. For example:

127.0.0.1   localhost
127.0.0.1   api.localhost
127.0.0.1   testsite2.localhost

On many UNIX-like systems, you can also use 127.0.0.2 and so forth because the whole 127.*.*.* range is routed to the "local loopback device / driver".

Answer 2

If your hosts file already contains a line for 127.0.0.1 then all you have to do is add your api.localhost at the end of it e.g.

127.0.0.1               localhost api.localhost

Answer 3

Yup, this should be safe on any reasonable system. In fact, it's a common ad-blocking technique - for example, you can download premade hosts files filled with the names of common ad servers all pointed at 127.0.0.1.