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

Solution 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".

Solution 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

Solution 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.