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?

Fedora maps the hostname given at install time to `127.0.0.1` under certain circumstances. If I'm not mistaking it happens when you have an Ethernet card, but no network connectivity, e.g. DHCP is not working. — Cristian Ciupitu, Feb 06 '11 at 15:47

score 12 · Accepted Answer · answered Feb 06 '11 at 15:33

12

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".

answered Feb 06 '11 at 15:33

vdboor

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Quoting from pRFC 5735 - "Special Use IPv4 Addresses"](http://tools.ietf.org/html/rfc5735): *127.0.0.0/8 - This block is assigned for use as the Internet host loopback addres*s. So any TCP/IP compliant system including Windows, Linux, MacOSX etc. should route 127.x.y.z addresses to the loopback. – Cristian Ciupitu Feb 07 '11 at 01:02

score 6 · Answer 2 · answered Feb 06 '11 at 14:15

6

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

answered Feb 06 '11 at 14:15

user9517

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It's perfectly safe, right? – Feb 06 '11 at 14:18
2

Yes :-) It's meant to do what you are doing ! – Antoine Benkemoun Feb 06 '11 at 15:17
Have a look at the [macos man page](http://developer.apple.com/library/mac/#documentation/Darwin/Reference/ManPages/man5/hosts.5.html) for the hosts(5) file which says each line has IP address official hosts name aliases – user9517 Feb 06 '11 at 15:19

score 4 · Answer 3 · answered Feb 06 '11 at 15:03

4

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.

answered Feb 06 '11 at 15:03

db2

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

3 Answers3