Can someone please tell me what 127.0.1.1 in the /etc/hosts file refers to?

It's localhost - see http://en.wikipedia.org/wiki/Localhost

Don't you mean 127.0.0.1? It's the localhost loop back address for the same machine you are using. Some programs are written generically to communicate with components or a client via the network. If you are running the client part and the server part on the same machine, using the localhost address, the bottom of the network stack can be bypasses. Sometimes a network socket is used for interprocess communication.

Actually I think according to the standard, that 127.0.0.0 is a class one network for localhost. I'm not certain on this. I have seen "127.0.0.2 localhost" in /etc/hosts.

There will not be 127.0.1.1 in /etc/hosts. If it exists just change it into 127.0.0.1.

127.0.0.1 localhost.localdomain localhost


special IP number (127.0.0.1) that is designated for the software loopback interface of a machine. 127.0.0.0 through 127.255.255.255 is also reserved for loopback and is used for internal testing on local machines.

It must be there irrespective you have a Ethernet card or not...

Do not take this advice. The IP 127.0.1.1 is a valid entry in your /etc/hosts file, and it should correspond to the hostname of your computer.

Read section 10.4 at this link.

http://www.debian.org/doc/manuals/re...html#s-net-dns

Yes, Quakeboy02 is correct.
You will in fact get a reply if you ping 127.0.1.1, even if you do not have this ip in your hosts file.

Nothing wrong with the 1.1 as any 127* address references the local machine. Having multiple such IP addresses can be convenient when you want/need your localhost to be addressed in more ways than one. For example, one could resolve to "localhost", another to a fully qualified name, etc.

From the computer I am using right now:
127.0.0.1 localhost Selena
127.0.1.1 Selena.Arcturus.net Selena

@jschiwal
the 0.2 address is used by some spam filters.

The local machine. All of 127/8 (and ipv6 ::1) refers to the loop back. Generally your hosts file will look something like:

By default after a new install. All 3 refer to the local machine.

It wouldn't be incorrect to change the secondary one to the true ip address of the local machine (if static) or remove it entirely. However, do not change it to 127.0.0.1 unless you know that is what you want. Generally speaking, you don't want to mess with it unless you have a specific reason.

Different distributions handle the 127.x.x.x addresses differently except for 127.0.0.1 typically. Just remember any 127/8 address refers to the local machine.

Thanks for all. Its really a useful discussion with you guys...

Sorry for my wrong INfo.

I was aware that 127.0.1.1 would refer to the local machine, but I don't think I have seen that pattern being used as the IP address for the FQDM of the local machine. Is this the convention of a certain distro, or is it based on an RFC?

It appears to be a convenience introduced by Debian:
http://www.linuxquestions.org/questi...1-mean-623421/