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Re: Address 127.0.1.1



On Fri, May 24, 2024 at 05:22:13PM +0100, Joe wrote:
> Long ago, lo used to be just 127.0.0.1, which is what most people would
> try to ping to check localhost, and what appeared in /etc/hosts. There
> is some subtle reason, which I used to know but have now long forgotten,
> why Debian started using 127.0.1.1 in /etc/hosts instead.

It's not "instead".  It's "in addition".

hobbit:~$ head -n2 /etc/hosts
127.0.0.1   localhost
127.0.1.1   hobbit.wooledge.org hobbit

The first line is traditional.  Exactly what it looks like.

The second line ensures that my hostname will always resolve to a
working IP address.  Lots of programs need that.  Some of the most
common reasons back in the old days were X clients that had been
told to use "myhostname:0" as their $DISPLAY.  If "myhostname" didn't
resolve to a working IP address (one which could contact the X server),
then X client programs wouldn't work.

A lot has changed since then, but the basic principle remains the same.
Some programs are going to expect to be able to open a network connection
to whatever IP address the system's hostname resolves to.  127.0.1.1
serves that purpose, without stepping on 127.0.0.1 which has its own
legacy role to fulfill.


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