Bug 496300

This isn't different from duplicating any line in /etc/hosts.  You will get duplicated entries returned.  This is a bug in the system configuration and getaddrinfo just does what it is supposed to do.  Just fix your system configuration.

setup-2.8.3-1.fc11.noarch contains /etc/hosts:
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6

Ulrich, are you saying that is a bug?

(I don't know if other tools overwrite it with better or worse definitions, but bug 491808 made anaconda no longer touch it.)


Testing this I see that for getaddrinfo with AF_INET then 127.0.0.1 is considered exactly the same as ::1, so it will see and return duplicate entries for localhost (and localhost.localdomain). Apparently this is magic for 127.0.0.1/::1 only? And apparently the magic only applies with AF_INET; with AF_UNSPEC or AF_INET6 the lines are not considered duplicates.

Is that correctly understood?

FWIW I find this behaviour surprising and can't see why it is needed. It makes getaddrinfo with AF_INET of localhost6 return 127.0.0.1. That might be useful in some cases, but it looks like a bug to me, and it seems to me that it would be better to fix the system configuration in these cases.

(In reply to comment #2)
> setup-2.8.3-1.fc11.noarch contains /etc/hosts:
> 127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
> ::1         localhost localhost.localdomain localhost6 localhost6.localdomain6

The ::1 entry should have no localhost names associated.

Ok. So /etc/hosts should look like
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost6 localhost6.localdomain6

For the record: That will cause applications looking localhost up with AF_UNSPEC to get 127.0.0.1 only, and with AF_INET6 they will get EAI_NONAME.

I will reopen and assign to setup.

Adding to cc Allen Kistler, as duplicate names to /etc/hosts were added due to his request in #483244 . It is required for IPv6 only system running correctly out of the box (and e.g. Gentoo provides IPv6 and IPv4 version of localhost in /etc/hosts as well). As the multi on is activated in /etc/host.conf in recent setups, I'm reluctant to change /etc/hosts one more time without consensus what's the right way.

It seems like there is disagreement on what the end result should be, with the crux being whether the localhost/loopback convention applies to IPv4 only or also to IPv6.

Obviously getaddrinfo of localhost with AF_INET should return 127.0.0.1 (without duplicates).

But Ulrich wants getaddrinfo of localhost with AF_UNSPEC to return 127.0.0.1 only, while Allen wants ::1 too.

And Ullrich wants getaddrinfo of localhost with AF_INET6 to return EAI_NONAME, while Allen wants ::1.

Without agreement on this we can't get a hosts file that makes everybody happy.

Another point of disagreement could be if getaddrinfo of localhost6 (if defined for ::1 only) with AF_INET should return 127.0.0.1 or EAI_NONAME.

Basically localhost (the name) should be the loopback, independent of address family.  For example, "ssh -X" sets DISPLAY=localhost:10.0, even if it's running over IPv6 (as it absolutely should set it).  It's true of dual-stacked machines, not just IPv6-only machines.  It's important to consider that dual-stacked machines are going to be common eventually.  RHEL, at least, should fully support that, preferably out-of-the-box, and Fedora leads the way.

The exact change decided by the maintainers
127.0.0.1 localhost localhost4 (etc.)
::1       localhost localhost6 (etc.)
is based, I believe, on what Gentoo does.  (I'm representing the maintainers' opinion there, although I'm not one of them.  I'm not a Gentoo user, either, but I am the one who pointed it out originally.)  Have we heard complaints of brokenness from the Gentoo direction?  I think the idea is to establish a convention.  Defining different names for the same thing is not a good convention, especially since apps which are already considered to be IPv6-capable might have to be rewritten again (maybe just to treat localhost differently, maybe not).

FWIW, I still toast the localhost4 and localhost6 entries on my setups.  If apps need loopback, they should ask for localhost.  If they get two addresses, they use whichever one that applies, the same as any other name that has both an IPv4 address and an IPv6 address.  For example, your browser should be smart enough (like Firefox and Apache mod_proxy already are), to use the right address to get to www.kame.net.

$ host www.kame.net
www.kame.net has address 203.178.141.194
www.kame.net has IPv6 address 2001:200:0:8002:203:47ff:fea5:3085

Anyway, apps looking for "localhost" on IPv6 machines generate errors, if "localhost" doesn't have IPv6 equivalence, like
Error: Can't open display: localhost:10.0
because ssh (to continue the first example) is listening on ::1:6010, not 127.0.0.1:6010.

The reason the adopted change to setup didn't toast the localhost6 name is because some apps apparently have taken up the use of it.  (That's me representing the maintainers again.)  By toasting the extra names on my machines, I'm looking for those apps using localhost6.  I must not use those apps, because I haven't had any difficulties.

Unfortunately there's no RFC that's definitive on the naming.

Asking specifically for the IPv4 value of localhost and getting back two copies of 127.0.0.1 is annoying.  Worse is the "magic" mentioned that made asking for localhost6 return 127.0.0.1.  Those are getaddr* problems, not setup rpm problems.  I'd agree that those are bugs.  Yanking out some well-established code, however goofy it may be, during the freeze would be a pretty gutsy move, but I'll cheer you on if you decide to go for it.  (Last chance before RHEL6?)

This bug appears to have been reported against 'rawhide' during the Fedora 11 development cycle.
Changing version to '11'.

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Ok, as I don't plan to do any change to the current settings at the moment, I'm closing that bugzilla NOTABUG. If any particular application has some troubles with it, bugzilla should be opened against that application.

(In reply to comment #0)
> But when I restrict to IPv4 then I get a duplicate:
> 
> [root@localhost ~]# python -c 'import socket; print
> socket.getaddrinfo("localhost", 7, socket.AF_INET, socket.SOCK_STREAM)'
> [(2, 1, 6, '', ('127.0.0.1', 7)), (2, 1, 6, '', ('127.0.0.1', 7))]

This is clearly wrong, still the case, and needs to be fixed. Moving to rawhide, adding upstream bug report.

This package has changed ownership in the Fedora Package Database.  Reassigning to the new owner of this component.

This bug appears to have been reported against 'rawhide' during the Fedora 19 development cycle.
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Still present in rawhide.

This bug appears to have been reported against 'rawhide' during the Fedora 29 development cycle.
Changing version to '29'.

This is being tracked upstream: https://sourceware.org/bugzilla/show_bug.cgi?id=14969