[PATCH RESEND] uts: Set default hostname to "localhost", rather than "(none)"

[PATCH RESEND] uts: Set default hostname to "localhost", rather than "(none)"

[Josh Triplett]

The "hostname" tool falls back to setting the hostname to "localhost" if
/etc/hostname does not exist.  Distribution init scripts have the same
fallback.  However, if userspace never calls sethostname, such as when
booting with init=/bin/sh, or otherwise booting a minimal system without
the usual init scripts, the default hostname of "(none)" remains,
unhelpfully appearing in various places such as prompts
("root@(none):~#") and logs.  Furthrmore, "(none)" doesn't typically
resolve to anything useful, while "localhost" does.

Change the default hostname to "localhost".  This removes the need for
the standard fallback, provides a useful default for systems that never
call sethostname, and makes minimal systems that much more useful with
less configuration.

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
---

Looked at "(none)" one too many times, and figured I ought to do
something about it.

Resending, and adding CCs for networking and UTS.

 include/linux/uts.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/include/linux/uts.h b/include/linux/uts.h
index 73eb1ed..610bec2 100644
--- a/include/linux/uts.h
+++ b/include/linux/uts.h
@@ -9,7 +9,7 @@
 #endif
 
 #ifndef UTS_NODENAME
-#define UTS_NODENAME "(none)"	/* set by sethostname() */
+#define UTS_NODENAME "localhost"	/* set by sethostname() */
 #endif
 
 #ifndef UTS_DOMAINNAME
-- 
1.7.4.1

Re: [PATCH RESEND] uts: Set default hostname to "localhost", rather than "(none)"

[Serge E. Hallyn]

Quoting Josh Triplett (josh@joshtriplett.org):
> The "hostname" tool falls back to setting the hostname to "localhost" if
> /etc/hostname does not exist.  Distribution init scripts have the same
> fallback.  However, if userspace never calls sethostname, such as when
> booting with init=/bin/sh, or otherwise booting a minimal system without
> the usual init scripts, the default hostname of "(none)" remains,
> unhelpfully appearing in various places such as prompts
> ("root@(none):~#") and logs.  Furthrmore, "(none)" doesn't typically
> resolve to anything useful, while "localhost" does.
> 
> Change the default hostname to "localhost".  This removes the need for
> the standard fallback, provides a useful default for systems that never
> call sethostname, and makes minimal systems that much more useful with
> less configuration.
> 
> Signed-off-by: Josh Triplett <josh@joshtriplett.org>

Seems good to me.  I'd have no idea if there were valid reasons to object
to such a thing so my ack means nothing, but

Acked-by: Serge Hallyn <serge.hallyn@ubuntu.com>

thanks,
-serge

> ---
> 
> Looked at "(none)" one too many times, and figured I ought to do
> something about it.
> 
> Resending, and adding CCs for networking and UTS.
> 
>  include/linux/uts.h |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/uts.h b/include/linux/uts.h
> index 73eb1ed..610bec2 100644
> --- a/include/linux/uts.h
> +++ b/include/linux/uts.h
> @@ -9,7 +9,7 @@
>  #endif
>  
>  #ifndef UTS_NODENAME
> -#define UTS_NODENAME "(none)"	/* set by sethostname() */
> +#define UTS_NODENAME "localhost"	/* set by sethostname() */
>  #endif
>  
>  #ifndef UTS_DOMAINNAME
> -- 
> 1.7.4.1
> 
> --
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Re: [PATCH RESEND] uts: Set default hostname to "localhost", rather than "(none)"

[Stephen Hemminger]

On Sun, 10 Apr 2011 22:01:59 -0700
Josh Triplett <josh@joshtriplett.org> wrote:

> The "hostname" tool falls back to setting the hostname to "localhost" if
> /etc/hostname does not exist.  Distribution init scripts have the same
> fallback.  However, if userspace never calls sethostname, such as when
> booting with init=/bin/sh, or otherwise booting a minimal system without
> the usual init scripts, the default hostname of "(none)" remains,
> unhelpfully appearing in various places such as prompts
> ("root@(none):~#") and logs.  Furthrmore, "(none)" doesn't typically
> resolve to anything useful, while "localhost" does.
> 
> Change the default hostname to "localhost".  This removes the need for
> the standard fallback, provides a useful default for systems that never
> call sethostname, and makes minimal systems that much more useful with
> less configuration.
> 
> Signed-off-by: Josh Triplett <josh@joshtriplett.org>
> ---
> 
> Looked at "(none)" one too many times, and figured I ought to do
> something about it.
> 
> Resending, and adding CCs for networking and UTS.
> 
>  include/linux/uts.h |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/uts.h b/include/linux/uts.h
> index 73eb1ed..610bec2 100644
> --- a/include/linux/uts.h
> +++ b/include/linux/uts.h
> @@ -9,7 +9,7 @@
>  #endif
>  
>  #ifndef UTS_NODENAME
> -#define UTS_NODENAME "(none)"	/* set by sethostname() */
> +#define UTS_NODENAME "localhost"	/* set by sethostname() */
>  #endif
>  
>  #ifndef UTS_DOMAINNAME

It makes sense but this behavior has existed so long in Linux
that some distro might actually be depending on it.

-- 

Re: [PATCH RESEND] uts: Set default hostname to "localhost", rather than "(none)"

[Linus Torvalds]

On Mon, Apr 11, 2011 at 8:02 AM, Stephen Hemminger
<shemminger@vyatta.com> wrote:
>
> It makes sense but this behavior has existed so long in Linux
> that some distro might actually be depending on it.

Yes. Also, quite frankly, I do _not_ think that "localhost" is in any
way a more correct hostname.

I'd rather have an obviously invalid hostname for a machine that
hasn't been set up correctly than one that might work by random
chance.

                                    Linus

Re: [PATCH RESEND] uts: Set default hostname to "localhost", rather than "(none)"

[Josh Triplett]

On Mon, Apr 11, 2011 at 08:12:40AM -0700, Linus Torvalds wrote:
> On Mon, Apr 11, 2011 at 8:02 AM, Stephen Hemminger
> <shemminger@vyatta.com> wrote:
> > It makes sense but this behavior has existed so long in Linux
> > that some distro might actually be depending on it.

I checked fairly thoroughly for evidence of userspace relying on
"(none)", and found no instances of that.  Userspace typically just says
"I haven't set it yet, so nobody has set it yet", and unconditionally
sets the hostname.  dhclient doesn't rely on "(none)", distro networking
scripts don't rely on "(none)", the hostname tool doesn't rely on
"(none)", and nothing else I've found looks for "(none)".

That said, I'll certainly acknowledge that some random userspace bits
somewhere could have relied on this behavior.  Would a transitional
period help at all here?  Alternatively, see below.

> Yes. Also, quite frankly, I do _not_ think that "localhost" is in any
> way a more correct hostname.
> 
> I'd rather have an obviously invalid hostname for a machine that
> hasn't been set up correctly than one that might work by random
> chance.

Choosing "localhost" for systems that don't configure a hostname at
least makes it fairly likely that you can resolve the system hostname.
So, "localhost" will have a tendency to Just Work, but seeing a hostname
of "localhost" will still obviously remind a user that they ought to set
the hostname to something more sensible on a network-connected box.  On
a non-networked box, localhost makes perfect sense, and the box need not
configure anything else.  Similarly, this default would also make sense
for various types of virtual systems.

Also, "(none)" doesn't necessarily represent an "invalid" hostname.
In general, tools seem to assume the validity of the system hostname,
and use it wherever the hostname appears.  (For that matter, as some
recent security vulnerabilities have demonstrated, "valid hostname"
doesn't necessarily mean "alphanumeric"; both DNS and DHCP will happily
hand out a hostname with crazy characters in it, including '(' and ')'.)

I wrote this patch with the same motivation as the option to mount
devtmpfs on /dev automatically: it makes systems behave more or less
sanely in the absence of explicit setup, even though more explicit setup
may produce a more optimal configuration (just as devtmpfs makes all
devices root:root in the absence of a better configuration).  It would
often make sense for embedded or virtual systems.

In general, I'd rather see the kernel provide a configuration that will
work in at least some cases and do no worse in others (requiring
explicit configuration), rather than a configuration which will not work
in any cases and *always* requires explicit userspace configuration.

If the above does not provide a sufficiently good argument for changing
the default (perhaps with a transition period added), would you consider
accepting a patch which added a CONFIG_DEFAULT_UTS_HOSTNAME, defaulting
to "(none)"?  Then systems could choose to use that configuration option
if they know their userspace will work with it.

- Josh Triplett

Re: [PATCH RESEND] uts: Set default hostname to "localhost", rather than "(none)"

[Valdis.Kletnieks]

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On Sun, 10 Apr 2011 22:01:59 PDT, Josh Triplett said:

> Change the default hostname to "localhost".  This removes the need for
> the standard fallback, provides a useful default for systems that never
> call sethostname, and makes minimal systems that much more useful with
> less configuration.

Seems sane enough to me.  Only possible objection I can think of is "if you're running
with 'init=/bin/sh' or similar config too crippled to run /bin/hostname, maybe your
network config *should* be intentionally toasted so you can't get further surprises".

I personally don't agree - just saying somebody might hold that position.

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