Re: X session and hostname changing policy

[Fırat Birlik <fbirlik gmail com>]

2010/6/14 Robby Workman <rw rlworkman net>:
> On Mon, 14 Jun 2010 15:26:06 -0500
> Robby Workman <rlworkman gmail com> wrote:
>
>> On Mon, 14 Jun 2010 23:16:52 +0300
>> Fırat Birlik <fbirlik gmail com> wrote:
>>
>> > Hi there,
>> >
>> > I experience a problem with hostname manipulation of NetworkManager
>> > and the X session.  DHCP server sends a hostname within the dhcp
>> > offer, which is different the current one.  There is no persistent
>> > hostname definition within the 'nm-system-settings.conf' as this is
>> > a default installation.  NetworkManager just changes the hostname
>> > and as new hostname is not authenticated (xhost cookie
>> > MIT-MAGIC-COOKIE-1 for new hostname does not exist) no new
>> > application can be started afterwards.
>> >
>> > To avoid this behavior, I can define a persistent hostname equal the
>> > content of /etc/HOSTNAME (this is a slackware system) as the
>> > following:
>> >
>> > --- /etc/NetworkManager/nm-system-settings.conf~
>> > +++ /etc/NetworkManager/nm-system-settings.conf
>> > @@ -1,2 +1,5 @@
>> >  [main]
>> >  plugins=keyfile
>> > +
>> > +[keyfile]
>> > +hostname=myhostname
>> >
>> >
>> > As persistent hostname has highest precedence, problem looks solved;
>> > but this should be repeated for each installation.
>> >
>> > What I'm asking is, is there any config option or some way to not
>> > let NetworkManager change the hostname?
>> >
>> > As a note, current precedence order for hostname (taken from
>> > NetworkManagerPolicy.c):
>> >
>> >      * 1) a configured hostname (from system-settings)
>> >      * 2) automatic hostname from the default device's config
>> > (DHCP, VPN, etc)
>> >      * 3) the original hostname when NM started
>> >      * 4) reverse-DNS of the best device's IPv4 address
>> >
>>
>>
>> Do you have NM built to use dhcpcd?  If so, dhcpcd should not change
>> the system hostname unless you have force_hostname=(YES|TRUE|1) in
>> /etc/dhcpcd.conf.   From dhcpcd(8):
>>
>>   If the hostname is currently blank, (null) or localhost, or
>>     force_hostname is YES or TRUE or 1 then dhcpcd sets the
>>     hostname to the one supplied by the DHCP server.
>>
>> -RW
>

I tested it with both dhcpcd and dhclient builds, but from the code
trace what I understand is, dhcp client (both of them) do not change
the hostname themselves.  If I'm not mistaken, NetworkManager sets the
hostname to the offered one (if any) with the following code:

---[ from NetworkManagerPolicy.c / update_system_hostname() ]---
	/* Grab a hostname out of the device's DHCP4 config */
	dhcp4_config = nm_device_get_dhcp4_config (best);
	if (dhcp4_config) {
		const char *dhcp4_hostname, *p;

		p = dhcp4_hostname = nm_dhcp4_config_get_option (dhcp4_config, "host_name");
		if (dhcp4_hostname && strlen (dhcp4_hostname)) {
			/* Sanity check */
			while (*p) {
				if (!isblank (*p++)) {
					set_system_hostname (dhcp4_hostname, "from DHCP");
					return;
				}
			}
			nm_warning ("%s: DHCP-provided hostname '%s' looks invalid; ignoring it",
			            __func__, dhcp4_hostname);
		}
	}
-------------------------------

By the way, if dhcp server does NOT offer a new hostname, then
hostname is set to the system hostname when NetworkManager first
started.  As it is not changed after launch, it is just left alone by
nm and everything is fine.

Firat