How to tell an eth port has link?

There has to be a way to tell if the ethernet port has a cable plugged in.

I see the kernel message go by telling me it has lost or established the
link when I plug the cable in... But I can't find anything that would
tell me the status from userspace.

I've been all through /proc and I don't see anything that would clue me
in....

So... How to tell if an ethX port has a valid hardware link? I need to
test this before networking comes up so I know if I should run DHCP or
not...

--Yan

On Mon, 02 Apr 2007 09:01:02 -0700, CptDondo wrote:

> There has to be a way to tell if the ethernet port has a cable plugged in.

Use ethtool and/or mii-tool. Depending on what type of card it is, one or
the other should work.

Regards, Ian

CptDondo wrote:
> There has to be a way to tell if the ethernet port has a cable plugged in.
>
> I see the kernel message go by telling me it has lost or established the
> link when I plug the cable in... But I can't find anything that would
> tell me the status from userspace.
>
> I've been all through /proc and I don't see anything that would clue me
> in....
>
> So... How to tell if an ethX port has a valid hardware link? I need to
> test this before networking comes up so I know if I should run DHCP or
> not...
>
> --Yan


Maybe you like to have ifplugd?

--

Tauno Voipio
tauno voipio (at) iki fi

CptDondo <yan@nsoesipnaemr.com> wrote:

> I see the kernel message go by telling me it has lost or established the
> link when I plug the cable in

Is there a hook for this that can call a script, or trigger an initd event
that can be used to call a script?

I am curious, because on my network, if I have a power failure, the network
hubs lose their connections, but the computers continue to run from a UPS
supply. The loss of the network hubs is a sure signal to all computers that
the power is out.

I was hoping to hook a shutdown script to the loss of ethernet connection
event, that shuts the computers down, if the outage lasts more than a couple
of minutes.

Regards,

Mark.

--
Mark Hobley
393 Quinton Road West
QUINTON
Birmingham
B32 1QE

Telephone: (0121) 247 1596
International: 0044 121 247 1596

Email: markhobley at hotpop dot donottypethisbit com

http://markhobley.yi.org/

Mark Hobley wrote:
> CptDondo <yan@nsoesipnaemr.com> wrote:
>
>> I see the kernel message go by telling me it has lost or established the
>> link when I plug the cable in
>
> Is there a hook for this that can call a script, or trigger an initd event
> that can be used to call a script?
>
> I am curious, because on my network, if I have a power failure, the network
> hubs lose their connections, but the computers continue to run from a UPS
> supply. The loss of the network hubs is a sure signal to all computers that
> the power is out.
>
> I was hoping to hook a shutdown script to the loss of ethernet connection
> event, that shuts the computers down, if the outage lasts more than a couple
> of minutes.
>

If I understand ifplugd correctly from reading the manpage, it should
detect the other end losing power, as the link will drop.

I have not gotten into ifplugd yet - I'm still hoping to get dhclient to
do what I want - but it looks promising. For my purposes it's a bit of
overkill...

--Yan

CptDondo <yan@nsoesipnaemr.com> wrote:
> I have not gotten into ifplugd yet - I'm still hoping to get dhclient to
> do what I want - but it looks promising. For my purposes it's a bit of
> overkill...

Yeah for mine too really, I don't want to configure the network, that is
already done here, and my IP addresses are static, so I don't use dhclient. All
I want to do is hook the cable dead event, possibly through initd, if it
supports the incident.

Regards,

Mark.

--
Mark Hobley
393 Quinton Road West
QUINTON
Birmingham
B32 1QE

Telephone: (0121) 247 1596
International: 0044 121 247 1596

Email: markhobley at hotpop dot donottypethisbit com

http://markhobley.yi.org/

Mark Hobley wrote:
> CptDondo <yan@nsoesipnaemr.com> wrote:
>> I have not gotten into ifplugd yet - I'm still hoping to get dhclient to
>> do what I want - but it looks promising. For my purposes it's a bit of
>> overkill...
>
> Yeah for mine too really, I don't want to configure the network, that is
> already done here, and my IP addresses are static, so I don't use dhclient. All
> I want to do is hook the cable dead event, possibly through initd, if it
> supports the incident.

I think what I am going to do is:

on boot, run mii-tools to see if the cable is hooked up
if it is, run dhclient {
if dhclient gets an address {
set up for networked database
exit }
}

assume no network
set up for local database

I think you could run mii-tools/ethtools from a loop every so often
(minute?) and see if the link is dead.

--Yan