How to tell what the negotiated link speed of the LAN ports are (in cli)?

> [...] Unfortunately, the grep command goes on forever and doesn't
> return anything meaningful. [...]

   _That_ (cheap and nasty) "grep" command might.  There could be things
under "/dev" (and perhaps FIFOs elsewhere) which simply return no data,
causing such a command to hang.  A more selective search might work
better.  For example:

   find / -xdev -type f -exec /sbin/grep 1000M {} \; -print

Around here, that found "ethctl" and "ethswctl".  See "ethctl", below.

> I was hoping that someone here knows the location of the files where
> this data is entered.

   Someone else might.  I managed to stumble into the /sys interface:

      ls -Ll /sys/class/net/eth*

For example:

# cat /sys/class/net/eth4/operstate
up

   Sadly, all the interesting bits failed:

# cat /sys/class/net/eth4/duplex
cat: read error: Invalid argument

# cat /sys/class/net/eth4/speed
cat: read error: Invalid argument

   Interestingly, "ifconfig" reports also lack these data.  For example:

# ifconfig eth2
eth2      Link encap:Ethernet  HWaddr 50:6A:03:E9:AE:86  
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:7085 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:1751635 (1.6 MiB)

   I assume that there's some subtlety (virtualness?)  in these entities
which hides the physical detail.  But I know nothing.

   One interesting fact which I gleaned while wasting too much time on
this was that on my D7000, "eth1" = "LAN4, ... "eth4" = "LAN1".

   I did also find ("find", that is) an "ethctl" command, and that seems
to provide the pay-off (at long last):

# ethctl eth1 media-type
Auto-negotiation enabled.
Link is down

# ethctl eth2 media-type
Auto-negotiation enabled.
The autonegotiated media type is 100baseTx-FD.

Link is up

# ethctl eth4 media-type
Auto-negotiation enabled.
The autonegotiated media type is 1000BT Full Duplex
Link is up

   Who could ask for more (other than consistent abbreviations)?

   That was educational.  Might also answer an old question about how to
fix the characteristics of an interface (and prevent Auto-negotiation).

   Until Netgear decides to disable all practical shell access, that is.