I'm trying to pro grammatically get the speeds of all my networks by looping though the 'speed' entries in /sys/devices. Works great for things like:

/sys/devices/pci0000:00/0000:00:1c.5/0000:01:00.0/net/eth0/speed

but for some devices like /sys/devices/virtual/net/lo/speed I'm getting "cat: /sys/devices/virtual/net/lo/speed: Invalid argument"

appending 2>&1 to the command doesn't help so I'm not sure where the error is coming from. Is there some way I can tell that I shouldn't try to access the data because it's not there? I've gotta believe there is some way to tell. I just did spot an operstate which says things like up, down or unknown that may be the answer. BUt I also found a 'tun' device with a state of unknown which DOES report a speed.

Ideally I'd rather not have to read a second file but I suppose it is what it is.

btw - I can't simply list of set of device names to ignore because I never know what's going to show up/

-mark

Maybe this is too simplistic, but how about checking the return code ?.

Those /sys/devices/virtual/net/lo/* pseudo files "exist" on my non-virtualized system; cat of speed gets rc=1, opstate gets rc=0. Just toss the message in the bit bucket ...