It is not installed by default in OSMC. You need to install the wireless-tools package.
Interesting, I can not recall that I installed it (as I only have wired connection) and I have the wireless-tools installed. Maybe installed it before to test something for the forum.
@MarkusLange sudo apt-get install wireless-tools and you are done
Sleepwalker installs 
confirm - I had to install wireless-tools package to get iwconfig.
Hi Guys, pi 3 wifi even with power management to off seems to not perform ok at all, it’s not possible to watch a descent size mkv from NAS with onboard wifi…
Any way to disable the onboard so we can use a usb wifi dongle??
(just adding a dongle seems to not work, it keeps using the bad onboard wifi)
Thank you so much that hint helped me out
I created /etc/modprobe.d/raspi-blacklist.conf and added into it:
blacklist brcmfmac
blacklist brcmutil
saved it and rebooted
After this it accepted my usb dongle and the world is again a better place… 
Should maybe an option inside the OSMC-addons to do that
Yes, that’s not a bad idea.
Sam
Thanks, if you put it inside the Installer it can be done from the beginning, but then you need to seperate between RPi 2 and Rpi 3 (but it shouldn’t affect the RPi 2 but maybe with the Original Dongle from the foundation)
I wouldn’t add it to the original installer. It’s an odd preseed step and would probably confuse some users. Disabling via My OSMC would be good enough.
how do I undo the above command sudo iwconfig wlan0 power off to /etc/rc.local - I have copied my osmc img onto another pi3 for my daughter on the wifi dongle does not start with osmc as in connect to the internet is there a way to undo this so it connects automatically when osmc boots thanks
If you added it to /etc/rc.local than just remove it and reboot.
But your problem might have other reasons so try to provide logs.
@fzinken hi mate thanks for the reply how do I delete it like so /etc/rc.local then rm iwconfig wlan0 power off … ? thanks
You remove stuff the same way you added it!
I don’t know which steps you followed but if you followed this one:
then you just edit /etc/rc.local and remove the lines again.
CTRL + K when you select the correct line
Hi there,
This thread is quite old but I was having the same problem. My solution was to change the channel of my wireless network. Apparently channel 12 and 13 are not stable for Raspberry Pi?
I hope this helps other people with the same problem.
It’s much more likely that those channels are not stable in your environment and not for any reason specific to the hardware itself. Glad you are up and running anyway.
Channels 12 and 13 are “overlapping” channels and will cause issues with other peoples networks and therefore should not be used.
Ok, thanks for the extra info about the channels.