"channel [21] (157) is disabled for use in AP mode"

[Jouni Malinen]

On Sun, Apr 28, 2013 at 05:05:44AM -0500, Zack Buhman wrote:
> I'd like to use channel 157, as I've done in the past. I've read [1] that
> 157 is perfectly valid to use in the US. Apparently hostapd disagrees
> with this assesment.

It's not hostapd, but the regulatory code or driver that has marked the
channel as not allowed for AP mode:
5785 MHz [157] (17.0 dBm) (passive scanning, no IBSS)

The passive scanning part there indicates that no radiation can be
initiated on the channel (i.e., need to see a master device operating on
the channel before transmitting any frames).

> I'm not quite understanding how hostapd came to the conclusion that I
> can't use channel 157, and, more importantly, how I can fix this.

hostapd follows the channel flags returned by the kernel regulatory
implementation.

-- 
Jouni Malinen                                            PGP id EFC895FA