Modifying operating channel in AP mode

Ben Greear greearb
Tue Feb 15 21:41:50 PST 2011

On 02/15/2011 07:41 PM, Lara Deek wrote:
> Hello,
> A device in master mode running hostapd has its operating channel set
> in hostapd.conf prematurely. While hostapd is running, I want to
> modify the operating channel, however, I am getting unusual behavior.
> First, I bring the master interface down with "sudo ifconfig wlan1
> down", then change channels with "sudo iw dev wlan1 set freq 5180
> HT20", followed by "sudo ifconfig wlan1 up". "iwconfig" shows that the
> frequency does not in fact change, but a separate device in monitor
> mode does in fact receive probe responses from the AP at the new
> frequency. The AP's beacon transmission is, however, terminated, even
> on its previous operating channel. Furthermore, devices in managed
> mode can no longer connect to the AP. Then, if I issue an "sudo iw dev
> wlan1 set freq 5180 HT20" on the AP device again, I do not get
> "command failed: Device or resource busy (-16)", but "iwconfig" shows
> that the channel is updated to the new channel. Normal AP activity
> ceases from modifying channels when running hostapd.
> If I return to the channel set in hostapd.conf, devices can connect to
> the AP, "iw dev wlan1 link" shows the connection, but the AP ceases
> beacon activity, and there is an unusually high rate of probe activity
> between the client and AP.
> I would appreciate any insight on how to address this issue. To change
> channels, must I just restart hostapd with a new "channel" value in
> hostapd.conf every time?

You can probably change the config file and send SIGHUP to hostapd
to tell it to re-configure itself?


> Regards,
> Lara
> _______________________________________________
> HostAP mailing list
> HostAP at

Ben Greear <greearb at>
Candela Technologies Inc

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