Wifi scan interval in Debian Wheezy, reconnect after sleep

Question

I want to reconnect to a wireless network as fast as possible when waking up my computer from sleep mode. It always takes a while (usually 15-30 seconds) before there's even a listing of available networks. Scanning with iwlist does not even take one second so I guess it takes a while before it even starts scanning.

Can I shorten the scan interval or solve my problem in a different way?

I'm running Debian Wheezy without any special configurations. Network connections are handled by the GUI but I'm a long time Debian user and not afraid of the command line. Even Bash solutions are welcome - anything which solves my problem.

Answer 1

It's going to depend on a number of factors.

Sleep vs Hibernate

Software Issues

• Connecting to an open wifi network or specific net

• Not Connecting without waiting for a BSID

• Accessing your password

• KWallet issue from KDE ?

Hardware Issues

• Sleep modes can differ with manufactures

• Wireless Drivers can be very different

Direction For research:

Although I can't directly answer your question, you would likely be able to execute a direct scan with iwlist, and join an open network based on the Power management hook in Wheezy.

ACPI (old way)

This action would be scripted through the ACPID event hooks.

You can learn more about acpid /etc/acpi/actions

PM-Utils launchpad

This action would be scripted through pm-util event hooks

• resume -- The hook MUST perform whatever action is appropriate when the system is coming out of suspend.

• thaw -- The hook MUST perform whatever action is appropriate when the system is coming out of suspend-to-disk.

Suspend/resume functionality can be easily modified by installing files into the /etc/pm/sleep.d directory. These files, known as hooks, can perform specific tasks on suspend/resume.

1. Some event happens to wake the machine up

2. Each of /etc/pm/sleep.d/* are executed in reverse C sort order, with a command line argument of "resume" or "thaw"

Answer 2

If your network uses only iPv4, the problem could be that Debian Linux is first trying to connect via iPv6 without success, before passing on to iPv4 and succeeding. Turning off iPv6 might in this case solve the problem.

For more details see the Debian IPv6 Project, and especially the section How to turn off IPv6.

Answer 3

You've mentioned you are running Debian Wheezy without any special configurations, so I assume you are using NetworkManager. What you can try to do is forcing NetworkManager to reconnect as soon as your machine wakes up.

To do that, try this way:

1. get the UUID of the connection you're interested in:

   $ nmcli con
   

2. ensure you have the pm-utils package installed and create a script in /etc/pm/sleep.d/ like this:

   nmcli con up uuid 9890c6b9-d2b4-4ed2-a743-ad07cb6c125f

Obviously, replace the UUID with the one you got in step 1. The script has to be executable, and it will be executed every time your laptop comes out of suspend (or suspend-to-disk).