Shallow Thoughts : tags : tip

How to enable/disable laptop wireless hardware

But when I suspend and resume, the settings aren't remembered. The machine always comes up with wireless active, even if it wasn't before suspending.

Since wireless can be a drain on battery life, as well as a potential security issue, I don't want it on when I'm not actually using it. So I wanted a way to turn it off programmatically.

The answer, it turns out, is rfkill.

$ rfkill list
0: tpacpi_bluetooth_sw: Bluetooth
        Soft blocked: yes
        Hard blocked: no
0: phy0: Wireless LAN
        Soft blocked: yes
        Hard blocked: no

To toggle something off,

$ rfkill block bluetooth
$ rfkill block wifi

Type rfkill -h for more details on arguments you can use.

Fn-F5 still works to enable or disable them together. I think this is being controlled by /etc/acpi/ibm-wireless.sh, though I can't find where it's tied to Fn-F5.

You can make it automatic by creating /etc/pm/sleep.d/. (That's on Ubuntu; of course, the exact file location may vary with distro and version.) To disable wireless on resume, do this:

#! /bin/sh

case "$1" in
  resume)
    rfkill block bluetooth
    rfkill block wifi
    ;;
esac
exit $?

Of course, you can also tie that into other things, like your current network scheme, or what wireless networks are visible (which you can get with iwlist wlan0 scan).

Set Ubuntu's system clock to use localtime, not UTC

Need your Ubuntu clock to stay in sync with a dual-boot Windows install? It seems to have changed over the years, and google wasn't finding any pages for me offering suggestions that still worked.

Turns out, in Ubuntu Oneiric Ocelot, it's controlled by the file /etc/default/rcS: set UTC=no.

Apparently it's also possible to get Windows to understand a UTC system clock using a registry tweak.

Ironically, that page, which I found by searching for windows system clock utc, also has the answer for setting Ubuntu to local time. So if I'd searched for Windows in the first place, I wouldn't have had to puzzle out the Ubuntu solution myself. Go figure!

Vim/Emacs tip: use modelines for files that need special behavior

Most of the time when I edit a text file in vim, I want lines to wrap automatically as I type, at somewhere around 70 columns wide. So I set textwidth=70 in .vimrc.

But sometimes that isn't appropriate. For instance, I have a procmail rules file where I put common spam patterns that programs like spamassassin don't seem to be able to catch. So I might have lines like:

*^Subject:.*(Ink Cartridges|Hummingbird Vine|who's who of executives|Avandia|Botox|Your Email ID|Zoosk|Best airfares on the internet|UGG Boots|police training)

But you can set special behavior for one specific file by adding a special comment called a "modeline" as the first line of the file.

Procmail treats any line starting with a hash, #, as a comment, and vim recognizes # as a comment. So I can add this as the first line of the procmail file:

# vim: set tw=0:

Vim understands most common comment styles, so it should understand lines like /* vim: set tw=0: */ and // vim: set tw=0: and ; vim: set tw=0: as well.

But to make this work I had to do one more thing: in .vimrc, I had to add

set modeline

Apparently on some versions of vim this is on by default; in others it's turned off for security reasons (someone could put an evil modeline into a file which would make your vim do something when you edited it). Definitely something to be aware of, but if you mostly edit files you created yourself on your local machine, and no one else uses your machine, it's your choice whether to worry about it.

Emacs has modelines too

Emacs has mode lines too, though it calls them Local variables lines. For instance, C++ files in Mozilla's source tend to start with:

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

It's awfully handy to be able to define specific indentation style for the files within a project, making it easy for emacs users, at least, to follow your preferred coding style. If only all editors understood them!

Starting a line with a slash in xchat

/join #channel

/me waves to everyone

Great, but what if I want to start a line with a slash?

On some IRC clients, you can type two slashes, e.g.

/ /me tries

On xchat, what you need is /say:

/say /me succeeds!

Silly little tip, but I know I'll forget it if I don't record it ... and I bet I'm not the only xchat user wondering how to do this.

//me tries

Quick tip: Disabling version control in Emacs

It wasn't obvious what keywords to search for, but I finally found a combination, emacs prevent OR disable autoload vc (the vc was the important part), which led me to the solution (found on this page):

;; Disable all version control
(setq vc-handled-backends nil)

Files load much faster now!