Jeff Kelley

Xcode 3.2: Using GDB as a Non-Admin User

New in Xcode 3.2 is an authorization setting that looks like this:

<dict>
	<key>allow-root</key>
	<false/>
	<key>class</key>
	<string>rule</string>
	<key>comment</key>
	<string>For use by Apple.  WARNING: administrators are advised not to
	        modify this right.</string>
	<key>k-of-n</key>
	<integer>1</integer>
	<key>rule</key>
	<array>
		<string>is-admin</string>
		<string>is-developer</string>
		<string>authenticate-developer</string>
	</array>
	<key>shared</key>
	<true/>
</dict>

The upshot of this is that if you aren’t in the _developer group in the local directory, you’ll have to authenticate as an administrator to use gdb or some of the performance tools. For the vast majority of developers on Mac OS X, who run as an administrator, this is fine, but if you’re running as a regular user, either for security reasons or because you’re in something like a lab setting, this can be a problem. To add a user to the _developer group, use the dscl command:

dscl . -append /Groups/_developer GroupMembership UserName

Replace UserName with the short name of your user account (or $(whoami)) and you should be all set.

If you’re administering Mac OS X in a lab setting, you can either create a LaunchAgent that handles this or a login hook. See the Apple tech note “Running At Login” for more information on login hooks. As an added touch, my login and logout scripts to handle this also remove all users from the group, like so:

dscl . -delete /Groups/_developer GroupMembership

If the GroupMembership key doesn’t exist, dscl will create it—and it doesn’t exist by default—so deleting it outright shouldn’t cause any problems.

Dealing with Special Characters in iPhone 4 Graphics Filenames with Subversion

With the iPhone 4’s high-resolution screen, designers need to create two sets of art; the guidelines are to name the files like so: SomeCoolImage.png and SomeCoolImage@2x.png. Unfortunately, if you try to add these files to an SVN repository, the @ symbol throws them off:

$ svn add Icon\@2x~iphone.png 
svn: warning: 'Icon' not found

The fix, thanks to the subversion_users Google Group, is to add another @ to the end of the filename, like so:

$ svn add ./Icon\@2x~iphone.png@ 
A  (bin)  Icon@2x~iphone.png

If you’d like to do this for all of your high-resolution art in a folder, here’s a tiny Bash command for the task:

for x in `ls *\@*`; do svn add $x\@; done

How-To: Run a LaunchDaemon That Requires Networking

I’m a big fan of using launchd to automate things in Mac OS X. That serves me well, as that’s how Apple wants things done moving forward. That said, one of launchd’s biggest shortcomings is a lack of a dependency system. There is currently no way, for instance, to specify in a LaunchDaemon’s property list that the daemon requires the network to be active in order to run. This is problematic for some things, such as a script I wrote to automatically set the computer’s hostname based on the DNS server (more on that later). Luckily, Apple has already defined a function, CheckForNetwork, in /private/etc/rc.common. Here it is in all its glory:

##
# Determine if the network is up by looking for any non-loopback
# internet network interfaces.
##
CheckForNetwork()
{
	local test

	if [ -z "${NETWORKUP:=}" ]; then
		test=$(ifconfig -a inet 2>/dev/null | sed -n -e '/127.0.0.1/d' -e '/0.0.0.0/d' -e '/inet/p' | wc -l)
		if [ "${test}" -gt 0 ]; then
			NETWORKUP="-YES-"
		else
			NETWORKUP="-NO-"
		fi
	fi
}

In your code, simply include rc.common, then call CheckForNetwork as needed. An example:

#!/bin/bash

# Example Daemon Starter
. /etc/rc.common

CheckForNetwork

while [ "${NETWORKUP}" != "-YES-" ]
do
        sleep 5
        NETWORKUP=
        CheckForNetwork
done

# Now do what you need to do.

Note that this will keep the script running indefinitely until CheckForNetwork sets NETWORKUP to “-YES-,” so if there’s a networking problem your code may never execute.

Google Earth Now Available Without Automatic Updates

A while back I blogged about Google Earth’s stealthy, silent automatic update feature. That post continues to be pretty popular, so I wanted to share an update: Google has released a version of Google Earth, including the Web plug-in, that does not include the self-updater. On the download page, the EULA features this paragraph:

(b) Automatic Updates. The Google Earth software may communicate with Google servers from time to time to check for available updates to the software, such as bug fixes, patches, enhanced functions, missing plug-ins and new versions (collectively, “Updates”). By installing the Google Earth software, you agree to automatically request and receive Updates.

However, if you navigate to the advanced setup page, there’s a box you can un-check labeled “Allow Google Earth to automatically install recommended updates.” This box directs you to a separate download that does not include the updater. The EULA, however, does not change when you deselect it. I don’t think that really matters as much in the grand scheme of things, so I’ve really got to give Google some kudos here for listening to systems administrators and concerned users on this one.

WordPress 3.0

I’ve updated the site to WordPress 3.0. So far all is well; I’ll likely create a new post type (excellent new feature) for software once I have more software to be creating posts about.