Apple Doesn’t Like “Die, You Gravy-Sucking Pig-Dog!”
There’s a relatively well-known Easter egg in BSD’s shutdown.c: a function named die_you_gravy_sucking_pig_dog (side note: I’ve got three-to-one odds that say whoever wrote that has a huge UNIX beard). It turns out that Apple doesn’t care to have such uncouth function names floating around, so they re-defined it:
#ifdef __APPLE__
void log_and_exec_reboot_or_halt(void);
#else
void die_you_gravy_sucking_pig_dog(void);
#endif
Sure, it does the same thing, but I don’t think log_and_exec_reboot_or_halt has the same panache.
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.
Updating dyld Shared Caches with Radmind: Best Practices
Similar to my last post about updating kernel extensions, you can run into problems with Radmind due to the dyld shared cache. You may see messages like this in your system log:
current cache invalid because /System/Library/Frameworks/WebKit.framework/Versions/A/WebKit has changed
Running the update_dyld_shared_cache command will fix this, but there’s a better way. Sure, there’s almost no overhead to that command, but where’s the fun in that? Here’s a pre-apply script that will delete any shared caches that have changed, which will then be re-built at reboot.
#!/bin/sh # update_dyld_caches: Inspects the applicable transcript for something that # might cause a dyld cache to become outdated. If it exists, # delete the cache so it's re-created at startup. DYLD_CACHE_FOLDER="/private/var/db/dyld" DYLD_PREFIX="dyld_shared_cache_" ARCHITECTURES="i386 x86_64 rosetta ppc ppc64" for arch in ${ARCHITECTURES}; do cache="${DYLD_CACHE_FOLDER}/${DYLD_PREFIX}${arch}" map="${DYLD_CACHE_FOLDER}/${DYLD_PREFIX}${arch}.map" if /bin/test -f "${cache}"; then if /bin/test -f "${map}"; then /bin/cat "${map}" | grep ^/ | sort --unique --ignore-case | while read line; do if /bin/test -n "$(grep ${line} ${1})"; then # found a match /bin/rm -f "${cache}" /bin/rm -f "${map}" break; fi done else # Cache exists, but there's no map. /bin/rm -f "${cache}" fi fi done
Updating Kernel Extensions with Radmind: Best Practices
One of the problems that I’ve run into so far using Radmind to manage Mac OS X—specifically, the Leopard to Snow Leopard transition—is that kextd helpfully starts recreating your kernel extension cache as soon as you modify anything in /System/Library/Extensions. This can be problematic when you’re updating core system files; as you update the 10.5 kernel extensions to their 10.6 counterparts, you don’t want the 10.5 version of kextd creating a cache of 10.6 kernel extensions, especially as the kernel extension cache has moved (from /System/Library/Extensions.mkext to /System/Library/Caches/com.apple.kext.caches/). So, should you handle this? My solution is to stop kextd if I know that I’m updating kernel extensions; that way, they won’t be re-created until reboot. Here’s the script:
/private/var/radmind/preapply/update_kernel_extensions:
#!/bin/sh # update_kernel_extensions: Manage the replacement of old kernel extensions. # If there are updates, kill kextd and destroy the # caches. KEXT_CACHE="/System/Library/Caches/com.apple.kext.caches" KEXT_FOLDER="/System/Library/Extensions" KEXTD_LAUNCHD="com.apple.kextd" SYSTEM_LAUNCHD_FOLDER="/System/Library/LaunchDaemons" transcript="${1}" result="${transcript}.$$" /usr/bin/grep "${KEXT_FOLDER}" "${transcript}" > "${result}" if test -n "${result}"; then #result is non-empty # Disable kextd to prevent it from recreating kernel extension caches, which # will be re-created at startup. if test -n "$(/bin/launchctl list | /usr/bin/grep ${KEXTD_LAUNCHD})"; then #kextd is running /bin/launchctl unload "${SYSTEM_LAUNCHD_FOLDER}/${KEXTD_LAUNCHD}.plist" fi # Remove kernel extension cache. /bin/rm -rf "${KEXT_CACHE}" fi rm -f "${result}"
In its present form, it only works on Snow Leopard, but I’ll be updating it to work on Leopard as well.
Take Me Home Now Free
Take Me Home is an ancient, buggy iPhone app that was my “Hello, World!” in the App Store. Its sale rate has plummeted to only a couple of buyers a week and, with the prevalence of real, honest-to-God GPS apps in the store these days, its usefulness is questionable. So from here on out, it’s free. I can’t promise to continue supporting it—especially for new devices and APIs—so the best I can do may be to remove it from the store in the event that some update breaks it.
Enjoy!
Quick Tip: Don’t Do This
I could not find out where a bug was coming from for the life of me today. Naturally it one of those “assignment instead of equality” bugs that seem to crop up when trying to code too quickly. The difference here was that I had implemented a subclass of NSObject that reimplemented the method +resolveInstanceMethod:. So, the code went like this:
+ ( BOOL )resolveInstanceMethod:( SEL )sel
{
if ( sel = @selector( setFoobar: )) {
return class_addMethod([ self class ], sel, ( IMP )setFB, "v@:@" );
} else if ( sel = @selector( foobar )) {
return class_addMethod([ self class ], sel, ( IMP )getFB, "@@:" );
} else {
return [ super resolveInstanceMethod:sel ];
}
}
For those of you keeping score at home, when the Objective-C runtime tried to resolve any selector, this method happily added a selector for -setFoobar: to self’s class and returned YES.
Don’t do this.