Tag: Systems Administration

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.

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.

Google Delivers Mac Google Earth API Plugin, But at What Cost?

UPDATE: Google has released a version of Google Earth (including the plugin) without the self-updating feature.

The Mac blogs around the ‘net are all abuzz today about Google’s release of a Mac version of the Google Maps API, but I noticed something funny when I installed it.  The plug-in is a standard Mac Internet Plug-In, meaning you can install it at either /Library/Internet Plug-Ins or ~/Library/Internet Plug-Ins.  So why does the install package prompt you for administrator credentials when you choose to install it into your home folder?  The answer lives at /Library/Google.

It turns out that when you install the plugin, the installer also installs a software update component, code-named “keystone.”  It installs the following components:

  • An application bundle at /Library/Google/GoogleSoftwareUpdate/GoogleSoftwareUpdate.bundle
  • A “Ticket Store” at /Library/Google/GoogleSoftwareUpdate/TicketStore/ — does anyone know what this does?  I sure don’t.
  • A LaunchDaemon that runs as root on demand, at /Library/LaunchDaemons/com.google.keystone.daemon.plist
  • A LaunchAgent (/Library/LaunchAgents/com.google.keystone.agent.plist) that runs when you’re logged in, presumably to fire up the daemon so you can receive updates without administrative privileges.

Interestingly enough, this software component is never mentioned by Google.  It isn’t an option you can deselect in the installer.  Even worse, the plugin’s uninstall instructions don’t say a thing about it.  This means that after you follow the plugin uninstall instructions, your computer is still checking in with Google’s servers to make sure that it’s up-to-date.  I’m reluctant to call this malware, but it sure seems like spyware, doesn’t it?  At the very least the installer ought to mention something.

Be cautious when installing this plugin onto any computer where security is essential.  Any software component that runs as root, such as the updater this installer installs, is another attack vector for intruders trying to get at your data.

For what it’s worth, the API plugin does work if you only copy the stuff in /Library/Internet Plug-Ins to a computer or to your user account, so it appears that you can still use the plugin in a secure environment, you’ll just have to update it yourself and not have Google do it for you.

I’ve also mentioned this on the official Google Group.