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Revision as of 21:56, 24 March 2007 by Dincio (talk | contribs) (How to disable Watchdog)
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What is Watchdog

Watchdog reboots the Apple TV it if the GUI isn't running. There's a kext called AppleTCOWatchdog.kext in the /System/Library/Extensions/ folder.

How to disable Watchdog

Yet another failed attempt:

Auto restart is for automatically rebooting after a power failure and is present also on Mac. You can turn it off using: pmset autorestart 0
As you can see with pmset -g:

System-wide power settings:
SleepDisabled          1
Active Profiles:
AC Power                -1*
Currently in use:
 disksleep      0 
 hibernatemode  0
 displaysleep   0
 powerbutton    0
 sleep          0
 autorestart    0
 hibernatefile  /var/vm/sleepimage

Apparently BackRow.framework tells Watchdog that "we are up and running":

strings /System/Library/PrivateFrameworks/BackRow.framework/Versions/A/BackRow
BRSettingsHelper tellWatchdogWeAreUpAndRunning

Here is the code needed to call BackRow functions. Note you must add the BackRow framework to your project.

#import <Cocoa/Cocoa.h>

@interface BRSettingsHelper : NSObject {


- (void) tellWatchdogWeAreUpAndRunning;  //This function seems to reset the boot count but does not prevent the machine from rebooting.
- (void) reboot;


And now to test it:

#import <Cocoa/Cocoa.h>
#include "BRSettingsHelper.h"

int main(int argc, char *argv[])
    BRSettingsHelper * test = [[BRSettingsHelper alloc] init];

        [test reboot]; 
    return NSApplicationMain(argc,  (const char **) argv);

Note that to get this to work, the app had to be run as root.
There is also the key:

which is probably used in one of:

-[RUIPreferences boolForKey:]
-[RUIPreferences boolForKey:withValueForMissingPrefs:]
-[RUIPreferences canSetPreferencesForKey:]
-[RUIPreferences descriptionForKey:]
-[RUIPreferences floatForKey:]
-[RUIPreferences integerForKey:]
-[RUIPreferences objectForKey:]
-[RUIPreferences setBool:forKey:]
-[RUIPreferences setFloat:forKey:]
-[RUIPreferences setInteger:forKey:]
-[RUIPreferences setObject:forKey:]
-[RUIPreferences stringForKey:]

This seems to indicate that the auto reboot interval is stored as a key somewhere. I don't know if this is simply used for the or if there is something else on the system that will use this.

SettingsHelper has a reference to /sbin/shutdown -r now

Symlinking /sbin/shutdown to /usr/bin/true makes the shutdown command do nothing.

There's also /usr/sbin/recovery_reboot shell script, which seems to tell OS X to reboot using recovery partition (only this time). Perhaps (pretty doubtful) it is called when watchdog sniffs something bad. Easiest way to check would that would be just adding something like:

echo 'oh no, I am being recovery_rebooted' > /blah

and then see if /blah exists after your ATV was rebooted by a watchdog.

Background information

This Apple document about Watchdog may shed some light: (However, on the Apple TV, there is no /etc/watchdog.conf, other than what this document is saying)

Watchdog is not used in Mac OS X 10.4: look at launchd. This is referring to a software watchdog and is probably unrelated to the rebooting problem.