Google Apps Directory Sync Administration Guide - Manual (Page 139)

Synchronization 139
Monitoring
After you have set up scheduled synchronization, make a policy of regularly
checking the status of your synchronizations.
Check Notification messages on a regular basis for signs of any problems.
Notifications will be sent to an address that you specify. For more information
about Notifications, see “Notifications” on page 127.
When looking through notifications logs, look for messages that indicate that
users were synchronized. If you expect that a particular user will be synchronized
and the user isn’t, check the notifications for information.
Also, check for new updates regularly. You can use the command
checkforupdate.exe in the same directory as sync-cmd.exe, to check online for
new versions of Google Apps Directory Sync.