When you use the sync yes option in the event cli command, the EEM applet runs before the CLI command is executed. The EEM applet should set the _exit_status variable to indicate whether the CLI command should be executed (_exit_status set to one) or not (_exit_status set to zero). A sample applet using the _exit_status variable in described in my “Schedule reload before configuring the router” post.
With the sync no option, the EEM applet is executed in background in parallel with the CLI command. As the CLI command starts at the same time as the EEM applet, you cannot use the _exit_status variable anymore; you have to specify whether you want the CLI command to execute with the skip yes|no option of the event cli command. A sample applet using sync no skip yes options is described in my “Can you disable the reload command?” post.
original post
http://blog.ioshints.info/2011/01/eem-event-cli-command-options-and.html
