How to Confirm Your Junos Configuration before You Commit
Junos provides a path for the timid and cautious user. You can try out a candidate configuration. If you don’t like it, Junos returns to the previous version of the configuration automatically. This approach is an easy way to get out of a jam. To try out a candidate configuration, instead of using the commit command, use commit confirmed:
 wiley@netnik# commit confirmed commit confirmed will be automatically rolled back in 10 minutes unless confirmed commit complete
The default wait is ten minutes, and you have to explicitly accept the commitment, either by typing the commit command again or by typing the commit check command. Then you see the commit complete message.
If ten minutes is too long to wait in your functional network, use a shorter delay, such as one minute, to tell whether the configuration is working:
 wiley@netnik# commit confirmed 1 commit confirmed will be automatically rolled back in 1 minutes unless confirmed commit complete
If the device operation isn’t correct, don't worry. When the confirm time expires, Junos automatically returns to the previous configuration, which you know is a working configuration:
Broadcast Message from root@netnik (no tty) at 16:36 PDT Commit was not confirmed; automatic rollback complete.
Even the most experienced Junos engineers and administrators use the commit confirmed command as an insurance policy on their own work. Doing so can sometimes save hours lost sending someone to a remote site so that they can physically access a device which has become inadvertently isolated from the rest of the network through a configuration misstep.