The switch boots from the backup root file partition. It is possible that the primary copy of Junos OS failed to boot properly, which could indicate that it is corrupted. This event is flagged in two ways:

• Upon login through the console or management port, the following warning message is displayed:

WARNING: THIS DEVICE HAS BOOTED FROM THE BACKUP JUNOS IMAGE      
                                                                   
It is possible that the primary copy of JUNOS failed to boot up  
properly, and so this device has booted from the backup copy.    
                                                                   
Please re-install JUNOS to recover the primary copy in case      
it has been corrupted.       
                                    

• The following alarm message is generated:

user@switch> show chassis alarms
1 alarms currently active
Alarm time               Class  Description
2011-02-17 05:48:49 PST  Minor  Host 0 Boot from backup root

If the switch is in a Virtual Chassis, the switch member number appears in the Description field, where the switch is called a host.

Install a new Junos OS image on the partition that had the corruption, or take a snapshot (use request system snapshot) of the currently active partition and use it to replace the image in the alternate partition:

If the switch is a standalone switch or a Virtual Chassis primary switch, enter this command:

• user@switch> request system snapshot slice alternate

If the switch is a Virtual Chassis member switch (not the primary), enter this command on the Virtual Chassis:

• user@switch> request system snapshot slice alternate member member-id

where member-id is the Virtual Chassis member ID number.