Recovering the Installation Using an Emergency Boot Device
If Junos OS on your device is damaged in some way that prevents the software from loading correctly,
you may need to perform a recovery installation using an emergency boot device (for example, a USB flash
drive) to restore the default factory installation. Once you have recovered the software, you need to
restore the device configuration. You can either create a new configuration as you did when the device
was shipped from the factory, or if you saved the previous configuration, you can simply restore that file
to the device.
If at all possible, you should try to perform the following steps before you perform the recovery installation:
1. Ensure that you have an emergency boot device to use during the installation. See “Creating an
Emergency Boot Device for QFX Series Switches” on page 579 for information on how to create an
emergency boot device.
2. Copy the existing configuration in the file /config/juniper.conf.gz from the device to a remote system,
such as a server, or to an emergency boot device. For extra safety, you can also copy the backup
configurations (the files named /config/juniper.conf.n, where n is a number from 0 through 9) to a
remote system or to an emergency boot device.
You can use the system snapshot feature to complete this step. The system snapshot feature takes a
“snapshot” of the files currently used to run the QFX Series switch—the complete contents of the
/config and /var directories, which include the running Juniper Networks Junos OS, the active
configuration, and the rescue configuration—and copies all of these files into a memory source. See
Creating a Snapshot and Using It to Boot a QFX Series Switch.
NOTE: System snapshot is not supported on QFX10000 and QFX5200 switches.
CAUTION: The recovery installation process completely overwrites the entire
contents of the internal flash storage.
3. Copy any other stored files to a remote system as desired.
To reinstall Junos OS:
1. Insert the emergency boot device into the device.
2. Power cycle the device.
The emergency boot device is detected. At this time, you can load the Junos OS from the emergency
boot device onto the internal flash storage.
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