Back Up the New Software
After a week or so, when you are satisfied that the new software is running successfully, we recommend that you back up the reinstalled software.
To back up the reinstalled software, use the following Junos OS CLI operational mode command:
The root file system is backed up to /altroot, and /config is backed up to /altconfig. The root and /config file systems are on the router’s internal flash drive, and the /altroot and /altconfig file systems are on the router’s hard drive.
After you issue the request system snapshot command, you cannot return to the previous version of the software because the running and backup copies of the software are identical.