HP 5920 series Fundamentals Configuration Manual page 120

you can use the install series displaying and maintaining commands with the issu series
configuration commands.
At reboot, a subordinate device automatically synchronizes the master device's configuration and
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status data. This process takes some time. You must wait for the synchronization to complete before
using the issu load command on the subordinate device. To check the synchronization progress, use
the display device command. The synchronization is completed when all subordinate device are in
normal state.
After an ISSU, you must log in again to the device before you can configure the device.
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