Juniper MX2010 Hardware Manual page 703

2. If the host subsystem is functioning as the master, switch it to backup by using the command:
user@host> request chassis routing-engine master switch
CAUTION:
a message appears indicating that the network traffic will be interrupted while
the Packet Forwarding Engine is reinitialized.
3. On the console or other management device connected to the Routing Engine you are removing, enter
CLI operational mode and issue the following command. The command shuts down the Routing Engine
cleanly, so its state information is preserved:
user@host> request system halt
CAUTION:
will be halted. You must use the request chassis both-routing-engines command
to halt both Routing Engines.
Wait until a message appears on the console confirming that the operating system has halted.
For more information about the command, see the
Reference.
NOTE: The Routing Engine might continue forwarding traffic for approximately 5 minutes
after the request system halt command has been issued.
RELATED DOCUMENTATION
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Maintaining the MX2020 Host Subsystem
When you request the host subsystem master to switch to backup,
When you request a host subsystem halt, only one Routing Engine
Junos OS System Basics and Services Command
687