Fixing A Juniper Switch That Was Shut Down Improperly

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Juniper switches need to be shut down properly, not just powered off. They're Unix-based, and Unix does not like being shut down improperly.

OS Primary Partition Corruption

You will know when you have a switch that has been shut down improperly. There will be an amber light on the chassis, and this alarm on the console:

user@switch> show chassis alarms
1 alarms currently active
Alarm time              Class  Description
2014-01-26 10:48:49 EST Minor  Host 0 Boot from backup root

As well as this banner:

**                                                                   **
**                                                                   **
**  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.                                           **
**                                                                   **

When installing the OS, a Juniper device makes two copies of the OS. One is a backup, in case the primary was not unmounted cleanly at shutdown (or just powered off).

To copy the backup image over top of the primary image (you must type this; it will not tab-complete):

request system snapshot media internal slice alternate

Note that using this command will only repair the OS; it won't clear the alarm.

Verify with the command:

show system storage partitions

You will get output like this:

Boot Media: internal (da0)
Active Partition: da0s1a
Backup Partition: da0s2a
Currently booted from: backup (da0s2a)

Note the "Currently booted from: backup" line.

Once the snapshot is done, the switch must be rebooted to clear the alarm. Normally, a Juniper will boot the last-known-good copy of the OS. It must be forced to use the primary.

request system reboot slice alternate media internal in 0

SSH Issue

Sometimes, SSH will also fail after an improper shutdown. When trying to SSH to the switch, you will see this:

user@COREBOX-re0> ssh
ssh_exchange_identification: Connection closed by remote host

To fix this, console into the switch and do the following:

start shell user root
cd /var
mkdir empty

Then you have two options: reboot the switch or restart SSH.

To restart SSH:

configure private
deactivate system services ssh
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