Junos MX5 error after OS upgrade: System is running on alternate media device (/dev/da1s1a)

After OS upgrade on Junos MX5, you are hit with following notice upon reboot;
— JUNOS 13.3R9.13 built 2016-03-01 07:16:35 UTC
NOTICE: System is running on alternate media device (/dev/da1s1a)

This error is as a result of various scenarios and below are the possible causes:
1.) A software failure/error on the primary media (flash)
2.) A hardware failure on the primary media (flash)
3.) A request issue reboot on the secondary media (disk)

How to fix it:

Remember Juniper routers store bootable copies of the JUNOS software in three (3) possible locations:
–> The internal flash (normal boot location)
–> The hard drive (as backup incase internal flash is corrupted)
–> A removable media (normally used for disaster recovery)

NB: Some platforms don’t come with installed hard disks instead they have two internal flash disks, nand-flash0 and nand-flash1.

The removeable media is first in boot order followed by the internal flash and then followed by the hard drive.
Errors that occur to the internal flash can cause the node to boot from an alternate media device. In this case, the alarm showed above is always displayed upon reboot.

Steps to follow:
1.) Verify the router’s boot list/order for present media in the list.
> start shell
% sysctl -a | grep bootdevs
machdep.bootdevs: usb,nand-flash0,nand-flash1
The result shows that there are two internal flash devices in the boot list and this should be okay.

2.) Do a mount
% mount
/dev/da1s1a on / (ufs, local, noatime)
devfs on /dev (devfs, local, multilabel)
/dev/md0 on /packages/mnt/jbase (cd9660, local, noatime, read-only, verified)
/dev/md1 on /packages/mnt/jkernel-ppc-13.3R9.13 (cd9660, local, noatime, read-only, verified)
/dev/md2 on /packages/mnt/jpfe-MX80-13.3R9.13 (cd9660, local, noatime, read-only)
/dev/md3 on /packages/mnt/jdocs-13.3R9.13 (cd9660, local, noatime, read-only, verified)
/dev/md4 on /packages/mnt/jroute-ppc-13.3R9.13 (cd9660, local, noatime, read-only, verified)
/dev/md5 on /packages/mnt/jcrypto-ppc-13.3R9.13 (cd9660, local, noatime, read-only, verified)
/dev/md6 on /tmp (ufs, asynchronous, local, noatime)
/dev/md7 on /mfs (ufs, asynchronous, local, noatime)
/dev/da1s1e on /config (ufs, local, noatime)
procfs on /proc (procfs, local, noatime)
/dev/da1s1f on /var (ufs, NFS exported, local, noatime)
%
%

The result shows that da0 device is not listed but da1. It is likely that during the installation of the new OS the da0 media got corrupted and cannot boot now.

3.) Copy OS on da1 to da0
>request system snapshot slice alternate
Verifying compatibility of destination media partitions…
Running newfs (899MB) on internal media / partition (da0s1a)…
Running newfs (99MB) on internal media /config partition (da0s1e)…
Copying ‘/dev/da1s1a’ to ‘/dev/da0s1a’ .. (this may take a few minutes)
Copying ‘/dev/da1s1e’ to ‘/dev/da0s1e’ .. (this may take a few minutes)
The following filesystems were archived: / /config

The command “request system snapshot slice alternate” operates by completely formatting the partition which the device didn’t boot from (da0), then it goes ahead to copy the OS from the partition on which the device booted (da1) and finally installs it on the the formatted partition, da0.

4.) Reboot the router

All should be well after the router reboots.

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