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[MX] Router unable to boot from primary partition



Article ID: KB35834 KB Last Updated: 13 Aug 2020Version: 2.0

The MX Series with a Routing Engine that has a Hard Disk or a solid-state drive (SSD) attempts to boot from the storage media in the following order:

  1. USB media emergency boot device (if present)
  2. Compact Flash card
  3. Hard Disk / Solid-state drive (SSD) in the SSD slot 1 or SSD slot 2 (if present)

One or more of the below symptoms can be seen:

  1. The "show system boot-messages",  will display a statement saying the device is unable to boot from Compact Flash (ada0)

  2. Compact Flash not listed in show chassis hardware.

  3. Boot messages indicate file system corruption messages.

  4. The current boot interface will be listed as Disk.

    root@jtac> start shell                                       
    % sysctl -a | grep bootdev

    machdep.currbootdev: disk1                         
  5. An active alarm on the affected RE:

    user@host> show chassis alarms no-forwarding

    1 alarms currently active
    Alarm time               Class  Description
    2020-05-05 19:53:05 PDT  Minor  Host 1 Boot from alternate media
  1. A transient issue with RE that usually appears after booting.
  2. An issue with storage media 
  3. RE failure

Verify the storage partitions detected in hardware output:

An ideal storage output should look like this:

user@host> show chassis hardware
Routing Engine 0 REV 18   74xx-xxxxx   xxxxxxxxxxxx    RE-S-2000
ada0    976 MB  xxxxxxxxxxxx    UNIxxxx xxxxxxx        Compact Flash
ada1  38154 MB  xxxxx           5xxxxxxxx              Hard Disk
usb0 (addr 1)  Uxxx root xxx 0       Intel             uhub0

Routing Engine 1 REV 18   74xx-xxxx   xxxxxxxxx        RE-S-2000
ada0    976 MB  Uxxxxxxxxxxxx    UNxxxx xxxxxxxx       Compact Flash 
ada1  38154 MB   xxxxxxxx       5xxxxxxx               Hard Disk 
usb0 (addr 1)  Uxxx root xxx 0       Intel             uhub0

Note: In case of devices that have SSDs instead of Hard Disk, you will be seeing (SSD 0: ad1 and SSD 1: ad2) in the output list

Check the boot list:

root@jtac> start shell                                       
% sysctl -a | grep bootdev
machdep.currbootdev: compact-flash
machdep.nextbootdev: usb
machdep.bootdevs: usb,compact-flash,disk1,lan

Step 1:

To clear the alarm, try to recover the Junos volume:
Login to  RE1 (default backup)                                         >>> Since the alarm is seen on Host 1

user@host> request system recover junos-volume

Now, run "request system reboot" RE1 and once device boots up, verify if the alarm clears off. If the alarm does not clear after recovery, please proceed with Step 2.

Step 2:

Reboot RE 1 again and wait until you see the Boot menu and hit the space bar to stop the Autoboot. ( Please ensure that you have the console connected to this RE just in case we lose access). You will be directed to boot options Menu as below:

Main Menu                
1.  Boot [J]unos volume
2.  Boot Junos volume in [S]afe mode                                  
3.  [R]eboot    
4.  [B]oot menu
5.  [M]ore options                  
Choice: Autoboot in 3 seconds...

Enter 5 to go to the Options menu:                                 

Options Menu
1.  Recover [J]unos volume
2.  Recovery mode - [C]LI                  
3.  Check [F]ile system                
4.  Enable [V]erbose boot                  
5.  [B]oot prompt                   
6.  [M]ain menu

Enter 3 to choose "Check [F]ile system".  Issue the following command:                

# fsck_ufs /dev/ada0p2    
You will see the below output:     
 # fsck_ufs /dev/ada0p2
            ** /dev/ada0p2
            ** Last Mounted on /.mount
 ** Phase 1 - Check Blocks and Sizes
 ** Phase 2 - Check Pathnames
 ** Phase 3 - Check Connectivity
 ** Phase 4 - Check Reference Counts
 ** Phase 5 - Check Cyl groups

19141 files, 2921404 used, 2110321 free (1529 frags, 263599 blocks, 0.0% fragmentation)

Run request system reboot on the backup RE.

Step 3:

In case you are still unable to recover the file system, please perform USB recovery.

Example for Step 3:

Login into root user and execute the below:

root@host% dd if=/var/tmp/filename of=/dev/da1 bs=1m    <-- Run for 20 seconds and press CNTRL+C to stop

The device writes the installation media image to the USB device:

root@host% dd if=<installation media image> of=/dev/da0 bs=1m
1399+0 records in
1399+0 records out
1466957824 bytes transferred in 394.081902 secs (3722469 bytes/sec)

Step 4:

If the above-mentioned steps do not work, it is most probable that there is a hardware issue with RE and you might need replacement. Please contact your JTAC Representative.

Modification History:
2020-08-13: Minor non-technical edit.

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