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[EX/QFX] Recover EX switch while it cannot get into loader prompt

  [KB27255] Show Article Properties


Summary:
This article describes the method to force EX stopped at loader mode while booting up.

EX switches may not able boot up normally due to a power outage or other failure. Standard procedure is to re- format and install from loader by following the instructions provided in KB20643, however under certain circumstances, the system cannot boot into loader mode as described in KB20643.

Symptoms:
EX cannot boot up normally as like with below console output:

FreeBSD/PowerPC U-Boot bootstrap loader, Revision 2.2
(builder@shoth.juniper.net, Wed May 19 06:04:27 UTC 2010)
Memory: 1024MB
Loading /boot/defaults/loader.conf <-- stuck here
or
FreeBSD/PowerPC U-Boot bootstrap loader, Revision 2.1
(marcelm@apg-bbuild01.juniper.net, Wed Feb 6 11:23:55 PST 2008)
Memory: 1024MB
Loading /boot/defaults/loader.conf
/kernel data=0xbc78dc+0x6989c Device NOT ready
Request Sense returned 00 00 00
Device NOT ready
Request Sense returned 00 00 00
Device NOT ready
Request Sense returned 00 00 00
Device NOT ready
Request Sense returned 00 00 00
Device NOT ready
Request Sense returned 00 00 00
Device NOT ready
Request Sense returned 00 00 00
Device NOT ready                  <-- Continuously outputting last two lines


To reinstall Junos for EX from loader, put EX into loader mode first.
This will require you press the space bar when prompted to do so:

Hit [Enter] to boot immediately, or space bar for command prompt. Booting [/kernel]...

The system failed before the message the prompt appeared and thus this method does not work. 
To recover from this situation, the system must be forced into loader mode and display the loader> prompt while booting.

Cause:
Switch fails to boot into loader mode after a power outage or other failure.

Solution:
To force the system to boot into loader, set the load device to an invalid disk from the U-boot mode by pressing [Control + C] key combination at the beginning of the system boot process.
 
U-Boot 1.1.6 (Mar 28 2011 - 04:05:40)

Board: EX4200-24PX 3.9
EPLD:  Version 8.0 (0x82)
DRAM:  Initializing (1024 MB)
FLASH: 8 MB
NAND:  1024 MiB                

Firmware Version: --- 01.00.00 ---
USB:   scanning bus for devices... 2 USB Device(s) found  <-- Type Control + C here.
       scanning bus for storage devices... 1 Storage Device(s) found

=>
=>  

Prompt "=>" means the system is in U-boot mode.  
While in U-bot mode, type this sequence of commands.  
=> setenv loaddev disk66
=> saveenv
=> reset
Note: you can use disk number other then 0 and 1 which are intentionally invalid disk numbers, example: disk99, or disk12, etc.

Reset command will let the system reboot, at this point, press the [Enter] key, when prompted to do so:

Press Enter to stop auto bootsequencing and to enter loader prompt.

For your reference, an output sample should look like this:

U-Boot 1.1.6 (Mar 28 2011 - 04:05:40)

Board: EX4200-24PX 3.9
EPLD:  Version 8.0 (0x82)
DRAM:  Initializing (1024 MB)
FLASH: 8 MB
NAND:  1024 MiB

Firmware Version: --- 01.00.00 ---
USB:   scanning bus for devices... 2 USB Device(s) found
       scanning bus for storage devices... 1 Storage Device(s) found

=> setenv loaddev disk66
=> saveenv
Saving Environment to Flash...
. done
Un-Protected 1 sectors
Erasing Flash...
. done
Erased 1 sectors
Writing to Flash... writing to flash...
done
. done
Protected 1 sectors
=> print loaddev
loaddev=disk66

> reset

U-Boot 1.1.6 (Mar 28 2011 - 04:05:40)

Board: EX4200-24PX 3.9
EPLD:  Version 8.0 (0x82)
DRAM:  Initializing (1024 MB)
FLASH: 8 MB
NAND:  1024 MiB

Firmware Version: --- 01.00.00 ---
USB:   scanning bus for devices... 2 USB Device(s) found
       scanning bus for storage devices... 1 Storage Device(s) found

ELF file is 32 bit
Consoles: U-Boot console  

FreeBSD/PowerPC U-Boot bootstrap loader, Revision 2.4
(builder@dagmath.juniper.net, Mon Mar 28 01:49:54 UTC 2011)
Memory: 1024MB
bootsequencing is enabled
bootsuccess is set
new boot device = disk66

can't load '/kernel'
can't load '/kernel.old'
Press Enter to stop auto bootsequencing and to enter loader prompt.   <-- Type Enter key here.

Type '?' for a list of commands, 'help' for more detailed help.
loader>

EX should now be in loader mode, follow KB20643 perform a format install.
 
KB20643 [EX Switch] Rewrite the entire file system by issuing "install --format" command from "Loader" mode (Format Install) 

If you are have a different type of issue at boot time, please refer to KB20464.

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