This article provides information about creating a bootable USB device to upgrade or downgrade devices to or from the Junos OS versions that they are currently running.
This article applies to the following devices:
ACX Series
M,T Series
MX Series
PTX Series
The USB recovery process is used when a router needs to be re-imaged from the beginning due to an error, which prevents Junos OS from booting, such as disk corruption.
Creating a USB for upgrading and downgrading Junos OS involves two steps:
Selecting the USB Junos
Creating a bootable USB and writing to the USB
To create a recovery USB, use the following steps end to end.
Selecting the USB Junos involves the following:
Arranging for a USB with 8/16gb or more of storage space
Performing a quick format to fat32 format type
Arranging for the USB image for the respective Junos OS release and OS type
The Junos OS image files include the following variations based on the models:
ACX
Tweak: install-media-ppc-18.2R3-S4.1 , junos-vmhost-install-usb-acx-x86-64-18.2R3-S4.1.img.gz
MD5: a5e60749c96f33dcc6095dd1fe71554a
MX
Tweak: junos-install-media-usb-mx-x86-64-20.X2-SX.img.gz, junos-vmhost-install-usb-mx-x86-64-18.2R3-S4.1.img.gz
MD5: 1b45568c1407483610c2244686f47124
PTX
Tweak: junos-vmhost-install-usb-ptx-x86-64-20.3X75-D30.10.img.gz
MD5: 852fba8cb8f65e8354c6a953fd2b9fe5
Check the md5 for the USB release after the download.
Extract the image file from the ZIP extension to obtain the disc.image file for the image.gz.
Download a software Win32 Disk Imager, which is a Windows tool for writing images to USB devices or SD/CF cards.
Select the destination under Image File.
Check the auto-populated path of the USB under Device.
After you have checked everything, perform a write operation to write the image.
For creating a bootable USB drive by using a non-Windows OS device, refer Boot Junos OS Evolved by Using a Bootable USB Drive | Junos OS Evolved | Juniper Networks.
Routing Engine Recovery Procedure
Insert the USB device into the RE USB slot.
Connect to the console port.
At this point, if the router is accessible, and you need to save some data from it, make a copy since everything will be lost going forward.
For a single Routing Engine (RE), reboot the device, manually power off the device by using the main power switch, wait 10 seconds, and then power the device back on.
For a dual RE, perform a request chassis cb slot X offline/online for the respective RE or press the reset button for 3-4 secs.
When the software prompts you with the following question, type yes:
WARNING: The installation will erase the contents of your disk. Do you wish to continue (y/n)? yes The device copies the software from the removable media emergency boot device onto your system, occasionally displaying status messages. Copying the software can take up to 45 minutes, depending on device.
When the process is complete, reboot system.
Perform system reboot (y/n)? yes
After pressing yes, immediately detach the USB from the Routing Engine. The router will load the Junos OS and boot into Amnesiac mode, following which the login prompt is displayed.
Amnesiac (ttyd0) login:
Log in as root on the device’s console port.
Create a new root user configuration as you did when the device was shipped from the factory or restore a previously saved configuration file to the system.
root@user-re0> edit Entering configuration mode root@User-re0# delete interfaces delete security delete chassis auto-image-upgrade delete protocols set system root-authentication plain-text-password: pass: ****** (please use the root password you prefer ) show|compare Commit check commit and-quit
If it’s not a brand-new installation, consider “commit sync” from the primary RE as your recovery option.
The boot process will automatically select the USB as the first preference of boot by default. If that is not the case, contact Support immediately.
2023-11-20: Initial version
2025-7-30 : Improved formatting
2025-8-12 : Filled in Modification History