Wednesday, 9 October 2019

Upgrading Junos OS on EX 3400 Switch using USB Format install method.

2 Comments so far

My intent of this post is to be a quick reference guide for recovering, installing and upgrading Junos OS using USB format install method. Juniper switches are well know for software corruption caused mainly due to unexpected power failure. This will be an easy and useful document for the engineers who use Juniper Switches in their organization.

Before you begin



  • Copy JUNOS OS upgrade image on a USB flash disk Copy JUNOS OS upgrade image on a USB flash disk
  • Check for adequate space on the EX Series device.
  • Preparing the Flash Drive

    •  Any USB key formatted with FAT or FAT32 file systems can be used
    •  Plug the USB key to a Windows PC/Laptop
    •  Right-Click  the removable disk and format the drive with FAT/FAT32 file system
    •  Copy the JUNOS OS package to the USB.

    Now insert the USB disk to the EX Series switch and follow the below commands.

    CLI Commands 


    root> start shell
    root@:RE:0% mount_msdosfs /dev/da1s1 /mnt
    root@:RE:0% cd /mnt
    root@:RE:0% ls
    root@:RE:0% cp junos-arm-32-18.1R3-S4.2.tgz /var/tmp/
    root@:RE:0% cd /var/tmp
    root@:RE:0% ls
    bcast.bdisp.log                 mmcq_sdb_bbe_mmcq
    bcast.disp.log                  pc
    bcast.rstdisp.log               pfe_debug_commands
    bcast.undisp.log                pics
    ex_autod_config                 pkg_cleanup.log.err
    ex_autod_rollback_cfg           rtsdb
    junos-arm-32-18.1R3-S4.2.tgz    sd-upgrade
    krt_rpf_filter.txt              stable
    root@:RE:0% cli
    root>request system software add /var/tmp/junos-arm-32-18.1R3-S4.2.tgz no-copy no-validate unlink force reboot

    Post reboot you switch firmware should be upgraded to the new version, you can verify this using below command

    root> show version

    Model: ex3400-48t
    Junos: 18.1R3-S4.2


Fahim Raza(Author)

Hi there! my name is Fahim Raza. I am a professional blogger. I like music(Linkin Park), playing games(football) and blogging...


  1. We are a full-service drywall company located in Bend, Oregon. Our drywall contractor offers all phases of drywall from installation to custom texture more about us visit website Drywall Company Bend Oregon.

  2. Really helpful down to the ground, happy to read such a useful post. I got a lot of information through it and I will surely keep it in my mind. Keep sharing. If you are looking for some useful data and information regarding custom usb then visit PR Design.