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[EX] Rewrite the entire file system by issuing "install --format" command from "Loader" mode (Format Install)



Article ID: KB20643 KB Last Updated: 28 Jul 2020Version: 8.0

The "Format Install" should be the last recovery method to restore the switch, as this will erase all files, including the configuration files, by formatting the file system.  Best backup procedures should be in place to recovery any possible file loss.


The "Format Install" is the final method to recover the EX Switch if you are unable to recover the switch using any of the recommended methods in KB20464 - Stage 4 – Troubleshoot Upgrade Failure/Crash.

NOTE: Performing a "Format Install" is going to format the entire file system and storage unit. Therefore, the EX Switch will lose all of the configuration files and log files. If this step is taken, a Root Cause Analysis, or recovery of any information from the EX Switch, will not be possible.
  • Contact your technical support representative if you need a Root Cause Analysis prior to system recovery.

Note that "Format Install" is equal to the "install --format" command which is executed from the "Loader" prompt.

The 'Format Install' can be performed with either of the following methods:

  • TFTP
  • USB
loader> set ipaddr=
loader> set netmask=
       loader> set gatewayip=
loader> set serverip=
loader> install --format tftp://<tftp server>/<Junos package name>

For example:
loader> install --format tftp://
  1. Connect a terminal to the EX switch console port and power on the switch.

  2. When you see the "loading /boot/defaults/loader.conf" display, hit ENTER. You will be prompted with:
    Hit [Enter] to boot immediately, or space bar for command prompt.

  3. Press the space bar to enter the manual loader. The loader> prompt displays.

  4. Set the EX Switch management IP address and netmask:

  5. Issue the install command with the format option to install the Junos image via TFTP:

  1. To perform this recovery installation, the USB Drive should be formatted to FAT-32 & should be empty. Review the USB compatibility specification under KB17435 - USB device compatibility / Specifications for EX Series Switch.

  2. Copy the Junos package to USB flash drive.

  3. Power off the EX switch

  4. Put the USB flash drive in the EX switch.

  5. Power on the EX switch.

  6. After the 'Loading getting /boot/default/loader.conf' displays, hit space bar for the loader> prompt.

  7. Issue the install command with the format option:

    loader> install --format file:///<Junos package name>

    For example:

    loader> install --format file:///jinstall-ex-4200-15.1R7-S6.3-domestic-signed.tgz

Note: Both the installation methods proceed as normal and ends with a login prompt. The username should be root & no password prompt since the file system been formatted.

Related link: Troubleshooting Software Installation

Modification History:
2020-07-21: Changed the version on the output to show a more recent and not EOS version as example
2020-03-19: Added link to KB17435 in step 1 of the USB instructions.
2019-11-14: Minor, non-technical edits.
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