This article explains the steps to bring the device up if it is

1. Stuck in boot loop.
2. Device went down and does not come up.
3. FPC going offline/Down

1) Stuck in boot loop after reboot/Power cycle

2) Not booting up after an upgrade/Downgrade.

1. Verify if you are able to console into the switch using a console cable. Check if there are any error logs seen on the screen. Based on the error observed, proceed with next steps.
   • For eg: If DMA errors are seen on the screen, refer the following KB Juniper switch fails with error "/kernel: ad1: FAILURE - WRITE_DMA"
   • Or for example, the RE on an MX device is stuck on the main menu during boot-up, (console prompt is stuck), you can refer KB32941 [juniper.net]
2. Power cycle the device.
3. Perform a Junos recovery.
   • KB36947 [juniper.net] for steps to perform Junos recovery for QFX5k devices
   • KB33990 [juniper.net] for QFX10k and PTX10k devices.
4. Format install the device. Refer below KBs to perform format install on EX and QFX switches
   • [EX/QFX] Procedure to format install QFX5K device using a USB
   • [QFX10K] Format Install procedure
   • [EX] How to format install EX2300s and EX3400s via USB
   • [EX4100-F] USB format install
   • Format install on PTX/MX devices: https://www.juniper.net/documentation/us/en/software/junos/junos-install-upgrade/topics/topic-map/install-software-on-mx.html