This article describes about how JTAC helped to recover the root password.

Unable to login to the device.

1.Connect Console to the device.

2.Hard reboot the box.

3.Press Ctrl+C at the following part in the reboot to bring up the Junos main menu:

FreeBSD/x86 bootstrap loader, Revision 1.1
([email protected], Sun Feb  4 13:06:24 PST 2018)
/
Autoboot in 1 seconds... (press Ctrl-C to interrupt)

4.At the Junos Main Menu, press M or 5 key to activate the 5. [M] ore options menu.

1.  Boot [J]unos volume
2.  Boot Junos volume in [S]afe mode

3.  [R]eboot

4.  [B]oot menu
5.  [M]ore option

5.Press the C or 2 key to access the 2. Recovery mode.

Device will reboot into the cli recovery mode.

6.You can login using root and set a password for root:

set system root authentication plain-text password.

type the password and commit the changes.

7.Reboot the box to come out from the recovery mode.

request system reboot.

Refer the document for more details:

https://www.juniper.net/documentation/us/en/software/junos/user-access/topics/topic-map/recovering-root-password.html