window 2026-06-29 → 07-01 · ticks + notes save on this device
0
SN4600C — Cumulus password recovery
Console cable required. Procedure differs by Cumulus version — determine version path first. Verified vs NVIDIA docs (5.16 + 5.6).
0 · Before you touch it
Connect console cable (serial). The mgmt login is unknown — that's expected.
Capture current state READ-ONLY before changing anything (this switch carries the GPU fabric).
You won't know the Cumulus version until you see the GRUB/boot text. Match the path below to what you see.
A · Single-user mode (Cumulus 4.x, 5.0–5.5, 5.7+, 5.16)
Reboot. On the 5-second countdown, press ESC or F4 for the GRUB menu. (Press once — extra presses drop to GRUB CLI; type normal + Enter to recover.)
Do NOT interrupt earlier autoboot lines (USB0/Net/SF…). Wait for the GRUB menu.
Select Advanced options for Cumulus Linux GNU/Linux.
Select the (recovery mode) kernel entry.
At the root shell: passwd → set new root password.
Also reset cumulus: passwd cumulus
If NVUE-managed (5.9+): the cumulus password also lives in YAML or it reverts on boot. Get the hash: /usr/bin/grep cumulus /etc/shadow | /usr/bin/cut -d ":" -f 2 then edit /etc/nvue.d/startup.yaml → set hashed-password: under system→aaa→user→cumulus.
Finish: sync then reboot -f
B · Cumulus 5.6 ONLY (single-user mode is BROKEN — use ONIE rescue)
In 5.6 you CANNOT reset via recovery mode. Use ONIE Rescue + chroot.
Reboot. In GRUB select ONIE, then ONIE Rescue. Press Enter when prompted.
Find root device: df / (note the device on /).
Mount it: mount $DEVICE /mnt (e.g. if onie-boot is /dev/sda2, try mount /dev/sda4 /mnt).
Confirm: ls /mnt shows a root fs; ls /mnt/etc/shadow exists.
chroot /mnt
passwd cumulus (and/or passwd root)
Exit chroot, sync, reboot.
5.9+ password rules
Min 8 chars; ≥1 lower, ≥1 upper, ≥1 digit, ≥1 special; not a username.
After reset
Store the new password → Vaultwarden (do not text/email it).
Then R-FABRIC: capture breakout/port state read-only, then breakout/LAG.
Source: NVIDIA Cumulus Linux docs — Single User Mode / Password Recovery (5.16, current) & 5.6 KB. Verify against the console.