PopOS Boot Failure After Adding Second NVMe Drive

Problem Statement

PopOS fails to boot with error ALERT! /dev/nvme0n1p5 does not exist. Dropping to a shell! after installing a second NVMe drive.

Root Cause

When a second NVMe drive is added, Linux device naming can change:

Before: First NVMe = /dev/nvme0n1

After: First NVMe = /dev/nvme1n1 (second drive takes nvme0n1)

PopOS has a hardcoded device path in /boot/efi/EFI/Pop_OS-[UUID]/cmdline that overrides all other boot configurations.

Quick Fix Procedure (Single Boot / PopOS as Primary)

Step 1: Boot Into PopOS

Remove the second NVMe drive temporarily

Boot into PopOS normally

Open terminal as root: sudo su

Step 2: Identify the Problem File

# Find your PopOS UUID directory
ls /boot/efi/EFI/ | grep Pop_OS

# Check the problematic cmdline file
cat /boot/efi/EFI/Pop_OS-*/cmdline

If output shows /dev/nvme0n1p5 or similar hardcoded path, proceed to fix.

Step 3: Get Your Root Partition UUID

# Find the UUID of your PopOS root partition
blkid | grep "TYPE=\"ext4\""
# Look for the partition that's currently mounted as /

Step 4: Fix the cmdline File

# Replace [YOUR-UUID] with actual UUID from step 3
echo "root=UUID=[YOUR-UUID] ro quiet loglevel=0 systemd.show_status=false splash" > /boot/efi/EFI/Pop_OS-*/cmdline

# Verify the fix
cat /boot/efi/EFI/Pop_OS-*/cmdline

Step 5: Update initramfs (Optional but Recommended)

update-initramfs -u -k all

Step 6: Test

# Shutdown
shutdown -h now

Reconnect the second NVMe drive

Boot normally - PopOS should now work

Multi-Boot Setup: Booting Pop!_OS from Another Linux Distribution's GRUB

If you're dual-booting Pop!_OS with another Linux distribution (like Garuda, Manjaro, Arch, etc.) that uses GRUB as the primary bootloader, you need additional steps.

The GRUB os-prober Problem

When GRUB's os-prober detects Pop!_OS, it creates boot entries with hardcoded device paths:

linux /boot/vmlinuz root=/dev/nvme0n1p5

Even though GRUB uses UUID for the search command, the root= kernel parameter is hardcoded, causing the same boot failure when NVMe devices reorder.

Complete Fix for Multi-Boot GRUB Setup

Step 1: Boot into your GRUB-based Linux distribution

Boot into your primary Linux distribution (the one with GRUB, e.g., Garuda, Arch, Manjaro).

Step 2: Identify your Pop!_OS partition

lsblk -f

Look for the ext4 partition that contains Pop!_OS (usually /dev/nvme0n1p5 or similar). Note its UUID.

Example output:

nvme0n1
├─nvme0n1p1 vfat   FAT32 EFI     D875-322B
├─nvme0n1p5 ext4   1.0           5c6578bb-18e0-48b1-b41b-714e75bd386c

Step 3: Fix the Pop!_OS cmdline file

# Get the UUID of your Pop!_OS partition
sudo blkid /dev/nvme0n1p5

# Update cmdline file (replace YOUR-UUID with actual UUID)
sudo bash -c 'echo "root=UUID=YOUR-UUID ro quiet loglevel=0 systemd.show_status=false splash" > /boot/efi/EFI/Pop_OS-YOUR-UUID/cmdline'

# Verify the fix
sudo cat /boot/efi/EFI/Pop_OS-YOUR-UUID/cmdline

Step 4: Mount and chroot into Pop!_OS

# Create mount point and mount Pop!_OS root
sudo mkdir -p /mnt/popos
sudo mount /dev/nvme0n1p5 /mnt/popos

# Bind necessary directories
sudo mount --bind /dev /mnt/popos/dev
sudo mount --bind /proc /mnt/popos/proc
sudo mount --bind /sys /mnt/popos/sys
sudo mount --bind /boot/efi /mnt/popos/boot/efi

# Enter chroot
sudo chroot /mnt/popos

# Fix PATH if needed
export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

Step 5: Update initramfs in chroot

# Update initramfs (warnings about firmware and NVRAM are normal in chroot)
update-initramfs -u -k all

# Update Pop!_OS boot configuration
kernelstub -v

# Exit chroot
exit

Step 6: Unmount Pop!_OS

sudo umount /mnt/popos/boot/efi
sudo umount /mnt/popos/dev
sudo umount /mnt/popos/proc
sudo umount /mnt/popos/sys
sudo umount /mnt/popos

Step 7: Disable os-prober in GRUB

Edit GRUB configuration:

sudo vim /etc/default/grub

Ensure this line exists or add it:

GRUB_DISABLE_OS_PROBER=true

Save and exit.

Step 8: Create custom GRUB entries

Edit the custom GRUB file:

sudo vim /etc/grub.d/40_custom

Add these entries at the end (replace UUIDs and kernel versions with your actual values):

menuentry "Pop!_OS 22.04 (Custom - UUID Boot)" {
    search --no-floppy --fs-uuid --set=root YOUR-POPOS-UUID
    linux /boot/vmlinuz-6.16.3-76061603-generic root=UUID=YOUR-POPOS-UUID ro quiet loglevel=0 systemd.show_status=false splash nvidia-drm.modeset=1
    initrd /boot/initrd.img-6.16.3-76061603-generic
}

menuentry "Windows Boot Manager" {
    insmod part_gpt
    insmod fat
    search --no-floppy --fs-uuid --set=root YOUR-EFI-PARTITION-UUID
    chainloader /EFI/Microsoft/Boot/bootmgfw.efi
}

To find the correct kernel version:

sudo ls /mnt/popos/boot/vmlinuz-*

To find EFI partition UUID:

sudo blkid /dev/nvme0n1p1

Save and exit.

Step 9: Make custom GRUB file executable

sudo chmod +x /etc/grub.d/40_custom

Step 10: Update GRUB

sudo update-grub

You should see output indicating that os-prober is disabled and your custom entries are added.

Step 11: Verify GRUB configuration

sudo cat /boot/grub/grub.cfg | grep -A 5 "Pop!_OS"

Verify that only your custom entry exists with root=UUID= (not root=/dev/nvme0n1p5).

Step 12: Reboot and test

sudo reboot

Select "Pop!_OS 22.04 (Custom - UUID Boot)" from the GRUB menu. Pop!_OS should now boot successfully with both NVMe drives connected.

Why This Multi-Boot Fix Works

Disabled os-prober: Prevents GRUB from auto-generating broken entries with hardcoded device paths

Custom GRUB entry: Uses UUID-based root parameter that works regardless of device ordering

Fixed cmdline file: Ensures Pop!_OS's own boot configuration also uses UUID

Updated initramfs: Ensures the boot image has the latest configuration

Verification Commands

From initramfs Emergency Shell

If you get dropped to initramfs, check:

# See what boot parameters kernel received
cat /proc/cmdline

# List available devices
ls /dev/nvme*

# Check partition table
cat /proc/partitions

From Working System

# Verify boot parameters are using UUID
cat /boot/efi/EFI/Pop_OS-*/cmdline
cat /boot/efi/loader/entries/Pop_OS-current.conf

# Check current kernelstub config
sudo kernelstub -p

Why Standard Fixes Don't Work

Prevention

Always use UUID instead of device paths:

✅ root=UUID=5d5e01e1-baee-48ea-86d5-b6a0c6639adb

❌ root=/dev/nvme0n1p5

File Locations Reference

Emergency Boot (If Fix Hasn't Been Applied)

From initramfs prompt:

# Wait for devices to initialize
sleep 5

# List available NVMe devices to find correct one
ls /dev/nvme*

# Mount correct root (adjust device and partition number as needed)
# Try nvme0n1p5 first, if that fails try nvme1n1p5
mount /dev/nvme1n1p5 /root
exit

Troubleshooting Multi-Boot Issues

If Pop!_OS still won't boot after following multi-boot steps:

Check if you booted the correct GRUB entry: Make sure you selected "Pop!_OS 22.04 (Custom - UUID Boot)" not the os-prober auto-detected entry

Verify cmdline file wasn't overwritten:

sudo cat /boot/efi/EFI/Pop_OS-YOUR-UUID/cmdline

It should show root=UUID=... not root=/dev/...

Check kernel version in custom GRUB entry matches:

sudo ls /boot/efi/EFI/Pop_OS-YOUR-UUID/

Ensure vmlinuz and initrd filenames in your custom GRUB entry match the actual files

Verify os-prober is actually disabled:

sudo cat /etc/default/grub | grep OS_PROBER

Should show GRUB_DISABLE_OS_PROBER=true

Notes

The cmdline file in the EFI directory is specific to PopOS's boot method

This file is read by the EFI stub loader before any other configuration

NVRAM errors in chroot are normal and can be ignored

Firmware warnings during initramfs updates are cosmetic and can be ignored

In multi-boot setups, keeping os-prober disabled prevents future issues

Custom GRUB entries need manual updates when Pop!_OS kernel is updated

Summary

Single Boot (Pop!_OS as primary):

Fix cmdline file with UUID

Update initramfs

Reboot with both drives

Multi-Boot (GRUB from another distro):

Fix cmdline file with UUID

Chroot and update initramfs

Disable os-prober in GRUB

Create custom GRUB entries with UUID

Update GRUB

Reboot and use custom entry