FAQ

nvme show-regs /dev/nvme0 returns: nvme0 failed to map

It's more of a "feature" than an issue. The kernel will not allow user space to map a device's IO memory when that config option is set and the tooling can't get around that limitation.

When the Linux kernel is configured with CONFIG_IO_STRICT_DEVMEM, the kernel prevents user space to map IO memory to userspace. Either compile a kernel without this option enabled or set the kernel command line option iomem=relaxed.

Also when secure boot is enabled the lockdown is activated, which prevents mapping PCI bars to user space.

nvme list shows wrong disk/block size

nvme-cli v2 relies on the kernel reporting the correct disk/block size via the sysfs interface.

Also ensure libnvme has:

• https://github.com/linux-nvme/libnvme/pull/754/commits/9b3435bc9b2ff61e40284ed2d5d36dc39a46b3a5
• https://github.com/linux-nvme/libnvme/pull/803/commits/00efe8364b0a94e7057333f9bdf579dbc982429c

and Linux kernel has (v6.8):

• https://github.com/torvalds/linux/commit/a1a825ab6a60380240ca136596732fdb80bad87a

nvme id-ns shows the correct disk/block size because it will issue a command to read the current value.

nvme list shows old firmware version after firmware udpate

nvme-cli reads the firmware version from sysfs. Older kernel don't update the firmware entry in sysfs after an firmware upgrade. After a reboot the correct version will be shown. Alternatively you can use nvme id-ctrl to check the firmware version.

Linux kernel fix (v6.2)

• https://github.com/torvalds/linux/commit/a8eb6c1ba48bddea82e8d74cbe6e119f006be97d

If this still doesn't fix your problem, it needs to be addressed in the kernel. nvme list is a non privileged operation and thus can't issue any NVMe Commands via the passthru interface. This is on purpose.

The workaround is to use nvme id-ctrl, reset the PCI device or reboot the machine.

Ensuring correct shutdown ordering for NVMe/TCP mounted filesystems

When using NVMe/TCP, it is common to have filesystems mounted from remote NVMe namespaces.

During shutdown, the correct ordering is:

1. Unmount all filesystems using the NVMe/TCP devices
2. Run nvme disconnect-all
3. Shut down networking

If nvme disconnect-all runs too early, mounted filesystems may hang or shutdown may fail because the remote block devices disappear before unmounting completes.

The recommended solution is to create a dedicated systemd service and use a systemd drop-in override instead of modifying vendor unit files directly.

Create a new service:

sudo tee /etc/systemd/system/nvme-disconnect.service >/dev/null <<'EOF'
[Unit]
Description=Disconnect NVMe Fabrics devices at shutdown
DefaultDependencies=no
Before=network.target shutdown.target
After=remote-fs.target umount.target

[Service]
Type=oneshot
ExecStart=/usr/sbin/nvme disconnect-all

[Install]
WantedBy=shutdown.target
EOF

Enable the service:

sudo systemctl daemon-reload
sudo systemctl enable nvme-disconnect.service

This ensures that:

• remote filesystems are unmounted first,
• nvme disconnect-all is executed afterwards,
• networking remains available until disconnect processing is complete.

Do not place local modifications into /usr/lib/systemd/system/.

If later versions of nvme-cli ship a vendor-provided unit, local customizations should instead be placed under:

/etc/systemd/system/<unit>.d/

using systemctl edit.

Additional information about systemd unit overrides can be found in:

man systemd.unit
man systemctl

Relevant project documentation:

• https://www.freedesktop.org/software/systemd/man/systemd.unit.html