• NAME
• DESCRIPTION
  • Easy mounting at boot time
  • Mounting using systemd mount points
• LIMITATIONS
• SEE ALSO
• AUTHORS
• COPYRIGHT
• LICENSE

NAME

nbdkit-client - how to mount NBD filesystems on a client machine

DESCRIPTION

For NBD exports that contain filesystems there are several approaches to mounting them on a client machine.

To ensure the nbd kernel module is loaded you may need to do:

 # echo nbd > /etc/modules-load.d/nbd.conf

This will not take effect until you reboot, so also do:

 # modprobe nbd

Easy mounting at boot time

For simple setups the following method is the easiest way to get an NBD filesystem to mount at boot. Create or edit /etc/rc.local or /etc/rc.d/rc.local:

 #!/bin/sh -
 nm-online
 modprobe nbd
 nbd-client server /dev/nbd0
 mount /dev/nbd0 /mnt

Mounting using systemd mount points

You can use systemd mount points to mount NBD filesystems at boot and/or on demand.

Set up an nbdtab(5) mapping. If /etc/nbdtab doesn't exist, then create it first. Add this line:

 nbd0 server / bs=512,persist

As a workaround for https://github.com/NetworkBlockDevice/nbd/issues/91 you must currently modify the nbd@.service file:

 # cp /usr/lib/systemd/system/nbd@.service /etc/systemd/system/
 # vi /etc/systemd/system/nbd@.service

and edit or create these settings in the [Service] section:

 [Service]
 Type=oneshot
 RemainAfterExit=yes
 ExecStart=/usr/sbin/nbd-client %i
 ExecStop=/usr/sbin/nbd-client -d /dev/%i

Finally create a systemd mount file called /etc/systemd/system/mnt.mount:

 [Unit]
 Requires=nbd@nbd0.service
 [Mount]
 What=/dev/nbd0
 Where=/mnt
 Type=ext4

You can either reboot now or do:

 # systemctl start mnt.mount

Other systemd services which need this mount point can depend on this mount unit.

LIMITATIONS

Red Hat Enterprise Linux 8 enabled the nbd.ko Linux kernel module but only for Unix domain sockets (ie. local connections). This means you cannot connect to an NBD server over a TCP network. This also affects Linux distributions derived from RHEL like CentOS, Alma and others.

This does not affect use of nbdkit as an NBD server, only the Linux kernel as an NBD client. Userspace Linux clients such as libnbd(3) tools will work.

SEE ALSO

nbdkit(1), nbdkit-loop(1), nbdkit-service(1), nbd-client(8), nbdtab(5), systemd(1), systemd.mount(5).

AUTHORS

Richard W.M. Jones

COPYRIGHT

Copyright Red Hat

LICENSE

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• Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

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• Neither the name of Red Hat nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

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