.\" -*- mode: troff; coding: utf-8 -*- .\" Automatically generated by Podwrapper::Man 1.49.4 (Pod::Simple 3.48) .\" .\" Standard preamble: .\" ======================================================================== .de Sp \" Vertical space (when we can't use .PP) .if t .sp .5v .if n .sp .. .de Vb \" Begin verbatim text .ft CW .nf .ne \\$1 .. .de Ve \" End verbatim text .ft R .fi .. .\" \*(C` and \*(C' are quotes in nroff, nothing in troff, for use with C<>. .ie n \{\ . ds C` "" . ds C' "" 'br\} .el\{\ . ds C` . ds C' 'br\} .\" .\" Escape single quotes in literal strings from groff's Unicode transform. .ie \n(.g .ds Aq \(aq .el .ds Aq ' .\" .\" If the F register is >0, we'll generate index entries on stderr for .\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index .\" entries marked with X<> in POD. Of course, you'll have to process the .\" output yourself in some meaningful fashion. .\" .\" Avoid warning from groff about undefined register 'F'. .de IX .. .nr rF 0 .if \n(.g .if rF .nr rF 1 .if (\n(rF:(\n(.g==0)) \{\ . if \nF \{\ . de IX . tm Index:\\$1\t\\n%\t"\\$2" .. . if !\nF==2 \{\ . nr % 0 . nr F 2 . \} . \} .\} .rr rF .\" .\" Required to disable full justification in groff 1.23.0. .if n .ds AD l .\" ======================================================================== .\" .IX Title "nbdkit-client 1" .TH nbdkit-client 1 2026-10-17 nbdkit-1.49.4 NBDKIT .\" For nroff, turn off justification. Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH NAME nbdkit\-client \- how to mount NBD filesystems on a client machine .SH DESCRIPTION .IX Header "DESCRIPTION" For NBD exports that contain filesystems there are several approaches to mounting them on a physical machine. .PP For virtual machines, see the section "ATTACHING NBD DEVICES TO A VIRTUAL MACHINE" at the end. .SS "Easy mounting at boot time" .IX Subsection "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 \fI/etc/rc.local\fR or \&\fI/etc/rc.d/rc.local\fR: .PP .Vb 5 \& #!/bin/sh \- \& nm\-online \& modprobe nbd \& nbd\-client server /dev/nbd0 \& mount /dev/nbd0 /mnt .Ve .SS "Mounting using systemd mount points" .IX Subsection "Mounting using systemd mount points" You can use systemd mount points to mount NBD filesystems at boot and/or on demand. .PP Set up an \fBnbdtab\fR\|(5) mapping. If \fI/etc/nbdtab\fR doesn\*(Aqt exist, then create it first. Add this line: .PP .Vb 1 \& nbd0 server / bs=512,persist .Ve .PP As a workaround for https://github.com/NetworkBlockDevice/nbd/issues/91 you must currently modify the \fInbd@.service\fR file: .PP .Vb 2 \& # cp /usr/lib/systemd/system/nbd@.service /etc/systemd/system/ \& # vi /etc/systemd/system/nbd@.service .Ve .PP and edit or create these settings in the \f(CW\*(C`[Service]\*(C'\fR section: .PP .Vb 5 \& [Service] \& Type=oneshot \& RemainAfterExit=yes \& ExecStart=/usr/sbin/nbd\-client %i \& ExecStop=/usr/sbin/nbd\-client \-d /dev/%i .Ve .PP Finally create a systemd mount file called \&\fI/etc/systemd/system/mnt.mount\fR: .PP .Vb 6 \& [Unit] \& Requires=nbd@nbd0.service \& [Mount] \& What=/dev/nbd0 \& Where=/mnt \& Type=ext4 .Ve .PP You can either reboot now or do: .PP .Vb 1 \& # systemctl start mnt.mount .Ve .PP Other systemd services which need this mount point can depend on this mount unit. .SH "LOADING THE LINUX KERNEL MODULE" .IX Header "LOADING THE LINUX KERNEL MODULE" The native Linux NBD client is a kernel module called \f(CW\*(C`nbd.ko\*(C'\fR. It is not always loaded on demand. To ensure it is loaded you may need to do: .PP .Vb 1 \& # echo nbd > /etc/modules\-load.d/nbd.conf .Ve .PP This will not take effect until you reboot, so to load it right away do: .PP .Vb 1 \& # modprobe nbd .Ve .SS "RHEL and nbd.ko" .IX Subsection "RHEL and nbd.ko" Red Hat Enterprise Linux 8 enabled the \f(CW\*(C`nbd.ko\*(C'\fR 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. .PP This does not affect use of nbdkit as an NBD server, only the Linux kernel as an NBD client. Userspace Linux clients such as \fBlibnbd\fR\|(3) tools will work. .SH "ATTACHING NBD DEVICES TO A VIRTUAL MACHINE" .IX Header "ATTACHING NBD DEVICES TO A VIRTUAL MACHINE" Notice in these cases that the virtual machine does not use the NBD protocol directly. Instead, the virtual machine sees a local disk. Thus there is no need to enable an NBD client or kernel module inside the virtual machine. Behind the scenes the hypervisor (eg. Qemu) converts the local disk into an NBD connection. .SS "Using libvirt XML" .IX Subsection "Using libvirt XML" Use the \fBvirsh\fR\|(1) \f(CW\*(C`edit\*(C'\fR subcommand to modify the libvirt XML of a virtual machine: .PP .Vb 1 \& # virsh edit guest\-name .Ve .PP The element should be placed in the section of the XML, after any other elements. For more information about libvirt XML see https://libvirt.org/formatdomain.html .PP For NBD devices served over a Unix domain socket (nbdkit \fI\-U\fR option) add: .PP .Vb 7 \& \& \& \& \& \& \& .Ve .PP If using a TCP socket (nbdkit \fI\-p\fR option): .PP .Vb 7 \& \& \& \& \& \& \& .Ve .SS "Using qemu directly" .IX Subsection "Using qemu directly" Qemu can open NBD URIs. To get nbdkit to show the URI it is serving use the \fI\-\-print\-uri\fR option. .PP For example: .PP .Vb 5 \& $ nbdkit \-f \-U \- \-\-print\-uri memory 1G \& nbd+unix://?socket=/tmp/nbdkitTV6kS8/socket \& Shell\-quoted URI: "nbd+unix://?socket=/tmp/nbdkitTV6kS8/socket" \& Command to query the NBD endpoint: \& nbdinfo "nbd+unix://?socket=/tmp/nbdkitTV6kS8/socket" \& \& $ qemu\-system\-x86_64 [...] \e \& \-drive file="nbd+unix://?socket=/tmp/nbdkitTV6kS8/socket",format=raw,if=virtio .Ve .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fBnbdkit\fR\|(1), \&\fBnbdkit\-loop\fR\|(1), \&\fBnbdkit\-service\fR\|(1), \&\fBnbd\-client\fR\|(8), \&\fBnbdtab\fR\|(5), \&\fBsystemd\fR\|(1), \&\fBsystemd.mount\fR\|(5), \&\fBvirsh\fR\|(1), https://libvirt.org/formatdomain.html. .SH AUTHORS .IX Header "AUTHORS" Richard W.M. Jones .SH COPYRIGHT .IX Header "COPYRIGHT" Copyright Red Hat .SH LICENSE .IX Header "LICENSE" Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: .IP \(bu 4 Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. .IP \(bu 4 Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. .IP \(bu 4 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. .PP THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS \*(Aq\*(AqAS IS\*(Aq\*(Aq AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.