nbdkit-loop(1) NBDKIT nbdkit-loop(1) NAME nbdkit-loop - use nbdkit with the Linux kernel client to create loop de- vices and loop mounts DESCRIPTION nbdkit (server) can be used with the Linux kernel nbd (client) in a loop mode allowing any of the plugins supported by nbdkit to be turned into Linux block devices. In addition to nbdkit(1) itself, the main commands you will use are: nbd-client localhost /dev/nbd0 Attaches a locally running nbdkit instance to the kernel device /dev/nbd0. nbd-client -unix /tmp/socket /dev/nbd0 Alternative method using a Unix domain socket instead of a public TCP/IP socket. Use "nbdkit -U /tmp/socket" to serve. nbd-client -d /dev/nbd0 Detaches /dev/nbd0. nbd-client -c /dev/nbd0 Queries whether /dev/nbd0 is attached or not. modprobe nbd You may be need to run this command once to load the nbd client kernel module. The nbd-client(8) and modprobe(8) commands must be run as root. Warning: Do not loop mount untrusted filesystems Untrusted filesystems and untrusted disk images should not be loop mounted because they could contain exploits that attack your host kernel. Use the tools from libguestfs(3) instead since it safely isolates untrusted filesystems from the host. Loop mount a filesystem from a compressed file If you have a filesystem or disk image in xz-compressed format then you can use nbdkit-xz-filter(1) and nbdkit-file-plugin(1) to loop mount it as fol- lows: nbdkit --filter=xz file disk.xz nbd-client localhost /dev/nbd0 mount /dev/nbd0p1 /mnt Loop mount a filesystem from a web server You can use nbdkit-curl-plugin(1) to loop mount a filesystem from a disk image on a web server: nbdkit [--filter=xz] curl https://example.com/disk.img nbd-client localhost /dev/nbd0 mount /dev/nbd0p1 /mnt Use --filter=xz if the remote image is XZ-compressed. Create a giant btrfs filesystem nbdkit is useful for testing the limits of Linux filesystems. Using nbd- kit-memory-plugin(1) you can create virtual disks stored in RAM with a vir- tual size up to 2a<paragraph>A^3-1 bytes, and then create filesystems on these: nbdkit memory $(( 2**63 - 1 )) nbd-client localhost /dev/nbd0 Partition the device using GPT, creating a single partition with all de- fault settings: gdisk /dev/nbd0 Make a btrfs filesystem on the disk and mount it: mkfs.btrfs -K /dev/nbd0p1 mount /dev/nbd0p1 /mnt Inject errors into Linux devices Using nbdkit-error-filter(1) you can see how Linux devices react to errors: nbdkit --filter=error \ memory 64M \ error-rate=100% error-file=/tmp/inject nbd-client localhost /dev/nbd0 mkfs -t ext4 /dev/nbd0 mount /dev/nbd0 /mnt Inject errors by touching /tmp/inject, and stop injecting errors by remov- ing this file. Write Linux block devices in shell script Using nbdkit-sh-plugin(3) you can write custom Linux block devices in shell script for testing. For example the following shell script creates a disk which contains a bad sector: #!/bin/bash - case "$1" in thread_model) echo parallel ;; get_size) echo 64M ;; pread) if [ $4 -le 100000 ] && [ $(( $4+$3 )) -gt 100000 ]; then echo EIO Bad block >&2 exit 1 else dd if=/dev/zero count=$3 iflag=count_bytes fi ;; *) exit 2 ;; esac Create a loop from this shell script using: nbdkit sh ./bad-sector.sh nbd-client localhost /dev/nbd0 You can then try running tests such as: badblocks /dev/nbd0 SEE ALSO nbdkit(1), nbdkit-client(1), nbdkit-plugin(3), loop(4), losetup(8), mount(8), nbdfuse(1), nbd-client(8), modprobe(8), libguestfs(3), http://libguestfs.org. AUTHORS Richard W.M. Jones COPYRIGHT Copyright Red Hat LICENSE Redistribution and use in source and binary forms, with or without modifi- cation, are permitted provided that the following conditions are met: * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. * Redistributions in binary form must reproduce the above copyright no- tice, this list of conditions and the following disclaimer in the docu- mentation and/or other materials provided with the distribution. * 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. THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY EX- PRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DIS- CLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE LIABLE FOR ANY DI- RECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SER- VICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABIL- ITY, 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 DAM- AGE. nbdkit-1.46.2 2026-08-30 nbdkit-loop(1)
NAME | DESCRIPTION | SEE ALSO | AUTHORS | COPYRIGHT | LICENSE
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