NAME

       nbdkit-loop - use nbdkit with the Linux kernel client to create loop devices 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 follows:

        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  nbdkit-memory-plugin(1)  you  can
       create  virtual disks stored in RAM with a virtual size up to 2⁶³-1 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 default 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 removing 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 modification, 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 notice, this list of conditions and
           the following disclaimer in the documentation 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 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.

nbdkit-1.36.3                                      2024-03-31                                     nbdkit-loop(1)