nbdkit-loop(1)

1nbdkit-loop(1)                      NBDKIT                      nbdkit-loop(1)
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NAME

6       nbdkit-loop - use nbdkit with the Linux kernel client to create loop
7       devices and loop mounts
8

DESCRIPTION

10       nbdkit (server) can be used with the Linux kernel nbd (client) in a
11       loop mode allowing any of the plugins supported by nbdkit to be turned
12       into Linux block devices.
13
14       In addition to nbdkit(1) itself, the main commands you will use are:
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16       nbd-client -b 512 localhost /dev/nbd0
17           which attaches a locally running nbdkit instance to the kernel
18           device /dev/nbd0.  -b 512 can be omitted when using
19           nbd-client(8) ≥ 3.19.
20
21       nbd-client -d /dev/nbd0
22           which detaches /dev/nbd0, and:
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24       nbd-client -c /dev/nbd0
25           which queries whether /dev/nbd0 is attached or not.
26
27       modprobe nbd
28           which may be needed to load the nbd client kernel module.
29
30       The nbd-client(8) and modprobe(8) commands must be run as root.
31
32   Warning: Do not loop mount untrusted filesystems
33       Untrusted filesystems and untrusted disk images should not be loop
34       mounted because they could contain exploits that attack your host
35       kernel.  Use the tools from libguestfs(3) instead since it safely
36       isolates untrusted filesystems from the host.
37
38   Loop mount a filesystem from a compressed file
39       If you have a filesystem or disk image in xz-compressed format then you
40       can use nbdkit-xz-filter(1) and nbdkit-file-plugin(1) to loop mount it
41       as follows:
42
43        nbdkit --filter=xz file disk.xz
44        nbd-client -b 512 localhost /dev/nbd0
45        mount /dev/nbd0p1 /mnt
46
47   Loop mount a filesystem from a web server
48       You can use nbdkit-curl-plugin(1) to loop mount a filesystem from a
49       disk image on a web server:
50
51        nbdkit [--filter=xz] curl https://example.com/disk.img
52        nbd-client -b 512 localhost /dev/nbd0
53        mount /dev/nbd0p1 /mnt
54
55       Use --filter=xz if the remote image is XZ-compressed.
56
57   Create a giant btrfs filesystem
58       nbdkit is useful for testing the limits of Linux filesystems.  Using
59       nbdkit-memory-plugin(1) you can create virtual disks stored in RAM with
60       a virtual size up to 2⁶³-1 bytes, and then create filesystems on these:
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62        nbdkit memory $(( 2**63 - 1 ))
63        nbd-client -b 512 localhost /dev/nbd0
64
65       Partition the device using GPT, creating a single partition with all
66       default settings:
67
68        gdisk /dev/nbd0
69
70       Make a btrfs filesystem on the disk and mount it:
71
72        mkfs.btrfs -K /dev/nbd0p1
73        mount /dev/nbd0p1 /mnt
74
75   Inject errors into Linux devices
76       Using nbdkit-error-filter(1) you can see how Linux devices react to
77       errors:
78
79        nbdkit --filter=error \
80               memory size=64M \
81               error-rate=100% error-file=/tmp/inject
82        nbd-client -b 512 localhost /dev/nbd0
83        mkfs -t ext4 /dev/nbd0
84        mount /dev/nbd0 /mnt
85
86       Inject errors by touching /tmp/inject, and stop injecting errors by
87       removing this file.
88
89   Write Linux block devices in shell script
90       Using nbdkit-sh-plugin(3) you can write custom Linux block devices in
91       shell script for testing.  For example the following shell script
92       creates a disk which contains a bad sector:
93
94        #!/bin/bash -
95        case "$1" in
96            get_size) echo 64M ;;
97            pread)
98                if [ $4 -le 100000 ] && [ $(( $4+$3 )) -gt 100000 ]; then
99                    echo EIO Bad block >&2
100                    exit 1
101                else
102                    dd if=/dev/zero count=$3 iflag=count_bytes
103                fi ;;
104            *) exit 2 ;;
105        esac
106
107       Create a loop from this shell script using:
108
109        nbdkit sh ./bad-sector.sh
110        nbd-client -b 512 localhost /dev/nbd0
111
112       You can then try running tests such as:
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114        badblocks /dev/nbd0
115

AUTHORS

121       Richard W.M. Jones
122

COPYRIGHT

124       Copyright (C) 2013-2018 Red Hat Inc.
125

LICENSE

127       Redistribution and use in source and binary forms, with or without
128       modification, are permitted provided that the following conditions are
129       met:
130
131       ·   Redistributions of source code must retain the above copyright
132           notice, this list of conditions and the following disclaimer.
133
134       ·   Redistributions in binary form must reproduce the above copyright
135           notice, this list of conditions and the following disclaimer in the
136           documentation and/or other materials provided with the
137           distribution.
138
139       ·   Neither the name of Red Hat nor the names of its contributors may
140           be used to endorse or promote products derived from this software
141           without specific prior written permission.
142
143       THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY
144       EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
145       IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
146       PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE
147       LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
148       CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
149       SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
150       BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
151       WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
152       OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
153       ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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157nbdkit-1.12.3                     2019-05-21                    nbdkit-loop(1)

NAME

DESCRIPTION

SEE ALSO

AUTHORS

COPYRIGHT

LICENSE