nbdkit-tar-plugin(1)

1nbdkit-tar-plugin(1)                NBDKIT                nbdkit-tar-plugin(1)
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NAME

6       nbdkit-tar-plugin - read and write files inside tar files without
7       unpacking
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SYNOPSIS

10        nbdkit tar tar=FILENAME.tar file=PATH_INSIDE_TAR
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EXAMPLES

13   Serve a single file inside a tarball
14        nbdkit tar tar=file.tar file=some/disk.img
15        guestfish --format=raw -a nbd://localhost
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17   Opening a disk image inside an OVA file
18       The popular "Open Virtual Appliance" (OVA) format is really an
19       uncompressed tar file containing (usually) VMDK-format files, so you
20       could access one file in an OVA like this:
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22        $ tar tf rhel.ova
23        rhel.ovf
24        rhel-disk1.vmdk
25        rhel.mf
26        $ nbdkit -r tar tar=rhel.ova file=rhel-disk1.vmdk
27        $ guestfish --ro --format=vmdk -a nbd://localhost
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29       In this case the tarball is opened readonly (-r option).  The plugin
30       supports write access, but writing to the VMDK file in the tarball does
31       not change data checksums stored in other files (the "rhel.mf" file in
32       this example), and as these will become incorrect you probably won't be
33       able to open the file with another tool afterwards.
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DESCRIPTION

36       "nbdkit-tar-plugin" is a plugin which can read and writes files inside
37       an uncompressed tar file without unpacking the tar file.
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39       The "tar" and "file" parameters are required, specifying the name of
40       the uncompressed tar file and the exact path of the file within the tar
41       file to access as a disk image.
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43       This plugin will not work on compressed tar files.
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45       Use the nbdkit -r flag to open the file readonly.  This is the safest
46       option because it guarantees that the tar file will not be modified.
47       Without -r writes will modify the tar file.
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49       The disk image cannot be resized.
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51   Alternatives to the tar plugin
52       The tar plugin ought to be a filter so that you can extract files from
53       within tarballs hosted elsewhere (eg. using nbdkit-curl-plugin(1)).
54       However this is hard to implement given the way that the tar(1) command
55       works.
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57       Nevertheless you can apply the same technique even to tarballs hosted
58       remotely, provided you can run tar(1) on them first.  The trick is to
59       use the "tar -tRvf" options to find the block number of the file of
60       interest.  In tar files, blocks are 512 bytes in size, and there is one
61       hidden block used for the header, so you have to take the block number,
62       add 1, and multiply by 512.
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64       For example:
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66        $ tar -tRvf disk.tar
67        block 2: -rw-r--r-- rjones/rjones 105923072 2020-03-28 20:34 disk
68        └──┬──┘                           └───┬───┘
69        offset = (2+1)*512 = 1536           range
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71       You can then apply the offset filter:
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73        nbdkit --filter=offset \
74                 curl https://example.com/disk.tar \
75                      offset=1536 range=105923072
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77       If the remote file is compressed then add nbdkit-xz-filter(1):
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79        nbdkit --filter=offset --filter=xz \
80                 curl https://example.com/disk.tar.xz \
81                      offset=1536 range=105923072
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VERSION

84       "nbdkit-tar-plugin" first appeared in nbdkit 1.2.
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AUTHORS

92       Richard W.M. Jones.
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94       Based on the virt-v2v OVA importer written by Tomáš Golembiovský.
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COPYRIGHT

97       Copyright (C) 2017-2020 Red Hat Inc.
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LICENSE

100       Redistribution and use in source and binary forms, with or without
101       modification, are permitted provided that the following conditions are
102       met:
103
104       ·   Redistributions of source code must retain the above copyright
105           notice, this list of conditions and the following disclaimer.
106
107       ·   Redistributions in binary form must reproduce the above copyright
108           notice, this list of conditions and the following disclaimer in the
109           documentation and/or other materials provided with the
110           distribution.
111
112       ·   Neither the name of Red Hat nor the names of its contributors may
113           be used to endorse or promote products derived from this software
114           without specific prior written permission.
115
116       THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY
117       EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
118       IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
119       PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE
120       LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
121       CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
122       SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
123       BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
124       WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
125       OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
126       ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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130nbdkit-1.18.4                     2020-04-16              nbdkit-tar-plugin(1)