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.\"
.IX Title "nbdkit-tar-plugin 1"
.TH nbdkit-tar-plugin 1 "2020-06-18" "nbdkit-1.20.6" "NBDKIT"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH "NAME"
nbdkit\-tar\-plugin \- read and write files inside tar files without unpacking
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& nbdkit tar tar=FILENAME.tar file=PATH_INSIDE_TAR
.Ve
.SH "EXAMPLES"
.IX Header "EXAMPLES"
.SS "Serve a single file inside a tarball"
.IX Subsection "Serve a single file inside a tarball"
.Vb 2
\& nbdkit tar tar=file.tar file=some/disk.img
\& guestfish \-\-format=raw \-a nbd://localhost
.Ve
.SS "Opening a disk image inside an \s-1OVA\s0 file"
.IX Subsection "Opening a disk image inside an OVA file"
The popular \*(L"Open Virtual Appliance\*(R" (\s-1OVA\s0) format is really an
uncompressed tar file containing (usually) VMDK-format files, so you
could access one file in an \s-1OVA\s0 like this:
.PP
.Vb 6
\& $ tar tf rhel.ova
\& rhel.ovf
\& rhel\-disk1.vmdk
\& rhel.mf
\& $ nbdkit \-r tar tar=rhel.ova file=rhel\-disk1.vmdk
\& $ guestfish \-\-ro \-\-format=vmdk \-a nbd://localhost
.Ve
.PP
In this case the tarball is opened readonly (\fI\-r\fR option).  The
plugin supports write access, but writing to the \s-1VMDK\s0 file in the
tarball does not change data checksums stored in other files (the
\&\f(CW\*(C`rhel.mf\*(C'\fR file in this example), and as these will become incorrect
you probably won't be able to open the file with another tool
afterwards.
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\f(CW\*(C`nbdkit\-tar\-plugin\*(C'\fR is a plugin which can read and writes files
inside an uncompressed tar file without unpacking the tar file.
.PP
The \f(CW\*(C`tar\*(C'\fR and \f(CW\*(C`file\*(C'\fR parameters are required, specifying the name of
the uncompressed tar file and the exact path of the file within the
tar file to access as a disk image.
.PP
This plugin will \fBnot\fR work on compressed tar files.
.PP
Use the nbdkit \fI\-r\fR flag to open the file readonly.  This is the
safest option because it guarantees that the tar file will not be
modified.  Without \fI\-r\fR writes will modify the tar file.
.PP
The disk image cannot be resized.
.SS "Alternatives to the tar plugin"
.IX Subsection "Alternatives to the tar plugin"
The tar plugin ought to be a filter so that you can extract files from
within tarballs hosted elsewhere (eg. using \fBnbdkit\-curl\-plugin\fR\|(1)).
However this is hard to implement given the way that the \fBtar\fR\|(1)
command works.
.PP
Nevertheless you can apply the same technique even to tarballs hosted
remotely, provided you can run \fBtar\fR\|(1) on them first.  The trick is
to use the \f(CW\*(C`tar \-tRvf\*(C'\fR options to find the block number of the
file of interest.  In tar files, blocks are 512 bytes in size, and
there is one hidden block used for the header, so you have to take the
block number, add 1, and multiply by 512.
.PP
For example:
.PP
.Vb 4
\& $ tar \-tRvf disk.tar
\& block 2: \-rw\-r\-\-r\-\- rjones/rjones 105923072 2020\-03\-28 20:34 disk
\& └──┬──┘                           └───┬───┘
\& offset = (2+1)*512 = 1536           range
.Ve
.PP
You can then apply the offset filter:
.PP
.Vb 3
\& nbdkit \-\-filter=offset \e
\&          curl https://example.com/disk.tar \e
\&               offset=1536 range=105923072
.Ve
.PP
If the remote file is compressed then add \fBnbdkit\-xz\-filter\fR\|(1):
.PP
.Vb 3
\& nbdkit \-\-filter=offset \-\-filter=xz \e
\&          curl https://example.com/disk.tar.xz \e
\&               offset=1536 range=105923072
.Ve
.SH "VERSION"
.IX Header "VERSION"
\&\f(CW\*(C`nbdkit\-tar\-plugin\*(C'\fR first appeared in nbdkit 1.2.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
https://github.com/libguestfs/nbdkit/blob/master/plugins/tar/tar.pl,
\&\fBnbdkit\fR\|(1),
\&\fBnbdkit\-offset\-filter\fR\|(1),
\&\fBnbdkit\-plugin\fR\|(3),
\&\fBnbdkit\-perl\-plugin\fR\|(3),
\&\fBnbdkit\-xz\-filter\fR\|(1),
\&\fBtar\fR\|(1).
.SH "AUTHORS"
.IX Header "AUTHORS"
Richard W.M. Jones.
.PP
Based on the virt\-v2v \s-1OVA\s0 importer written by Tomáš Golembiovský.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (C) 2017\-2020 Red Hat Inc.
.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
\&\s-1THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS\s0 ''\s-1AS IS\s0'' \s-1AND
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\s0 (\s-1INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES\s0; \s-1LOSS OF
USE, DATA, OR PROFITS\s0; \s-1OR BUSINESS INTERRUPTION\s0) \s-1HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT\s0 (\s-1INCLUDING NEGLIGENCE OR OTHERWISE\s0) \s-1ARISING IN ANY WAY OUT
OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.\s0