nbdkit-tar-filter - Man Page

read and write files inside tar files without unpacking

Synopsis

 nbdkit file FILENAME.tar --filter=tar tar-entry=PATH_INSIDE_TAR

Examples

Serve a single file inside a tarball

 nbdkit file file.tar --filter=tar tar-entry=some/disk.img
 guestfish --format=raw -a nbd://localhost

Opening a disk image inside an OVA file

The popular “Open Virtual Appliance” (OVA) format is really an uncompressed tar file containing (usually) VMDK-format files, so you could access one file in an OVA like this:

 $ tar tf rhel.ova
 rhel.ovf
 rhel-disk1.vmdk
 rhel.mf
 $ nbdkit -r file rhel.ova --filter=tar tar-entry=rhel-disk1.vmdk
 $ guestfish --ro --format=vmdk -a nbd://localhost

In this case the tarball is opened readonly (-r option).  The plugin supports write access, but writing to the VMDK file in the tarball does not change data checksums stored in other files (the rhel.mf file in this example), and as these will become incorrect you probably won't be able to open the file with another tool afterwards.

Open a disk image inside a remote tar file

You can use other plugins apart from nbdkit-file-plugin(1) to provide the tar file.  For example if the tar file is located on a web server use:

 nbdkit -r curl https://example.com/file.tar \
        --filter=tar tar-entry=disk.img

Open a compressed tar file (read-only)

This filter cannot handle compressed tar files itself, but you can combine it with nbdkit-gzip-filter(1) or nbdkit-xz-filter(1):

 nbdkit file filename.tar.gz \
        --filter=tar tar-entry=disk.img --filter=gzip
 nbdkit file filename.tar.xz \
        --filter=tar tar-entry=disk.img --filter=xz

Description

nbdkit-tar-filter is a filter which can read and writes files inside an uncompressed tar file without unpacking the tar file.

The tar file is provided by the underlying plugin.  You must tell the filter which entry in the tar file you wish to read and write using the tar-entry parameter.  tar-entry must exactly match the file name in the tar index.  Use tar tf filename.tar to list the index of a tar file.

This filter will not work directly on compressed tar files.  You have to combine it with another filter as shown in the example above.

Use the nbdkit -r flag to open the file readonly.  This is the safest option because it guarantees that the tar file will not be modified.  Without -r writes will modify the tar file.

The disk image cannot be resized.

Parameters

[tar-entry=]PATH_INSIDE_TAR

The path of the file inside the tarball to serve.  This parameter is required.  It must exactly match the name stored in the tarball, so use tar tf filename.tar

tar=gtar
tar=/PATH/TO/GTAR

Specify the program name or full path of GNU tar, in case tar on $PATH is not GNU tar.  This filter requires GNU tar and will not normally work with other tar programs (eg. on FreeBSD).

Version

nbdkit-tar-filter first appeared in nbdkit 1.22.  It is derived from nbdkit-tar-plugin which first appeared in nbdkit 1.2.

See Also

nbdkit(1), nbdkit-curl-plugin(1), nbdkit-file-plugin(1), nbdkit-gzip-filter(1), nbdkit-offset-filter(1), nbdkit-plugin(3), nbdkit-ssh-plugin(1), nbdkit-xz-filter(1), tar(1).

Authors

Richard W.M. Jones.

Based on the virt-v2v OVA importer written by Tomáš Golembiovský.

License

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

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.

Referenced By

nbdkit(1), nbdkit-captive(1), nbdkit-cdi-plugin(1), nbdkit-curl-plugin(1), nbdkit-filter(3), nbdkit-gzip-filter(1), nbdkit-offset-filter(1), nbdkit-release-notes-1.22(1), nbdkit-tar-plugin(1).

2020-10-05 nbdkit-1.23.7