NAME

       nbdkit-tar-filter - read and write files inside tar files without unpacking

SYNOPSIS

        nbdkit file FILENAME.tar
               --filter=tar tar-entry=PATH_INSIDE_TAR
                            [tar=TAR_COMMAND] [tar-limit=SIZE]

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-limit=]SIZE
           When opening the tar file we have to locate the file ("tar-entry") inside the tarball.
           Because tar files do not have a central index we must iterate over the tar file to
           find the entry, and that may be costly (especially with untrusted tar files).  In the
           worst case where "tar-entry" starts near the end of the file we may have to iterate
           over the whole tar file.  If this is a problem you may set "tar-limit" to some smaller
           value, eg:

            nbdkit -r curl https://example.com/file.tar \
                   --filter=tar tar-entry=disk.img \
                                tar-limit=10M

           which ensures no more than 10 megabytes are read before we give up and reject the tar
           file (sending an error back to the NBD client).

           The default is 0 meaning no limit.

       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).

FILES

       $filterdir/nbdkit-tar-filter.so
           The plugin.

           Use "nbdkit --dump-config" to find the location of $filterdir.

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.

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.

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