NAME

       ch-convert - Convert an image from one format to another

SYNOPSIS

          $ ch-convert [-i FMT] [-o FMT] [OPTION ...] IN OUT

DESCRIPTION

       Copy  image  IN  to  OUT  and convert its format. Replace OUT if it already exists, unless
       --no-clobber is specified. It is an error if IN and OUT have  the  same  format;  use  the
       format’s own tools for that case.

       ch-run  can  run  container  images  that  are  plain directories or (optionally) SquashFS
       archives. However, images can take on a variety of other formats as well. The main purpose
       of this tool is to make images in those other formats available to ch-run.

       For  best  performance, ch-convert should be invoked only once, producing the final format
       actually needed.

          IN     Descriptor for the input image. For image builders, this is an image  reference;
                 otherwise, it’s a filesystem path.

          OUT    Descriptor for the output image.

          -h, --help
                 Print help and exit.

          -i, --in-fmt FMT
                 Input image format is FMT. If omitted, inferred as described below.

          -n, --dry-run
                 Don’t read the input or write the output. Useful for testing format inference.

          --no-clobber
                 Error if OUT already exists, rather than replacing it.

          -o, --out-fmt FMT
                 Output image format is FMT; inferred if omitted.

          --tmp DIR
                 A  sub-directory  for temporary storage is created in DIR and removed at the end
                 of a successful conversion. If this script crashes or errors out, the  temporary
                 directory  is  left  behind  to assist in debugging. Storage may be needed up to
                 twice the uncompressed size of the image, depending  on  the  input  and  output
                 formats. Default: $TMPDIR if specified; otherwise /var/tmp.

          -v, --verbose
                 Print extra chatter. Can be repeated.

IMAGE FORMATS

       ch-convert knows about these values of FMT:

          ch-image
                 Internal  storage  for  Charliecloud’s  unprivileged  image  builder (Dockerfile
                 interpreter) ch-image.

          dir    Ordinary filesystem directory (i.e., not a mount point) containing  an  unpacked
                 image.  Output  directories that already exist are replaced if they look like an
                 image; otherwise, exit with an error.

          docker Internal storage for Docker.

          squash SquashFS filesystem archive containing the flattened  image.  SquashFS  archives
                 are  much  like  tar  archives but are mountable, including by ch-run’s internal
                 SquashFUSE mounting. Most systems have at  least  the  SquashFS-Tools  installed
                 which  allows  unpacking  into  a  directory, just like tar. Due to this greater
                 flexibility, SquashFS is preferred to tar.

                 Note: Conversions to and from SquashFS are quite noisy due to the  verbosity  of
                 the underlying mksquashfs(1) and unsquashfs(1) tools.

          tar    Tar archive containing the flattened image with no layer sub-archives; i.e., the
                 output of docker export works but the output of docker  save  does  not.  Output
                 tarballs  are  always gzipped and must end in .tar.gz; input tarballs can be any
                 compression acceptable to tar(1).

       All of these are local formats; ch-convert does not know how to push or pull images.

FORMAT INFERENCE

       ch-convert tries to save typing by guessing formats when they are reasonably  clear.  This
       is done against filenames, rather than file contents, so the rules are the same for output
       descriptors that do not yet exist.

       Format inference is done for both IN and OUT. The first matching  glob  below  yields  the
       inferred format. Paths need not exist in the filesystem.

          1. *.sqfs, *.squash, *.squashfs: SquashFS.

          2. *.tar, *.t?z, *.tar.?, *.tar.??: Tarball.

          3. /*, ./*, i.e. absolute path or relative path with explicit dot: Directory.

          4. If ch-image is installed: ch-image internal storage.

          5. If Docker is installed: Docker internal storage.

          6. Otherwise: No format inference.

EXAMPLES

       Typical  build-to-run  sequence for image foo/bar using ch-run’s internal SquashFUSE code,
       inferring the output format:

          $ sudo docker build -t foo/bar -f Dockerfile .
          [...]
          $ ch-convert foo/bar:latest /var/tmp/foobar.sqfs
          input:   docker    foo/bar:latest
          output:  squashfs  /var/tmp/foobar.sqfs
          copying ...
          done
          $ ch-run /var/tmp/foobar.sqfs -- echo hello
          hello

       Same conversion, but no format inference:

          $ ch-convert -i ch-image -o squash foo/bar:latest /var/tmp/foobar.sqfs
          input:   docker    foo/bar:latest
          output:  squashfs  /var/tmp/foobar.sqfs
          copying ...
          done

REPORTING BUGS

       If Charliecloud was obtained from your Linux distribution,  use  your  distribution’s  bug
       reporting procedures.

       Otherwise, report bugs to: https://github.com/hpc/charliecloud/issues

SEE ALSO

       charliecloud(7)

       Full documentation at: <https://hpc.github.io/charliecloud>

COPYRIGHT

       2014–2021, Triad National Security, LLC