Ubuntu Manpage: ch-convert - Convert an image from one format to another

Provided by: charliecloud-builders_0.38-2_amd64

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.

--no-xattrs
Ignore xattrs and ACLs when converting. Overrides $CH_XATTRS.

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

-q, --quiet
Be quieter; can be repeated. Incompatible with -v. See the FAQ entry on
verbosity for details.

-s, --storage DIR
Set the storage directory. Equivalent to the same option for ch-image(1) and
ch-run(1).

--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.

--xattrs
Preserve xattrs and ACLs when converting.

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. If the output directory is empty, the conversion should use the directory
without overwriting it. If the directory doesn’t look like an image and isn’t
empty, exit with an error.

docker Internal storage for Docker.

podman Internal storage for Podman.

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 Podman is installed: Podman internal storage.

          6. If Docker is installed: Docker internal storage.

          7. 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

COPYRIGHT

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