ch-run-oci - Man Page

OCI wrapper for "ch-run"

Synopsis

$ ch-run-oci OPERATION [ARG ...]

Description

NOTE:: This command is experimental. Features may be incomplete and/or buggy. The quality of code is not yet up to the usual Charliecloud standards, and error handling is poor. Please report any issues you find, so we can fix them!

Open Containers Initiative (OCI) wrapper for ch-run(1). You probably don’t want to run this command directly; it is intended to interface with other software that expects an OCI runtime. The current goal is to support completely unprivileged image building (e.g. buildah --runtime=ch-run-oci) rather than general OCI container running.

Support of the OCI runtime specification is only partial. This is for two reasons. First, it’s an experimental and incomplete feature. More importantly, the philosophy and goals of OCI differ significantly from those of Charliecloud. Key differences include:

OCI is designed to run services, while Charliecloud is designed to run scientific applications.
OCI containers are persistent things with a complex lifecycle, while Charliecloud containers are simply UNIX processes.
OCI expects support for a variety of namespaces, while Charliecloud supports user and mount, no more and no less.
OCI expects runtimes to maintain a supervisor process in addition to user processes; Charliecloud has no need for this.
OCI expects runtimes to maintain state throughout the container lifecycle in a location independent from the caller.

For these reasons, ch-run-oci is a bit of a kludge, and much of what it does is provide scaffolding to satisfy OCI requirements.

Which OCI features are and are not supported is provided in the rest of this man page, and technical analysis and discussion are in the Contributor’s Guide.

This command supports OCI version 1.0.0 only and fails with an error if other versions are offered.

Operations

All OCI operations are accepted, but some are no-ops or merely scaffolding to satisfy the caller. For comparison, see also:

create

$ ch-run-oci create --bundle DIR --pid-file FILE [--no-new-keyring] CONTAINER_ID

Create a container. Charliecloud does not have separate create and start phases, so this operation only sets up OCI-related scaffolding.

Arguments:

--bundle DIR: Directory containing the OCI bundle. This must be /tmp/buildahYYY, where YYY matches CONTAINER_ID below.
--pid-file FILE: Filename to write the “container” process PID to. Note that for Charliecloud, the process given is fake; see above. This must be DIR/pid, where DIR is given by --bundle.
--no-new-keyring: Ignored. (Charliecloud does not implement session keyrings.)
CONTAINER_ID: String to use as the container ID. This must be buildah-buildahYYY, where YYY matches DIR above.

Unsupported arguments:

--console-socket PATH: UNIX socket to pass pseudoterminal file descriptor. Charliecloud does not support pseudoterminals; fail with an error if this argument is given. For Buildah, redirect its input from /dev/null to prevent it from requesting a pseudoterminal.

delete

$ ch-run-oci delete CONTAINER_ID

Clean up the OCI-related scaffolding for specified container.

kill

$ ch-run-oci kill CONTAINER_ID

No-op.

start

$ ch-run-oci start CONTAINER_ID

Eexecute the user command specified at create time in a Charliecloud container.

state

$ ch-run-oci state CONTAINER_ID

Print the state of the given container on standard output as an OCI compliant JSON document.

Unsupported Oci Features

As noted above, various OCI features are not supported by Charliecloud. We have tried to guess which features would be essential to callers; ch-run-oci fails with an error if these are requested. Otherwise, the request is simply ignored.

We are interested in hearing about scientific-computing use cases for unsupported features, so we can add support for things that are needed.

Our goal is for this man page to be comprehensive: every OCI runtime feature should either work or be listed as unsupported.

Unsupported features that are an error:

Pseudoterminals
Hooks (prestart, poststart, and prestop)
Annotations
Joining existing namespaces
Intel Resource Director Technology (RDT)

Unsupported features that are ignored:

Mounts other than the root filesystem
User/group mappings beyond one user mapped to EUID and one group mapped to EGID
Disabling prctl(PR_SET_NO_NEW_PRIVS)
Root filesystem propagation mode
sysctl directives
masked and read-only paths (remaining unprivileged protects you)
Capabilities
rlimits
Devices (all devices are inherited from the host)
cgroups
seccomp
SELinux
AppArmor
Container hostname setting

Environment Variables

CH_LOG_FILE

If set, append log chatter to this file, rather than standard error. This is useful for debugging situations where standard error is consumed or lost.

Also sets verbose mode if not already set (equivalent to --verbose).

CH_LOG_FESTOON

If set, prepend PID and timestamp to logged chatter.

CH_XATTRS

If set, save xattrs in the build cache and restore them when rebuilding from the cache (equivalent to --xattrs).

CH_RUN_OCI_HANG

If set to the name of a command (e.g., create), sleep indefinitely when that command is invoked. The purpose here is to halt a build so it can be examined and debugged.