github.com/containers/podman/v2@v2.2.2-0.20210501105131-c1e07d070c4c/pkg/hooks/README.md (about)

     1  # OCI Hooks Configuration
     2  
     3  For POSIX platforms, the [OCI runtime configuration][runtime-spec] supports [hooks][spec-hooks] for configuring custom actions related to the life cycle of the container.
     4  The way you enable the hooks above is by editing the OCI runtime configuration before running the OCI runtime (e.g. [`runc`][runc]).
     5  CRI-O and `podman create` create the OCI configuration for you, and this documentation allows developers to configure them to set their intended hooks.
     6  
     7  One problem with hooks is that the runtime actually stalls execution of the container before running the hooks and stalls completion of the container, until all hooks complete.
     8  This can cause some performance issues.
     9  Also a lot of hooks just check if certain configuration is set and then exit early, without doing anything.
    10  For example the [oci-systemd-hook][] only executes if the command is `init` or `systemd`, otherwise it just exits.
    11  This means if we automatically enabled all hooks, every container would have to execute `oci-systemd-hook`, even if they don't run systemd inside of the container.
    12  Performance would also suffer if we exectuted each hook at each stage ([pre-start][], [post-start][], and [post-stop][]).
    13  
    14  The hooks configuration is documented in [`oci-hooks.5`](docs/oci-hooks.5.md).
    15  
    16  [oci-systemd-hook]: https://github.com/projectatomic/oci-systemd-hook
    17  [post-start]: https://github.com/opencontainers/runtime-spec/blob/v1.0.1/config.md#poststart
    18  [post-stop]: https://github.com/opencontainers/runtime-spec/blob/v1.0.1/config.md#poststop
    19  [pre-start]: https://github.com/opencontainers/runtime-spec/blob/v1.0.1/config.md#prestart
    20  [runc]: https://github.com/opencontainers/runc
    21  [runtime-spec]: https://github.com/opencontainers/runtime-spec/blob/v1.0.1/spec.md
    22  [spec-hooks]: https://github.com/opencontainers/runtime-spec/blob/v1.0.1/config.md#posix-platform-hooks