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Diffstat (limited to 'docs/CONTAINER_INTERFACE.md')
| -rw-r--r-- | docs/CONTAINER_INTERFACE.md | 47 |
1 files changed, 39 insertions, 8 deletions
diff --git a/docs/CONTAINER_INTERFACE.md b/docs/CONTAINER_INTERFACE.md index 460cc67..e64953c 100644 --- a/docs/CONTAINER_INTERFACE.md +++ b/docs/CONTAINER_INTERFACE.md @@ -164,10 +164,15 @@ manager, please consider supporting the following interfaces. issuing `journalctl -m`. The container machine ID can be determined from `/etc/machine-id` in the container. -3. If the container manager wants to cleanly shutdown the container, it might +3. If the container manager wants to cleanly shut down the container, it might be a good idea to send `SIGRTMIN+3` to its init process. systemd will then do a clean shutdown. Note however, that since only systemd understands - `SIGRTMIN+3` like this, this might confuse other init systems. + `SIGRTMIN+3` like this, this might confuse other init systems. A container + manager may implement the `$NOTIFY_SOCKET` protocol mentioned below in which + case it will receive a notification message `X_SYSTEMD_SIGNALS_LEVEL=2` that + indicates if and when these additional signal handlers are installed. If + these signals are sent to the container's PID 1 before this notification + message is sent they might not be handled correctly yet. 4. To support [Socket Activated Containers](https://0pointer.de/blog/projects/socket-activated-containers.html) @@ -189,12 +194,14 @@ manager, please consider supporting the following interfaces. unit they created for their container. That's private property of systemd, and no other code should modify it. -6. systemd running inside the container can report when boot-up is complete - using the usual `sd_notify()` protocol that is also used when a service - wants to tell the service manager about readiness. A container manager can - set the `$NOTIFY_SOCKET` environment variable to a suitable socket path to - make use of this functionality. (Also see information about - `/run/host/notify` below.) +6. systemd running inside the container can report when boot-up is complete, + boot progress and functionality as well as various other bits of system + information using the `sd_notify()` protocol that is also used when a + service wants to tell the service manager about readiness. A container + manager can set the `$NOTIFY_SOCKET` environment variable to a suitable + socket path to make use of this functionality. (Also see information about + `/run/host/notify` below, as well as the Readiness Protocol section on + [systemd(1)](https://www.freedesktop.org/software/systemd/man/latest/systemd.html) ## Networking @@ -272,6 +279,30 @@ care should be taken to avoid naming conflicts. `systemd` (and in particular 7. The `/run/host/credentials/` directory is a good place to pass credentials into the container, using the `$CREDENTIALS_DIRECTORY` protocol, see above. +8. The `/run/host/unix-export/` directory shall be writable from the container + payload, and is where container payload can bind `AF_UNIX` sockets in that + shall be *exported* to the host, so that the host can connect to them. The + container manager should bind mount this directory on the host side + (read-only ideally), so that the host can connect to contained sockets. This + is most prominently used by `systemd-ssh-generator` when run in such a + container to automatically bind an SSH socket into that directory, which + then can be used to connect to the container. + +9. The `/run/host/unix-export/ssh` `AF_UNIX` socket will be automatically bound + by `systemd-ssh-generator` in the container if possible, and can be used to + connect to the container. + +10. The `/run/host/userdb/` directory may be used to drop-in additional JSON + user records that `nss-systemd` inside the container shall include in the + system's user database. This is useful to make host users and their home + directories automatically accessible to containers in transitive + fashion. See `nss-systemd(8)` for details. + +11. The `/run/host/home/` directory may be used to bind mount host home + directories of users that shall be made available in the container to. This + may be used in combination with `/run/host/userdb/` above: one defines the + user record, the other contains the user's home directory. + ## What You Shouldn't Do 1. Do not drop `CAP_MKNOD` from the container. `PrivateDevices=` is a commonly |