# Context Signalling (OSC 3008)

> Tell the terminal when a shell, a command, a container or a privileged session starts and ends.

- **Sequence:** `OSC 3008 ; start=id ; type=… ST`
- **ECMA-48:** [§8.3.89 OSC – Operating System Command, p. 51](https://archive.org/details/ecma-48-5th-edition-june-1991/page/n64/mode/1up)
- **Specification:** [UAPI.15 OSC 3008: Hierarchical Context Signalling](https://uapi-group.org/specifications/specs/osc_context/)

Control of a terminal passes from program to program: a shell runs a
command, `ssh` connects to another machine, `run0` acquires root, a
container manager starts a container. `OSC 3008` lets each say so, so that
the terminal can mark where each began and ended, tint the output of a
privileged session, or offer to open a new shell in the same place. Its
definition is the UAPI group's
[OSC 3008: Hierarchical Context Signalling](https://uapi-group.org/specifications/specs/osc_context/),
and systemd's tools send it.

| Sequence | Does |
| --- | --- |
| `OSC 3008 ; start=id ; field=value ; … ST` | opens the context `id`, or updates it, with metadata |
| `OSC 3008 ; end=id ; field=value ; … ST` | closes it, and every context opened inside it |

The `id` is chosen by whoever opens the context, up to 64 printable
characters, and should be unique, such as a UUID. The fields include
`type`, which is one of `boot`, `container`, `vm`, `elevate`, `chpriv`,
`subcontext`, `remote`, `shell`, `command`, `app`, `service` and `session`,
and others such as the user, the host name and the working directory.
Contexts nest: a new one becomes the active one, and the one before it its
parent.

A default xterm does not have it and ignores it
([the OSC numbers it knows](https://github.com/ThomasDickey/xterm-snapshots/blob/xterm-411a/misc.c#L3476-L3504)).
libghostty-vt parses it and does nothing more. What a case can see is that
nothing is printed or answered, and libghostty-vt passes.

## Validation

### OSC3008-1: Nothing on screen

Input, one step per line:

```text
A
\e]3008;start=5f1c;type=shell\e\\
\e]3008;start=9a2e;type=command\e\\
B
\e]3008;end=9a2e;exit=success\e\\
C
```

Expected screen:

```text
|ABC___|
cursor 1,4
reply none
```

---

This is the Markdown version of <https://control-codes.page/osc/context/>. On that page every validation case runs live in libghostty-vt, the terminal emulation core of Ghostty, compiled to WebAssembly.

The validation cases are written in the notation described in <https://control-codes.page/notation/index.html.md>.