# Sessions and workspaces
How kraal is organised, and how a workspace is declared once in a file and opened in one command.
## Concepts
- A **session** is one background server (`kraal -s work` for another one). It owns the processes;
clients attach and detach.
- A session holds **workspaces** (listed in the sidebar, which shows up once there is more than
the one workspace to see: other workspaces, agents, ports, tunnels), each with **tabs** (named
after their focused pane until you rename them), each with **panes**:
tiled, or floating on top.
- A pane is a terminal (a shell, or a command such as `ssh host`), or a **preview** of a file:
rendered Markdown, an image, text, or a directory listing. Previews reload when the file changes.
- A **command pane** stays open when its program exits, showing the exit code: press Enter to run
it again (handy when an SSH connection drops) or `x` to close it.
## Persistence
Sessions keep running when you close the terminal or lose the connection: `kraal` attaches
again. After a restart of the server or a reboot, the processes are gone, but kraal rebuilds the
layout, reconnects SSH shells and resumes agent conversations; other commands wait for Enter
before they run again.
## Workspace files
Workspaces live in `~/.config/kraal/workspaces/*.kdl`, in KDL:
```kdl
layout {
cwd "~/Dev/api"
tab name="servers" focus=true {
pane split_direction="vertical" {
pane name="db" command="ssh" { args "admin@db.lan"; }
pane name="web" command="ssh" { args "-p" "2222" "admin@web.lan"; }
}
}
tab name="work" {
pane split_direction="vertical" {
pane agent="claude" size="60%" // a shell that starts `claude`
pane preview="README.md" // a live Markdown preview
}
}
}
```
`split_direction="vertical"` places children side by side, `"horizontal"` stacks them. Sizes are
percentages or cells. Besides a command, a pane can say `agent="<name>"` to start an agent in a
shell, or `preview="<path>"` to show a file. `ctrl+b W s` or `kraal save <name>` writes the layout
back as a file (`<name>.kdl` in the definitions directory; the file it replaces is kept as
`.kdl.bak`). An agent started on an account is saved as `agent="claude:pro"` with its arguments,
and a command that has not run yet keeps `start_suspended=true`.