archy/.claude/skills/podman/references/uid-mapping.md

# Rootless Podman UID Mapping Reference

## How Rootless UID Mapping Works

When Podman runs as the `archipelago` user (UID 1000), container processes don't run as their "apparent" UID on the host. Instead, Linux user namespaces remap UIDs.

**Mapping formula**: `host_uid = 100000 + container_uid`

This is configured in `/etc/subuid` and `/etc/subgid`:
```
archipelago:100000:65536
```

This means:
- Container UID 0 (root inside container) → Host UID 100000 (unprivileged on host)
- Container UID 70 (postgres) → Host UID 100070
- Container UID 101 (bitcoin) → Host UID 100101
- etc.

## Why This Matters

Volume directories (bind mounts) on the host must be owned by the **mapped** UID, not the container UID. If Bitcoin runs as UID 101 inside its container, the host directory must be owned by UID 100101.

If ownership is wrong, the container gets `permission denied` when trying to read/write its data.

## Complete UID Mapping Table

| Container UID | Host UID | Containers | Fix Command |
|---|---|---|---|
| 0 (root) | 100000 | lnd, fedimint, fedimint-gateway, homeassistant, jellyfin, vaultwarden, photoprism, ollama, filebrowser, electrumx, btcpay-server, nbxplorer, immich, nostr-rs-relay, strfry, nextcloud, searxng, onlyoffice, tailscale, uptime-kuma | `sudo chown -R 100000:100000 /var/lib/archipelago/{app}` |
| 70 | 100070 | postgres (btcpay-db, immich-db, penpot-postgres) | `sudo chown -R 100070:100070 /var/lib/archipelago/postgres-*` |
| 101 | 100101 | bitcoin-knots, bitcoin-core | `sudo chown -R 100101:100101 /var/lib/archipelago/bitcoin` |
| 472 | 100472 | grafana | `sudo chown -R 100472:100472 /var/lib/archipelago/grafana` |
| 999 | 100999 | MariaDB (mysql-mempool) | `sudo chown -R 100999:100999 /var/lib/archipelago/mysql-mempool` |

## How to Find a Container's UID

If you encounter a new container with permission issues:

```bash
# Check what user the container runs as
podman inspect CONTAINER_NAME --format "{{.Config.User}}"

# If empty, it runs as root (UID 0) → host UID 100000

# If it shows a username, find the UID inside the image
podman run --rm IMAGE_NAME id

# Then calculate: host_uid = 100000 + container_uid
```

## Fix Script

Run this after any fresh install, migration, or when containers have permission errors:

```bash
#!/bin/bash
# Fix all rootless podman volume ownership

# UID 0 → 100000 (most containers)
for dir in lnd fedimint fedimint-gateway homeassistant jellyfin vaultwarden photoprism \
           ollama filebrowser electrumx btcpay nbxplorer immich nostr-rs-relay nextcloud \
           searxng onlyoffice uptime-kuma; do
  [ -d "/var/lib/archipelago/$dir" ] && sudo chown -R 100000:100000 "/var/lib/archipelago/$dir"
done

# UID 101 → 100101 (Bitcoin)
[ -d "/var/lib/archipelago/bitcoin" ] && sudo chown -R 100101:100101 /var/lib/archipelago/bitcoin

# UID 70 → 100070 (PostgreSQL)
for dir in /var/lib/archipelago/postgres-* /var/lib/archipelago/btcpay-db /var/lib/archipelago/immich-db; do
  [ -d "$dir" ] && sudo chown -R 100070:100070 "$dir"
done

# UID 999 → 100999 (MariaDB)
[ -d "/var/lib/archipelago/mysql-mempool" ] && sudo chown -R 100999:100999 /var/lib/archipelago/mysql-mempool

# UID 472 → 100472 (Grafana)
[ -d "/var/lib/archipelago/grafana" ] && sudo chown -R 100472:100472 /var/lib/archipelago/grafana
```

## Rootful vs Rootless Comparison

| Aspect | Rootful (old) | Rootless (current) |
|--------|---------------|-------------------|
| Podman command | `sudo podman` | `podman` (as archipelago user) |
| Container storage | `/var/lib/containers/storage` | `~/.local/share/containers/storage` |
| Container subnet | `10.88.0.0/16` | `10.89.0.0/16` |
| Volume ownership | Container UID directly | Mapped UID (100000 + container_uid) |
| Requires root? | Yes | No (except fixing volume ownership) |
| XDG_RUNTIME_DIR | Not needed | Required: `/run/user/1000` |
| User lingering | Not needed | Required: `loginctl enable-linger` |
| Systemd restrictions | All can be enabled | Must disable: RestrictNamespaces, SystemCallFilter |