Runtime environment

Every binary in this tree runs on a developer machine with nothing set, and on the LattePanda image with a few variables the systemd units provide. libs/core is where they are read (core::paths, core::setupLogging, core::systemd); nothing else in the tree reads them directly.

Variable	Set by	Meaning
REDLINE_DATA_DIR	the image: /data	Where deployment data lives: map archives, road graphs, recordings. Configs write ${REDLINE_DATA_DIR}/maps/socal.mbtiles. Unset on a desktop, which means $XDG_DATA_HOME/redline or ~/.local/share/redline (Linux) and ~/Library/Application Support/redline (macOS). Set it to point at your own data directory.
REDLINE_LOG_DIR	nobody by default	When set, every program also writes a rotating log <dir>/<program>.txt. Unset means console only: under systemd stderr is already the journal, and a tool writing into the checkout by default was a surprise. REDLINE_LOG_DIR=logs restores the old logs/ files.
REDLINE_DISPLAY_<ROLE>_CONNECTOR _MODE _PROFILE	redline-display-setup on the image	The detected display modules; the dashboard binds windows to them. See displays.md.
NOTIFY_SOCKET	systemd, for Type=notify units	The dashboard sends READY=1 after its first frame is on screen, so the unit becomes active when the cluster is visible rather than when the process starts. No libsystemd; unset means no-op.

REDLINE_MFI_I2C_DEV	the image: /dev/i2c-13 (the redline-node@carplay drop-in)	The I2C adapter the Apple MFi coprocessor is on. Unset on a desktop, where the driver auto-detects an MCP2221A bridge (and otherwise takes the first adapter, which on a board with a GPU is its DDC bus – so the image names it). carplay --mfi-i2c-device and apple_mfi_demo /dev/i2c-N override it.
PUB_SUB_NO_DISCOVERY	tests and tools	1 keeps a zenoh session off the machine’s bus.
REDLINE_REPO_ROOT, REDLINE_BUILD_DIR	developers	Where the MCP supervisor finds the checkout and its binaries. See agent_control.md.

An operator’s dashboard config lives at ${REDLINE_DATA_DIR}/dashboard/config.yaml; see config-on-target.md.

Config files may use ${REDLINE_DATA_DIR}, any ${VARIABLE}, and ~/; relative paths resolve against the config file’s own directory. Today the map server’s tilesets, graphs and tracksets go through this; a new config key that names a file should call core::paths::expand() too.

Shipped resources (the eds/ directory, for one) are found with core::paths::resource(): next to the installed binaries first (/opt/redline/bin/../eds), then by walking up from the binary to the checkout a developer build sits in, then REDLINE_REPO_ROOT. No build path is compiled in.