UDHCPCTL

UDHCPCTL is a small control utility used by Lichee-Jack to manage multiple udhcpd DHCP server instances via systemd template units.

It provides a unified and safe interface to start, restart, stop, or stop all DHCP servers defined by configuration files under:

/root/config/udhcpd/<unit>.conf

Each configuration file corresponds to a systemd service:

udhcpd@<unit>.service

Design Goals

• Support multiple isolated DHCP servers (per interface / per mode)
• Avoid manual systemctl calls in payloads
• Ensure safe state transitions (no duplicate instances)
• Provide clear logging via logger
• Fail fast and visibly on critical errors

How It Works

UDHCPCTL is a thin dispatcher around systemctl that operates on templated units:

udhcpd@<unit>.service

Where:

• <unit> is the basename of a config file in /root/config/udhcpd/
• The systemd service loads the matching config

Example:

/root/config/udhcpd/usb.conf
→ udhcpd@usb.service

Usage

UDHCPCTL <ACTION> <UNIT>

Actions

Examples

Start a DHCP server

UDHCPCTL START usb

Starts:

udhcpd@usb.service

Restart a DHCP server

UDHCPCTL RESTART eth

Safely stops and re-starts:

udhcpd@eth.service

Stop a specific DHCP server

UDHCPCTL STOP usb

If the unit is not active, the command exits gracefully without error.

Stop all DHCP servers

UDHCPCTL STOP_ALL

Stops all running udhcpd@* instances.

Safety Checks

UDHCPCTL performs several validations:

• Checks whether a unit is already active before starting
• Avoids stopping inactive units unnecessarily
• Verifies the unit remains active after startup
• Logs all operations via logger:

[*] Normal operations
[!] Errors (syslog level: err)

On fatal failures, the script exits immediately.

Logging

All actions are logged under the tag:

LicheeJack

You can inspect logs using:

journalctl -t LicheeJack

Typical Integration

UDHCPCTL is commonly invoked by:

• NETMODE scripts
• Payloads requiring DHCP services
• Boot-time network role selection

Example flow:

MODE switch → NETMODE → UDHCPCTL START usb

Failure Behavior

On critical errors (e.g. systemd failure):

• An error is logged
• The script exits with non-zero status
• Higher-level controllers (e.g. RUN, NETMODE) can react accordingly

Summary

UDHCPCTL provides a robust, scriptable, and mode-aware way to control DHCP services on Lichee-Jack.

It abstracts systemd complexity and ensures DHCP state remains predictable across payload execution and mode switches.