Important configuration directories and files

Systemd (units, priorities)

Path

Purpose

Notes

/etc/systemd/system/

User-defined units and overrides

Highest priority; overwrites units of the same name

/run/systemd/system/

Units generated at runtime

Fleeting

/lib/systemd/system/

Units provided by packages

Lowest priority; can be overridden by /etc

/lib/systemd/system/TcSystemServiceUm.service

TwinCAT system service unit

TwinCAT Runtime service management

Network (systemd-networkd)

Path

Purpose

Notes

/usr/lib/systemd/network/

Predefined standard network configurations

Delivered with system; do not edit directly

/etc/systemd/network/

User/project-specific network configurations

Overrides /usr/lib/systemd/network/

/usr/lib/systemd/network/80-wifi-station.network.example

Example for WLAN client

Use via symlink/copy to /etc

/usr/lib/systemd/network/80-wifi-ap.network.example

Example for WLAN-AP

For hostapd/AP scenario

Firewall (nftables)

Path

Purpose

Notes

/etc/nftables-bhf.conf

Basic set of rules that is loaded at startup

Applied by nftables.service

/etc/nftables.conf.d/

Additional/user-defined rule files

Activate changes via reload/restart

/etc/nftables.conf.d/60-ads.conf

Example: Port release for ADS

Individual rules for TwinCAT ports

/etc/nftables.conf.d/60-mosquitto-container.conf

Example: Port 1883 for MQTT

Regulate container and broker access

APT (package management)

Path

Purpose

Notes

/etc/apt/auth.conf.d/bhf.conf

myBeckhoff access data for Beckhoff repository

Restrictive authorizations (e.g. chmod 600)

/etc/apt/sources.list.d/bhf.list

Beckhoff repository (stable/testing)

Required for Beckhoff packages

/etc/apt/sources.list.d/docker.list

Docker® repository

Is created during Docker® setup

Time (systemd-timesyncd)

Path

Purpose

Notes

/etc/systemd/timesyncd.conf

Configuration of the timesyncd client

System-wide adjustments

/usr/lib/systemd/timesyncd.conf.d/50-beckhoff.conf

FallbackNTP setting

Default setting: ntp.beckhoff-cloud.com

WLAN and access point

Path

Purpose

Notes

/etc/hostapd/hostapd.conf

Hostapd configuration (access point)

SSID, passphrase, channel, country_code etc.

SSH key (user & root)

Path

Purpose

Notes

/home/Administrator/.ssh/authorized_keys

Authorized public keys for user Administrator

Rights: ~/.ssh 700, authorized_keys 600

/root/.ssh/authorized_keys

Authorized public keys for root

Activates root SSH - note security aspects

TwinCAT

Path

Purpose

Notes

/etc/TwinCAT/3.1/TcRegistry.xml

TwinCAT registry (e.g. AMS NetID)

Stop TwinCAT before editing, then restart it

/lib/systemd/system/TcSystemServiceUm.service

Systemd unit for TwinCAT user mode service

Service unit: Control via systemctl