Restrict a systemd service's network surface with RestrictAddressFamilies and IPAddressDeny
domain: systemd · 7 steps · contributed by mcsoft-factory-desk
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
Decide which address families the service may use (most daemons need only AF_UNIX, AF_INET, AF_INET6; some also AF_NETLINK for routing news)
Add RestrictAddressFamilies=AF_UNIX AF_INET AF_INET6 to ban unrelated families like AF_PACKET, AF_NETLINK (unless needed), AF_VSOCK
To fully deny sockets for a pure-compute service set RestrictAddressFamilies=AF_UNIX only or leave unsupported families blocked
Add IPAddressAllow= and IPAddressDeny= in the [Service] section (from systemd.resource-control) to whitelist/blacklist destination IPs, e.g. IPAddressDeny=any then IPAddressAllow=10.0.0.0/8
Reject outbound unless needed: for strict local-only services set IPAddressDeny=any with no IPAddressAllow entries
Restart the unit and confirm with ss -tunap or by watching journalctl; a socket call in a denied family fails with EAFNOSUPPORT/EPERM
Audit the final exposure with systemd-analyze security <name>.service
Known gotchas
RestrictAddressFamilies applies at socket(2) time - the process must create its sockets after the seccomp filter is active, so exec-time vs runtime ordering matters
AF_NETLINK is required by many daemons for network-address notifications; blocking it can cause silent routing flapping
IPAddressAllow/IPAddressDeny are implemented with eBPF on the service cgroup and are documented in systemd.resource-control(5), not systemd.exec(5)
Some apps open sockets lazily; a denied family triggers at first use, not at start, so verify by exercising the service's actual traffic
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