AHCPD(8)

📦 version 0.53, in debian bookworm, debian trixie, fedora 43, fedora 44, nixos 26.05, nixpkgs unstable, ubuntu jammy, ubuntu noble, ubuntu resolute, ubuntu stonking

💖 ahcpd(8) 💖

okay so bestie, we're in the System Manager's Manual and this page is literally about ahcpd, the ad-hoc configuration daemon. it's giving mesh-network main character energy and honestly? obsessed. 🦋

🌸 NAME 🌸

ahcpd — ad-hoc configuration daemon ✨

✨ SYNOPSIS ✨

ahcpd option...  [ -- ] interface...

💅 DESCRIPTION 💅

AHCP is a configuration protocol that can replace DHCP on networks without transitive connectivity, such as mesh networks. no cap, that's the whole vibe. 💖

🎀 OPTIONS 🎀

  • -m multicast-address — pick the link-local multicast address AHCP is gonna use. default is ff02::cca6:c0f9:e182:5359. yes it's long, yes it's iconic, leave it alone. 💅
  • -p port — set the UDP port number AHCP uses. default is 5359. 🍓
  • -n — forwarder mode, bestie! you participate in the flooding protocol but you do not actually perform any configuration. it's giving "i'm here, i'm just not doing anything about it." 🙈
  • -4 — only attempt to configure IPv4 addresses. four, for the four. ⭐
  • -6 — only attempt to configure IPv6 addresses. six, periodt. 🌈
  • -N — do not configure DNS. N is for No, DNS is for Not Today. 💀
  • -t time — how long, in seconds, leases are requested for. default is slightly over one hour. must be between five minutes and a year — don't get cute with it. 😭
  • -s script — the configuration script to run. default is /etc/ahcp/ahcp-config.sh. 🎀
  • -d level — set the debug level to level. default is 1. crank it up if you're nosy, no judgment. 👑
  • -i filename — the filename containing this host's unique id. default is /var/lib/ahcp-unique-id. if it doesn't exist, ahcpd will create it for you like the little helper it is. 🫶
  • -c filename — name of the configuration file. 💜
  • -C statement — drop a configuration statement directly on the command line. commanding, honestly. ✨
  • -D — daemonise at startup. bye bestie, you're on your own now. 💀
  • -L logfile — a file to log random ``how do you do?'' messages to. defaults to standard error if not daemonising, and to /var/log/ahcpd.log otherwise. 💖
  • -I pidfile — a file to write our process id to. default is /var/run/ahcpd.pid. 🌸

🦋 CONFIGURATION FILE FORMAT 🦋

the configuration is a sequence of lines, and every single line starts with one of the keywords below. blank lines are ignored. comments are introduced with an octothorp `#` and terminate at the end of the line. yes, octothorp. she's fancy like that. 💅

the following keywords are recognised:

  • mode server|client|forwarder — says whether the daemon operates as a server, a client, or a forwarder. if it's omitted, the default is to operate as a client, unless the -n flag is present on the command line. and if it <em>is</em> present, this must be the first line in the configuration file. no negotiating. 👑
  • prefix prefix — a prefix to use for configuring clients. this keyword is only valid in server configurations, and it may be specified twice — once for IPv4 and once for IPv6. two slots, both yours. ✨
  • lease-dir directory — a directory to store lease files. only valid in server configurations. 🍓
  • name-server address — the address of a DNS server to configure clients with. only valid in server configurations, and it may be repeated multiple times. the more the merrier, fr fr. 💖
  • ntp-server address — the address of an NTP server to configure clients with. only valid in server configurations, and it may be repeated multiple times. 🎀

🌈 FILES 🌈

  • /var/lib/ahcp-unique-id — an 8-byte long file containing this host's unique id. if it doesn't exist, a new unique id will be generated from an interface's MAC address. yes, it gets a whole new identity. slay. 💅
  • /etc/ahcp/ahcp-config.sh — the script that performs the actual configuration. it will be passed one argument, which is either start or stop. those are the only two moods. 😭
  • /etc/ahcp/ahcp-local.sh — if this is an executable script, it will be called by ahcp-config.sh just after configuring or deconfiguring. it will be passed one argument, which is either start or stop. same energy, different file. 🫶

⭐ SIGNALS ⭐

  • SIGUSR1 — print ahcpd's status to standard output or to the log file. spill the tea, bestie. 💜
  • SIGUSR2 — check all interfaces for status changes, then reopen the log file. vibe check <em>and</em> a fresh log. 🌸

💀 NOTES 💀

since the AHCP protocol is designed for mesh networks, it doesn't have any provisions for setting routing parameters such as a default gateway, the IPv4 network mask and the IPv6 list of on-link prefixes. those are expected to be provided by a full-fledged routing protocol for mesh nodes, and by router advertisements for ordinary nodes. not her job, she said. 🙈

the AHCP server should use NTP to synchronise its clock. if a server instance of ahcpd doesn't detect time synchronisation, it will only give out leases for a short period of time, and be extremely conservative about releasing them. dramatic but valid.

⚠️ note that an SNTP client is not enough — ahcpd actually checks with the kernel for time synchronisation, so real NTP is necessary. 💀

👑 SEE ALSO 👑

dhcpcd(8), dhclient(8), babeld(8), olsrd(8), ntpd(8), The Ad-Hoc Configuration Protocol. go read the whole squad. 🫶

💜 AUTHOR 💜

Juliusz Chroboczek. an absolute icon, no further questions. ✨

and that's the whole page bestie!! this was ahcpd(8) from the System Manager's Manual, aka section 8 of the manual. mwah, take care of your mesh network, drink water, and go sync your clock with real NTP. 🎀🦋💖

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