dhcpcd

-4
    IPv4 only, disables IPv6 Router Advertisements

-6
    IPv6 Router Advertisements only, disables DHCPv4

-a, --all
    Configure all interfaces marked 'allowinterfaces'

-A, --nobackground
    Don't run as a daemon; foreground only

-b, --background
    Background immediately, even with debug

-B, --noarp
    Don't validate offered/requested IP with ARP

-c, --script SCRIPT
    Use custom script instead of /lib/dhcpcd/dhcpcd-runhooks

-C, --nohook HOOK
    Skip named hook script

-d
    Increase debug verbosity (repeat for more)

-D
    Return non-zero exit code on DHCP failure

-E, --lastlease
    Fail if no lease available; use last lease if present

-e, --env VAR=VALUE
    Set a script environment variable

-f, --config FILE
    Use alternate config file

-g, --user GID
    Change to group ID after config

-h, --hostname HOSTNAME
    Send hostname to DHCP server

-i, --vendorclassid ID
    Set vendor class identifier

-I, --clientid CLIENTID
    Set client identifier (default: MAC)

-j
    Write to systemd journal

-k, --kill
    Kill dhcpcd instance for interface

-l, --leasetime TIME
    Minimum lease time; ignore shorter offers

-L, --nolink
    Don't receive link messages for hotplug

-m, --metric METRIC
    Metric for interface routes

-n, --noipv4ll
    Don't use IPv4LL fallback

-N
    Reload config files

-O, --nooption OPTION
    Don't request DHCP OPTION

-o, --option OPTION
    Request DHCP OPTION

-p, --pidfile PIDFILE
    Alternate PID file

-q
    Quiet mode; syslog only

-r, --request IP
    Request specific IP address

-s, --static IP
    Use static config; IP[/prefix][gateway]

-S
    Static config only; no DHCP

-t, --timeout SEC
    Timeout after SEC seconds

-T, --test
    Drop privileges for testing

-u, --userclass CLASS
    User class ID

-U, --dumplease
    Dump lease and exit

-v
    Verbose logging

-V, --version
    Print version

-w, --waitip [4|6|if]
    Wait for IPv4/IPv6 address before exit

-x, --exit
    Exit on SIGTERM

-z
    Zombie process; don't fork

dhcpcd is a robust, lightweight implementation of a DHCP client for Linux and other UNIX-like systems, compliant with RFC 2131 (DHCPv4) and supporting RFC 2132 (BOOTP), RFC 3927 (IPv4 Link-Local), and IPv6 Router Advertisements (RFC 4861). It automatically configures network interfaces by requesting and applying IP addresses, subnet masks, routes, DNS resolvers, NIS servers, NTP servers, and other parameters from a DHCP server.

Key capabilities include fallback to IPv4LL (AutoIP) on DHCP failure, static configuration support, customizable vendor class IDs and client identifiers, and extensible scripting via hooks for actions like hostname updates or NTP sync. It runs as a setuid root daemon, forking to background unless specified otherwise, and handles carrier detection, lease renewal, and interface hotplug events.

dhcpcd is ideal for embedded devices, servers, and minimal desktops due to low dependencies (no glibc required) and small footprint. It supports dual-stack IPv4/IPv6, static leases, and vendor extensions. Logging goes to syslog by default, with options for console or journald output. Configuration is via /etc/dhcpcd.conf for per-interface settings like static IPs or deny/allow lists.

Common use: dhcpcd eth0 for single interface or dhcpcd -a for all auto interfaces.

Requires root privileges; conflicts with other DHCP clients like dhclient. Default config may auto-configure unintended interfaces. IPv6 support limited to RA, not DHCPv6. Leases stored in /var/lib/dhcpcd/. Not suitable for complex managed networks (use NetworkManager). Signals: SIGHUP reloads config, SIGTERM releases lease.

/etc/dhcpcd.conf: Global and per-interface settings. Examples: denyinterfaces wlan*, interface eth0 static ip_address=192.168.1.100/24.

Scripts in /lib/dhcpcd/dhcpcd-hooks/ run on events (e.g., 01-network for routes, 20-resolv.conf for DNS). Custom hooks via -C.

Leases in /var/lib/dhcpcd/dhcpcd-IFACE.lease. Use dhcpcd -U IFACE to dump.

Developed by Roy Marples starting in 2006 for the Bionic libc in Android. Evolved into standalone dhcpcd project (dhcpcd5), now at v10+ (2023). Focus on portability, minimalism; used in Alpine Linux, Raspberry Pi OS, Void Linux. Key milestones: IPv6 RA (2009), hooks system (2010), journald support (2015).

dhclient(8), dhcpd(8), ip(8), ifup(8), systemd-networkd(8), wpa_supplicant(8)