dhclient-script

dhclient-script interface reason [parameter=value …]

interface
    Network interface name (e.g., eth0)

reason
    DHCP event: PREINIT, BOUND, RENEW, REBIND, REBOOT, EXPIRE, RELEASE, STOP, etc.

ip_address
    Assigned IPv4 address

subnet_mask
    Subnet mask for the interface

routers
    Space-separated list of default gateways

domain_name_servers
    Space-separated DNS server IPs

domain_name
    Domain name from DHCP

domain_search
    Search domains for DNS resolution

new_lease_time
    Lease duration in seconds

new_broadcast_address
    Broadcast address

new_classless_static_routes
    Classless static routes from DHCP

The dhclient-script is a shell script used by the ISC DHCP client (dhclient) to configure network interfaces based on DHCP lease events. It is automatically invoked by dhclient during lease acquisition, renewal, release, or expiration.

The script interprets a reason argument indicating the DHCP event (e.g., BOUND, RENEW) and environment variables containing lease details like IP address, subnet mask, routers, and DNS servers. It performs actions such as assigning IP addresses with ifconfig or ip, adding routes, updating /etc/resolv.conf for DNS, and running custom hooks.

Customizable via editing the script or /etc/dhcp/dhclient-enter-hooks.d/ and exit hooks directories. Primarily used on Linux systems with ISC DHCP; not for direct user invocation but system integration. Supports IPv4; IPv6 handled separately by dhclient6-script.

Not intended for direct execution; relies on dhclient. Modern systems prefer NetworkManager or systemd-networkd. Script may need updates for ip vs. deprecated ifconfig. IPv6 separate.

Extend via /etc/dhcp/dhclient-enter-hooks.d/ (pre-config) and /etc/dhcp/dhclient-exit-hooks.d/ (post-config) directories for site-specific actions.

BOUND/REBOOT: Configure interface up with full lease. RELEASE: Deconfigure (down interface). RENEW/REBIND: Update without full tear-down.

Part of ISC DHCP client since version 3.x (early 2000s); evolved from original DHCP implementation by ISC (1995). Migrated to Kea DHCP in newer distros, but dhclient-script persists in many Linuxes like Debian/RHEL.

dhclient(8), dhclient.conf(5), dhcpd(8), ip(8), ifconfig(8)