dhclient

dhclient is the ISC DHCP client, a network configuration daemon used on many Unix-like systems to obtain IP configuration information from a DHCP server. It supports IPv4 and, in some implementations, the IPv6 counterpart via a separate client (often dhclient6). When started, dhclient negotiates with a DHCP server to obtain an IP address, subnet mask, default gateway, and other parameters such as DNS servers, domain search lists, and NTP servers. It can also renew or release leases, and is commonly used in environments that rely on dynamic addressing. The client applies configuration changes by invoking a user-supplied script that updates system networking state and related files.

dhclient reads configuration from a config file such as /etc/dhcp/dhclient.conf and writes lease information to a lease file (for example /var/lib/dhcp/dhclient.leases). Typical operation is to run as a background daemon or be invoked by the system’s network startup, sometimes via ifup, NetworkManager, or systemd-networkd. Common invocation options include running dhclient on a specific interface, -v for verbose logging, -1 to perform a single lease transaction, -pf to write a pid file, -lf to specify a lease file, and -cf to specify a custom configuration file. For IPv6, the equivalent client dhclient6 is used with similar options.

In practice, dhclient is a foundational tool in DHCP-based networks, though many modern systems rely on alternative network managers. Security considerations include the risk of rogue DHCP servers; administrators may employ protections such as DHCP snooping and appropriate network policies to mitigate abuse. It is released under the ISC license and is widely distributed with many Unix-like operating systems.