# dhcpcd

Related articles

- Network configuration
- Wireless network configuration
- dhcpd

dhcpcd is a DHCP and DHCPv6 client. It is currently the most feature-rich open source DHCP client, see the home page for the full list of features.

Note: `dhcpcd` (DHCP client daemon) is not the same as `dhcpd` (DHCP (server) daemon).

## Installation

The dhcpcd package is available in the official repositories. It is part of the base group, so it is likely already installed on your system.

You might be interested in dhcpcd-ui, which is a GTK+ frontend for the dhcpcd daemon (and optionally wpa_supplicant). It features a configuration dialogue and the ability to enter a pass phrase for wireless networks.

## Running

dhcpcd is usually controlled via the provided service file `dhcpcd@interface_name.service`. The interface_name serves as an argument to control which network interface the daemon should listen for.

To start dhcpcd manually, simply run the following command:

    # dhcpcd interface_name

    dhcpcd: version 5.1.1 starting
    dhcpcd: interface_name: broadcasting for a lease
    ...
    dhcpcd: interface_name: leased 192.168.1.70 for 86400 seconds

## Configuration

The main configuration is done in `/etc/dhcpcd.conf`, see `dhcpcd.conf(5)` for details. Some of the frequently used options are highlighted below.

### DHCP static route(s)

If you need to add a static route client-side, create a new dhcpcd hook-script in `/usr/lib/dhcpcd/dhcpcd-hooks`. The example shows a new hook-script which adds a static route to a VPN subnet on `10.11.12.0/24` via a gateway machine at `192.168.192.5`:

    /usr/lib/dhcpcd/dhcpcd-hooks/40-vpnroute

    ip route add 10.11.12.0/24 via 192.168.192.5

The `40` prefix means that it is the final hook-script to run when dhcpcd starts.

### DHCP Client Identifier

The DHCP client may be uniquely identified in different ways by the server:

- hostname (or the hostname value sent by the client),
- MAC address of the network interface controller through which the connection is being made, linked to this is the third,
- Identity Association ID (IAID), which is an abstraction layer to differentiate different use-cases and/or interfaces on a single host,
- DHCP Unique Identifier (DUID).

For a further description, see RFC 3315.

It depends on the DHCP-server configuration which options are optional or required to request a DHCP IP lease. If the dhcpcd default configuration fails to obtain an IP, the following options are available to use in `dhcpcd.conf`:

- `hostname` sends the hostname set in `/etc/hostname`
- `clientid` sends the MAC address as identifier
- `IAID <interface>` derives the IAID for the `interface <interface>` to use for DHCP discovery. Both have to be used together, but more frequently the next option is used:
- `duid` triggers using a combination of DUID and IAID as identifier.

The DUID value is set in `/etc/dhcpcd.duid`.

Care must be taken on a network running Dynamic DNS to ensure that all three are unique. If duplicate DUID values are presented to the DNS server, e.g. in the case where a virtual machine has been cloned and the hostname and MAC have been made unique but the DUID has not been changed, then the result will be that as each client with the duplicated DUID requests a lease the server will remove the predecessor from the DNS record.

### Speed up DHCP by disabling ARP probing

dhcpcd contains an implementation of a recommendation of the DHCP standard (RFC2131 section 2.2) to check via ARP if the assigned IP address is really not taken. This seems mostly useless in home networks, so you can save about 5 seconds on every connect by adding the following line to `/etc/dhcpcd.conf`:

    noarp

This is equivalent to passing `--noarp` to `dhcpcd`, and disables the described ARP probing, speeding up connections to networks with DHCP.

### Fallback static profile

It is possible to configure a static profile within dhcpcd and fall back to it when DHCP lease fails. This is useful particularly for headless machines such as Raspberry Pi, where the static profile can be used as "recovery" profile to ensure that it is always possible to connect to the machine.

The following example configures a `static_eth0` profile with `192.168.1.1` as IP address, `192.168.1.23` as gateway and name server, and makes this profile fallback for interface `eth0`.

    /etc/dhcpcd.conf

    # define static profile
    profile static_eth0
    static ip_address=192.168.1.1
    static routers=192.168.1.23
    static domain_name_servers=192.168.1.23

    # fallback to static profile on eth0
    interface eth0
    fallback static_eth0

More complicated configurations are possible, for example combining with the `arping` option. See `dhcpcd.conf(5)` for details.

## Hooks

dhcpcd executes all scripts found in `/usr/lib/dhcpcd/dhcpcd-hooks/` in a lexical order. See `dhcpcd(5)` and `dhcpcd-run-hooks(8)` for details.

Note:

- Each script can be disabled using the `nohook` option in `dhcpcd.conf`.
- The `env` option can be used to set an environment variable for all hooks. For example, you can force the hostname hook to always set the hostname with `env force_hostname=YES`.

### 10-wpa_supplicant

The `10-wpa_supplicant` hook automatically launches WPA supplicant on wireless interfaces. It is started only if:

- no wpa_supplicant process is already listening on that interface.
- a wpa_supplicant configuration file exists. dhcpcd checks

    /etc/wpa_supplicant/wpa_supplicant-"$interface".conf
    /etc/wpa_supplicant/wpa_supplicant.conf
    /etc/wpa_supplicant-"$interface".conf
    /etc/wpa_supplicant.conf

by default, in that order, but a custom path can be set by adding `env wpa_supplicant_conf=configuration_file_path` into `/etc/dhcpcd.conf`.

Note: The hook stops at the first configuration file found, thus you should take this into consideration if you have several wpa_supplicant configuration files, otherwise dhcpcd might end up using the wrong file.

If you manage wireless connections with wpa_supplicant itself, the hook may create unwanted connection events. For example, if you stop wpa_supplicant the hook may bring the interface up again. To disable it, add `nohook wpa_supplicant` to `dhcpcd.conf`.

## Tips and tricks

### Remove old DHCP lease

The file `/var/lib/dhcpcd/dhcpcd-interface.lease`, where `interface` is the name of the interface on which you have a lease, contains the actual DHCP lease reply sent by the DHCP server. It is used to determine the last lease from the server, and its `mtime` attribute is used to determine when it was issued. This last lease information is then used to request the same IP address previously held on a network, if it is available. If you do not want that, simply delete this file.

## Troubleshooting

### Client ID

If you are on a network with DHCPv4 that filters Client IDs based on MAC addresses, you may need to change the following line:

    /etc/dhcpcd.conf

    # Use the same DUID + IAID as set in DHCPv6 for DHCPv4 Client ID as per RFC4361.
    duid

To:

    /etc/dhcpcd.conf

    # Use the hardware address of the interface for the Client ID (DHCPv4).
    clientid

Else, you may not obtain a lease since the DHCP server may not read your DHCPv6-style Client ID correctly. See RFC 4361 for more information.

### Check DHCP problem by releasing IP first

Problem may occur when DHCP get wrong IP assignment. For example when two routers are tied together through VPN. The router that is connected to me by VPN may assigning IP address. To fix it. On a console, as root, release IP address:

    # dhcpcd -k

Then request a new one:

    # dhcpcd

Maybe you had to run those two commands many times.

### Problems with incompliant routers

For some (incompliant) routers, you will not be able to connect properly unless you comment the line

    require dhcp_server_identifier

in `/etc/dhcpcd.conf`. This should not cause issues unless you have multiple DHCP servers on your network (not typical); see this page for more information.

### dhcpcd and systemd network interfaces

dhcpcd.service can be enabled without specifying an interface. This may, however, create a race condition at boot with systemd-udevd trying to apply a predictable network interface name:

    error changing net interface name wlan0 to wlp4s0: Device or resource busy"

To avoid it, enable dhcpcd as described in Dhcpcd#Running per interface it should listen on instead.

## See also

- dhcpcd(8)
- dhcpcd.conf(5)

Category:

- Networking