# dhcpcd (日本語)

関連記事

- ネットワーク設定
- ワイヤレス設定
- dhcpd

dhcpcd は DHCP と DHCPv6 のクライアントです。現在は最も機能豊富なオープンソースの DHCP クライアントであり、ホームページに全ての機能のリストが載っています。

Note: `dhcpcd` (DHCP client デーモン) は `dhcpd` (DHCP (server) デーモン) とは違います。

## インストール

dhcpcd パッケージは公式リポジトリから入手できます。base グループに含まれているため、通常は既にあなたのシステムにインストールされているはずです。

また、dhcpcd デーモン (と任意で wpa_supplicant) の GTK+ フロントエンドである dhcpcd-ui を使うこともできます。設定ダイアログで、パスフレーズを入力して無線ネットワークに接続することができます。

## 実行

dhcpcd は基本的にサービスファイル `dhcpcd@.service` で操作します、インターフェイス名を引数として指定します (詳しくは systemd (日本語)#ユニットを使う を見て下さい):

    # systemctl start dhcpcd@interface.service
    # systemctl enable dhcpcd@interface.service

手動で dhcpcd を起動するには、次のコマンドを実行してください:

    # dhcpcd interface

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

## 設定

メインの設定は `/etc/dhcpcd.conf` で行います、詳細は `dhcpcd.conf(5)` を参照してください。よく使われるオプションについては以下で説明します。

### DHCP スタティックルート

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 クライアント ID

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.

### ARP プローブを無効にして DHCP を高速化

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.

### 予備の固定プロファイル

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.

## 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.

## トラブルシューティング

### クライアント ID

また、MAC アドレスに基づくクライアント ID をフィルタリングしている DHCPv4 ネットワークを使う場合は、次の行を:

    /etc/dhcpcd.conf

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

以下のように変更してください:

    /etc/dhcpcd.conf

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

こうしないと、DHCP サーバーがあなたの DHCPv6 クライアント ID を正しく読み込めない可能性があります。詳しくは RFC 4361 を見て下さい。

### まず IP を開放して DHCP の問題を確認する

DHCP が間違った IP の割り当てを取得している時、問題が起こることがあります。例えば2つのルーターが VPN で結び付けられている場合が考えられます。修正するには、コンソールで、root 権限を使って IP アドレスを開放してください:

    # dhcpcd -k

それから新しい IP アドレスをリクエストしてください:

    # dhcpcd

おそらくこの2つのコマンドを何度も実行する必要があります。

### 強情なルーターの問題

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, systemd & wpa_supplicant

Note: See also relevant bug report: FS#39527

archlinux dhcpcd package is delivered with a client configuration script to run wpa_supplicant (/lib/dhcpcd/dhcpcd-hooks/10-wpa_supplicant).

When you manage wpa_supplicant daemon with systemd this can result in unexpected behavior e.g.

- you stop wpa_supplicant via systemd and dhcpcd starts wpa_supplicant via hook
- dhcpcd starts wpa_supplicant daemon during boot (this can result in systemd-udevd error: "error changing net interface name wlan0 to wlp4s0: Device or resource busy" and can prevent "Predictable Network Interface Names" )

To disable the `wpa_supplicant` hook, add `nohook wpa_supplicant` into `dhcpcd.conf`.

## フック

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`.

Category:

- Networking (日本語)