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# OpenNTPD

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- System time

OpenNTPD (part of the OpenBSD project) is a daemon that can be used to synchronize the system clock to internet time servers using the Network Time Protocol, and can also act as a time server itself if needed. It implements the Simple Network Time Protocol version 4, as described in RFC:5905, and the Network Time Protocol version 3, as described in RFC:1305.

## Installation

Install the openntpd package. The default configuration is actually usable if all you want is to sync the time of the local computer.

## Configuration

To configure OpenNTPD, you need to edit `/etc/ntpd.conf`. See ntpd.conf(5) for all available options.

Tip After configuring, check the configuration file for validity by executing:

    $ ntpd -n

### Client

This article or section needs expansion.

Reason: Document HTTPS constraints. (Discuss in Talk:OpenNTPD)

To sync to a single particular server, edit the `server` directive.

    /etc/ntpd.conf

    server time.cloudflare.com

The `servers` directive works the same as the `server` directive. However, if the DNS name resolves to multiple IP address, all of them will be synced to. The default, `2.arch.pool.ntp.org`, is working and should be acceptable in most cases. You can find the server's URL in your area at www.pool.ntp.org/zone/@.

    /etc/ntpd.conf

    servers 2.arch.pool.ntp.org

Any number of `server` or `servers` directives may be used.

### Server

If you want the computer you run OpenNTPD on to also be a time server, simply uncomment and edit the "listen" directive.

For example:

    /etc/ntpd.conf

    listen on *

will listen on all interfaces, and

    /etc/ntpd.conf

    listen on 127.0.0.1
    listen on ::1

will only listen on the loopback interface.

Your time server will only begin to serve time after it has synchronized itself to a high resolution. This may take hours, or days, depending on the accuracy of your system.

## Usage

### Start OpenNTPD at boot

Enable `openntpd.service`.

### Making openntpd dependent upon network access

If you have intermittent network access (you roam around on a laptop, you use dial-up, etc.), it does not make sense to have `openntpd` running as a system daemon on start up. Here are a few ways you can control `openntpd` based on the presence of a network connection.

#### Using NetworkManager dispatcher

OpenNTPD can be brought up/down along with a network connection through the use of NetworkManager's dispatcher scripts.

Install networkmanager-dispatcher-openntpdAUR.

#### Using dhclient hooks

This article or section needs expansion.

Reason: hook example needed (Discuss in Talk:OpenNTPD)

Another possibility is to use dhclient hooks to start and stop openntpd. When dhclient detects a change in state, it will run the following scripts:

- `/etc/dhclient-enter-hooks`
- `/etc/dhclient-exit-hooks`

See dhclient-script(8).

#### Using dhcpcd hooks

    /etc/dhcpcd.exit-hook

    if $if_up; then
    	systemctl start openntpd.service
    elif $if_down; then
    	systemctl stop openntpd.service
    fi

See dhcpcd-run-hooks(8).

## Troubleshooting

### Error adjusting time

If you find your time set incorrectly and in the log, you see:

    openntpd adjtime failed: Invalid argument

Try:

    # ntpd -d

This is also how you would manually sync your system.

### constraint: failed to load constraint ca

OpenNTPD will fail to start on a system with AppArmor if HTTPS constraints are configured in `/etc/ntpd.conf`. The journal will show `constraint: failed to load constraint ca`.

This is because AppArmor's `usr.sbin.ntpd` profile does not have read access to LibreSSL's CA certificate file `/etc/libressl/cert.pem`.[1]

The solution is to grant access with a local override:

    /etc/apparmor.d/local/usr.sbin.ntpd

    ...
    /etc/libressl/{,cert.pem} r,

After editing, reload the AppArmor profile:

    # apparmor_parser -r /etc/apparmor.d/usr.sbin.ntpd

## See also

- https://www.openntpd.org
- OpenNTPD Portable

Categories:

- Network Time Protocol
- OpenBSD

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