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Enforce desired TCP operation mode (v4 or v6)

Signed-off-by: Joachim Wiberg <>

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January 6, 2023 14:02
January 4, 2021 06:34

Internet Automated Dynamic DNS Client

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The latest release is always available from GitHub at

Table of Contents


Tip: the HTML UNIX manual is at, e.g., inadyn.conf(5)

Inadyn, or In-a-Dyn, is a small and simple Dynamic DNS, DDNS, client with HTTPS support. Commonly available in many GNU/Linux distributions, used in off the shelf routers and Internet gateways to automate the task of keeping your Internet name in sync with your public¹ IP address. It can also be used in installations with redundant (backup) connections to the Internet.

Most people are unaware they share a pool of Internet addresses with other users of the same Internet Service Provider (ISP). Protocols like DHCP, PPPoE, or PPPoA are used to give you an address and a way to connect to the Internet, but usually not a way for others to connect to you. If you want to run an Internet server on such a connection you risk losing your IP address every time you reconnect, or as in the case of DHCP even when the lease is renegotiated.

By using a DDNS client like inadyn you can register an Internet name with a DDNS provider, like FreeDNS. The DDNS client updates your DNS record periodically and/or on demand when your IP address changes. Inadyn can maintain multiple host records with the same IP address, use a combination of a script, the address from an Internet-facing interface, or default to using the IP address change detector of the DDNS provider.

¹ Public IP address is the default, private addresses can also be used.

Supported Providers

Some of these services are free of charge for non-commercial use, some take a small fee, but also provide more domains to choose from.

The following tier-one providers have dedicated "plugins", even though many share the original DynDNS plugin. Below is a list of known DDNS providers, ordered by the plugin that support them:

DDNS providers not supported natively can be enabled using the custom, or generic, DDNS plugin. E.g. See below for configuration examples.

In-A-Dyn defaults to HTTPS, but not all providers may support this, so try disabling SSL for the update (ssl = false) or the checkip phase (checkip-ssl = false) in the provider section, in case you run into problems.

HTTPS is enabled by default since it protects your credentials from being snooped and reduces the risk of someone hijacking your account.


In-A-Dyn supports updating several DDNS servers, several accounts even on different DDNS providers. The following /etc/inadyn.conf example show how this can be done. To verify your configuration, without starting the daemon, use:

inadyn --check-config

This looks for the default .conf file, to check any file, use:

inadyn --check-config -f /path/to/file.conf


# In-A-Dyn v2.0 configuration file format
period          = 300
user-agent      = Mozilla/5.0

# The FreeDNS username must be in lower case
# The password (max 16 chars) is case sensitive
provider freedns {
    username    = lower-case-username
    password    = case-sensitive-pwd
    hostname    =

# We override checkip server with the In-a-dyn built-in 'default',
#, for details on this, see below.
provider freemyip {
    password       = YOUR_TOKEN
    hostname       =
    checkip-server = default

provider dyn {
    ssl         = false
    username    = charlie
    password    = snoopy
    hostname    = { peanuts, woodstock }
    user-agent  = Mozilla/4.0

provider {
    username         = YOUR_TOKEN
    password         = noPasswordForDuckdns
    hostname         =

# With multiple usernames at the same provider, index with :#
provider {
    username    = ian
    password    = secret
    hostname    =
    user-agent  = inadyn/2.2

# With multiple usernames at the same provider, index with :#
provider {
    username       = james
    password       = bond
    hostname       =
    checkip-ssl    = false
    checkip-server =

# With multiple usernames at the same provider, index with :#
provider {
    username        = spaceman
    password        = bowie
    hostname        =
    checkip-command = "/sbin/ifconfig eth0 | grep 'inet6 addr'"

# Google Domains - notice use of '@' to update root entry
provider {
    hostname =
    username = your_username
    password = your_password

# Wildcard subdomains - notice the quotes (required!)
provider {
    hostname = "*"
    username = your_username
    password = your_password

# Note: hostname == update-key from Advanced tab in the Web UI
provider {
    username    = futurekid
    password    = dreoadsad/+dsad21321    # update-key-in-advanced-tab
    hostname    = 1234534245321           # tunnel-id

# update using a custom checkip-command, which works
# if you have access to an Internet-connected interface.  Make
# sure to verify the command works on your system first
allow-ipv6 = true                # required option for IPv6 atm.
provider {
    username = your_token
    password = not_used
    hostname = {, }
    checkip-command = "/sbin/ip -6 addr | grep inet6 | awk -F '[ \t]+|/' '{print $3}' | grep -v ^::1 | grep -v ^fe80"

provider {
    username = your_api_key
    password = your_secret_key
    hostname =

provider {
     username = your_api_id
     password = your_api_token
     hostname =

# Create a unique custom API token with the following permissions:
# -> Zone.Zone - Read, Zone.DNS - Edit.
provider {
    username =
    password = api_token_important_read_comment
    hostname =
    ttl = 1 # optional, value of 1 is 'automatic'.
    proxied = false # optional.

provider {
    username =
    password = user.password
    hostname =

Notice how the config has three different users of the No-IP provider -- this is achieved by appending a :ID to the provider name.

We also define a custom cache directory, default is to use /var/cache. In our case /mnt is a system specific persistent store for caching your IP address as reported to each provider. Inadyn use this to ensure you are not locked out of your account for excessive updates, which may happen if your device Internet gateway running inadyn gets stuck in a reboot loop, or similar.

However, for the caching mechanism to be 100% foolproof the system clock must be set correctly -- if you have issues with the system clock not being set properly at boot, e.g. pending receipt of an NTP message, use the command line option --startup-delay=SEC. To tell inadyn it is OK to proceed before the SEC timeout, use SIGUSR2.

The last system defined is the IPv6 service provided by Hurricane Electric. Here hostname is set to the tunnel ID and password must be the Update key found in the Advanced configuration tab.

Note: the checkip-command for dynv6, above, is just one way to do it. Here's another variant, from their own script: ip -6 addr list scope global $device | grep -v " fd" | sed -n 's/.*inet6 \([0-9a-f:]\+\).*/\1/p' | head -n 1

Sometimes the default checkip-server for a DDNS provider can be very slow to respond, to this end In-a-dyn now support overriding it with a custom one, or a custom command. The easiest way to change it is to set checkip-server = default, triggering In-a-dyn to use, which it also use for custom DDNS providers. See the man pages, or the below section, for more information.

Some providers require using a specific browser to send updates, this can be worked around using the user-agent = STRING setting, as shown above. It is available both on a global and on a per-provider level.

NOTE: In a multi-user server setup, make sure to chmod your .conf to 600 (read-write only by you/root) to protect against other users reading your DDNS server credentials.

Custom DDNS Providers

In addition to the default DDNS providers supported by Inadyn, custom DDNS providers can be defined in the config file. Use custom {} in instead of the provider {} section used in examples above.

In-A-Dyn use HTTP basic authentication (base64 encoded) to communicate username and password to the server. If you do not have a username and/or password, you can leave these fields out. Basic authentication, will still be used in communication with the server, but with empty username and password.

A custom DDNS provider can be setup like this:

custom example {
    username       = myuser
    password       = mypass
    checkip-server =
    checkip-path   = /
    ddns-server    =
    ddns-path      = "/update?hostname="
    hostname       =

The following variables can be substituted into the configuration:

 %u - username
 %p - password, if HTTP basic auth is not used
 %h - hostname
 %i - IP address

For it can look as follows. Notice how the hostname syntax differs from above:

custom namecheap {
    username    = YOURDOMAIN.TLD
    password    = mypass
    ddns-server =
    ddns-path   = "/update?domain=%u&password=%p&host=%h&ip=%i"
    hostname    = { "@", "www", "test" }

Here three hostnames are updated, one HTTP GET update request for every listed hostname. Some providers, like FreeDNS, support setting up CNAME records (aliases) to reduce the amount of records you need to update. FreeDNS even default to linking multiple records to the same update, which may be very confusing if you want each DNS record to be updated from a unique IP address -- make sure to check your settings at the DDNS provider!

The generic plugin can also be used with providers that require the client's new IP address in the update request. Here is an example of how this can be done if we pretend that is not supported by inadyn. The ddns-path differs between providers and is something you must figure out. The support pages sometimes list this under an API section, or similar.

# This emulates
custom dyn {
    username    = DYNUSERNAME
    password    = DYNPASSWORD
    ddns-server =
    ddns-path   = "/nic/update?"
    hostname    = { YOURHOST, alias }

Here a fully custom ddns-path with format specifiers are used, see the inadyn.conf(5) man page for details on this.

Another example:

# Custom configuration for dnsmadeeasy
custom dyn {
    ddns-server =
    ddns-path   = "/servlet/updateip?username=%u&password=%p&id=DNSMADEEASYHOSTID&ip=%i"
    hostname    = HOST

When using the generic plugin you should first inspect the response from the DDNS provider. By default Inadyn looks for a 200 HTTP response OK code and the strings "good", "OK", "true", "success", or "updated" in the HTTP response body. If the DDNS provider returns something else you can add a list of possible ddns-response = { Arrr, kilroy }, or just a single ddns-response = Cool -- if your provider does give any response then use ddns-response = "".

If your DDNS provider does not provide you with a checkip-server, you can use other services, like, which is the default if you do not specify one for your custom provider config:

checkip-server =

or even use a script or command:

checkip-command = /sbin/ifconfig eth0 | grep 'inet addr'

These two settings can also be used in standard provider{} sections.

Note: hostname is required, even if everything is encoded in the ddns-path! The given hostname is appended to the ddns-path used for updates, unless you use the append-myip setting, in which case your IP address will be appended instead. When using append-myip you probably need to encode your DNS hostname in the ddns-path instead, as is done in the last example above.

Build & Install


For a long time, the project maintained its own .deb packaging and basic apt infrastructure. However, the increasing level of features in In-a-dyn, and thus amount of dependencies, as well as the demands for supporting more architectures and different distributions, the pre-built .deb support has been discontinued as of v2.9.1.

The Debian project now has an active maintainer for inadyn, which is the upstream for Ubuntu and others. Please report issues and requests to your respective distribution:

Note: the project's packaging files have been moved to a separate debian branch in the GIT repository. It is not actively updated or supported for releases. To use it, check out the branch and edit debian/changelog) to build new .deb files for your system.


Automatically built images available here:

A Dockerfile is provided to simplify building and running inadyn.

docker build -t inadyn:latest .
docker run --rm -v "$PWD/inadyn.conf:/etc/inadyn.conf" inadyn:latest

How to update ip periodically using cronjob :

  • Create your inadyn.conf file
  • Create folder for cache
  • Add the following line inside crontab crontab -e
* * * * * docker run --rm -v "path/to/inadyn.conf:/etc/inadyn.conf" -v "path/to/cache:/var/cache/inadyn" troglobit/inadyn:latest -1 --cache-dir=/var/cache/inadyn > /dev/null 2>&1

Homebrew (macOS)

To run the latest stable version on macOS, type:

brew install inadyn

To run the latest version from the master branch, install the git tap instead:

brew install --HEAD troglobit/inadyn/inadyn

Either of these will install all dependencies.

Building from Source

First download the latest official In-A-Dyn release from GitHub:

In-A-Dyn requires a few libraries to build. The build system searches for them, in their required versions, using the pkg-config tool:

They are available from most UNIX distributions as pre-built packages. Make sure to install the -dev or -devel package of the distribution packages when building Inadyn. On Debian/Ubuntu (derivatives):

$ sudo apt install gnutls-dev libconfuse-dev

To build you also need a C compiler, the pkg-config tool, and make:

$ sudo apt install build-essential pkg-config

When building with HTTPS (SSL/TLS) support, make sure to also install the ca-certificates package on your system, otherwise Inadyn will not be able to validate the DDNS provider's HTTPS certificates.

Configure & Build

The GNU Configure & Build system use /usr/local as the default install prefix. In many cases this is useful, but this means the configuration files and cache files will also use that same prefix. Most users have come to expect those files in /etc/ and /var/run/ and configure has a few useful options that are recommended to use:

$ ./configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var
$ make -j5
$ sudo make install-strip

You may want to remove the --prefix=/usr option.

SSL/TLS Support

By default inadyn tries to build with GnuTLS for HTTPS support. GnuTLS is the recommended SSL library to use on UNIX distributions which do not provide OpenSSL/LibreSSL as a system library. However, when OpenSSL or LibreSSL is available as a system library, for example in many embedded systems:

./configure --enable-openssl

To completely disable inadyn HTTPS support (not recommended!):

./configure --disable-ssl

For more details on the OpenSSL and GNU GPL license issue, see:

Static Build

Some people want to build statically, to do this with autoconf add the following LDFLAGS= after the configure script. You may also need to add LIBS=..., which will depend on your particular system:

./configure LDFLAGS="-static" ...

RedHat, Fedora, CentOS

On some systems the default configure installation path, /usr/local, is disabled and not searched by tools like ldconfig and pkg-config. So if configure fails to find the libConfuse libraries, or the .pc files, create the file /etc/ with this content:


update the linker cache:

sudo ldconfig -v |egrep libconfuse

and run the Inadyn configure script like this:

PKG_CONFIG_PATH=/usr/local/lib/pkgconfig ./configure

Integration with systemd

For systemd integration you need to install pkg-config, which helps the Inadyn build system figure out the systemd paths. When installed simply call systemctl to enable and start inadyn:

$ sudo systemctl enable inadyn.service
$ sudo systemctl start  inadyn.service

Check that it started properly by inspecting the system log, or:

$ sudo systemctl status inadyn.service

To stop the service:

$ sudo systemctl stop   inadyn.service

Embedded applications

When built into a router, some features aren't usually used and can be disabled to save space. The configure option --enable-reduced will build such a reduced-functionality binary. Currently, this disables verbose log messages and error strings and eliminates config file checking & some backward compatibility.

Building from GIT

If you want to contribute, or simply just try out the latest but unreleased features, then you need to know a few things about the GNU build system:

  • and a per-directory are key files
  • configure and are generated from, they are not stored in GIT but automatically generated for the release tarballs
  • Makefile is generated by configure script

To build from GIT; clone the repository and run the script. This requires the GNU tools automake, autoconf and libtool to be installed on your system. Released tarballs do not require these tools.

$ sudo apt install git automake autoconf

Then you can clone the repository and create the configure script, which is not part of the GIT repo:

git clone
cd inadyn/
./configure && make

Building from GIT requires, at least, the previously mentioned library dependencies. GIT sources are a moving target and are not recommended for production systems, unless you know what you are doing!

Origin & References

This is the continuation of Narcis Ilisei's original INADYN. Now maintained by Joachim Wiberg. Please file bug reports, or send pull requests for bug fixes and proposed extensions at GitHub.

A personal Thank you! goes out to Robert Högberg, who sponsored a little D-Link DIR-645 router so I could get back on the interwebs :-)