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Internet Automated Dynamic DNS Client

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Inadyn 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.

DDNS providers not supported natively like, can be enabled using the generic DDNS plugin. 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 {
    username   = lower-case-username
    password   = case-sensitive-pwd
    hostname   =

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

# 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'

# 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

provider {
    username = your_token
    password = n/a
    hostname = {, }

Notice how this configuration file has two 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.

Sometimes the default checkip-server for a DDNS provider can be very slow to respond, to this end Inadyn now supports overriding this server with a custom one, like for custom DDNS provider, or even a custom command. 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 DDNS provider like can be setup like this:

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

For DDNS can look as follows. Notice how the hostname syntax differs between these two DDNS providers. You need to investigate details like this yourself when using the generic/custom DDNS plugin:

custom namecheap {
    username    = myuser
    password    = mypass
    ddns-server =
    ddns-path   = "/update?domain=YOURDOMAIN.TLD&password=mypass&host="
    hostname    = { "alpha", "beta", "gamma" }

Here three hostnames are updated, one HTTP GET update request for every DDNS provider is performed, 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!

Your hostname is automatically appended to the end of the ddns-path, as is customary, before it is communicated to the server. Username is your Namecheap username, and password would be the one given to you in the Dynamic DNS panel from Namecheap. Here is an alternative config to illustrate how the hostname setting works:

custom kruskakli {
    username    = myuser
    password    = mypass
    ddns-server =
    ddns-path   = "/update?password=mypass&domain="
    hostname    = YOURDOMAIN.TLD

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.

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", 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 free services, like

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 append-myip 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

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.

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.

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 as a system library. However, when OpenSSL is available as a system library, for example in many embedded systems:

./configure --enable-openssl

To completely disable inadyn HTTPS support:

./configure --disable-ssl

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

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

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
  • Makefile is generated by configure script

To build from GIT you first need to clone the repository and run the script. This requires automake and autoconf to be installed on your system.

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 Nilsson. Please file bug reports, or send pull requests for bug fixes and proposed extensions at GitHub.