YoctoIRCd

YoctoIRCd is an extremely minimalistic IRC server with only one purpose: send the MOTD to clients that connect to it and disconnect them immediately. Its intended use is for servers that listen on SSL-only; YoctoIRCd can provide a (non-SSL) message informing users trying to connect on the default port that they'll have to use a different port with SSL enabled. It also makes a good fallback server that can relay messages about downtime, etc. while the main IRC server is down. It also has an extremely simple (read: non-standard-compliant) HTTP server that just sends the MOTD and disconnects, as well. The HTTP server can be disabled, in which case it won't be compiled at all.

Requirements

YoctoIRCd requires a C compiler to build, and nothing but the C standard library and a POSIX environment to run. YoctoIRCd officially supports FreeBSD and Linux, but should run in any other POSIX-ish environment. Windows is not supported.

Compiling

To compile YoctoIRCd, download it and run make in the folder where you have the source. By default, yoctoircd will be built in release mode. See the "Debugging" section for information about creating a debug build.

For advanced users, you can edit some compile-time configuration in config.h. This is where you can disable the HTTP server as well as changing buffer sizes and tweak how other internals work.

If for whatever reason you do not have make on the system where you're trying to compile YoctoIRCd, you can compile it with something similar to cc -Os -o yoctoircd src/*.c in the folder where the source is.

Configuring

A sample configuration for YoctoIRCd is provided as yoctoircd.cfg. You should copy it with a different name (so it doesn't get overwritten on updates) before editing it. The sample configuration file is documented, but for convenience, here are the configuration options available:

• Port: The TCP port to listen on
• Timeout: The maximum amount of time a client can be connected (in seconds)
• MotdPath: The path to the file containing the MOTD
• ServerAddress: The address of the server (no spaces)
• ServerName: The nickname of the server
• ChrootFolder: The folder to chroot into (optional, requires root)
• SetUser: The user to setuid to (optional, requires root)
• SetGroup: The group to setgid to (optional, requires root)

NOTE: The configuration parser is quite strict; comments (beginning with #) must start at the beginning of the line and any unrecognized option will cause an error.

Running

Just run ./yoctoircd $PATH_TO_CONFIG, replacing $PATH_TO_CONFIG with the path to the configuration file you created.

Updating the MOTD

You can update the MOTD without stopping YoctoIRCd. To do so, update the MOTD file that your configuration file points to, then send a SIGUSR1 signal to YoctoIRCd. To do so, you can use the one-liner killall -USR1 yoctoircd. The child processes will ignore SIGUSR1, but the parent process will reload the MOTD when it recieves the signal.

Updating the Configuration File

You can update the configuration file without stopping YoctoIRCd, just like updating the MOTD. Instead of sending SIGUSR1, send SIGUSR2 in the exact same manner.

NOTE: You cannot update the port that YoctoIRCd listens on or any security options (ChrootFolder, SetUser, and SetGroup) with SIGUSR2. You must restart YoctoIRCd. You can, however, change the path to the MOTD file. YoctoIRCd will update the MOTD automatically, as well.

Security

Though I've done my best to eliminate bugs, it's impossible to get rid of all of them. That being said, it's possible that some of the bugs may cause security flaws. I've been extra careful to avoid those kinds of bugs, but it's still best to err on the side of caution.

YoctoIRCd supports chroot, setuid, and setgid through configuration options. For the best security, you should create a user and group just for YoctoIRCd, create a folder with the configuration file and the MOTD (and nothing else), set the folder and files read-only for YoctoIRCd, then set ChrootFolder to that folder, and SetUser and SetGroup to that user and group. For those options to work, however, you will need to run yoctoircd as root. If you do so, it will drop to the specified user and group as soon as possible. If you have set those security options, but don't run yoctoircd as root, it will cause an error and refuse to run because it will be unable to use chroot, setuid, and setgid.

How It Works

YoctoIRCd forks a child process for each connection. Each child process sets an alarm to go off after the timeout has been reached, which will close the connection and kill the process. Because the child process does not write to that much memory, the forking should be fairly inexpensive on COW systems, such as Linux. Even on systems that don't have COW forking, YoctoIRCd's memory usage is low enough that forking shouldn't have an excessively large overhead. A threaded mode may be added in the future.

Debugging

To produce a debug build, first set your CFLAGS to enable debug information. For example, if you're using bash and gcc, run export CFLAGS="-ggdb -O0" then make debug. It's important to both add debug flags to CFLAGS as well as using the debug target instead of the default release target. The release target runs strip over the built binary which strips all the debug information that the C compiler added. Also, setting your CFLAGS will remove the -DNDEBUG from the default CFLAGS, which will enable assertions.

License

As noted in the source files, YoctoIRCd is licensed under the Apache License, Version 2.0. A copy of the license is also available in the source distribution, named LICENSE.md. LICENSE.md is the plain-text version ported to Markdown, using the HTML version as a guide.

Donate

If you use YoctoIRCd and find it useful, it would be greatly appreciated if you donated to the project. Donations are primarily accepted through Flattr although other arrangements can be made by contacting me through GitHub if you don't want to use Flattr.