The standard IRC client is the original ircII client. It's part of most Linux distributions.
It's easy to use ircII. Let's say you want to connect to irc.openprojects.net with the nick mini-HOWTO.
At the command line, type:
$ irc mini-HOWTO irc.openprojects.net
You can also export variables so you won't need to use them at the command line:
$ export IRCNICK=mini-HOWTO IRCSERVER=irc.openprojects.net
Add them to your shell profile (e.g. ~/.bash_profile or ~/.zprofile) when you're done.
Other common variables are IRCNAME and IRCUSER, to respectively
set the ircname part of a /whois and username as seen at the first line
'mini-HOWTO is ~username@hostname (IRCNAME)'. Keep in mind that IRCUSER
won't work if you run an ident daemon (default on most distributions).
If you still need to change your username (not recommended, and I hope
you're not using IRC logged as root!), install oidentd from http://ojnk.sourceforge.net/,
create /etc/identd.spoof with a list of users allowed to spoof their
ident, and ~/.ispoof with their reply (e.g. reply). Finally run
'/usr/local/sbin/oidentd -g nobody -N -s -u nobody'. Add this to your
startup scripts (e.g. /etc/rc.d/rc.local) when you're done.
If not set, IRCNICK, IRCUSER, and IRCNAME will be retrieved from /etc/passwd .