You should know that I only recommend doing this on systems that you ABSOLUTELY trust. If you have any doubt what so ever, do NOT continue.

I never thought i’d actually need this but i ended up actually providing it as a solution for securing database accounts.

To get this working on CentOS 5, I had to do the following

# yum install xinetd authd

authd is an xinetd service and authd is the RFC 1413 identd service

Out of the box, authd comes a little more secure than I expected. It’s not bad but it’s definitely a hindrance for other systems when they don’t know what to send.

/etc/xinetd.d/auth will come by default with

server_args = -t60 --xerror --os -E


This tells inetd to expect the ‘uname’ instead of ‘UNIX’ as the OS name. It’s great that it offers this option but I don’t know if all identd clients need to know what OS it is. You can leave it in if you like. Lastly, it tells identd to encrypt the username and then send it. I’m not sure how many identd clients can handle that.

I changed it to


server_args = -t60 --xerror


start or restart xinetd and you should see 113 listening.

I’m a lazy guy so I can’t be bothered to open more than one connection to a server. You can open two if you prefer.

I login and start tcpdump


tcpdump -i lo -nn "port 113" &
telnet localhost 113


It should show you distinctly what port two ports are involved in the connection you just made.

IP 127.0.0.1.SOURCE_PORT_NUM > 127.0.0.1.113

Next type in “SOURCE_PORT_NUM,113″ and hit Enter. Note that “SOURCE_PORT” here is a NUMBER not actually “SOURCE_PORT”

Amidst all the messy tcpdump output, you should see a line

SOURCE_PORT_NUM , 113 : USERID : UNIX :root

That shows you that identd is working properly. At least locally.

So if you ever find any of this useless knowledge helpful, let me know.

Unix/Linux admins are taught to hate identd because it’s pretty much the least secure protocol but I have to believe that it has a place in an environment that is completely trusted. You don’t have random users logging in or random accounts being created.

I think the overall advantage here is that you can use this to provide an additional layer of security across your trusted enterprise.