Solved

Servers started by inetd.

Posted on 1998-11-30
2
278 Views
Last Modified: 2010-04-21
If you have a service defined in /etc/services, and inetd fires up your server when a requested arrives on your port, file descriptors 0, 1 and 2 are available to the server process. As sockets are bidirectional, which ones do we use for send/recv? Should I be using 0 for recv and 1 for send? I have tried using only 0 and it works fine. But why have 0,1 and 2 as socket descriptors as we need only one socket descriptor for operations.

Please e-mail me at vividh@hotmail.com

Thanks in advance.

Vividh
0
Comment
Question by:vividh
2 Comments
 
LVL 51

Accepted Solution

by:
ahoffmann earned 100 total points
ID: 2008168
0 is STDIN, 1 is STDOUT and 2 is STDERR
This is a standard, somehow, in UNIX ;-)
0
 
LVL 2

Expert Comment

by:seedy
ID: 2008169
The inet daemon accepts the connection(if it is stream socket), forks and the child process handles the service request.  The child closes all file descriptors other than the accepted socket descriptor, calls dup2 to duplicate the accepted socket descriptor on to file descriptors 0,1 and 2.  The original socket descriptor is also then closed.  Doing this the only file descriptors that are open in the child are 0,1 and 2.  It does few other stuff related to security, and then does an exec to the execute the appropriate server-program to handle the request.

As said above 0,1 and 2 are the same physical socket connection.  I guess the reason may be to provide flexibility in writing your server.  You do not have to use 0 for recv and 1 for send; though it may not hurt either.
0

Featured Post

Gigs: Get Your Project Delivered by an Expert

Select from freelancers specializing in everything from database administration to programming, who have proven themselves as experts in their field. Hire the best, collaborate easily, pay securely and get projects done right.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Attention: This article will no longer be maintained. If you have any questions, please feel free to mail me. jgh@FreeBSD.org Please see http://www.freebsd.org/doc/en_US.ISO8859-1/articles/freebsd-update-server/ for the updated article. It is avail…
My previous tech tip, Installing the Solaris OS From the Flash Archive On a Tape (http://www.experts-exchange.com/articles/OS/Unix/Solaris/Installing-the-Solaris-OS-From-the-Flash-Archive-on-a-Tape.html), discussed installing the Solaris Operating S…
Learn how to find files with the shell using the find and locate commands. Use locate to find a needle in a haystack.: With locate, check if the file still exists.: Use find to get the actual location of the file.:
This video shows how to set up a shell script to accept a positional parameter when called, pass that to a SQL script, accept the output from the statement back and then manipulate it in the Shell.

776 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question