Linux Migration: Page 4 of 9

There are three file permissions on a Linux file system: read, write and execute, which are grouped into categories--owner, group and other. This is the file (or directory) mode. If you need more information on Linux file modes and how to change them, type man chmod.

Linux's network and service subsystems both get started at boot time. The good news is that these services are brought up using command-line utilities. This results in consistent behavior when you try to reproduce a problem--a process that fails at boot will almost surely fail later at the command line. Then you can fix the problem more easily because you can trace it, vary the command, and poke and prod until you figure it out.

Here's a simple example of assigning a static IP address to your Ethernet card: # ifconfig eth0 192.168.0.55 netmask 255.255.255.0. Essential information for DNS is stored in the file "/etc/resolv.conf."

Some Linux systems--most notably Red Hat--abstract this functionality in "service" system scripts, batch files that are in human-readable format. You can run these scripts manually, and if you're feeling adventuresome, you can view and edit them, too. The syntax for any Linux service is # service network [ start | stop | restart ] .

These scripts are in the "/etc/init.d" directory for your viewing pleasure. (Think of them as multiple AUTOEXEC.BAT files--one for each service.) Many network services get started this way, though some start via Xinetd, a server that listens on behalf of the program and invokes the program only when an incoming socket is opened (on some systems, an older version of Xinetd, called Inetd, is used). If you want to drill down deeper into how this works, try man xinetd or man inetd.