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You could use the 'ifconfig -a' from the cli to see if the device is there, even if down. You could then use the 'ifconfig eth0 up' if the device was shown in the previous command. If you don't have a recognized device the issue of the command won't produce results.
If the 'eth0' device is not recognized you could use the commands 'dmesg |grep -i eth';
# dmesg |grep -i eth0
eth0: Broadcom 44xx/47xx 10/100BaseT Ethernet 00:19:b9:51:81:1a
To see if the system even recognized the device. If not then you will need to find out which device is available on your system with a 'lspci -vv';
~# lspci -vv |grep -i ethernet
08:00.0 Ethernet controller: Broadcom Corporation BCM4401-B0 100Base-TX (rev 02)
Once you have identified the device then you would need to be sure that your kernel supports the device. If you are lucky then the driver is available for your use. You could then use the 'modprobe device_driver' to load the driver module. Once you issue the 'modprobe' command for the device, any other necessary modules that associate with the driver will be loaded. You could see the modules with the 'lsmod' command.
You can 'man command' to get a better understanding of the above commands.
Just a few links to aid you;
Linux Documentation Project
Rute Tutorial & Exposition
Linux Command Guide
Utimate Linux Newbie Guide
Getting Started with Linux
Advanced Bash-Scripting Guide
Linux Home Networking
The above links and others can be found at 'Slackware-Links
'. More than just SlackwareŽ links!