Best of Technical Support

Our experts answer your technical questions.
Network config Tools

In Windows NT there is a command-line utility (ipconfig) that lets you see the current ip configuration. Is there a utility in Linux for this? —Skip Bigelow, sbigelow@aarp.org

Even though there are graphical tools to give the information you've asked (including Red Hat's netcfg command), you can always use /sbin/ifconfig. It will give you detailed information regarding all active interfaces (ethernet, ppp, loopback etc.). —Mario, mneto@argo.com.br

Sharing a Cable Modem

I have been browsing many different Linux web sites to look for any FAQ or guide on this topic: How to share a cable modem connection at home between a Linux and a Windows machine, which is where the cable modem installed. I would appreciate it if you would give me some pointers. —Samuel Fung, samfz@hotmail.com

I would move the cable modem to the Linux machine and share it with your other computers from there. Why? Because Windows has no provision, off the shelf, to serve as a router, enable security features such as packet filtering, masquerading, forwarding, etc., while Linux does all that quite naturally and quite well. You do not specify the cable modem you have, but I would suggest looking at http://www.linuxdoc.org/ for documents on networking and connecting network devices to your Linux box. After that, look at the how-to articles on connecting to an ISP. —Felipe Barousse, fbarousse@piensa.com

Booting without Messages

Is it possible to turn off the kernel boot-up messages? —Nicholas, vunch@pacific.net.sg

The easiest way is to set console=ttyS3,38400n8, or something similar, on the LILO command line to redirect console output to a serial port. —Marc Merlin, marc_bts@valinux.com

Root Compromise

When I tried to log in to my Linux box this morning, I was surprised to find out that I was no longer able to do this. The login prompt appears as usual, but when I type the user name and press Enter, instead of the password prompt a new login prompt appears. No messages appear except a line that says: /var/hackr0x/login: No such file or directory. This line disappears so quickly that I had to repeat the procedure of typing the user name a couple of times in order to decipher it. —Victor, victor@angolatelecom.com

Your machine was indeed compromised. At this point you don't want to fix your machine, you just want to get your data off and re-install it. You don't know what's been modified nor how. In cases where you can't log in at all, you can always boot with linux init=/bin/bash at the LILO prompt, and then do: mount -wno remount/mount -a /etc/rc.d/init.d/network start (if you want to back up data over the Net). You can also boot from a rescue floppy or CD. Once you get your machine re-installed, do not just connect it to the Internet again without securing it properly. Make sure you have all the updates installed; do not run any unnecesary dæmons, and firewall the machine if possible. —Marc Merlin, marc_bts@valinux.com

Every major distribution has an “announce” list for security updates. After you reinstall, get on the list for the distribution you run. Also, remove unused software—it's the cheapest, fastest security precaution you can take. —Don Marti, dmarti@linuxjournal.com

Slash Notation for Netmasks

Nowadays I'm working with Linux firewalls, and I'm configuring one in a client organization. I found the following lines in the script that applies the rules of the firewall (IPCHAINS):

INT0="eth0"
IP0="192.168.1.125/24"
NET0="192.168.1.0"

What is “/24” in the IP number?

Also can I put two networks in the same variable? For example:

NET0="192.168.1.0,192.168.10.0"

—Fabio Losnak, fabiolosnak@yahoo.com

The “/24” in the IP number means the network 192.168.1.0 with a netmask of /24 or 255.255.255.0. You probably cannot put two networks in the same variable but that would really depend on the script that is parsing this. —Marc Merlin, marc_bts@valinux.com

Can't Unlink Files

As root, I cannot get rid of the following files; they should belong to the deb package r-base, but in this case they seem to be some kind of links:

pimento:/home/ottoz# ls -l /usr/lib/R/library/ts/latex/
........
br-xr-srw-    1 25955    26473    116,  32 mar 20  1987 beavers.tex
br-xrwSr--    1 8301     31084    114,  32 ott 12  2021 sunspot.tex
br-srw-rw-    1 29281    8302     116, 108 set 27  2031 ts.union.tex

I get a message like cannot unlink. operation not permitted —Odoardo Zecca, odoardo.zecca@galactica.it

You had some file system corruption. chattr -i *.tex should remove the incorrectly set immutable flag and let you delete the files. —Marc Merlin, marc_bts@valinux.com

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