Best of Technical Support

Our experts answer your technical questions.
SSH Won't Let Me In

I've installed Red Hat 7.3 and Red Hat 8.0, and when I use SSH I get an error that says “Connection Refused”. I can SSH on either machine to itself, but not from another machine. I've shut off the iptables service, and I've made sure that in /etc/xinetd.d/telnet the line disable=no is present. I've done a netstat -t | grep telnet and netstat -t | grep ssh, and they tell me that these services are running.

—Robert Haack, haack@nclack.k12.or.us

Check to be sure you can ping from one box to the other. If so, use a tool such as Nmap to verify that the port appears to be open end-to-end from one system to the other.

—Chad Robinson, crobinson@rfgonline.com

Look at /var/log/messages or /var/log/auth.log, which should show you why SSH is dropping the connection. Odds are your machine checks the reverse DNS mapping for your IP addresses and fails. One way to fix that is to populate /etc/hosts with the IP and hostnames of your machines.

—Marc Merlin, marc_bts@google.com

Check the /etc/hosts.allow and add sshd: ALL (or the IP address of the remote machine), because this is probably the reason you can connect locally but not from another machine.

—Mario Bittencourt, mneto@argo.com.br

SSH does everything Telnet does and more, and uses encryption, so you should leave the obsolete Telnet service off. Especially now that wireless networks are everywhere, you can't afford to reveal your password on the Net. You're right to use netstat to check for a listening SSH dæmon; however, you need to add the -a option. Do this:

$ netstat -at | grep ssh

And look for a line that looks like:

tcp  0 0 *:ssh  *:*   LISTEN

to see that sshd is listening for incoming connections.

—Don Marti, dmarti@ssc.com

If the SSH dæmon isn't running, start it with service sshd start or set it to come up automatically with:

chkconfig --level 2345 sshd on

—Felipe E. Barousse Boué, fbarousse@piensa.com

Modem Lights Won't Let Me Log Off

I can use the Modem Lights applet in Red Hat 8.0 to establish a PPP connection, but I can't use it for disconnecting. When I press the button a second time in order to disconnect, I'm once again confronted with the question “Do you want to connect?” If I answer No, nothing happens. If I answer Yes, I get disconnected and then connected again. How can I configure Modem Lights to do what it's actually supposed to do?

—Martin A. Boegelund, goblin@linuxmail.org

The default setup is the problem here. In the Preferences window for the Modem Lights applet, you will find an Advanced tab. Click it, then set the modem lock file appropriately. Try setting it to /var/lock/LCK..modem.

—Ben Ford, ben@kalifornia.com

Dual-Boot Hangs on Install

I just bought a Compaq Presario 1516US, and it came with Microsoft Windows XP. I partitioned the hard drive using Partition Magic, and when I put in the Red Hat 8.0 install CD it goes through the initial checking screen. When it gets to the following it hangs:

Partition Check:
 hda:

The cursor only blinks and nothing happens.

—Avran, idontlikemail@earthlink.net

This page has a useful tutorial on how to set up the Linux GRUB boot loader to handle a dual-boot system on machines that have Windows installed before Linux: www.geocities.com/epark/linux/grub-w2k-HOWTO.html.

—Felipe E. Barousse Boué, fbarousse@piensa.com

No repartitioning tool is 100% foolproof. All of them warn you to do a good backup first. Dual-boot is an inefficient way to work, because the application you need always seems to be on the other OS. But if you are going to dual-boot, make sure you have a good backup of your original OS and can restore it.

—Don Marti, dmarti@ssc.com

SMP System Won't Power Off

I am running Red Hat 8 with SMP. I have noticed that when I am running the kernel for a single processor the system powers off normally. If I select the SMP kernel during boot and then shut down, however, the system will shut down all processes and then produce the prompt to shut power off. My question is, why doesn't the system power off automatically when using SMP?

—Ron Oliva, rmoliva@citlink.net

Power off uses an APM call on Linux, but APM is unsafe in SMP mode, so Linux disables it. There is one command you give to the kernel to enable just enough APM to allow for power off. With newer kernels, add this to your append= line in lilo or grub:

apm=power-off

—Marc Merlin, marc_bts@google.com

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