Best of Technical Support

Our experts answer your technical questions.
Restricting E-Mail Accounts with Sendmail

I have a mail server (RH 6.2, Sendmail Single Switch) acting as a smart relay on our DMZ. Internally, we have a mail server (RH 7.0, Sendmail Single Switch) that acts as both an SMTP and POP3 server.

We need to be able to differentiate between local-only and WAN e-mail accounts. Local-only accounts would be limited to local delivery/receipt and WAN accounts would be granted access to the world for inbound and outbound mail.

To further complicate matters, all users should have the format of for e-mail addresses. Is there a method of doing this within the capabilities of Sendmail or, if not, what package(s) will allow me to do this? —Michael Phillips,

There are many approaches to solve your riddle. For instance, an easy one would be to restrict e-mail relaying with the /etc/mail/access file on an client IP address basis. Your actual request is not a complex one, you just need a bit of a planning on your network layout, the addressing scheme and a bit of tuning on the Sendmail side. Go to the site and look for all relaying-related documents. That will help you solve your requirements. —Felipe Barousse,

Telnet Sessions Time Out

Is there a Telnet time-out setting on Linux? My sessions time out after about five minutes. —Jan Dubroca,

You are probably Telneting outside of your network, through an IP masquerading server that times out TCP connections after five minutes. On Linux, the fix for this (on the firewall) is:

# Fix the masquerading timeouts
#                  tcp     tcpfin  udp
ipchains -M -S     86400   60      120

—Marc Merlin,

I don't believe that there is a tim-eout setting for Telnet. I assume that what's timing out is your shell. The shell time-out can be set in /etc/profile. My guess is you've got an entry that looks something like this:


The value here is in seconds. You can change this to give yourself more time or simply remove the line to disable shell time-out completely. —Paul Christensen,

Loading vmlinuz, Then Nothing

I used Red Hat 6.0 to install Linux. I booted the machine from CD-ROM successfully, and I pressed Enter after boot: This message appeared:

Loading initrd.img.....................
Loading vmlinuz........

Then the computer stopped.

When I booted my computer from the floppy disk (Win98 bootdisk), I ran the /dosutils/autoboot from the Red Hat CD-ROM. Unexpected, it appeared that I had installed Linux successfully and even configured the X Windows System well. In the end, the computer told me:

Congratulations, you have installed linux successfully,......
The system reboot....

And when it rebooted, this message appeared:

Loading linux..........
Then the computer stopped again.

I have also tried Red Hat 5.0, Bluepoint1.0 and 2.0, TurboLinux, Slackware. The results were all the same. WHY? —ekun,

Apparently, you can boot Linux from loadlin (which you did when you started the Linux install from Windows), but, for some unknown reason, it fails when you boot with LILO. One option is to do an install from Windows, like you already did, and then boot from the RH rescue CD-ROM. Copy your kernel (in/boot) to the Windows partition (which you will need to mount too). Copy and configure loadlin (you should have them on your RH CD-ROM), and use loadlin to boot Linux. A sample loadlin config from my system looks like this:

moremagic:/drv/c$ cat linux.bat
c:\linux\loadlin\loadlin @c:\linux\loadlin\boot
moremagic:/drv/c$ cat linux/loadlin/boot

—Marc Merlin,

I've seen this happen as the result of booting a kernel that's optimized for the wrong processor, but if this is happening right away after a fresh install (in fact, after EVERY install of any of a number of distributions) you most likely have a serious hardware problem. You should try different RAM if you have any available. I can't say for sure that the RAM is the culprit, but that's where I'd start. —Robert Connoy,

Recompiling the Kernel

I have installed an IDE Atapi Zip drive and need to know how to have Linux to find it. I have tried to recompile but get the following error:

Makefile Makefile: 213 arch/i386/Makefile:
No such file or directory
Makefile: 481 Rule make: No such file or directory
make *** No rule to make target Rules.make. Stop

—Bob Parry,

Did you read README in /usr/src/linux? You compile a kernel like this:

make menuconfig; make clean; make dep;
make install; make modules; make modules_install

More details can also be found here: If you already have the right module compiled, modprobe ide-floppy should do the trick. —Marc Merlin,