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Best of Technical Support Various Issue #35, March 1997

Various

Issue #35, March 1997

Our experts answer your technical questions.

Removing a Boot Manager

How can I remove the boot manager from the master boot block of my hard disk? —Ralph Wu

A Linux Solution

A backup copy of your MBR is stored in /boot when first installing LILO. You can restore it with:

dd if=/boot/boot.0300 of=/dev/hda bs=446 count=1     (IDE-Disk)
dd if=/boot/boot.0800 of=/dev/sda bs=446 count=1     (SCSI-Disk)

Klaus Franken, S.u.S.E. GmbH kfr@suse.de

A DOS Alternative

Find any MS-DOS boot disk with fdisk.exe on it. Execute fdisk with the undocumented parameter /mbr:

fdisk /mbr

It may appear not to work since this usage will return no messages and will exit immediately. It will overwrite your master boot record with a fresh copy, and LILO, Bootlin or whatever other boot manager you may be using will be gone.

Chad Robinson, BRT Technical Services Corporation chadr@brtgate.brttech.com

E-mail Error Message

I have a small network of Sun SPARC Solaris 2.4-based machines and a couple of Linux systems. The Suns use NIS+ and the Linux systems use /etc/hosts files to know about other hosts on the net. My problem is that I cannot send e-mail from a Linux system to another host. I have no problem when I am connected to the Internet using DNS to resolve host names. Why can’t sendmail resolve a host name from /etc/hosts? I have no problem with telnet or FTP, but sendmail always says unknown host.

—Tim Bower

Configuring Sendmail to Use DNS

Your sendmail must be configured to not use DNS.

If you use the m4-macros, try /usr/doc/packages/sendmail/cf/linux.smtp-nodns.mc:

include(`../m4/cf.m4')
VERSIONID(`linux for smtp-only without dns setup'dnl
OSTYPE(linux)
FEATURE(nouucp)dnl
FEATURE(always_add_domain)dnl
FEATURE(nodns)dnl
MAILER(local)dnl
MAILER(smtp)dnl

If you edit your /etc/sendmail.cf, try the following parameters:

# service switch file (ignored on Solaris, Ultrix, OSF/1, others) O ServiceSwitchFile=/etc/service.switch

# hosts file (normally /etc/hosts)
O HostsFile=/etc/hosts

Then you have to create a file /etc/service.switch:

hosts   files
aliases files

Klaus Franken, S.u.S.E GmbH kfr@suse.de

Modem Won’t Hang Up

We are attempting to set up a dial-in server for the Internet site at our community college. We are using Getty_ps and have it up and working fine but cannot figure out how to get the modems to hang up automatically when the user exits the system. Any suggestions on how we can accomplish this? –Barre BullPrince George’s Community College

Use Mgetty Instead

Getty-ps may be capable of what you are trying to do, but since you are using it specifically for modem dial-in lines, you should take a hard look at Mgetty. Mgetty is a getty replacement specifically designed for use with modems. It supports almost all of the capabilities that Getty-ps supports alone.

I recommend it since it is designed explicitly for a modem. You should find it much better suited to your task.

You can get Mgetty from any Sunsite mirror. You will find that it also has support for FAX and voice capable modems.

Chad Robinson, BRT Technical Services Corporation chadr@brttech.com

Root Password Won’t Change

I’ve just loaded Linux and I can’t add/change my root password. It says that I’m denied access, but when I do change attributes and reboot the system, the system defaults back to where it was: root access with no password protection.

—Dan Sapach

Try This

Have you possibly cleaned up files in your [cw]/etc[ecw] directory? Several files there are not meant to be cleaned up, and doing so will cause change-password attempts to fail. You should have /etc/passwd, /etc/passwd.OLD and /etc/passwd.old.

Also be sure your /usr/bin/passwd is setuid to root. If it isn’t, try:

chown root.bin /usr/bin/passwd
chmod 4711 /usr/sbin/passwd

Finally, make sure that only root can modify /etc/passwd:

chmod 644 /etc/passwd

Chad Robinson, BRT Technical Services Corporation chadr@brttech.com

Another Possible Solution

It sounds like your root file system isn’t getting remounted read-write when the system boots up. Try logging in as root and running mount -w -n -o remount / by hand and see if there is a useful error message, or if you can then change the password.

Steven Pritchard, Southern Illinois Linux Users Group steve@silug.org

Can I Use a ZIP Drive?

Is the IOMEGA ZIP Drive a supported device?

—David Jones

Linux Supports ZIP and JAZ Drives

Yes, both the SCSI and parallel port drives are supported under the 2.0.x kernels. You will need either the parallel support compiled in, or support for your SCSI controller. You can alternatively use modules to get the support you need. There are documents covering topics such as these in the Documentation directory at the top level of the kernel sources.

You should also get the latest eject package from sunsite.unc.edu or contrib on ftp.redhat.com. It can handle software ejecting of ZIP and JAZ drives under Linux.

Donnie Barnes, Red Hat Software redhat@redhat.com

ZIP Drive HOWTO

You may want to read the Linux ZIP Drive mini-HOWTO. It is available from any Linux Documentation Project mirror, including www.silug.org/LDP/HOWTO/mini/ZIP-Drive.

Steven Pritchard, Southern Illinois Linux Users Group steve@silug.org

Cannot Execute Binary File

I’ve been having this problem with some binary files I downloaded recently. When I try to execute the binary file, I get the following error:

If the shell is bash : cannot execute binary file
If the shell is tcsh : Exec format error. Wrong Architecture.

Along with this, there will be a message in /var/adm/messages saying:

"N_TXTOFF < BLOCK_SIZE. Please convert binary."

I’ve installed Slackware 96 with the Linux kernel upgraded to 2.0.24.

Tushar

Support Needed in Kernel

My first guess is that you are trying to run a.out programs without a.out support in the kernel. Make sure that when you run make config, make menuconfig, or make xconfig in your kernel source directory you answer yes to the following question:

Kernel support for a.out binaries (CONFIG_BINFMT_AOUT)
[Y/m/n/?]

and, for that matter, to this one as well:

Kernel support for ELF binaries (CONFIG_BINFMT_ELF)
[Y/m/n/?]

While the majority of Linux software is now based on the ELF binary format, there is still a lot of software based on the older a.out format.

Steven Pritchard, Southern Illinois Linux Users Group steve@silug.org

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