100 Linux Tips and Tricks

Tip 24: LILO and boot problems

When a computer starts, the number of beeps the BIOS outputs tells you the state of the computer. On some computers, one beep means all is ok, but 2 beeps mean there is an error. LILO uses the same kind of codes. The number of letters you see from the word LILO on the screen says what is wrong. The whole word means everything is fine, only LI means only the first part of LILO could be loaded. A full description of this is available from the Bootdisk HOWTO.

When LILO can't load, it's a major problem. This often means that the boot code was corrupted. The only way to boot is from a floppy disk. In RedHat, you can use the rescue disk, in Slackware, you can use the boot disk with the "mount" image.

When LILO is fine, it's often easier to figure a boot problem. If the kernel panics when it tries to boot, it is usualy due to a configuration error. You can tell LILO to mount another kernel you may have, like a "safe" or "old" image you kept for these cases. If the problem is in initialization scripts, you can tell LILO to boot directly into a shell with the following boot command line:

LILO boot: linux init=/bin/sh

Where "linux" would be your kernel image.

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100 Linux Tips and Tricks

Tip 25: Making CD-ROM images

With other operating systems, such as Microsoft Windows or IBM OS/2, you are not allowed in the license to make your own CD-ROM with the OS on it and then distribute it.

Linux, being Open Source and free, can be copied. You can download a distribution or buy it from an online store and burn your own copy, and then install it on many computers, or give it to your friends. Usually, you will find instructions on how to do that on the FTP server for your favorite distribution. You will need the main directory on the CD-ROM. The sources are not needed since they are available from the FTP site.

Some distributions also come with ISO images of their CD-ROM. This is a single file that can be put onto a CD-ROM, and will create a full file system with files on it.

One thing you have to be careful is not to copy commercial programs. The basic CD-ROM where the Linux distribution is located is composed of free software. But some distributions may come with other commercial programs, and you should read the license first.

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100 Linux Tips and Tricks

Tip 26: FTP access restrictions

When you first install Linux, it comes with a lot of Internet services running, including mail, telnet, finger and FTP. You really should disable all those that you don't need from /etc/inetd.conf and your startup scripts.

FTP may be very useful, but must be configured correctly. It can allow people to log into their accounts, it can allow anonymous users to login to a public software directory, and it can display nice messages to them.

The files that you will probably want to modify are /etc/ftpusers and /etc/ftpaccess.

The file /etc/ftpusers is very simple. It lists the people that will not be allowed to use FTP to your system. The root account, and other system accounts should be in that file.

The file /etc/ftpaccess is a bit more complex and controls the behaviour of the FTP server. It tells it what to use as README file to display on a directory listing, what kind of logs to create and what messages to display.

Note that if you create an anonymous FTP area, you will need to read the FTP man page and do exactly what it tells you to avoid possible security risks.

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100 Linux Tips and Tricks

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