Reading Log Files

This chapter has covered what logging on a SUSE Linux system means and what you can do with the messages that are generated both by the kernel and processes that you run.

However, reading log files is a skill in itself. There is no good way to teach people how to read log files; rather, it is something that comes with experience. We will give you our short rundown of common entries you will find in /var/log/messages and explain how to interpret them to help you on your way. The following line is an example of a log entry indicating an SSH login failure:

May 27 23:23:35 bible sshd[5019]: error: PAM: Authentication failure

From this example, you can see certain things about log entries that are generic to all of them. The first entry is the date and time this entry was created, with the host name of the machine that the message originated from (in this case, bible). The next entry is usually the process that actually created the log entry (in this case the ssh daemon). The number you see next to the process name is the process number, followed by the message itself.

The message you see in this example is self-explanatory, saying that there was an authentication error. The PAM: entry is something you will see with most authentication errors in Linux as PAM (Pluggable Authentication Modules) is used to take a username and password for a process and decide if this user with the password they have entered is actually allowed to log in to the system.

This next example is an informational message from the kernel after a kernel driver has been loaded:

May 27 22:19:22 bible kernel: IPv6 over IPv4 tunneling driver

This means that the driver that deals with tunneling IPv6 traffic over IPv4 has been loaded successfully.

So here you have seen two extremes of what you might find in a log file. The latter example is a general informational message telling you all is fine. The other is a bit more serious, telling you that someone attempted to log in to the system but failed because they provided the wrong authentication information (wrong username or password).

Log files are there to help you in your running of your Linux system. You have to be vigilant in your efforts to keep the system running nicely, and log files help you with this.

Have you checked your logs recently?

The graphical interface that comes with Linux is provided by an implementation of the X Window system. The X Window system is a set of protocols and standards for a cross-platform, network-transparent graphics display system. On Linux, the implementation chosen was traditionally from the XFree86 project. Arguments about licensing have resulted in the major Linux distributors switching from XFree86 to the project from In the case of SUSE, this change was made with the release of the 9.2 version. However, this makes no difference to the principles discussed here.

[. ' i."'1 Historically, the original developers of the X Window system have been very insistent about the fact that it is a window system named X, and thus should not simply be referred to as X. In this book, we refer to the X Window system as X because it is more convenient and common to do so. Computer history fans should note that the designation X originally came from the fact that the project that inspired the X Window system was the W Window system from Stanford University — X is simply the next letter of the alphabet.

The big difference between X and (for example) the graphics display systems found in Microsoft Windows or Mac OS X is that X is inherently network-transparent and is designed from the ground up as a client-server system. That means that, using X, you can run a graphical program in one place and display its output somewhere else. This is a capability for which you may need special add-ons in the Windows world, but that is built into Linux. The "somewhere else'' where you will be displaying the graphical output can be any platform for which an X server implementation is available, including virtually any operating system capable of TCP/IP networking and running a graphical display. In a typical Linux desktop


X Window system concepts

Configuring X

The KDE desktop

The GNOME desktop

Using window managers

Building X applications situation, you will of course be running the display on the same machine that the applications are running on. However, the network transparency of X provides huge benefits that we examine later in this chapter.

The common complaints that are often heard about X are the problems of configuration (largely but not entirely a thing of the past), problems with fonts (anti-aliased display of fonts in all situations took a long time to become available on Linux), lack of direct support for hardware acceleration, and other performance issues. Some of these difficulties are directly related to the fact that implementations of X have to be backward-compatible and standards-compliant.

Largely through the efforts of open source operating systems such as Linux, FreeBSD, OpenBSD, and NetBSD, X Window system configuration today is quite easy, rivaling the ease of installing and configuring graphics on any modern operating system. The XFree86 project's generic xf86config utility is quite easy to use but requires some knowledge of your system's graphical capabilities. The project's xorgcfg utility is very similar and has similar information requirements. The vendors that sell and support Linux and BSD distributions have stepped in to make things even easier. Applications such as the sax2 utility developed by SUSE and provided with all SUSE Linux distributions provide a simpler, almost automatic mechanism for configuring and fine-tuning X on a modern Linux system.

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