Introduction To Linux - Online Article

Linux is an operating system that was initially created as a hobby by a young student, Linus Torvalds, at the University of Helsinki in Finland. Linus had an interest in Minix, a small UNIX system, and decided to develop a system that exceeded the Minix standards. He began his work in 1991 when he released version 0.02 and worked steadily until 1994 when version 1.0 of the Linux Kernel was released. The kernel, at the heart of all Linux systems, is developed and released under the GNU General Public License and its source code is freely available to everyone. It is this kernel that forms the base around which a Linux operating system is developed. There are now literally hundreds of companies and organizations and an equal number of individuals that have released their own versions of operating systems based on the Linux kernel. The current full-featured version is RHEL v5 (released 2007) and the development continues.

Apart from the fact that it's freely distributed, Linux's functionality, adaptability and robustness, has made it the main alternative for proprietary Unix and Microsoft operating systems. IBM, Hewlett-Packard and other giants of the computing world have embraced Linux and support its ongoing development. Well into its second decade of existence, Linux has been adopted worldwide primarily as a Server platform. Its use as a Home and Office Desktop operating system is also on the rise. The operating system can also be incorporated directly into microchips in a process called "Embedding" and is increasingly being used this way in appliances and devices.

Throughout most of the 1990's, tech pundits, largely unaware of Linux's potential, dismissed it as a computer hobbyist project, unsuitable for the general public's computing needs. Through the efforts of developers of desktop management systems such as KDE and GNOME, office suite project OpenOffice.org and the Mozilla web browser project, to name only a few, there are now a wide range of applications that run on Linux and it can be used by anyone regardless of his/her knowledge of computers.

Those curious to see the capabilities of Linux can download a live CD version called Knoppix. It comes with everything you might need to carry out day-to-day tasks on the computer and it needs no installation. It will run from a CD in a computer capable of booting from the CD drive. Those choosing to continue using Linux can find a variety of versions or "distributions" of Linux that are easy to install, configure and use. Information on these products is available online.

Linux Compatibility

Linux runs successfully on most computers, laptops, and platforms. There are several projects underway to port Linux to other hardware configurations. An overview of hardware compatibility resources are listed below:

Supported PC-based CPUs include

  • Intel/AMD/Cyrix 486SX/DX/SL/SX2/DX2/DX4.
  • AMD K5, K6, K6-2, K6-3 and K7/Athlon.
  • Cyrix 6x86, 6x86MX.
  • Intel Pentium, Pentium Pro, Pentium II (including the Celeron series) Pentium III and Pentium IV.
  • IDT WinChip C6.
  • Symmetrical Multiprocessing (multiple CPUs).

Supported non-PC based platforms include

  • Digital Alpha.
  • Sun SPARC.
  • Macintosh.

Also supported by most Laptops and Notebooks.

Linux File System Structure

We now move on to the layout or the directory structure of the Linux file system. Linux normally consist of three main partition root ( / ), /boot, /swap. Given below is the result of an 'ls -p' in the root directory.

bin/	dev/	home/	lost+found/	proc/	sbin/	usr/
boot/	etc/	lib/	mnt/		root/	tmp/	var/

/sbin - This directory contains all the binaries that are essential to the working of the system. These include system administration as well as maintenance and hardware configuration programs. Find lilo, fdisk, init, ifconfig etc in this directory. These are the essential programs that are required by all the users. Another directory that contains system binaries is /usr/sbin. This directory contains other binaries of use to the system administrator. This is where you will find the network daemons for your system along with other binaries that only the system administrator has access to, but which are not required for system maintenance, repair etc.

/bin - In contrast to /sbin, the bin directory contains several useful commands that are used by both the system administrator as well as non-privileged users. This directory usually contains the shells like bash, csh etc. as well as much used commands like cp, mv, rm, cat, ls. There also is /usr/bin, directory which contains other user binaries. These binaries on the other hand are not so much essential for the user.

/boot - This directory contains the system file as well as the Linux kernel. Lilo places the boot sector backups in this directory.

/dev - This is a very interesting directory that highlights one important characteristic of the Linux filesystem - everything is a file or a directory. Look through this directory and you should see hda1, hda2, hda3 etc, which represent the various partitions on the first master drive of the system. /dev/cdrom and /dev/fd0 represent your CDROM drive and your floppy drive. This may seem strange but it will make sense if you compare the characteristics of files to that of your hardware. Both can be read from and written to. Take /dev/dsp, for instance. This file represents your speaker device. So any data written to this file will be re-directed to your speaker. Try 'cat /etc/lilo.conf > /dev/dsp' and you should hear some sound on the speaker. That's the sound of your lilo.conf file! Similarly, sending data to and reading from /dev/ttyS0 ( COM 1 ) will allow you to communicate with a device attached there - your Modem.

/etc - This directory contains all the configuration files for your system. Your lilo.conf file lies in this directory as does hosts, resolv.conf and fstab. Under this directory will be X11 sub-directory which contains the configuration files for X. More importantly, the /etc/rc.d directory contains the system startup scripts. This is a good directory to backup often. It will definitely save you a lot of re-configuration later if you re-install or lose your current installation.

/home - Linux is a multi-user environment so each user is also assigned a specific directory which is accessible only to them and the system administrator. These are the user home directories, which can be found under /home/username. This directory also contains the user specific settings for programs like IRC, X etc.

/lib - This contains all the shared libraries that are required by system programs. Windows equivalent to a shared library would be a DLL file.

/lost+found - Linux should always go through a proper shutdown. Sometimes your system might crash or a power failure might take the machine down. Either way, at the next boot, a lengthy filesystem check using fsck will be done. Fsck will go through the system and try to recover any corrupt files that it finds. The result of this recovery operation will be placed in this directory. The files recovered are not likely to be complete or make much sense but there always is a chance that something worthwhile is recovered.

/mnt - This is a generic mount point under which you mount your filesystems or devices. Mounting is the process by which you make a filesystem available to the system. After mounting your files will be accessible under the mount-point. This directory usually contains mount points or sub-directories where you mount your floppy and your CD. You can also create additional mount-points here if you want. There is no limitation to creating a mount-point anywhere on your system but convention says that you do not litter your file system with mount-points.

/opt - This directory contains all the software and add-on packages that are not part of the default installation. Generally you will find KDE and StarOffice here. Again, this directory is not used very often as it's mostly a standard in UNIX installations.

/root - We talked about user home directories earlier and well this one is the home directory of the user root. This is not to be confused with the system root, which is directory at the highest level in the filesystem.

/tmp - This directory contains mostly files that are required temporarily. Many programs use this to create lock files and for temporary storage of data. On some systems, this directory is cleared out at boot or at shutdown.

/usr - This is one of the most important directories in the system as it contains all the user binaries. X and its supporting libraries can be found here. User programs like telnet, ftp etc are also placed here. /usr/doc contains useful system documentation. /usr/src/linux contains the source code for the Linux kernel.

/var - This directory contains spooling data like mail and also the output from the printer daemon. The system logs are also kept here in /var/log/messages. You will also find the database for BIND in /var/named and for NIS in /var/yp.

This was a short and basic look at the Linux filesystem structure. You do need to have at least this basic knowledge of the layout of the filesystem to fully utilize its potential.

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