A Guided Tour from the Linux command line by OnWorks

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A Guided Tour

The file system layout on a Linux system is much like that found on other Unix-like sys- tems. The design is actually specified in a published standard called the Linux Filesystem Hierarchy Standard. Not all Linux distributions conform to the standard exactly but most come pretty close.

Next, we are going to wander around the file system ourselves to see what makes our

Linux system tick. This will give us a chance to practice our navigation skills. One of the things we will discover is that many of the interesting files are in plain human-readable text. As we go about our tour, try the following:

1. cd into a given directory

2. List the directory contents with ls -l

3. If you see an interesting file, determine its contents with file

4. If it looks like it might be text, try viewing it with less

Remember the copy and paste trick! If you are using a mouse, you can double click on a filename to copy it and middle click to paste it into commands.

As we wander around, don't be afraid to look at stuff. Regular users are largely prohibited from messing things up. That's the system administrator's job! If a command complains about something, just move on to something else. Spend some time looking around. The system is ours to explore. Remember, in Linux, there are no secrets!

Table 3-4 lists just a few of the directories we can explore. There may be some slight dif- ferences depending on the distribution. Don't be afraid to look around and try more!

Table 3-4: Directories Found On Linux Systems

Directory Comments

/ The root directory. Where everything begins.

/bin Contains binaries (programs) that must be present for the system to boot and run.

/boot Contains the Linux kernel, initial RAM disk image (for drivers needed at boot time), and the boot loader.

Interesting files:

● /boot/grub/grub.conf or menu.lst, which are used to configure the boot loader.

● /boot/vmlinuz (or something similar), the Linux

kernel

/dev This is a special directory which contains device nodes. “Everything is a file” also applies to devices. Here is where the kernel maintains a list of all the devices it understands.

/etc The /etc directory contains all of the system-wide configuration files. It also contains a collection of shell scripts which start each of the system services at boot time. Everything in this directory should be readable text.

Interesting files: While everything in /etc is interesting, here are some all-time favorites:

● /etc/crontab, a file that defines when

automated jobs will run.

● /etc/fstab, a table of storage devices and their associated mount points.

● /etc/passwd, a list of the user accounts.

/home In normal configurations, each user is given a directory in

/home. Ordinary users can only write files in their home directories. This limitation protects the system from errant user activity.

/lib Contains shared library files used by the core system programs. These are similar to DLLs in Windows.

/lost+found Each formatted partition or device using a Linux file system, such as ext3, will have this directory. It is used in the case of a partial recovery from a file system corruption event.

Unless something really bad has happened to your system, this directory will remain empty.

/media On modern Linux systems the /media directory will contain the mount points for removable media such as USB drives, CD-ROMs, etc. that are mounted automatically at insertion.

/mnt On older Linux systems, the /mnt directory contains mount points for removable devices that have been mounted manually.

/opt The /opt directory is used to install “optional” software. This is mainly used to hold commercial software products that may be installed on your system.

Directory Comments

/proc The /proc directory is special. It's not a real file system in the sense of files stored on your hard drive. Rather, it is a virtual file system maintained by the Linux kernel. The “files” it contains are peepholes into the kernel itself. The files are readable and will give you a picture of how the kernel sees your computer.

/root This is the home directory for the root account.

/sbin This directory contains “system” binaries. These are programs that perform vital system tasks that are generally reserved for the superuser.

/tmp The /tmp directory is intended for storage of temporary, transient files created by various programs. Some configurations cause this directory to be emptied each time the system is rebooted.

/usr The /usr directory tree is likely the largest one on a Linux system. It contains all the programs and support files used by regular users.

/usr/bin /usr/bin contains the executable programs installed by

your Linux distribution. It is not uncommon for this directory to hold thousands of programs.

/usr/lib The shared libraries for the programs in /usr/bin.

/usr/local The /usr/local tree is where programs that are not

included with your distribution but are intended for system- wide use are installed. Programs compiled from source code are normally installed in /usr/local/bin. On a newly installed Linux system, this tree exists, but it will be empty until the system administrator puts something in it.

/usr/sbin Contains more system administration programs.

/usr/share /usr/share contains all the shared data used by

programs in /usr/bin. This includes things like default configuration files, icons, screen backgrounds, sound files, etc.

/usr/share/doc Most packages installed on the system will include some

kind of documentation. In /usr/share/doc, we will find documentation files organized by package.

/var With the exception of /tmp and /home, the directories we have looked at so far remain relatively static, that is, their contents don't change. The /var directory tree is where data that is likely to change is stored. Various databases, spool files, user mail, etc. are located here.