4. Exploring the system

To explore the system we use these steps:

Use cd to go to a directory.
List the directory contents with ls -l.
If you see an interesting file, determine its contents with the command file.
If it looks like it might be text, try viewing it with less.

Let's try some of these:

Go to /bin and list its content:
```
cd /bin
```
```
ls -l
```
```
ls -l b*
```
```
ls -l bzless
```
Check the type of some files and their contents:
```
file bzless
```
The file bzless is a symbolic link, a kind of shortcut, or alias, or a reference to another file. There are also hard links which we will see later.
```
ls -l bzmore
```
```
file bzmore
```
The file bzmore is a shell script and actually a text file, so we can read its content:
```
less bzmore
```
Press [Space] a couple of times, and then quit with q.

Shell scripts are like programs and contain Linux commands.

The command less displays the contents of a text file page-by-page.

Note: The command less is an improved replacement of an earlier Unix command that was called more. So, sometimes it is said that: less is more. Or: less is more or less more.
Let's check another file:
```
ls -lh bash
```
```
file bash
```
The file bash is an executable program, and a binary (non-text) file. Let's try to read its content:
```
less bash
```
Exit with q.

As you see, text files have a content that is readable by humans, non-text files (or binary files) have a content that is not readable by humans (but it may be read and interpreted by some programs).
Let's check /etc:
```
file /etc
```
```
ls -l /etc/passwd
```
```
file /etc/passwd
```
It is plain text. Let's check its content:
```
less /etc/passwd
```
This file contains the accounts of the system.

The files on /etc are usually configuration files, and almost all of them are text files (readable and writable by humans).
In contrast, the files on /bin are programs or commands and they are mostly binary files or shell scripts. The same goes for /sbin, /usr/bin, /usr/sbin, /usr/local/bin, etc.
```
ls /sbin
```
```
ls /usr/bin
```
```
ls /usr/sbin
```
```
ls /usr/local/bin
```
Some other important directories are:
```
ls /boot
```
```
ls /boot/grub
```
Contains the Linux kernel, initial RAM disk image, the boot loader, etc.
```
ls /dev
```
```
file /dev/tty
```
```
file /dev/pts/1
```
Contains device nodes.
```
ls /home
```
Contains home directories of the users.
```
ls /lib
```
```
ls /usr/lib
```
Contains shared libraries.
```
ls /proc
```
```
less /proc/cpuinfo
```
This is a special directory that exposes the settings and the state of the kernel itself.
```
ls /var
```
```
ls /var/log
```
Contains data that are likely to change frequently (like log files).
```
ls /tmp
```
Temporary data which might be erased on each reboot.

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