Figure 3.1 Starting QTerminal
51
Chapter 3 — Linux Fundamentals
For instance, on a default Kali Linux system, QTerminal can be started from the list of favorite
applications. You can also type “terminal” while in the applications menu (the one that gets acti-
vated when you move the mouse to the top-left corner) and click on the correct application icon
that appears (Figure
3.1
, “
Starting QTerminal
” [page 51]).
In the event that your graphical interface is broken, you can still get a command line on virtual
consoles (up to six of them can be accessible through the six key combinations of CTRL+ALT+F1
through CTRL+ALT+F6 — the CTRL key can be omitted if you are already in text mode, outside of
Xorg or Wayland’s graphical interface). You get a very basic login screen where you enter your
login and password before being granted access to the command line with its shell:
Kali GNU/Linux Rolling kali tty3
kali login: kali
Password:
Linux kali 5.7.0-kali1-amd64 #1 SMP Debian 5.7.6-1kali2 (2020-07-01) X86_64
The programs included with the Kali GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.
Kali GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
kali@kali:~$
The program handling your input and executing your commands is called a shell (or a command-
line interpreter). The default shell provided in Kali Linux is Bash (it stands for Bourne Again SHell).
The trailing “$“ or “#” character indicates that the shell is awaiting your input. It also indicates
whether Bash recognizes you as a normal user (the former case with the dollar, $) or as a super
user (the latter case with the hash, #).
3.2.2. Command Line Basics: Browsing the Directory Tree and Managing Files
This section only provides a brief overview of the covered commands, all of which have many
options not described here, so please refer to the abundant documentation available in their re-
spective manual pages. In penetration tests, you will most often receive shell access to a system
after a successful exploit, rather than a graphical user interface. Proficiency with the command
line is essential for your success as a security professional.
Once a session is open, the
pwd
command (which stands for print working directory) displays your
current location in the filesystem. The current directory is changed with the
cd directory
com-
mand (
cd
is for change directory). When you don’t specify the target directory, you are taken to
your home directory. When you use
cd -
(dash), you go back to the former working directory
(the one in use before the last
cd
call). The parent directory is always called .. (two dots), whereas
52
Kali Linux Revealed
the current directory is also known as . (one dot). The
ls
command allows listing the contents of
a directory. If you don’t provide parameters,
ls
operates on the current directory.
$ pwd
/home/kali
$ cd Desktop
$ pwd
/home/kali/Desktop
$ cd .
$ pwd
/home/kali/Desktop
$ cd ..
$ pwd
/home/kali
$ ls
Desktop
Downloads
Pictures
Templates
Documents
Music
Public
Videos
You can create a new directory with
mkdir directory
, and remove an existing (empty) directory
with
rmdir directory
. The
mv
command allows moving and renaming files and directories; remov-
ing a file is achieved with
rm file
, and copying a file is done with
cp source-file target-file
.
$ mkdir test
$ ls
Desktop
Downloads
Pictures
Templates
Videos
Documents
Music
Public
test
$ mv test new
$ ls
Desktop
Downloads
new
Public
Videos
Documents
Music
Pictures
Templates
$ rmdir new
$ ls
Desktop
Downloads
Pictures
Templates
Videos
Documents
Music
Public
The shell executes each command by running the first program of the given name that it finds
in a directory listed in the PATH environment variable. Most often, these programs are in
/bin
,
/sbin
,
/usr/bin
, or
/usr/sbin
. For example, the
ls
command is found in
/bin/ls
; the
which
command reports the location of a given executable. Sometimes the command is directly handled
by the shell, in which case, it is called a shell built-in command (
cd
and
pwd
are among those); the
type
command lets you query the type of each command.
$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
$ which ls
/bin/ls
$ type rm
53
Chapter 3 — Linux Fundamentals
rm is /bin/rm
$ type cd
cd is a shell builtin
Note the usage of the
echo
command, which simply displays a string on the terminal. In this case,
it is used to print the contents of an environment variable since the shell automatically substitutes
variables with their values before executing the command line.
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