Each of these streams can be redirected. Normally, STDOUT and STDERR go to the
same place (typically, the console). STDIN originates from the console. If you want
your output to go somewhere else, you can use the
>
operator. If, for instance, I
wanted to send the output of
ps
to a file, I might use
ps auxw > ps.out
. When you
redirect the output, you don’t see it on the console anymore. In this example, if there
were an error, you would see that, but not anything going to STDOUT. If you wanted
to redirect input, you would go the other way. Rather than
>
, you would use
<
, indi‐
cating the direction you want the information to flow.
Understanding the different I/O streams and redirection will help you down the path
of understanding the
|
(pipe) operator. When you use
|
, you are saying, “Take the out‐
put from what’s on the left side and send it to the input for what’s on the right side.”
You are effectively putting a coupler in place between two applications, STDOUT →
STDIN, without having to go through any intermediary devices.
One of the most useful uses of command chaining or piping is for searching or filter‐
ing. As an example, if you have a long list of processes from the
ps
command, you
might use the pipe operator to send the output of
ps
to another program,
grep
, which
can be used to search for strings. As an example, if you want to find all the instances
of the program named
httpd
, you use
ps auxw | grep httpd
.
grep
is used to search an
input stream for a search string. While it’s useful for filtering information, you can
also search the contents of files with
grep
. As an example, if you want to search for the
string
wubble
in all the files in a directory, you can use
grep wubble *
. If you want to
make sure that the search follows all the directories, you tell
grep
to use a recursive
search with
grep -R wubble *
.
User Management
When you start up Kali, you have the root user in place. Unlike other Linux distribu‐
tions, you won’t be asked to create another user. This is because much of what you
may be doing in Kali will require superuser (root) permissions. As a result, there’s no
reason to create another user, even though it’s not good practice to stay logged in as
the root user. The expectation is that someone using Kali probably knows enough of
what they are doing that they wouldn’t be as likely to shoot themselves in the foot
with the root permissions.
However, it is still possible to add and otherwise manage users in Kali, just as it is
with other distributions. If you want to create a user, you can just use the
useradd
command. You might also use
adduser
. Both accomplish the same goal. When you
are creating users, it’s useful to understand some of the characteristics of users. Each
user should have a home directory, a shell, a username, and a group at a minimum. If
I want to add my common username, for instance, I would use
useradd -d /home/
kilroy -s /bin/bash -g users -m kilroy
. The parameters given specify the home directory,
the shell the user should execute when logging in interactively, and the default group.
