Linux Installation and
Administration
Lesson 2
Tutor: George Papamarkos
Lesson Outline
• Getting help in Linux
– Using ‘man’ command
• Shell Prompt Basics
• Linux Authentication Settings
– Working as ‘root’
– Managing users and groups
• Getting System Information
– Memory/CPU Usage
– Disk Usage
Getting Help
• Applications, utilities, and shell prompt commands
usually have corresponding manual pages (also called
man pages)
• Man pages show the reader the available options and
values of file or executable.
• Man Pages can be accessed via shell prompt by
typing the command man and the name of the
executable.
• E.g. man ls to see the manual page of ‘ls’ command
Getting Help (cont.)
•
•
•
•
•
The NAME field shows the executable's
name and a brief explanation of what
function the executable performs.
The SYNOPSIS field shows the common
usage of the executable, such as what
options are declared and what types of input
(such as files or values) the executable
supports.
The DESCRIPTION field shows available
options and values associated with a file or
executable. See Also shows related terms,
files, and programs.
To navigate the man page you can use the
[Page Down] and [Page Up] keys or use
the [Spacebar] to move down one page
and [B] to move up. To exit the man page,
type [Q].
To search a man page for keywords type [/]
and then a keyword or phrase and press
[Enter]. All instances of the keyword will be
highlighted throughout the man page,
allowing you to quickly read the keyword in
context.
Shell Prompt Basics
• Create a directory
– mkdir <dir_name>
• Copy a file from one dir to another
– cp <fname> <destination_dir>
• Make a copy of a file with another name
– cp <fname> <other_fname>
• Move a file
– mv <fname> <destination_dir>
• Rename a file
– mv <fname> <new_fname>
• Remove a file
– rm <fname>
Shell Prompt Basics (cont.)
•
Determining your current directory by 'pwd' command:
–
$ pwd
/home/gpapa05
•
Create a directory with 'mkdir' command
–
$ mkdir <dir_name>
E.g. mkdir lesson2
•
Change Directory with 'cd' command
$ cd lesson2
$ pwd
/home/gpapa05/lesson2
Shell Prompt Basics
(cont.)
•
View directory contents with 'ls' command
•
The following is a short list of some options commonly used with ls. Remember, you can
view the full list by reading the ls man page (man ls).
•
-a — all. Lists all the files in the directory, including the hidden files (.filename). The ..
and . at the top of your list refer to the parent directory and the current directory,
respectively.
•
-l — long. Lists details about contents, including permissions (modes), owner, group,
size, creation date, whether the file is a link to somewhere else on the system and
where its link points.
•
-F — file type. Adds a symbol to the end of each listing. These symbols include / to
indicate a directory; @ to indicate a symbolic link to another file; and * to indicate an
executable file.
•
-r — reverse. Lists the contents of the directory from back to front.
•
-R — recursive. This option lists the contents of all directories below the current
directory recursively.
•
-S — size. Sorts files by their sizes.
Shell Prompt Basics
(cont.)
•
Linux has a utility which can help you keep short lists, gather lists
together, and even show you information about your system.
•
The utility is called cat, short for concatenate, which means to combine
files.
•
The command cat will also display the contents of an entire file on the
screen (for example, type cat filename.txt). If the file is fairly long, it will
quickly scroll past you on the screen. To prevent this, use the ‘cat
filename.txt | less’ command.
•
The ‘grep’ command
– The grep command is useful for finding specific character strings in a file.
– For example, if you want to find every reference made to "coffee" in the file
sneakers.txt, you would type:
grep coffee sneakers.txt
Shell Prompt Basics
(cont.) – Pipes and Pagers
•
•
In Linux, pipes connect the standard output of one command to the
standard input of another command.
E.g. ls -al /etc | less
Redirects the output of the ‘ls’ command to the ‘less’ command. (Try it
out)
•
Pipes can also be used to print only certain lines from a file. E.g.
– grep coffee sneakers.txt | lpr
This command prints every line in the sneakers.txt file that mentions the word
"coffee"
•
The ‘more’ command
– Similar to ‘less’ command
– The main difference between more and less is that less allows backward and
forward movement using the arrow keys, while more uses the [Spacebar] and
the [B] key for forward and backward navigation.
Shell Prompt Basics (cont.)
•
The ‘head’ command
–
You can use the head command to look at the beginning of a file. The command is:
head <filename>
•
•
The ‘tail’ command
–
The reverse of ‘head’ command. Using tail, you can view the last ten lines of a file
–
Using the -f option, tail automatically print new messages from an open file to the screen in real-time
–
E.g. tail -f /var/log/messages
Wildcards and Regular Expressions
–
Using wildcards or regular expressions, you can perform actions on a file or files without knowing the
complete filename.
–
Wildcards are special symbols that you can substitute for letters, numbers, and symbols
–
E.g. ls s*.txt will result all the files in the current dir that start with ‘s’ and are suffixed with ‘.txt’
–
Here is a brief list of wildcards and regular expressions:
•
* — Matches all characters
•
? — Matches one character in a string
•
\* — Matches the * character
•
\? — Matches the ? character
•
\) — Matches the ) character
Create a user account
• Creating a user account
– You should avoid working in the root account for
daily tasks
– In case that you want to perform a task that requires
root privileges use the command ‘su –’. You will be
asked to provide the ‘root’ password. If everything
goes fine you will get a root prompt 
– You HAVE TO create a user account to work on
– Two ways to create a user
• Graphically from “User Manager”
• From a shell prompt
Create a user account
graphically
•
•
•
•
Click the Start Here icon on the
desktop. In the new window that opens,
click the System Settings icon, and
then click the Users & Groups icon. You
can also select Main Menu => System
Settings => Users & Groups from the
panel.
You can also start the User Manager by
typing redhat-config-users at a shell
prompt.
If you are not logged in as root, you will
be prompted for your root password.
The ‘User Manager’ window appears
Create a user account
graphically (cont.)
•
•
•
•
•
•
•
To add a new user, click the Add User button.
Type the username and full name for the new user
in the appropriate fields
Type the user's password in the Password and
Confirm Password fields. The password must be
at least six characters.
Select a login shell. If you are not sure which shell
to select, accept the default value of /bin/bash.
The default home directory is /home/username.
You can change the home directory that is created
for the user, or you can choose not to create the
home directory by unselecting Create home
directory. If you select to create the home
directory, default configuration files are copied
from the /etc/skel directory into the new home
directory.
To specify a user ID for the user, select Specify
user ID manually. If the option is not selected,
the next available user ID starting with number
500 will be assigned to the new user. Red Hat
Linux reserves user IDs below 500 for system
users.
Click OK to create the user.
Create a user from shell
prompt
To create a user account from a shell prompt:
1. Open a shell prompt.
2. If you are not logged in as root, type the command ‘su –’ and enter
the root password.
3. Type useradd followed by a space and the username for the new
account you are creating at the command line (for example, useradd
jsmith). Press [Enter]. Often, usernames are variations on the user's
name, such as gpapam for George Papamarkos, but the final choice is
yours.
4. Type passwd followed by a space and the username again (for
example, passwd jsmith).
5. At the New password: prompt enter a password for the new user and
press [Enter].
6. At the Retype new password: prompt, enter the same password to
confirm your selection.
7. For more options on user creation see man useradd
Modifying User Properties
•
•
To view the properties of an existing user, click on the
Users tab, select the user from the user list, and click
Properties from the button menu
The User Properties window is divided into multiple
tabbed pages:
–
–
–
–
•
User Data — Shows the basic user information
configured when you added the user. Use this tab to
change the user's full name, password, home directory,
or login shell.
Account Info — Select Enable account expiration if
you want the account to expire on a certain date. Enter
the date in the provided fields. Select User account is
locked to lock the user account so that the user cannot
log in to the system.
Password Info — This tab shows the date that the
user's password last changed. To force the user to
change passwords after a certain number of days, select
Enable password expiration. The number of days
before the user's password password, the number of
days before the user is warned to change passwords,
and days before the account becomes inactive can also
be changed.
Groups — Select the groups that you want the user to
be a member of and the user's primary group.
Command ‘usermod’ gives the same functionality from
command line
User Groups
• In Linux/Unix systems users are
organised in groups
• A group is a smart way to manage
authentication setting in Linux
• Each group defines an access policy over
an certain system resource (e.g. cdrom,
audio devices etc.)
• Each user belongs to a set of groups
Adding a New Group
graphically
• In the ‘User & Groups’ application
• To add a new user group, click the
Add Group button
• Type the name of the new group to
create.
• To specify a group ID for the new
group, select Specify group ID
manually and select the GID.
• Red Hat Linux reserves group IDs
lower than 500 for system groups.
• Click OK to create the group. The
new group will appear in the group
list.
Adding a Group from the
shell prompt
• To add a group to the system, use the
command groupadd
groupadd <group-name>
• The command line options for groupadd are:
Option
-g gid
Description
Group ID for the group, which must be unique and greater than 499.
-r
Create a system group with a GID less than 500.
-f
Exit with an error if the group already exists. (The group is not altered.) If -g and -f
are specified, but the group already exists, the -g option is ignored.
Modifying Group
Properties
• To view the properties of an
existing group, select the
group from the group list
and click Properties from
the button menu
• The Group Users tab
displays which users are
members of the group.
• Select additional users to be
added to the group, or
unselect users to be
removed from the group
• Click OK or Apply to modify
the users in the group.
Getting system information
– System Processes
• To get information about the processes running on your system
we can use ‘ps’ command from the shell prompt.
• The ‘ps ax’ (‘ax’ are the parameters passed) command displays
a list of current system processes, including processes owned by
other users.
• To display the owner of the processes along with the processes
use the command ‘ps aux’.
• The ps output can be long. To prevent it from scrolling off the
screen, you can pipe it through ‘less’ command:
– ps aux | less
• You can use the ps command in combination with the ‘grep’
command to see if a process is running. E.g. to see if ‘mozilla’ is
running type:
– ps ax | grep emacs
Getting system information
– System Processes (2)
• The ‘top’ command displays currently running processes and
important information about them including their memory and
CPU usage.
• In contrast to ‘ps’ command ‘top’ is interactive and real-time
• To exit top, press the [q] key.
Getting system information
– System Processes (3)
•
•
•
•
In GNOME and KDE you can use a
Graphic System Monitor as well.
In GNOME for example select Main
Menu Button (on the Panel) =>
System Tools => System
Monitor or type gnome-systemmonitor at a shell prompt from
within the X Window System to get
the GNOME System Monitor tool
GNOME System Monitor gives
you almost all the facilities provided
by ‘top’ command but graphically
You can end a process, search a
process by name etc.
Getting System Information
– Memory Usage
• The ‘free’ command displays the total amount of physical
memory and swap space for the system as well as the amount
of memory that is used, free, shared, in kernel buffers, and
cached.
• The command ‘free –m’ shows the same information in
megabytes, which are easier to read.
• This information can also be taken by getting the contents of
‘meminfo’ file in ‘proc’ directory. To do so type:
– cat /proc/meminfo
• Graphically you can still use GNOME System Monitor and
select the ‘System Monitor’ tab
Getting System Information
– Monitor Disks
•
•
•
The ‘df’ command reports the system's disk space usage.
By default, this utility shows the partition size in 1 kilobyte blocks and
the amount of used and available disk space in kilobytes. To view the
information in megabytes and gigabytes, use the command ‘df –h’. The
-h argument stands for human-readable format.
For more see the appropriate manual page
That’s all folks !
Thanks a lot for your attention !!