Getting Started

Topics:

• Log in to and out of a Linux system
• Creating a user account
• Describe the structure of Linux/UNIX commands
• Basic Linux/UNIX commands
• Shutdown the computer
• Commands to communicate with other users on our Linux system

Commands:

Logging On and Off the System

hostname login: username
Password: (password does not echo)
[username@hostname username]$

$ logout
$ exit
$ <Ctrl-d>

Logging Out: Using the GUI

• Click on GNOME footprint
• choose Log out
• KDE: right click somewhere on desktop background
• choose log out

Moving Around

• Open a shell window
• In Ubutu Gnome desktop, choose Applications -> Accessories -> Terminal
• Print the current directory

$ pwd
• Change to the etc directory

$ cd /etc
• Change to your home directory

  $ cd

• List the contents of the current directory

  $ ls

• List the contents of another directory

  $ ls /etc

• Do a long listing (more details) of a directory

  $ ls -l /etc

• Pipe the output of one command to less

  $ ls -l /etc | less

• Why less better than more?

  $ ls -l /etc | more

Creating User Accounts

• Users account are created by the root user
• Note the difference in prompts
• Pound sign for root (#), dollar sign for users ($)
[root@hostname /root]# useradd userx

[root@hostname /root]# adduser userx

• Initial passwords are also set by the root user

[root@hostname /root]# passwd username

Root is equivalent to the local Administrator account in Windows 2000/NT

Where are these new user account records stored? Use the cat command to print the ascii passwd file to the terminal.

# cat /etc/passwd

sudo

• sudo permits a user to exectute a command as the superuser (or another user)
• The sudo config file is /etc/sudoers
• What are the benefits of the sudo command?
  • logging, audit trail of command executed as root
  • no need to provide root password to all admins
  • won't suffer from the syndrom of forgetting you are logged in as priviledged account

Creating Groups

• In order to add a user to a specific group, the group must exist first

$ groupadd 
usage: groupadd [-g gid [-o]]  [-r] [-f] group

$ sudo  groupadd mynewgroup

• Take a look at the new group
• What GID did the command assign?

# tail /etc/group

Passwords

• Initial user passwords are set by root
• Users can change their own passwords after logging in

$ passwd
Changing password for


• There are rules for good passwords

• Make them at least eight characters long;
• Don't let them contain dictionary words;
• Don't make a new one similar to the current/last one;
• They have to have a varied selection of characters;
• They are case-sensitive;
• No, the system administrator should NOT have a record of it.

Command Syntax

$ command option(s) argument(s)

• Be aware that the order of the elements is important, as well as the separation of the elements.

The elements of a command are:

• the command
• one or more options
• one or more arguments

Primary Group and Additional Groups

• You don't need to memorize this complicated command but it gives you an idea of the various options and arguments that can be found.

$ sudo useradd -c "Test Account" -d /home/test -s /bin/bash -g users testuser



• This command also created a home directory for the user, testuser, under /home
  
• Please take a look at the new directory using cd and ls -la

Lab

1. Create the account student, with the primary group users specified

• Remember, the primary group is part of the user's passwd file record

$ sudo useradd student -g users -m -d /home/student

• How do you know the users group exists?
• Take a look at the /etc/group file

    $ less /etc/group
    $ less /etc/group | grep users
    

• Look at the passwd file to see the new account
• Field 1, is the user account name, field 3 is the UID, field 4 is the primary group (the fields are separated by a colon)
  

    $ tail /etc/passwd
    

2. Add the user account student to the additional group, admins

• First create the group

    $ sudo groupadd admins
    $ tail /etc/group
    

• Add the user to admins

    $ sudo  usermod -G admins student
    $ tail /etc/group
    

3. Delete an account

   $ sudo useradd pattyo -m -d /home/pattyo
   $ ls -l /home
   $ sudo userdel -r pattyo
   $ ls -l /home
    

• The '-r' tells userdel to remove all the files in the user's home directory.
• Why use the command line when a GUI is available?

Help Files and Man Pages

$ man useradd
$ useradd -h
$ useradd -help

Shutdown and Reboot from command line

# halt

# /sbin/shutdown -h now

# init 0

# /sbin/shutdown -r now

# /usr/bin/reboot

Note: You can also use the GUI to shutdown your machine without being root -- look for the red icon in the upper right hand corner of your GNOME desktop.

Getting around...recalling other commands

• From the bash and tcsh shells you can edit commands and recall previous commands using the arrow keys.

The date and cal commands

$ date
Wed Nov 29 11:14:26 PST 2000

• The time is based on a 24 hour clock.
• No options are required by default

Use two '!!' to recall the last command:

$ !!
Wed Nov 29 11:14:27 PST 2000

Looking at a Whole Month

$ cal 12 1999
      December 1999
 Su  Mo  Tu  We  Th  Fr  Sa
              1   2   3   4
  5   6   7   8   9  10  11
 12  13  14  15  16  17  18
 19  20  21  22  23  24  25
 26  27  28  29  30  31

Looking at a Whole Year

$ cal 2002

Piping output through the more (I prefer less) command

$ cal 2002 | more
$ cal 2002 | less

The pipe is used to pipe the output of one command into the input of another. We'll talk more about it later.

The who and finger Commands

$ who
root  console Feb 12 09:02
user10  tty1  Feb 12 11:10
 
• Use the who command with the -u option for more login details on your users.

$ who -u

• The w command is very useful for seeing who is logged in and what they are doing.

$ w

$ who am i
user10  tty1  Feb 12 11:10  - OR -  user10

$ whoami
user10

• For information about specific logged in users

$ finger userxx
Name:
Login: userxx      Shell: /bin/bash
Directory: /home/userxx
On since Fri Feb 12 10:32 (CST) on tty2
No mail.
No Plan

The .project and .plan files live in your home directory. You can create these to add details to your login information.

    Sending a Message to Someone on the Same System

• You may have to download the mail package first
  • Is mail installed?

       $ which mail
    

  • What packages pertain to mail?

       $ aptitude search mail
    

  • Download mailx.

       $ sudo apt-get install mailx
    

$ mail student
Subject: Meeting
Hey there!  Don't forget the party this weekend.
Fred
<Ctrl-d>
Cc: <Enter>

Note: the <Ctrl-d> exit the body of the message. Or a single '.' on a line by itself

    Sending a Message to Someone on Another System

$ mail userxx@stationxx
Subject: Meeting Still OK?
Are we still getting together tonight at your house?
I already told the guys!

Userxy
.
Cc: <Enter>

Receiving Mail

Actually, by default, Linux will tell you when you login:

You have mail.

To check your mail without using the GUI:

$ mail
Mail version 8.1.6/6/93  Type ? for help
"/var/spool/mail/team01": 2 messages 1 new
  U 1 team05@hostname.local Mon Jan 25 10:50 10/267 "Call Us, re:Meeting"
>N 2 team02@hostname.local Tue  Jan 26 09:05 16/311 "Meeting Postponed"
& <Enter>
Message 1:
From team05 Mon Jan 25 10:50:32 1999
Date: Mon, Jan 25 1999 10:50:32 -600
From: team05@hostname.localdomain
To: pattyo@hostname.localdomain
Subject: Meeting
Please call us regarding the status of the meeting we called for Thursday morning.

• The N is for new mail, the U for unread.

• type 1 to read the first message
• type 2 to skip the first message and read the second
• to read the messages in sequence type <Enter>
• d deletes messages (you can delete ranges of messages as well)
• m forwards messages
• r sends a reply
• q exits mail and leaves unread messages in the queue
• s appends a message to a file
• ? will let you know all the options available

Configuring mail

In order to send mail to another domain from your workstation, you will need to install, configre, and run an MTA (Mail Transport Agent). Postfix is easy to install and configure. This is a great website to use as a reference: http://flurdy.com/docs/postfix/.

   $ sudo apt-get install postfix
   $ cd /etc/postfix
   $ sudo vi main.cf
   $ sudo /etc/init.d/postfix start

• I modified the following after installing and choosing "Internet" install option:

     myhostname = mymachine.mydomain.com
     relayhost = smtphost.mydomeain.com
  

The wall Command

  # wall textofmessage

    This is what 'root' might send:

# wall Warning -- System Going Down Immediately!

This is what every logged in user would receive:

Broadcast message from root (ttyp1) Tue Jan 26 14:04:48 1999
Warning!! System Going Down!

To reboot the system and notify users:

# /sbin/shutdown -r +5 "rebooting to clear hung mounts in 5 minutes... "

The write and talk commands

• displays a message immediately on a specified users terminal
• If the users is logged into more than one terminal you can use the w command to specify which one.

$ w
 12:31am  up 10 days, 57 min,  8 users,  load average: 0.21, 0.22, 0.15
USER     TTY      FROM          LOGIN@   IDLE   JCPU   PCPU  WHAT
pattyo   tty1     -            22Aug02  8days  0.50s  0.03s  /bin/sh /usr/X1
pattyo   pts/0    michoacan.home Wed 1pm  8:12m  0.32s  0.17s  -bash
pattyo   pts/5    -            24Aug02  8days  0.00s   ?     -
pattyo   pts/6    -            24Aug02  8:44m  0.36s  0.36s  /bin/bash
pattyo   pts/7    -            24Aug02  0.00s  1.49s  0.05s  w
pattyo   pts/8    -            24Aug02  8:31m  0.81s  0.81s  /bin/bash

$ write pattyo pts/8

Note: you may need to make yourself available to receive messages:

$ mesg y