User's Guide
Chapter 4 - Starting and Stopping the System and Graphical Interface

Like any version of Linux, Debian has strict procedures for starting and stopping a system. These procedures are part of the operating system's security features. They also prevent accidental damage to the system.

To start your computer, you must choose the operating system to load from the boot manager, and then log in to a user account.

To stop your computer, you must log out of the user account, then halt or reboot the system.

This chapter explains:

• Working with User Accounts.

• Choosing an operating system from the boot manager.

• Logging in to a user account with a desktop or a command line.

• Shutting down the system.

• Starting and closing the graphical interface.

• Changing user accounts after logging in.

4.1 Working With User Accounts

Linux is designed for multiple users. To use the system, you must log in with a user account. To use an account, you must know both the user name and the password.

User accounts are organized into groups of accounts with similar access to the system. The software and the hardware you can use depends on the user account that you are using and the groups to which it belongs.

For more information,

When you install Debian, create at least two user accounts: a regular user account for everyday computing, and a root account for system administration. Normally, you also want one regular user account for each person who uses the system.

4.1.1 Understanding Regular User Accounts

A regular account is used for everyday computing. Each account has a home directory. By default, users' home directories are beneath the / home directory. This home directory is usually the same as the user name for the account.

When you are logged in with an account, you usually can:

• Read, write, and use files and directories in the account's home directory.

• Read, write, and use all files and directories to which other users give you permission.

• Read, but not write or use basic system files.

On some systems, the system administrator may choose to make basic system files unreadable by regular users.

Accounts may annoy those familiar with other operating systems. However, user accounts have several advantages:

• Your private files are secure. You can change your setting so that other regular users cannot change, nor even see your files.

• Your desktop and command line interfaces can be customized.

• Viruses are less likely to infect the computer. While viruses are not the problem on Linux that they are on other operating systems, any damage is likely to affect only one user's files.

• Only the root user can use important files. Mistakes, like viruses, are likely to affect only a user's personal files.

4.1.2 Understanding the Root Account

The root account has full access to all software and hardware on the system. In most cases, it should be the only account that has full access. For this reason, the root user is sometimes called the super user or privileged user. The root user's home directory is /root.

[Note]

The /root directory is different from the root directory at the top of the Linux directory tree. Nor is it the same as the root partition - the partition that the root directory is on.

To avoid damaging your system, take the following precautions when using the root account:

• Use the root account only for configuration or administration.

• Use the root account as briefly as possible.

• Give the root password to as few people as possible. Each of those people should use another account for everyday computing.

• Do not give root privileges to any other account.

• Do not use the root account on the Internet.

• Use these precautions even on a single, unnetworked computer.

Using the Boot Loader

img/Login-2.png

Many users have multiple operating systems or Linux kernels on the same computer. Using a boot loader, you can choose which operating system or kernel to start your computer with.

Debian uses grub (Grand Unified Boot Loader). However, other boot loaders are widely used, including lilo (the Linux Loader).

grub is the first thing that you see when starting a Debian system.

You can edit grub to display any installed operating system or kernels. Your Debian system also includes a single-user mode. The single-user mode starts the machine with a basic system that the root user can use for troubleshooting.

To choose an operating system from grub , do one of the following:

• Highlight a menu item by using the arrow keys. Then press the Enter key. or

• Wait for the default choice to start. The default choice starts in 10 seconds if you make no selection.

In either case, Debian starts. After processes are started and some tests are run, the graphical display starts and the log in screen opens.

You can reconfigure grub and add other operating systems to it. See Configuring the Boot Loader, Section 13.3.4.

4.2 Logging in to Debian

img/Login-3.png

After Debian has started its initial processes and run some checks, the log in screen opens.

Logging in is the process of entering your user account and your password.

[Note]

You cannot bypass this process, the way you can in some operating systems.

By default, you log in graphically. However, you can also configure Debian to start in a command line instead.

4.2.1 Logging in Graphically

From the login window:

• 1 If you want, select options from the menu:

• Choose a desktop or window manager from the Session menu.

• Choose a language from the Language menu. In both cases, if you do not make a choice, then the last choices you made are used as defaults. Usually, you do not need to make a choice.

• 2 Type your user account name in the login field and press the Enter key. The field changes to the password field.

[Note]

Use the root account only for configuration or administration work.

• 3 Type the password for your user account. If you have changed any options since the last time you logged in, a dialogue window displays. Select the Yes button to make the new options the default. If you type an account name and password that are entered into the system, then the desktop starts. If the account name or password are incorrect, then you return to the login window.

4.2.2 Logging in from a Command Line

You can log in from a command line if you configure Debian not to start the graphical interface automatically.

You can also start Debian in single-user mode, which does not include the graphical interface. If you press Ctrl-D from the log prompt in single-user mode, the graphical interface starts.

• 1 At the login prompt, type your user account name and press the Enter key. The password prompt displays.

[Note]

Use the root account only for configuration or administration work.

• 2 Type the password for your user account. If you type an account name and password that are entered into the system, then a command prompt displays and you are ready to work. If the account name or password are incorrect, you return to the login prompt.

4.3 Shutting Down Debian

Linux is generally running many processes at once. Many of these run in the background, where they are easy to forget. For this reason, shutting down the system properly is essential.

A proper shutdown is often called a graceful shutdown or exit. During a graceful shutdown:

• All processes and programs are closed.

• All information in ram memory or on the swap partition is written to the hard drive.

• All log files are updated.

• All partitions are dismounted.

[Warning]

If you do not shut down properly, you may damage the operating system or lose files. At best, the next time you start your computer, you have a long delay while the root partition is checked.

You can shut down from:

• The desktop.

• A command line.

• The keyboard.

4.3.1 Shutting Down from the Desktop

• 1 From the menu, select Logout. A confirmation window displays.

• 2 If you have any unsaved changes to the desktop, select the Save current setup box.

• 3 Select the Yes button to log out and return to the log in screen.

• 4 From the login screen, you can:

• Log in as another user. If you only need to change user accounts briefly, you may prefer to use su instead. See Changing User Accounts, Section 4.5.

• Select System > Reboot from the menu. The system shuts down and restarts.

• System > Halt from the menu. The system shuts down. If you select Reboot or Halt, a confirmation screen appears.

• 5 Select the Yes button to reboot or halt the system.

[Warning]

If you do not shut down properly, then you risk damaging the operating system. Even if no damage is done, your system checks the root partition before restarting.

A quicker alternative is to open the command line and shut down from there. See Shutting Down Debian, Section 4.3-check: enabled?

4.3.2 Shutting Down From the Command Line

• 1 Log in as the root user.

• 2 From the command line or from a command line window, enter one of the following commands:

• halt : All processes immediately stop and the system shuts down.

• shutdown halt + minutes or shutdown halt hh:mm : A warning message displays until all processes stop and the system shuts off. minutes is the number of minutes before the system shuts down. hh:mm sets the time in hours and minutes for the shutdown using a 24 hour clock.

• reboot : The system shuts down and restarts.

[Note]

Use the shutdown command to give regular users time to save their work.

[Warning]

If you do not shut down properly, then you risk damage the operating system. Even if you don't, your system will check and, if necessary, repair the root partition before restarting.

4.3.3 Shutting Down From the Keyboard

• 1 Press the Ctrl-Alt-Backspace keys in sequence. The desktop closes, and the log in screen opens.

• 2 From the login screen, you can:

• Log in as another user. If you only need to change user accounts briefly, you may prefer to use su instead. See Changing User Accounts, Section 4.5.

• Select System > Reboot from the menu. The system shuts down and restarts.

• System > Halt from the menu. The system shuts down. If you select Reboot or Halt, a confirmation screen appears.

• 3 Select the Yes button to reboot or halt the system.

4.4 Starting and Shutting Down the Graphical Interface

Linux uses the X Window system for a graphical interface, such as a desktop and/or a window manager. See Understanding Graphical Interfaces, Section 6.1.

You can choose to start a graphical interface automatically when you start your computer. This is the default setup for Debian. Alternatively, you can start the X Window system from the command line.

4.4.1 Starting a Graphical Interface From the Command Line

You must have the X Window System installed as well as a desktop and/ or window manager.

• 1 Log in to a command line. See Logging in from a Command Line, Section 4.2.2.

• 2 Type: startx . The X Window System starts and the login window displays.

[Note]

The X Window System is not loaded if you are starting from single-user mode.

• 3 Log in. See Logging in Graphically, Section 4.2.1.

4.4.2 Exiting the Graphical Interface

You can:

• Exit the X Window System and keep it running in the background.

• Close down a X Window System session that you started from the command line.

4.4.3 Keeping the X Window System Running in the Background

• 1 Press Ctrl-Alt-F1. A full screen command line displays with a login prompt.

• 2 Log in. See Logging in from a Command Line, Section 4.2.2. To return to the desktop, press Alt+F7. You return to your original user account.

4.4.4 Closing Down an X Window System

• 1 Open a command line from the panel.

• 2 Log in as the root user. See Changing User Accounts, Section 4.5.

• 3 From a command line, type /etc/init/d/gdm stop. Then press the Enter key. A full screen command line displays with a login prompt.

4.5 Changing User Accounts

From both the command line and the desktop, you can logout as one user, then login as another. However, a more convenient way to change accounts is to use the su command ("switch user" or "set user").

This command is especially useful if you need to log in briefly as the root user while using a graphical interface. However, to use it effectively, you need to be comfortable working from the command line.

To change user accounts:

• 1 If necessary, open a command line from the panel.

• 2 From a command line, type su - user command. You do not need to enter a command. If you do enter a command, you use the other user account only to run that command. Then you return to your original account. A password prompt appears if you are logged in as a regular user. If you are logged in as the root user, then no password prompt displays.

• 3 If necessary, enter the password for the account that you are logging into.

[Note]

You have changed accounts only for the command line you are using. If you are running a desktop, then you are still logged in with your original account in other windows.

• 4 If you changed accounts without running a command, repeat this process to return to your original account. If you run a command, you return to your original account as soon as the command is carried out.

User's Guide