Using virtual consoles

When booting from a hard disk, the PC system BIOS loads and executes the boot loader code in the MBR. The MBR then needs to know which partitions on the disk have boot loader code specific to their operating systems in their boot sectors and then attempts to boot one of them.

Fedora Linux is supplied with the GRUB boot loader which is fairly sophisticated and therefore cannot entirely fit in the 512 bytes of the MBR. The GRUB MBR boot loader merely searches for a special boot partition and loads a second stage boot loader. This then reads the data in the /boot/grub/grub.conf configuration file, which lists all the available operating systems and their booting parameters. When this is complete, the second stage boot loader then displays the familiar Fedora branded splash screen that lists all the configured operating system kernels for your choice.

Note: In some operating systems, such as Debian / Ubuntu, the /boot/grub/grub.conf file may also be referred to by the name /boot/grub/menu.lst.

default=0
timeout=10
splashimage=(hd0,0)/grub/splash.xpm.gz
title Fedora Core (2.6.8-1.521)
        root (hd0,0)
        kernel /vmlinuz-2.6.8-1.521 ro root=LABEL=/
        initrd /initrd-2.6.8-1.521.img
title Windows 2000
      rootnoverify (hd0,1)
      chainloader +1

When Linux begins to boot with its kernel, it first runs the /sbin/init program, which does some system checks, such as verifying the integrity of the file systems, and starts vital programs needed for the operating system to function properly. It then inspects the /etc/inittab file to determine Linux's overall mode of operation or runlevel. A listing of valid runlevels can be seen in Table 7-1.

Table 7-1 Linux Runlevels

Based on the selected runlevel, the init process then executes startup scripts located in subdirectories of the /etc/rc.d directory. Scripts used for runlevels 0 to 6 are located in subdirectories /etc/rc.d/rc0.d through /etc/rc.d/rc6.d, respectively.

Here is a directory listing of the scripts in the /etc/rc.d/rc3.d directory:

[root@bigboy tmp]# ls /etc/rc.d/rc3.d
...    ...    K75netfs      K96pcmcia    ...    ...
...    ...    K86nfslock    S05kudzu     ...    ...
...    ...    K87portmap    S09wlan      ...    ...
...    ...    K91isdn       S10network   ...    ...
...    ...    K92iptables   S12syslog    ...    ...
...    ...    K95firstboot  S17keytable  ...    ...
[root@bigboy tmp]#

As you can see, each filename in these directories either starts with an "S" which signifies the script should be run at startup, or a K, which means the script should be run when the system is shutting down. If a script isn't there, it won't be run.

Most Linux packages place their startup script in the /etc/init.d directory and place symbolic links (pointers) to this script in the appropriate subdirectory of /etc/rc.d. This makes file management a lot easier. The deletion of a link doesn't delete the file, which can then be used for another day.

The number that follows the K or S specifies the position in which the scripts should be run in ascending order. In our example, kudzu with a value 05 will be started before wlan with a value of 09. Fortunately you don't have to be a scripting/symbolic linking guru to make sure everything works right because Fedora comes with a nifty utility called chkconfig while Debian / Ubuntu uses the update-rc.d command to do it all for you. This is explained later.

Determining the Default Boot runlevel

The default boot runlevel is set in the file /etc/inittab with the initdefault variable. When set to 3, the system boots up with the text interface on the VGA console; when set to 5, you get the GUI. Here is a snippet of the file (delete the initdefault line you don't need):

# Default runlevel. The runlevels used by RHS are:
# 0 - halt (Do NOT set initdefault to this)
# 1 - Single user mode
# 2 - Multiuser, without NFS (The same as 3, if you do not have networking)
# 3 - Full multiuser mode
# 4 - unused
# 5 - X11
# 6 - reboot (Do NOT set initdefault to this)
# 
id:3:initdefault:                         # Console Text Mode
id:5:initdefault:                         # Console GUI Mode

Note the following:

• Most home users boot up with a Windows like GUI (runlevel 5)
• Most techies will tend to boot up with a plain text-based command-line-type interface (runlevel 3)
• Changing initdefault from 3 to 5, or vice-versa, has an effect upon your next reboot. See the following section on how to get a GUI login all the time until the next reboot.
• Of course, don't set the initdefault value to 6 or your system will constantly reboot. Setting it to 0 will never allow it to start!

Getting a GUI Console

Manual Method: You can start the X terminal GUI application each time you need it by running the startx command at the VGA console. Remember that when you log out you will get the regular text-based console again.

[root@bigboy tmp]# startx

Automatic Method: You can have Linux automatically start the X terminal GUI console for every login attempt until your next reboot by using the init command. You will need to edit your initdefault variable in your /etc/inittab file, as mentioned in the preceding section to keep this functionality even after you reboot.

[root@bigboy tmp]# init 5

When the CPU capacity or available memory on your server is low or you want to maximize all system resources, you might want to operate in text mode runlevel 3 most of the time, using the GUI only as necessary with the startx command.

Servers that double as personal workstations, or servers that might have to be operated for an extended period of time by relatively nontechnical staff, may need to be run at runlevel 5 all the time through the init 5 command. Remember you can make runlevel 5 permanent even after a reboot by editing the /etc/inittab file.

Using Virtual Consoles

There are a number of ways for you to get a command prompt when running a Linux GUI. This can be important if you need quick access to commands or you are not familiar with the GUI menu option layout.

Using a GUI Terminal Window

You can open a GUI-based window with a command prompt inside by doing the following:

• Click on the Fedora logo button in the bottom left hand corner of the screen.
• Click on Systems Tools and then Terminal

Using Virtual Consoles

By default, Linux runs six virtual console or TTY sessions running on the VGA console. These are defined by the mingetty statements in the /etc/inittab file. The X terminal GUI console creates its own virtual console using the first available TTY that is not controlled by mingetty. This makes the GUI run as number 7:

• You can step through each virtual console session by using the Ctl-Alt-F1 through F6 key sequence. You'll get a new login prompt for each attempt.
• You can get the GUI login with the sequence Ctl-Alt-F7 only in run level 5, or if the GUI is running after launching startx.

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Last modified: March 12, 2019