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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
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
Note: In some operating systems, such as Debian / Ubuntu, the
file may also be referred to by the name
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.
|Mode||Directory||Run Level Description|
|2||/etc/rc.d/rc2.d||Not used (user-definable)|
|3||/etc/rc.d/rc3.d||Full multi-user mode (no GUI interface)|
|4||/etc/rc.d/rc4.d||Not used (user-definable)|
|5||/etc/rc.d/rc5.d||Full multiuser mode (with GUI interface)|
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
Here is a directory listing of the scripts in the
[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
directory and place symbolic links (pointers) to this script in the appropriate
/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
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
Debian / Ubuntu uses the
update-rc.d command to do it all for you.
This is explained later.
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:
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.
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.
You can open a GUI-based window with a command prompt inside by doing the following:
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:
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