Controlling Linux with Boot Parameters

Before you select a partition to boot, you can get a text-mode prompt from the boot loader and enter other commands.

To provide boot parameters to the Linux kernel, press a when the GRUB screen appears. This causes GRUB to prompt you for commands to add to its default boot command (which, I assume, is set to boot Linux). Then, you can type anything else you want to add to that command. For example, to boot the system into single user mode, press the Spacebar and type:


You can pass many more parameters to the Linux kernel. To learn the kernel boot parameters, type man bootparam in a terminal window (after you boot Linux).

As the Linux kernel starts, you see a long list of opening messages, often referred to as the boot messages. (Because of the graphical boot screen, you may not see all the messages, but you can see these messages at any time by typing the command dmesg in a terminal window.) These messages include the names of the devices that Linux detects. One of the first lines in the boot messages reads (to see this message, type dmesg | grep BogoMIPS):

Calibrating delay loop... 4997.12 BogoMIPS (lpj=2498560)

BogoMIPS is Linux jargon for a measure of time. The number that precedes BogoMIPS depends on your PC's processor speed, whether it's an old 400 MHz Pentium II or a new 3.6 GHz Pentium 4. The kernel uses the BogoMIPS measurement when it has to wait a small amount of time for some event to occur (like getting a response back from a disk controller when it's ready).

insider As you may know, MIPS is an acronym for millions of instructions per second —a meas-insight ure of how fast your computer runs programs. As such, MIPS is not a very good measure of performance because comparing the MIPS of different types of computers is difficult. BogoMIPS is bogus MIPS, which refers to an indication of the computer's speed. Linux uses the BogoMIPS number to calibrate a delay loop, in which the computer processes some instructions repeatedly until a specified amount of time has passed.

The BogoMIPS numbers can range anywhere from 1 to 6,000 or more, depending on the type of processor (386, 486, or Pentium) and the processor's speed. An older 33 MHz 80386DX system has a BogoMIPS of about 6, whereas a 66 MHz 80486DX2/66 system shows a BogoMIPS of about 33. The BogoMIPS for newer Pentium systems is much higher. For example, on an old 200 MHz Pentium MMX system, Linux reports a BogoMIPS of 398.13. However, on a PC with a 2.53 GHz Celeron processor, the BogoMIPS is 4997.12. It's higher yet on more recent 3 GHz or better Pentium 4 systems.

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