How to change BIOS settings to boot Linux from Live CD / USB

One of the great steps to be interpose between the less experienced users and the use of other operating systems is usually the BIOS setting. plunge simple but critical y necesario for test e to install any distribution Linux.

General remarks

Once the live-cd or live-usb of your favorite distro has been created, it only remains to configure the BIOS so that the system boots from the corresponding drive.

As a brief explanation, let's say that when starting a computer, the first thing that is loaded is the BIOS (Basic Input / Output System), whose main objective is to execute routines that verify the correct operation of the hardware and later load the operating system. In other words, it's that screen you see before the operating system starts to load (be it Windows or any other).

What we must do to test and / or install Linux is to enter the BIOS configuration screen and tell it that instead of starting the operating system that is installed on the hard disk, start the one found on our live-cd or live-usb, as the case may be.

How to enter the BIOS setup screen

Unfortunately, there is no universal method to accomplish this task as each motherboard model comes with a specific BIOS and it would be impossible to document the full range of configuration managers. However, if we get carried away by intuition, the process is quite simple.

To do this, when you connect the equipment and as soon as the first messages begin to appear, you can press the «Pause» key to stop the boot process and see what appears on the screen with confidence. This must be done quickly since the mentioned messages are visible only a few seconds.

If you can't stop the startup process, just look carefully at the initial screen. At the bottom of this screen you will usually find a line similar to this: «Press F2 to enter SETUP». Of course, the key can be any other. The most common are: [DEL] or [Del], [Insert], [Esc], [F2], [F1], [F10] or any other function key.

Some newer BIOSes also allow you to select the boot device using another key, without accessing the BIOS setup page. This is because it is usually common to modify these settings and because in this way the user is prevented from making another modification by mistake. If the BIOS has this "shortcut", just use the arrows on the keyboard and select the corresponding boot device.

This "shortcut", however, only works for 1 start; the next time the operating system installed on the hard disk will boot. So, recapping, to make the change "permanently", or in the event that the BIOS does not have the aforementioned "shortcut", you have to press the corresponding key to enter the BIOS configuration screen, which may have a totally different aspect to the one shown here, but with similar characteristics and benefits.

Configure the boot drive

This is where we can only give general guidelines, since the BIOS setup screen varies from board to board. However, in general terms, you must find a tab similar to "Boot" or an entry called "Boot sequence" or "Boot priority" within a more "general" tab of the "Advanced BIOS Features" style.

At this point it is important to remember that this is where the sequence of boot. This means that we will establish a chain of priorities: first, that it tries to boot from the cd or the usb (depending on how we want to test our distro); if that fails, let it try to boot from the operating system installed on the hard drive, and so on.

The way to select the tabs or change the settings is very varied. Sometimes it is a matter of simply using the arrows, other times you have to use the PgUp and PgDn keys, etc. However, in a column on the right you will always find an explanatory table that indicates the steps to follow. At the bottom, for its part, appear the keys to press to perform the most common tasks. A rudimentary knowledge of English is enough to understand what to do.

Last but not least, save your changes and exit the setup program. To do this, you have to press the corresponding key (in the case of the previous screenshot, F10).

Old BIOS

Some older BIOSes do not come with support for booting from a USB drive. In that case, the best option is usually to use a live-CD to test your preferred Linux distro. However, it is also possible to force boot from USB (without corresponding BIOS support for this) using PLOP Boot Manager.

Other, older BIOSes don't even include support for booting from the CD-ROM drive. In that case, the natural alternative would be to use boot floppies, which only a few Linux mini-distros have available. Fortunately, if the machine has a CD reader, it is possible to boot from a live-cd, even if the BIOS does not support it, using Smart Boot Manager o PLOP Boot Manager.

UEFI and Secure Boot

The Unified Extensible Firmware Interface (UEFI) is a specification that seeks to replace the old BIOS interface, which for many was too "eighty" and with a similar aspect to the old DOS. In addition, it incorporates several extra functionalities, which are not the objective of this article, among which the so-called "secure boot" or "secure boot" stands out.

Secure Boot prevents the computer from starting the operating system if the boot loader does not have a valid digital certificate, the product of arbitrary modification of malicious code. In this way, any bootkit type malware will not be able to work effectively.

However, the fact that Microsoft forced manufacturers to distribute their computers with this option enabled in order to obtain Windows 8 certification generated great stir. In particular, it is concerned that this feature serves the sole purpose of preventing users from starting an operating system other than Windows. In this case, the requirement is more of a restriction on users, not a security feature.

According to Microsoft, there are two "guarantees" that this will not happen. On the one hand, both UEFI (through a boot using a "BIOS compatible mode", also known as "Legacy Boot") and Secure Boot can be disabled. On the other hand, the authorization required by Secure Boot for a digital signature is issued by an independent authority, which is not the manufacturer or Microsoft.

The truth is that currently Linux distributions are just giving their first steps to run on UEFI and Secure Boot enabled machines.

In the current state of affairs, it is best to disable Secure Boot before installing Linux. Support for UEFI, on the other hand, is more developed, although it still has some flaws. In case of error, there will be no alternative but to choose the "Legacy Boot" and disable the UEFI.