cis 191 - lesson 5 lesson 5 new skills boot time grub edits (review) changing bios boot order on a...

CIS 191 - Lesson 5

Lesson 5New Skills

• Boot time GRUB edits (review)

• Changing BIOS boot order on a VM (review)

• Mounting CD ISO and floppy Image files on loopback devices

(new)

• Making a diagnostics boot diskette (new)

Boot timeGRUB edits

CIS 191 - Lesson 5

GRUB boot editsFedora 9

Press any key to get boot menu

CIS 191 - Lesson 5


Move up and down using arrow keys. Press e to edit selection.

CIS 191 - Lesson 5


Make changes by moving the cursor and replacing or inserting characters.

CIS 191 - Lesson 5


For this example we replace UUID specification of the / partition with /dev/sda5, remove the rhgb and quiet options and add single to boot up in single user mode. Hit Enter when finished.

CIS 191 - Lesson 3


Now press b to boot up using the changes

CIS 191 - Lesson 5


The system now boots into single user mode.

NOTE: The GRUB changes are temporary. /boot/grub/grub.conf must be edited to make changes permanent

NOTE: The single option on the kernel line is very handy when troubleshooting boot problems.

BIOS bootorder

CIS 191 - Lesson 3

BIOS Boot OrderVMware BIOS

1) Click inside the VM so it has the focus

2) Tap F2 repeatedly to enter BIOS configuration.

Note: You don't get much time for this so have your finger over the F2 key!

CIS 191 - Lesson 3


Right arrow over to the Boot menu.

CIS 191 - Lesson 3


Re-order to suit your needs. This VM will look first on a floppy, then a CD, then the hard drive and then try network boot.

CIS 191 - Lesson 3


A + means the group can be expanded (use Enter)

Noter: VMware BIOS does not support USB pen drive boots.

CIS 191 - Lesson 3


If you have multiple hard drives, they can be searched in order as well

CIS 191 - Lesson 3


Save any changes you make.

loopbackmounts

CIS 191 - Lesson 5

Lesson 5Mounting CD ISO and floppy Image files on loopback devices

Desired: Be able to directly mount an CD ISO image file. Avoids having to burn downloaded ISO's on to CD's , then loading the new CD into computer, and then finally mounting /dev/cd0.

Solution: Use loopback devices.

/boot

/dev

/

/bin /etc /mnt

cdrom/

/dev/boot /home

cis191/

grub/

lost+found/

lost+found/

floppy/

/lib

/dev/sdb1

/dev/sda1

/dev/sda5

Mounting File SystemsLike pinning the tail on the donkey

mount /dev/sdb1 /mnt

/lib

/bin

CIS 191 - Lesson 5

/

/bin /etc /mnt

bin/

/dev/boot /home

cis191/

grub/

lost+found/

lost+found/boot/

dev/

/lib

/dev/sda1

/dev/sda5

Mounting File SystemsLike pinning the tail on the donkey

/dev/sda6

mount /dev/sdb1 /mnt

lib/

CIS 191 - Lesson 5

/

/bin /etc /mnt

cdrom/

/dev/boot /home

cis191/

grub/

lost+found/

lost+found/

floppy/

/lib

/dev/sda1

/dev/sda5

Mounting Image FilesLike pinning the tail on the donkey

mount –o loop Desktop/rescue-cd.iso /mnt

rescue-cd.iso

CIS 191 - Lesson 5

/

/bin /etc /mnt

/images

/dev/boot /home

/rsimms

/grub

/lost+found

/lost+found

/isolinux

TRANS.TBL

/lib

/dev/sda1

/dev/sda5

Mounting Image FilesLike pinning the tail on the donkey

/dev/loop0

mount –o loop Desktop/rescue-cd.iso /mnt

CIS 191 - Lesson 5

HWDiags

CIS 191 - Lesson 5

Diagnostics boot disketteChecking out your system prior to installing Linux

• Check RAM quantity

• Check drive sizes

• Inspect other hardware resources as necessary

CIS 191 - Lesson 5

Diagnostics boot disk

BIOS code

Floppy with boot code for DOS

Boot order with floppy drive at top

When DOS loads, autoexec.bat run diagnostics program

CIS 191 - Lesson 5

DiagnosticsDIAG, the diagnostic program

CIS 191 - Lesson 5

InstallationRAM Requirements & Configuration Issues

• The more RAM the better

• Graphics (X Windows) runs best with a minimum of 64MB

RAM

• Swap space size should be 1.5 to 2 times RAM – up to

256 MB. At 256MB RAM and above, swap space should

equal RAM

CIS 191 - Lesson 5

Troubleshooting

CIS 191 - Lesson 5

Booting the System

1. Power On Self Test (POST) – loads the BIOS.

2. BIOS loads the Master Boot Record.

3. MBR read its partition table to determine which

partition to boot into.

4. MBR loads the boot program in the active partition.

5. Boot program presents user with boot prompt menu.

6. Based upon user selection, boot program loads

desired kernel along with and supplied boot options

7. Kernel uncompresses and loads into memory.

8. Kernel detects hardware and initializes its data.

fdisk

boot order

grub.conf

grub.conf

CIS 191 - Lesson 5

Rooting the System

1. Kernel mounts the root file system2. Kernel creates and starts the init process3. init reads /etc/inittab for its instructions4. init performs system initialization:

• presents some kind of welcome banner• allows for and interactive startup• set up keyboard mapping, system fonts, plug and play

devices, …• checks for dirty file systems, can clean them if

necessary• checks disk quotas and swap space• mounts all file systems

5. Chooses which runlevel to come up in and executes those scripts via rc script

6. daemons load7. getty processes are spawned on terminal devices

/etc/inittab

grub.conf

/etc/rc.d

CIS 191 - Lesson 5

Preparing for trouble

• Record your partition and mount information (output from fdisk –l and mount)

• Make a copy of your MBR. For example:dd if=/dev/sda of=mbr bs=512 count=1

• Create a bootable rescue floppy with GRUB installed that roots to your / partition on your Linux system.

• Record grub.conf

• Record MBR xxd output

• Record /etc/inittab

CIS 191 - Lesson 5

Rescue boot devices

• Put pristine GRUB stage1 and stage2 files• Add GRUB config files for more control• Add a kernel for more options• Make vender rescue disk• Add a kernel and small root file system with tools• Use small Linux distribution like Knoppix

CIS 191 - Lesson 5

Making rescue floppyRH9 example

Boot Sector

/dev

/fd0

Method I The "simplest rescue diskette"

cd /usr/share/grub/i386-redhatcat stage1 stage2 > /dev/fd0

Note: this will allow you to boot directly into GRUB. At boot time you would manually enter (use tab completes!):grubgrub> root (hd0,0)grub> kernel /vmlinuz-2.4.20-6 ro root=/dev/sda2grub> initrd /initrd-2.4.20-6.imggrub> boot

Method IIgrubgrub> root (hd0,0)grub> setup (fd0)grub> quit

Boot Sector

/boot

MBR

Boot Sector

/

Boot Sector

swap

/dev

/sda

2

/dev

/sda

3

/dev

/sda

1

CIS 191 - Lesson 5

Making rescue floppyInstalling boot code into floppy boot sector

Boot Sector

/dev

/fd0

Method III (RH9) mkbootdisk --device /dev/fd0 $(uname –r)

Method IVPut grub files to floppy and setup boot sector to use them. See Howto on "Trouble"

Boot Sector

/boot

MBR

Boot Sector

/

Boot Sector

swap

/dev

/sda

2

/dev

/sda

3

/dev

/sda

1

CIS 191 - Lesson 5

The faces of trouble

CIS 191 - Lesson 5

For the command/file collection

Task Command or file

The simplest boot floppy. cd /usr/share/grub/i386-redhat/cat stage1 stage2 > /dev/fd0

After booting into grub, manually enter appropriate grub commands you would normally see in grub.cong

Make RH9 emergency boot disk mkbootdisk --device /dev/fd0 $(uname –r)

Mount CD ISO or floppy disk images on loopbacks

mount –o loop Desktop/rescue-cd.iso /mntmount –o loop Desktop/rescue-floppy.img /mnt

Backup MBR to file named mbr dd if=/dev/sda of=mbr bs=512 count=1

Make rescue floppy for specific system

grub> root (hd0,0) (location of /boot)> setup (fd0)> quit

cis 191 - lesson 5 lesson 5 new skills boot time grub edits (review) changing bios boot order on a...

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bios boot ordervmware

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grub changes