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CIS 191

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					                    CIS 191 - Lesson 5
                       Lesson 5
                        New 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 time
GRUB edits
 CIS 191 - Lesson 5
GRUB boot edits
     Fedora 9




  Press any key to get boot menu
 CIS 191 - Lesson 5
GRUB boot edits
     Fedora 9




  Move up and down using arrow
  keys. Press e to edit selection.
 CIS 191 - Lesson 5
GRUB boot edits
      Fedora 9




   Move up and down using arrow
   keys. Press e to edit selection.
 CIS 191 - Lesson 5
GRUB boot edits
     Fedora 9




   Make changes by moving the
   cursor and replacing or
   inserting characters.
 CIS 191 - Lesson 5
GRUB boot edits
      Fedora 9




   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
GRUB boot edits
        Fedora 9




Now press b to boot up using
the changes
   CIS 191 - Lesson 5
GRUB boot edits
        Fedora 9




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 boot
  order
 CIS 191 - Lesson 3
BIOS Boot Order
   VMware 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
BIOS Boot Order
   VMware BIOS




                 Right arrow over to
                 the Boot menu.
                           CIS 191 - Lesson 3
                        BIOS Boot Order
                              VMware BIOS




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
             BIOS Boot Order
                   VMware BIOS




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

Noter: VMware BIOS does not support
USB pen drive boots.
                        CIS 191 - Lesson 3
                    BIOS Boot Order
                          VMware BIOS




If you have multiple hard drives, they can
be searched in order as well
        CIS 191 - Lesson 3
      BIOS Boot Order
          VMware BIOS




Save any changes
you make.
loopback
 mounts
                   CIS 191 - Lesson 5
                      Lesson 5
Mounting 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.
     CIS 191 - Lesson 5

   Mounting File Systems
Like pinning the tail on the donkey

                                                mount /dev/sdb1 /mnt


                             /


     /bin     /boot   /etc   /dev     /home       /lib   /mnt




                                    lost+found/          cdrom/

            lost+found/               cis191/            floppy/

              grub/                 /dev/sda5

            /dev/sda1
                                                                     /bin
                                                                     /boot
                                                                     /dev
                                                                      /lib
                                                                   /dev/sdb1
     CIS 191 - Lesson 5

   Mounting File Systems
Like pinning the tail on the donkey

                                                mount /dev/sdb1 /mnt


                             /


     /bin     /boot   /etc   /dev     /home       /lib    /mnt




                                                           bin/
                                    lost+found/
                                                           boot/
            lost+found/               cis191/
                                                           dev/
              grub/                 /dev/sda5
                                                           lib/
            /dev/sda1
                                                         /dev/sda6
     CIS 191 - Lesson 5

    Mounting Image Files
Like pinning the tail on the donkey
 mount –o loop Desktop/rescue-cd.iso /mnt



                             /


     /bin     /boot   /etc   /dev     /home       /lib   /mnt




                                    lost+found/          cdrom/

            lost+found/               cis191/            floppy/

              grub/                 /dev/sda5

            /dev/sda1



                                                                   rescue-cd.iso
     CIS 191 - Lesson 5

    Mounting Image Files
Like pinning the tail on the donkey
 mount –o loop Desktop/rescue-cd.iso /mnt



                             /


     /bin     /boot   /etc   /dev     /home       /lib    /mnt




                                    /lost+found           /images

            /lost+found              /rsimms              /isolinux

                                    /dev/sda5            TRANS.TBL
              /grub
                                                         /dev/loop0
            /dev/sda1
 HW
Diags
                  CIS 191 - Lesson 5

           Diagnostics boot diskette
    Checking 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



                Boot order with
                floppy drive at top


Floppy with
boot code for
DOS




  When DOS
  loads,
  autoexec.bat
  run diagnostics
  program
    CIS 191 - Lesson 5
     Diagnostics
DIAG, the diagnostic program
                 CIS 191 - Lesson 5

                    Installation
       RAM 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




 Trouble
shooting
                              CIS 191 - Lesson 5
                        Booting the System

             1.   Power On Self Test (POST) – loads the BIOS.
boot order   2.   BIOS loads the Master Boot Record.
fdisk        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.
grub.conf    6.   Based upon user selection, boot program loads
                  desired kernel along with and supplied boot options
             7.   Kernel uncompresses and loads into memory.
grub.conf    8.   Kernel detects hardware and initializes its data.
                               CIS 191 - Lesson 5
                          Rooting the System

               1.   Kernel mounts the root file system
grub.conf      2.   Kernel creates and starts the init process
               3.    init reads /etc/inittab for its instructions
               4.    init performs system initialization:
                    •   presents some kind of welcome banner
/etc/inittab        •   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
/etc/rc.d      5.   Chooses which runlevel to come up in and executes those
                    scripts via rc script
               6.   daemons load
               7.   getty processes are spawned on terminal devices
                 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 floppy
                            RH9 example

Method I                                              Boot Sector
    The "simplest rescue diskette"
         cd /usr/share/grub/i386-redhat
         cat stage1 stage2 > /dev/fd0
    Note: this will allow you to boot directly into
    GRUB. At boot time you would manually enter
                                                         MBR
    (use tab completes!):
    grub                                              Boot Sector
    grub> root (hd0,0)                                  /boot
    grub> kernel /vmlinuz-2.4.20-6 ro
    root=/dev/sda2                                    Boot Sector
    grub> initrd /initrd-2.4.20-6.img                     /
    grub> boot                                        Boot Sector

Method II                                               swap
    grub
    grub> root (hd0,0)
    grub> setup (fd0)
    grub> quit
                                CIS 191 - Lesson 5

                    Making rescue floppy
    Installing boot code into floppy boot sector

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

Method IV
Put grub files to floppy and setup boot sector to use
them. See Howto on "Trouble"
                                                           MBR
                                                        Boot Sector

                                                          /boot

                                                        Boot Sector
                                                            /
                                                        Boot Sector

                                                          swap
   CIS 191 - Lesson 5

The faces of trouble
   CIS 191 - Lesson 5

The faces of trouble
   CIS 191 - Lesson 5

The faces of trouble
   CIS 191 - Lesson 5

The faces of trouble
   CIS 191 - Lesson 5

The faces of trouble
   CIS 191 - Lesson 5

The faces of trouble
   CIS 191 - Lesson 5

The faces of trouble
   CIS 191 - Lesson 5

The faces of trouble
   CIS 191 - Lesson 5

The faces of trouble
   CIS 191 - Lesson 5

The faces of trouble
   CIS 191 - Lesson 5

The faces of trouble
   CIS 191 - Lesson 5

The faces of trouble
   CIS 191 - Lesson 5

The faces of trouble
   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        mount –o loop Desktop/rescue-cd.iso /mnt
                                   mount –o loop Desktop/rescue-floppy.img /mnt
images on loopbacks
Backup MBR to file named mbr       dd if=/dev/sda of=mbr bs=512 count=1


Make rescue floppy for specific    grub
                                   > root (hd0,0)     (location of /boot)
system                             > setup (fd0)
                                   > quit

				
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posted:8/19/2011
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