LILO Overview

TODO: {{#todo:In Progress(11.27.13-01:00->MD+);(11.27.13-17:50->MD+)|Mike Dean|oe 4,oe 5,md,Review,ky}}

The LInux LOader - LILO

LILO is a bootloader which was created for Linux. LILO was the default bootloader used for most desktop and server distributions for many years. It is still used on x86 embedded systems because it provides everything an embedded system needs to boot into embedded Linux.

Using LILO

When LILO is installed on a drive or partition, LILO will provide a menu at boot time. This menu typically shows a list of available operating system kernels and/or operating systems from which a user may select. On embedded systems, this menu is typically streamlined down to a very simple interface.

When LILO is configured with a timeout, as it usually is, a user may simply wait for the duration of the timeout for LILO to boot the operating system and kernel which have been configured as default for the system. If the user doesn't wish for the default to boot, the user may press any key other than the enter key before the timeout duration has expired to access alternative options. If the user presses enter during the timeout delay, the timeout immediately expires and the boot process continues with the default configured OS and kernel. The default boot process starts as shown here:

LILO 22.8 boot:
Loading emac-oe................................................
BIOS data check successful

Pressing the TAB key will show a list of available OS configurations to boot. Usually, there will only be one available.

LILO 22.8 boot:
emac-oe
boot:

Typing the name of the OS configuration (the OS + kernel) will boot the system with that configuration.

LILO 22.8 boot:
emac-oe
boot: emac-oe
Loading emac-oe................................................
BIOS data check successful
EMAC OpenEmbedded Linux 4.0 (stable-2009)
Some code contained within Copyright 2008-2010 EMAC, Inc.

emac 2009-stable vortex86 ttyS0

vortex86 login:

Once the system has booted to the login prompt, the user may log into the system as usual. On EMAC products, the default password for the root account is emac_inc. Please see System Log In for more information regarding the login process.

Additional Abilities of LILO

In addition to the normal boot selection described above, LILO is also able to pass arguments to the Linux kernel for booting. These arguments can be useful for enabling output of boot messages, configuring a video driver, and configuring a good number of other things which can accept kernel command line configuration options.

For example, the console=ttyS0,115200 option can be passed to a kernel to enable boot message output to the serial console:

LILO 22.8 boot:                                                                 
emac-oe                                                                         
boot: emac-oe console=ttyS0,115200                                              
Loading emac-oe................................................                 
BIOS data check successful                                                      
Linux version 2.6.30.10 (mdean@engineering0) (gcc version 4.2.4) #1 PREEMPT Fri Feb 1 18:38:41 CST 2013
KERNEL supported cpus:
  Intel GenuineIntel
  AMD AuthenticAMD
  NSC Geode by NSC
  Cyrix CyrixInstead
  Centaur CentaurHauls
  Transmeta GenuineTMx86
  Transmeta TransmetaCPU
  UMC UMC UMC UMC
CPU: vendor_id 'Vortex86 SoC' unknown, using generic init.
...
...
...
EMAC OpenEmbedded Linux 4.0 (stable-2009)
Some code contained within Copyright 2008-2010 EMAC, Inc.

emac 2009-stable vortex86 ttyS0

vortex86 login:

Other arguments to the kernel are passed in a similar manner. The available options to pass will depend on the specific configuration of the kernel LILO is booting.

Installing LILO

LILO can be installed onto a disk for use by the local machine, or it can be installed onto a removable storage device for use in booting on a different machine. Both installation methods are discussed here. Usually, the former method will be used to update the existing bootloader for new kernels, new kernel configurations, or new boot time options. The latter method is generally used to initially set up a bootable storage device which will later be inserted into the embedded system for which it is being created.

Installing Onto the Local Machine

Before LILO can be used to boot a system, it must be installed on the boot device. It must also be reinstalled any time the configuration is changed, or the new configuration will not take effect. Fortunately, installing LILO is easy.

The easiest way to install LILO on the local system's Master Boot Record with the default configuration file (/etc/lilo.conf), is to type:

root@oe:/# lilo

Unfortunately, you may not want to install LILO this way. This method works well for systems where only a small change is required to the default configuration, but is often not what you want on an embedded system. Many times, you will want to use an alternate file to store your new configuration so that you don't make a breaking change to your known-good configuration file. If you prefer to use a configuration file in an alternate location, you will need to type:

root@oe:/# lilo -C /etc/alternate_lilo_configuration_file.conf

The -C (capital C) switch tells lilo to use the configuration file specified after the switch when installing itself.

---

Installing LILO Onto a Removable Drive

Unfortunately, the last method shown above is still not what you need to do when your embedded machine's root drive is not in the running embedded system. If you have a Compact Flash disk, for instance, containing your Linux filesystem, and it is mounted on your desktop Linux development machine, you will need to jump through a few hoops to install the bootloader onto the Compact Flash card. This method is usually necessary when you don't yet have a bootable disk for your embedded machine.

Two sets of directions for doing this are given here. The first set of directions is generic, and will work for desktop Linux distributions which do not include an automounter or have an automounter which doesn't interfere with the process. The second set of details a known workaround The following steps will need to be performed to install LILO onto a removable drive:

Installing from a System with No Automounter or a Non-Interfering Automounter

For simpler systems without an automounter, or with an automounter that doesn't try to protect the user from possible malicious code, follow these directions.

1. Mount the drive.

   1. Insert the flash card into your card reader.

   2. Find out where the device node for the card was created (assuming you have udev on your system) by using dmesg.

      user@ldc:~/# dmesg | tail -n 15
      ...
      [126468.154762] sd 6:0:0:0: [sdb] 7831152 512-byte logical blocks: (4.00 GB/3.73 GiB)
      [126468.182196]  sdb: sdb1
      [126468.688061] kjournald starting.  Commit interval 5 seconds
      [126468.691223] EXT3-fs (sdb1): using internal journal
      [126468.691225] EXT3-fs (sdb1): recovery complete
      [126468.694526] EXT3-fs (sdb1): mounted filesystem with ordered data mode
      [173828.541718] sdb: detected capacity change from 4009549824 to 0
      [179577.977554] sd 6:0:0:0: [sdb] 7831152 512-byte logical blocks: (4.00 GB/3.73 GiB)
      [179577.994839]  sdb: sdb1
      [179578.376157] kjournald starting.  Commit interval 5 seconds
      [179578.381428] EXT3-fs (sdb1): using internal journal
      [179578.381433] EXT3-fs (sdb1): recovery complete
      [179578.384661] EXT3-fs (sdb1): mounted filesystem with ordered data mode
      

   3. Since the device node sdb1 was created for the flash card (in this example), we need to mount that device somewhere where we can access it. In this example, we'll use /mnt/cfcard:

      user@ldc:~/# sudo su
      [sudo] password for user:
      root@ldc:~/# mkdir -p /mnt/cfcard
      root@ldc:~/# mount /dev/sdb1 /mnt/cfcard
      root@ldc:~/#
      

2. Copy device nodes into the filesystem:

   root@ldc:~/# cd /mnt/cfcard
   root@ldc:/mnt/cfcard# cp -a /dev/sdb* dev/
   root@ldc:/mnt/cfcard#
   

3. chroot into the filesystem:

   root@ldc:/mnt/cfcard# chroot .
   root@ldc:/#
   

4. Run lilo with the appropriate LILO configuration file. Be sure to double check to ensure that the configuration file is correct, because a mistake here could render your desktop system unbootable.

   root@ldc:/# lilo -C /etc/lilo.conf.boot
   Warning: '/proc/partitions' does not exist, disk scan bypassed
   Added emac-oe *
   One warning was issued.
   root@ldc:/#
   

   Note that the warning here is normal, because you're installing LILO inside a chroot which doesn't have a mount /proc virtual filesystem.

5. Exit the chroot and unmount the device:

   root@ldc:/# exit
   root@ldc:/mnt/cfcard# cd ..
   root@ldc:/mnt# umount cfcard
   

6. It is now safe to remove the flash card and put it into your embedded machine.

Workaround for the Ubuntu Automounter (and Possibly Others)

On many Linux desktops, a memory card will be automounted when it is inserted. While this is a nice convenience feature for most users, it comes at the expense of developers. This automount feature can be a source of frustration for those who haven't already found a way around the issues it causes.

Fortunately, we at EMAC have already found a method which works reliably on our recommended Linux distribution, Ubuntu 12.04 LTS, and have documented it here. On other systems, such as Debian, a workaround may not be needed. If your system does not automount, see below.

1. Insert the flash card into your card reader, and wait for the file browser window to appear. If a messagebox appears asking you to choose what to do, tell it to open a file browser for browsing the files on the card.

2. Keep the file browser window open, and stash it away for later use.

3. Open a terminal and create a /mnt/cfcard directory, if it does not exist:

   user@ubuntu:/# mkdir /mnt/cfcard
   

4. Find out the device name of the card by looking for where the card was mounted. The file browser window will list the name of the card under Devices in the left pane. Often times, the name will be EMAC_OE. Look for this name in the output of the df command:

   user@ubuntu:/# df -hT | grep EMAC
   /dev/sdb1                       ext3      3.7G  223M  3.3G   7% /media/EMAC_OE
   

5. From the output of this command, we can see that the /media/EMAC_OE mountpoint was mounted onto the /dev/sdb1 device. Therefore, this is the device in which we're interested.

6. Mount the device on the directory from step i, without unmounting it first:

   user@ubuntu:/# mount /dev/sdb1 /mnt/cfcard
   user@ubuntu:/#
   

7. Now, switch to the root user account (if you aren't already root) and copy the device node files into the destination filesystem. The device node file will be needed so that LILO will be able to talk to the flash card. NOTE: Use your user's password to switch to root if you use the method shown here:

   user@ubuntu:/# sudo su
   [sudo] password for user: 
   root@ubuntu:/# cd /mnt/cfcard
   root@ubuntu:/mnt/cfcard#
   root@ubuntu:/mnt/cfcard# cp -a /dev/sdb* dev/
   root@ubuntu:/mnt/cfcard#
   

8. Now, use the chroot command to make the directory where you mounted the card the effective root directory for your terminal session:

   root@ubuntu:/mnt/cfcard# chroot .
   root@ubuntu:/#
   

9. Now that you're effectively running inside the filesystem on the flash card, you are able to run LILO to install the bootloader. First, be sure to double check to ensure that the configuration file you're using points to the correct device node (in this example, /dev/sdb1) so that you don't overwrite the bootloader on your desktop. If you overwrite the bootloader on your desktop, it will render your desktop system unbootable! So, make sure to double check first.

10. When you are sure you're using the right device node, run LILO to install the bootloader:

    root@ubuntu:/# lilo -C /etc/lilo.conf.boot
    Warning: '/proc/partitions' does not exist, disk scan bypassed
    Added emac-oe *
    One warning was issued.
    root@ubuntu:/#
    

    The warning, in this case, is normal. It appears because you're in a fake "running system," which means the virtual files in the /proc/ filesystem aren't mounted and able to provide information; hence, the non-existence of the /proc/partitions file.

11. Now, you need to umount the device:

    root@ubuntu:/# exit
    root@ubuntu:/mnt/cfcard# cd ..
    root@ubuntu:/mnt# umount cfcard
    root@ubuntu:/mnt# exit
    user@ubuntu:/#
    

12. Retrieve the file browser you stashed away earlier, and unmount the automounted directory for the card by clicking on the eject symbol next to the name of the device in the left pane.

13. It is now safe to eject the card and put it into your embedded machine.

Configuring LILO

As with any software of moderate or better complexity, configuration is required for LILO to function as desired. The configuration created by EMAC and shipped with a system will usually suffice. However, sometimes enough customization is required that the bootloader itself will need to be reconfigured. Even if custom configuration isn't required, some of this information is important for ensuring that you will not accidentally overwrite the bootloader on your desktop with a bootloader intended for an embedded machine.

This section describes the parts of the LILO bootloader configuration file, and provides guidance on how to work with it. The previous sections describe how to install and use the bootloader after it has been configured.

Sections of the LILO Configuration File

The LILO configuration file is split into two sections: global and per-image. The global section, as the name implies, specifies options that pertain to LILO itself and to all images specified in the file. The per-image section specifies options that apply to a specific image, some of which may override the global options.

Global Options

The LILO configuration file needs the following options, at a minimum, configured for the global settings:

• disk This option specifies the disk to which the LILO bootloader needs to be written. This should always point to the device node currently associated with the disk. For example, when mounted on a desktop, this may be /dev/sdc, which is (usually) the third "SCSI" device connected to the system. The first would be /dev/sda, the second /dev/sdb, etc. Even though the device may not be a SCSI device, it may be mounted via a generic SCSI driver, which is why it can appear as a SCSI device. If it were mounted through the IDE subsystem instead, its device node would appear like /dev/hdc instead.
• map This option specifies the location of the map file to use. Usually, this will be /boot/map.
• lba32 This option tells LILO to use 32-bit Logical Block Addresses instead of cylinder/head/sector addresses. This is needed for any disk with more than 1024 cylinders. Since the vast majority of modern drives have more than 1024 cylinders, this option should always be specified.
• boot This option specifies the device which contains the boot sector. As with the disk option, this should always be the device node associated with the disk on the current system. For example, boot=/dev/sdc

Additional useful options:

• vga This option specifies the video mode the device should use, for systems which have video. The parameter to pass comes from the BSP (Board Support Profile) layer for the board. If you are unsure what to set here, EMAC can provide assistance with this.
• serial This useful option specifies a serial device to which a console should be attached, as well as the configuration settings for the console. For example, to use the /dev/ttyS0 serial device (the default console port on many boards) as a serial console which communicates as 115,200 baud, 8 bits, with no stop bits: serial=0,115200n8
• timeout This specifies the amount of time to wait before timing out and continuing on with the boot process using the configured defaults. This value is specified in deciseconds. For example, to set this value to 4.3 seconds: timeout=43
• read-only This option tells LILO to mount the root filesystem as read-only. This is usually desired, since the Linux kernel will remount the device as writeable (if it needs to) once the boot process has been handed over to it.
• install This option specifies the type of screen which will be seen when the bootloader starts. Normally, this will be set to text, which presents the simple interface shown in the examples on this page. The menu option provides a nicer way to select an image to boot, but is usually not desirable to have on an embedded machine. The bitmap option provides a graphical boot screen which looks very nice on a desktop installation, but is usually only used on an embedded machine when the product calls for showing graphics as early in the boot process as possible; a logo is typically placed here in such a case.

Per-Image Options

The following options are needed to configure images to be available to boot with LILO:

• image This option specifies the location of the kernel to boot. Commonly, this will be /boot/bzImage or /boot/bzImage-custom-3.10.2
• root This option specifies the root partition to mount for the image. This is typically /dev/hda1 or /dev/sda1
• label This option tells LILO by what name to call the image. For instance, this is usually label=emac-oe for a standard EMAC image, but for a custom product under development, it might be label=custom-image-test-v3

Working with LILO Configurations

The above information tells you about the common options and how to set them. Additional information can be found be reading through the manual page for lilo.conf. This manpage is available on many sites online.

Actually using these options to create a configuration file is done most easily by copying the EMAC provided LILO configuration file, then modifying the copy. It is a good practice to make sure you have a bootable flash card set aside in case you have difficulty getting your modified flash card back into a bootable state.