• Présentation sur les sujet 101.1 + 101.2

• HAL (Hardware Abstraction Layer)
• dbus (message bus system, allows application to talk to one another)
• udev (device manager for the Linux kernel, generate /dev/)

Conceptual understanding needed for LPIC

Dynamically generated at startup.

• /sys (SysFS)
• /proc linux.about.com
• /dev linux.about.com

running process appear as folder in /proc/

• Running process appear as folder in /proc/??? (??? = process number)

• information about the processor: /proc/cpuinfo
• how long the system has been running /proc/uptime
• Version of the kernel in /proc/version
• Info about swap /proc/swaps
• List of module with additional info /proc/modules

• /proc/interrupts list interrupts (first column is IRQ)

• /dev/tty* terminal of the current process
• /dev/ttyS0 usually a serial port
• /dev/sda First s-ata device
• /dev/sda1 First partition of first s-ata device
• /dev/hda First p-ata device
• /dev/hdb3 3rd partition on second p-ata device

• /dev/null (“black hole”)

• /dev/random and * /dev/urandom random number generator wikipedia

/dev$ ls -hal
(...)
crw-rw----   1 root dialout     4,  89 Dec  2 19:51 ttyS25
brw-rw---- 1 root disk 8, 0 Dec  2 19:51 sda
brw-rw----   1 root disk        1,  14 Dec  2 19:51 ram14
(...)

• p FIFO
• b block (buffered) special file
• c character (buffered) special file
• u Character (unbuffered) special file

(source)

Commands:

• insmod (takes absolute path to module)
• modprobe (takes the name of the module, dependencies-aware)
• rmmod (remove kernel module)
• lsmod (list all kernel module loaded)
• modinfo (display information about a module)

• lsusb list usb devices
• lspci list pci devices
• lshw list detailed info about hardware

1. BIOS - Basic Input Output System
2. Booloader
3. OS (Kernel)

Note: The boot order (ressource the computer will boot on) is definted in the BIOS.

GRUB = GNU GRand Unified Bootloader ( https://en.wikipedia.org/wiki/GNU_GRUB ) LILO = LInux LOder ( https://en.wikipedia.org/wiki/LILO_%28boot_loader%29 )

GRUB is typically installed on a harddrive (but can also be on CR-ROM, USB, network drive).

• Can load unlimited number of Harddrive
• Can boot from network drive
• Command line interface

GRUB display list of OS. Including sometimes more than one kernel version. It can include additional entries (recovery mode, memory test…)

LILO is not covered in LPIC 1 anymore

LILO is hardly used anymore

• Can't boot from Network
• MBR must be rewritten everytime the configuration file has been modified
• NO interactive command line

The bootloader is written on the Master Boot Record. The BIOS looks at a specific area of the harddrive to load the bootloader.

MBR is being replace with the GUID Partition Table.

• Grub Tutorial: http://www.dedoimedo.com/computers/grub.html
• Grub website: http://www.dedoimedo.com/computers/grub.html
• MBR https://en.wikipedia.org/wiki/Master_boot_record
• GUID Partition Table https://en.wikipedia.org/wiki/GUID_Partition_Table
• Grub 2 - Ubuntu help https://help.ubuntu.com/community/Grub2

There are many options that can be passed to the kernel by the bootloader. The most essential one are:

The harddrive on which the OS is present

• UUID (unique identifier)
• root (hd0,0)

Where the linux kernel is located

• vmlinux https://en.wikipedia.org/wiki/Vmlinux
  • Etymology: '/unix' + virtual memory + compressed (z)
  • Kernel in either / or /boot (Filesystem Hierarchy Standard)

An initial ram disk that contain kernel module and tools necessary to boot

• initrd https://en.wikipedia.org/wiki/Initrd
  • Temp root file system (initial RAM disk)
  • Tool needed for kernel
  • Device driver as lodable modules

The system load both vmlinux and initrd in memory and then start the kernel

Other boot options

• 'ro quiet splash'
  • quiet: display less verbose information
  • splash: show a splash screen instead of kernel message

Changing boot options at boot time is non-persistent

• Linux initial RAM disk (initrd) overview http://www.ibm.com/developerworks/library/l-initrd/index.html
• Vmlinux https://en.wikipedia.org/wiki/Vmlinux

• Check content of /boot
• Play with GRUB commad line interface

dmesg refers to the kernel message

The log file /var/log/dmesg show the kernel message up to when the system finished booting (log prompt).

/var/log/messages

Contain kernel message and additional message from other deamon.

/!\ Not present in latest ubuntu (12.10), has been replaced by /var/log/syslog

Process that starts all other process. (parent process)

Being replaced with upstart / systemd.

• Init https://en.wikipedia.org/wiki/Init
• Upstart (used by ubuntu) https://en.wikipedia.org/wiki/Upstart
• Systemd https://en.wikipedia.org/wiki/Systemd
  • http://www.freedesktop.org/wiki/Software/systemd

• Check log files and 'dmesg' command
• command 'pstree' show all process started by init