Chris Clark

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• Chris Clark
• President, SwitchDesk, Inc.
• chrisclark_at_switchdesk.com

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Understanding Linux A Look Under the Hood

• THE BIG THREE
• What goes where?
• The key to editing configuration files
• What are runlevels?

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Linux Fundamental Number 1
Everything in Linux is a file
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What goes where?

• Linux complies with the File System Hierarchy
  Standard (FHS)
  
• Specifies which directories must be located on
  the first level (directly under / ) and what they
  contain
  
• Provides consistency across distributions

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What goes where?

• /bin
• /boot
• /dev
• /etc
• /home

/lib /lostfound /media /mnt /opt
/proc /root /sbin /tmp /usr /var
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What goes where?
C
D
F
E
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What goes where?
/dev/hda1
/boot
/
/dev/hda7
/dev/hda5
/usr
/var
/dev/hda6
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What goes where?
/
usr
boot
var
mnt
dev
floppy
cdrom
hda1
hda2
cdrom
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/boot
/
/usr
cdrom
/var
/
usr
boot
var
mnt
dev
floppy
cdrom
hda1
hda2
cdrom
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The key to editing configuration files

• One simple program - vi
• vi is an integral part of Linux
• Default text editor in just about every Linux
  distribution
  
• Quick and easy to use
• Can now use the Delete, Backspace and Insert keys
  on your keyboard

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The key to editing configuration files

• vi Commands
• vi filename
• i insert mode
• esc command mode
• wq write and quit
• q! quit without saving

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The key to editing configuration files

• vi Shortcuts
• o opens a new line and puts you in insert
  mode
  
• dd delete line
• /word search

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Linux Fundamental Number 2
Linux is always case sensitive!
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What are runlevels?

• System V Runlevels
• A runlevel is a software configuration of the
  system which allows only a selected group of
  services to exist
  
• The characteristics of each runlevel determine
  which services are killed or started
  
• The System V runlevel system provides a standard
  process for controlling which services are killed
  or started when initializing a runlevel

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What are runlevels?

• Runlevels
• 0 System halt
• 1 Single-user mode
• 2 Multi-user mode without networking or X
• 3 Multi-user mode with networking
• 4 Multi-user mode with networking (unused)
• 5 Multi-user mode with networking and X
• 6 System reboot

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What are runlevels?

• Changing runlevels
• init n where n is the runlevel to which you
  wish to change

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What are runlevels?

• Changing runlevels
• init n where n is the runlevel to which you
  wish to change
  
• To change your runlevel permanently, edit
  /etc/inittab
  
• id3initdefault for a text login (best for
  servers)
  
• id5initdefault for a graphical login (best
  for desktops)

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What are runlevels?

• Also in /etc/init.d
• boot.local file in which to put commands you
  want run at boot up
  
• equivalent to autoexec.ncf or autoexec.bat
• rc manages the runlevel processes
• skeleton runlevel script template

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Thank You!
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