Previous Page | Next Page

  1. Introduction
  2. Abbreviated Boot
  3. The Boot Process
  4. Startup and Run Levels
  5. Initialization Scripts
  6. Runlevel Scripts
  7. Login Process
  8. Bash Shell
  9. Filesystems
  10. LILO, Kernel and Root Filesystem
  11. The Kernel
  12. Passwords, Users, Groups, and Quotas
  13. The Environment
  14. The /etc/sysconfig directory
  15. The /proc filesystem
  16. Process Control
  17. Devices
  18. Daemons Services
  19. Inetd and Network Services
  20. Programs and Libraries
  21. Security and PAM
  22. The printer services
  23. Mouse support with gpm
  24. Mail
  25. News
  26. UUCP
  27. LDAP
  28. NFS and RPC
  29. Samba, NetBIOS, WINS, nmbd
  30. Identd (auth)
  31. Telnet and FTP
  32. Apache web server
  33. DNS and named
  34. How X Works
  35. X Scripts
  36. Support for Text
  37. Keymapping for Programs
  38. Keycode Table
  39. Example Keymap File
  40. Terminfo Commands
  41. VT100 ESC sequences
  42. Kernel Revisited
  43. Configuration Files
  44. Credits

An abbreviated description of the Linux Boot up process

  1. The LILO boot loader starts the kernel
  2. The Linux kernel configured by lilo or rdev decompresses and must find and mount the root filesystem. If LILO or the kernel were not configured properly there can be a problem here.
  3. The kernel after loading the root filesystem, starts the "init" program which may be located in /sbin/init. Reads /etc/inittab for configuration information.
  4. /etc/inittab - init reads this file for configuration information. This file determines the starting run level and contains a line like:

    si::sysinit:/etc/rc.d/rc.sysinit

  5. /etc/rc.d/rc.sysinit - In this case this entry in "/etc/inittab" causes the script file "/etc/rc.d/rc.sysinit" to be run.
    To add terminals or dial in modem lines on a system, add more lines in the /etc/inittab file, one for each terminal or dial in line similar to the following:

    7:2345:respawn:/sbin/mingetty tty7

  6. One of /etc/rc.d/rc or /etc/rc or /etc/init.d/rc is started from inittab which does initialization commands for boot at the set runlevel. This is done by running startup and shutdown scripts for various services to be run at the given run level.
  7. /etc/rc.local is started from one of the startup scripts in the rc script file. This is where you should add custom features for your system.
  8. getty - Init starts a separate getty (or mingetty) for each terminal for which logins are to be allowed. Getty is restarted by init after each user has logged out so new users can log in. Network logins are not done by getty but by a different deamon per way of logging in (telnet or rlogin handled by the inetd internet super daemon).
  9. Getty outputs the welcome message in /etc/issue, reads the username and runs the login program. If the user is telnetting, the message in /etc/issue.net is first output.
  10. The login program reads the password and runs the shell if the username and password are correct. The shell is based on entries in the /etc/passwd file and will run at the user's privilege level rather than with root privileges.
  11. The shell (such as bash) runs the /etc/profile script file. However in the case of a system with shadow passwords, environment strings can be set first in a file called /etc/login.defs. Also a users resources can be limited in a file called /etc/limits. The $HOME/.bash_profile script is then run, but if it is missing /etc/.profile is run.

Pertinent files:

  • /dev/console - A virtual console device usually called /dev/ttyn where "n" is a terminal number.
  • /etc/ioctl.save - Contains the consoles ioctl(2) states
  • /var/run/utmp - A file where information on current system users is stored. The commands "w" and "who" can be used to display information in this file.
  • /var/log/wtmp - Has a record of all logins and logouts
  • /dev/initctl - Init's control fifo buffer file. Init listens on this fifo file for messages. Telinit uses this to communicate with init. The file initctl is not a script file.
  • /etc/passwd - Contains information about the user including the ID, name, home directory, and the path to the preferred shell program. If not using shadow passwords, this file may also contain user passwords.

In /etc/rc.d/rc0.d are kill and start scripts for various services. The kill scripts start with the letter "K" and the startup scripts start with the letter "S".