Linux: Init Process and PC Boot Procedure
[pic]
Linux Init Process / PC Boot Procedure
[pic]
| |PC Boot and Linux Init Process: |
| | |
| |BIOS: The Basic Input/Output System is the lowest level interface between the computer and peripherals. |
| |The BIOS performs integrity checks on memory and seeks instructions on the Master Boor Record (MBR) on the floppy drive or hard drive. |
| |The MBR points to the boot loader (GRUB or LILO: Linux boot loader). |
| |Boot loader (GRUB or LILO) will then ask for the OS label which will identify which kernel to run and where it is located (hard drive and partition specified). |
| |The installation process requires to creation/identification of partitions and where to install the OS. GRUB/LILO are also configured during this process. The |
| |boot loader then loads the Linux operating system. |
| |The first thing the kernel does is to execute init program. Init is the root/parent of all processes executing on Linux. |
| |The first processes that init starts is a script /etc/rc.d/rc.sysinit |
| |Based on the appropriate run-level, scripts are executed to start various processes to run the system and make it functional. |
| |The Linux Init Processes: |
| | |
| |The init process is the last step in the boot procedure and identified by process id "1". Init is responsible for starting system processes as defined in the |
| |/etc/inittab file. Init typically will start multiple instances of "getty" which waits for console logins which spawn one's user shell process. Upon shutdown, |
| |init controls the sequence and processes for shutdown. The init process is never shut down. It is a user process and not a kernel system process although it does|
| |run as root. |
| |System Processes: |
| |Process ID |
| |Description |
| | |
| |0 |
| |The Scheduler |
| | |
| |1 |
| |The init process |
| | |
| |2 |
| |kflushd |
| | |
| |3 |
| |kupdate |
| | |
| |4 |
| |kpiod |
| | |
| |5 |
| |kswapd |
| | |
| |6 |
| |mdrecoveryd |
| | |
| |Init config file (Red Hat 7.3-9.0, Fedora Core 1-3): /etc/inittab |
| |# Author: Miquel van Smoorenburg, |
| |# Modified for RHS Linux by Marc Ewing and Donnie Barnes |
| | |
| |id:3:initdefault: |
| | |
| |# System initialization. |
| |si::sysinit:/etc/rc.d/rc.sysinit |
| | |
| |l0:0:wait:/etc/rc.d/rc 0 |
| |l1:1:wait:/etc/rc.d/rc 1 |
| |l2:2:wait:/etc/rc.d/rc 2 |
| |l3:3:wait:/etc/rc.d/rc 3 |
| |l4:4:wait:/etc/rc.d/rc 4 |
| |l5:5:wait:/etc/rc.d/rc 5 |
| |l6:6:wait:/etc/rc.d/rc 6 |
| | |
| |# Things to run in every runlevel. This line is only in Red Hat 7.X Used to flush disk buffers. |
| |ud::once:/sbin/update |
| | |
| |# Trap CTRL-ALT-DELETE |
| |ca::ctrlaltdel:/sbin/shutdown -t3 -r now |
| | |
| |# When our UPS tells us power has failed, schedule a shutdown for 2 minutes from now. |
| |pf::powerfail:/sbin/shutdown -f -h +2 "Power Failure; System Shutting Down" |
| | |
| |# If power was restored before the shutdown kicked in, cancel it. |
| |pr:12345:powerokwait:/sbin/shutdown -c "Power Restored; Shutdown Cancelled" |
| | |
| |# Run gettys in standard runlevels |
| |1:2345:respawn:/sbin/mingetty tty1 |
| |2:2345:respawn:/sbin/mingetty tty2 |
| |3:2345:respawn:/sbin/mingetty tty3 |
| |4:2345:respawn:/sbin/mingetty tty4 |
| |5:2345:respawn:/sbin/mingetty tty5 |
| |6:2345:respawn:/sbin/mingetty tty6 |
| | |
| |# Run xdm in runlevel 5 |
| |x:5:respawn:/etc/X11/prefdm -nodaemon |
| | |
| |Note that this config file directs the init process to run the shell script /etc/rc.d/rc.sysinit. This script should be used as is and NOT changed. Extend |
| |rc.local and NOT this script. This will (not in exact order): |
| |Run /sbin/initlog |
| |Run devfs to generate/manage system devices |
| |Run network scripts: /etc/sysconfig/network |
| |Start graphical boot (If so configured): rhgb |
| |Start console terminals, load keymap, system fonts and print console greeting: mingetty, setsysfonts |
| |The various virtual console sessions can be viewed with the key-stroke: ctrl-alt-F1 through F6. F7 is reserved for the GUI screen invoked in run level 5. |
| |Mount /proc and start device controllers. |
| |Done with boot configuration for root drive. (initrd) Unmount root drive. |
| |Re-mount root file system as read/write |
| |Direct kernel to load kernel parameters and modules: sysctl, depmod, modprobe |
| |Set up clock: /etc/sysconfig/clock |
| |Perform disk operations based on fsck configuration |
| |Check/mount/check/enable quotas non-root file systems: fsck, mount, quotacheck, quotaon |
| |Initialize logical volume management: vgscan, /etc/lvmtab |
| |Activate syslog, write to log files: dmesg |
| |Configure sound: sndconfig |
| |Activate PAM |
| |Activate swapping: swapon |
| |Local system boot processes can be placed in file: /etc/rc.d/rc.local |
| |The system will then boot to the runlevel set by the directive initdefault. |
| |Also see: |
| |init man page |
| |inittab man page |
| |[pic] |
| |Linux init Run Levels: |
| | |
| |LINUX has six states of operation of which "0" is the shutdown state and "3" and above are fully operational with all essential processes running for user |
| |interaction. Upon system boot the LINUX system /sbin/init program starts other processes by performing the following: |
| |Init will bring up the machine by starting processes as defined in the /etc/inittab file. |
| |The computer will be booted to the runlevel as defined by the initdefault directive in the /etc/inittab file. |
| | |
| |id:5:initdefault: |
| | |
| | |
| |In this example a runlevel of "5" is chosen. Runlevel "5" will boot the system into GUI mode using XDM and X-Windows. Booting to runlevel "3" (often called |
| |console mode) is often used by servers which do not need a graphical user interface. If booted to init level "3" one can promote the run level with the command |
| |[root prompt]# init 5. See the more detailed explanation of run levels below. |
| |The inittab file will allow you to capture key sequences (ctrl-alt-del), start dial in internet connections etc. |
| |One of these process started by init is /sbin/rc. This script runs a series of scripts in the directories /etc/rc.d/rc0.d/, /etc/rc.d/rc1.d/, /etc/rc.d/rc2.d/, |
| |etc |
| |Scripts in these directories are executed for each boot state of operation until it becomes fully operational. Scripts beginning with S denote startup scripts |
| |while scripts beginning with K denote shutdown (kill) scripts. Numbers follow these letters to denote the order of execution. (lowest to highest) |
| |[pic] |
| |Runlevel "3" will boot to text or console mode and "5" will boot to the graphical login mode ( "4" for slackware) |
| |Runlevel |
| |Scripts Directory |
| |(Red Hat/Fedora Core) |
| |State |
| | |
| |0 |
| |/etc/rc.d/rc0.d/ |
| |shutdown/halt system |
| | |
| |1 |
| |/etc/rc.d/rc1.d/ |
| |Single user mode |
| | |
| |2 |
| |/etc/rc.d/rc2.d/ |
| |Multiuser with no network services exported |
| | |
| |3 |
| |/etc/rc.d/rc3.d/ |
| |Default text/console only start. Full multiuser |
| | |
| |4 |
| |/etc/rc.d/rc4.d/ |
| |Reserved for local use. Also X-windows (Slackware/BSD) |
| | |
| |5 |
| |/etc/rc.d/rc5.d/ |
| |XDM X-windows GUI mode (Redhat/System V) |
| | |
| |6 |
| |/etc/rc.d/rc6.d/ |
| |Reboot |
| | |
| |s or S |
| | |
| |Single user/Maintenance mode (Slackware) |
| | |
| |M |
| | |
| |Multiuser mode (Slackware) |
| | |
| |One may switch init levels by issuing the init command with the appropriate runlevel. Use the command "init #" where # is one of s,S,0,1,3,5,6. The command |
| |telinit does the same. |
| |The scripts for a given run level are run during boot and shutdown. The scripts are found in the directory /etc/rc.d/rc#.d/ where the symbol # represents the run|
| |level. i.e. the run level "3" will run all the scripts in the directory /etc/rc.d/rc3.d/ which start with the letter "S" during system boot. This starts the |
| |background processes required by the system. During shutdown all scripts in the directory which begin with the letter "K" will be executed. This system provides |
| |an orderly way to bring the system to different states for production and maintenance modes. |
| |If you installed all demons (background processes), Linux will run them all. To avoid slowing down your machine, remove uneeded services from the start-up |
| |procedure. You can start/stop individual demons by changing to the directory: |
| |/etc/rc.d/init.d/ (Red Hat/Fedora ) |
| |/etc/init.d/ (S.u.s.e.) |
| |/etc/init.d/ (Debian) |
| |and issuing the command and either the start, stop, status, restart or reload option i.e. to stop the web server: |
| |cd /etc/rc.d/init.d/ |
| |(or /etc/init.d/ for S.u.s.e. and Debian) |
| |httpd stop |
| |Use the command ps -aux to view all process on your machine. |
| |TIP: List state and run level of all services which can be started by init: chkconfig --list |
| |or |
| |service --status-all | grep running (Red Hat/Fedora Core based systems) |
| |GUI tool: /usr/X11R6/bin/tksysv |
| |[pic] |
| |Run Level Commands: |
| | |
| |Shutdown: |
| |init 0 |
| |shutdown -h now |
| |-a: Use file /etc/shutdown.allow |
| |-c: Cancel scheduled shutdown. |
| |halt -p |
| |-p: Turn power off after shutdown. |
| |poweroff |
| |Reboot: |
| |init 6 |
| |shutdown -r now |
| |reboot |
| |Enter single user mode: |
| |init 1 |
| |Init Script Activation: |
| | |
| |Adding a script to the /etc/rc.d/rc#.d/ directory with either an S or K prefix, adds the script to the boot or shutdown process. The scripts are run in numerical|
| |order. S20abc is run before S30xyz. The extensibility to the boot and shutdown procedures of the operating system is one of the strengths of UNIX. The orderly |
| |sequential initiation of processes can be coordinated for dependent processes. The orderly shutdown of processes is often required of complex programs such as |
| |databases. This is how it is done. Individual processes may be monitored, shutdown and started at any time using these scripts. i.e. /etc/rc.d/rc2.d/httpd start.|
| |The modifiers start, stop or status may be used. |
| |The start/stop/status scripts actually reside in the directory: |
| |/etc/rc.d/init.d/ (Red Hat/Fedora) |
| |/etc/init.d/ (S.u.s.e. and Debian) |
| |and are linked to the appropriate directories. These links may be created or destroyed using the chkconfig command. i.e. chkconfig --del httpd will remove the |
| |web server from the startup and shutdown process. Inversely chkconfig --add httpd will add it to the startup/shutdown process by generating links from the script|
| |in /etc/rc.d/init.d/ to the appropriate /etc/rc.d/rc#.d/ directory. For more information see the LINUX manual page on init. |
| |Basic services include: |
| |System Service |
| |Description |
| | |
| |anacron |
| |Run jobs which were scheduled for execution while computer was turned off. Catch up with system duties. |
| | |
| |arpwatch |
| |Keeps track of IP address to MAC address pairings |
| | |
| |Atd |
| |Run scheduled batch jobs. |
| | |
| |Autofs |
| |automounts file systems on demand. |
| | |
| |Crond |
| |Job sheduler for periodic tasks. |
| | |
| |Gpm |
| |Allows console terminal cut and paste. (Non X-window consoles) |
| | |
| |https |
| |Apache web server. |
| | |
| |iptables |
| |Firewall rules interface to kernel. |
| | |
| |keytable |
| |Loads selected keyboard map as set in /etc/sysconfig/keyboard |
| | |
| |kudzu |
| |New harware probe/detection during system boot. |
| | |
| |lpd |
| |Network printer services. |
| | |
| |microcode_ctl |
| |Uploads microcode to kernel and ultimately to the Intle Pentium processor. (Hardware specific.) |
| | |
| |mysqld |
| |Database services |
| | |
| |named |
| |DNS name services (Bind) |
| | |
| |network |
| |Active network services during system boot. |
| | |
| |nfs |
| |Network file system. Unix file sharing services. |
| | |
| |nscd |
| |Password and group lookup services for use with network authentication (NIS, LDAP,...). |
| | |
| |ntpd |
| |Network Time Protocol time synchronization services. |
| | |
| |random |
| |Random number generation tool used for encryprion. |
| | |
| |rawdevices |
| |Enables raw IO. Useful for Oracle and software which utilizes this for high speed disk access. |
| | |
| |smb |
| |SAMBA: MS/Windows PC file sharing services |
| | |
| |syslog |
| |System log file facility. |
| | |
| |ypbind |
| |NIS file sharing/authentication infrastructure service. |
| | |
| |yppasswd |
| |NIS file sharing/authentication infrastructure service. |
| | |
| |ypserv |
| |NIS file sharing/authentication infrastructure service. |
| | |
| |xfs |
| |X-Windows font server. |
| | |
| |Recommended basic services: anacron, ard, autofs, crond, gpm, iptables, keytable, kudzu, microcode_ctl (Intel32 hardware only), network, random. syslog |
| |Graphics Workstation - add: xfs |
| |File Server for PC clients - add: smb |
| |Print Server - add: lpd or cups |
| |File server Linux/Unix clients - add: nfs, netfs, nfslock, portmap, ypbind, yppasswd, ypserv |
| |Web Server - add: httpd, tux, xinetdi, sshd |
| |[pic] |
| |GUI configuration tools: |
| |GUI tools can help you configure the appropriate services to start and provide a description of each service available: |
| |Red Hat 8.0/9.0: /usr/bin/redhat-config-services |
| |Fedora/RHEL: /usr/bin/system-config-services |
| |Ubuntu 6 / Debian: |
| |/usr/bin/services-admin |
| |bum (Boot Up Manager) |
| |Red Hat / Fedora Core GUI: system-config-services (and redhat-config-services) |
| |[pic] |
| |Red Hat/Fedora Core text console services selection tool: /usr/sbin/ntsysv |
| |[pic] |
| |Init Script: |
| | |
| |A single copy of the script is located in the directory: /etc/rc.d/init.d/script-name (Red Hat/Fedora) or /etc/init.d/script-name (Debian). |
| |Use the command chkconfig to generate soft links to the appropriate directories for the various run levels. |
| |#!/bin/sh |
| |# |
| |# Startup script for program |
| |# |
| |# chkconfig: 345 85 15 - This statement tells the chkconfig command how to add or delete this process to the boot process |
| |# description: Description of program |
| |# processname: process-name |
| |# pidfile: /var/run/process-name.pid |
| | |
| |# Source function library. This creates the operating environment for the process to be started |
| |. /etc/rc.d/init.d/functions |
| | |
| |case "$1" in |
| |start) |
| |echo -n "Starting process-name: " |
| |daemon process-name - Starts only one process of a given name. |
| |echo |
| |touch /var/lock/subsys/process-name |
| |;; |
| |stop) |
| |echo -n "Shutting down process-name: " |
| |killproc process-name |
| |echo |
| |rm -f /var/lock/subsys/process-name |
| |rm -f /var/run/process-name.pid - Only if process generates this file |
| |;; |
| |status) |
| |status process-name |
| |;; |
| |restart) |
| |$0 stop |
| |$0 start |
| |;; |
| |reload) |
| |echo -n "Reloading process-name: " |
| |killproc process-name -HUP |
| |echo |
| |;; |
| |*) |
| |echo "Usage: $0 {start|stop|restart|reload|status}" |
| |exit 1 |
| |esac |
| | |
| |exit 0 |
| | |
| | |
| |The bash script functions daemon, killproc and status can all be found in the script /etc/rc.d/init.d/functions. (Red Hat/Fedora distributions) |
| |[pic] |
| |The script must be executable to work. (chmod +x script-name). |
| |The script may be used to start and stop processes. i.e.: |
| |/etc/rc.d/init.d/httpd restart |
| |(S.u.s.e.: /etc/init.d/apache2 restart) |
| |/etc/rc.d/init.d/httpd stop |
| |/etc/rc.d/init.d/httpd start |
| |OR use the Red Hat/Fedora core based service command: |
| |service httpd restart |
| |service httpd stop |
| |service httpd start |
| |Note that two lines in the script enable the chkconfig command to control the script for the boot and shutdown process. |
| |# chkconfig: 345 85 15 |
| |# description: Description of program |
| |When added to the boot process using the "chkconfig --add script-name" command the start order/priority will be set to 80 while the stop/shutdown order will be |
| |set to 15. The process will be added to runlevels 3, 4 and 5. This is enabled by generating links from the location of the script (/etc/rc.d/init.d/) to the |
| |directory for the appropriate run level: /etc/rc.d/rc#.d/. The file name in the run level directory will reflect if it is used for boot (starts with an "S") or |
| |shutdown (starts with a "K") |
| |chkconfig: |
| | |
| |The (Red Hat/Fedora/IRIX) chkconfig command generates and breaks links between the directory /etc/rc.d/init.d/ and the appropriate run level directory: |
| |/etc/rc.d/rc[0-6].d/ to control boot process initiation and process shutdown. |
| |chkconfig [--level ] on | off | reset > |
| |chkconfig --list |
| |chkconfig --list |
| |chkconfig --add |
| | |
| |chkconfig --del |
| |chkconfig --level 0123456 off |
| |Examples: |
| |chkconfig --level 345 httpd on - forces apache to be invoked for run levels 3, 4 and 5. |
| |chkconfig --add httpd - Start the web server daemon upon system boot. |
| |chkconfig --del sendmail - Do not start the sendmail daemon upon system boot. |
| |chkconfig --list - List all services and init levels. |
| |chkconfig --list | grep on - List all services to be started upon system boot. |
| |Using chkconfig to administer xinetd processes. |
| |chkconfig wu-ftpd on - Turn on FTP service managed by xinetd. |
| |chkconfig ipop3 off - Turn off POP3 service managed by xinetd. |
| |This will reconfigure the appropriate xinetd file (in directory /etc/xinetd.d/) and restart the xinetdprocess. |
| | |
| | |
| | |
| | |
| | |
| |service |
| |Display status of system services. |
| |Example: service --status-all |
| |Help: service --help |
| | |
| | |
................
................
In order to avoid copyright disputes, this page is only a partial summary.
To fulfill the demand for quickly locating and searching documents.
It is intelligent file search solution for home and business.
Related download
- automation scripting process
- department of veterans affairs
- camtasia recorder user document
- macro express macros for your windows automation needs
- java script interview questions and answers
- linux init process and pc boot procedure
- tga overall process manual
- encyclopedia of cognitive science
- william paredes
Related searches
- people process and technology concept
- people process and technology model
- people process and technology framework
- curriculum development process and models pdf
- python run process and wait
- people process and technology
- process and procedure definition
- process and instrumentation diagram
- accounting process and procedures template
- accounting process and procedures manual
- difference between process and procedures
- accounts payable process and procedures