1. CIT 470: Advanced Network and System AdministrationSlide #1 CIT 470: Advanced Network and System Administration Booting and Runlevels

2. CIT 470: Advanced Network and System AdministrationSlide #2 Topics 1.Booting 2.Bootstrap loaders 3.Run levels 4.Startup scripts 5.Shutdown and reboot

3. CIT 470: Advanced Network and System AdministrationSlide #3 Booting ROM boot code (BIOS) Bootloader Kernel Init

4. CIT 470: Advanced Network and System AdministrationSlide #4 BIOS 1.Load CMOS settings. 2.Initialize registers and power management. 3.POST (Power On Self Test.)‏ 4.Display system settings (if key pressed.)‏ 5.Activate other BIOSes Disk interfaces Graphics cards Network interfaces 6.Find bootable device. 7.Load MBR. 8.Run MBR program.

5. Dell BIOS Screenshot CIT 470: Advanced Network and System Administration

6. MBR contains Bootloader Only 446 bytes! MBR bootloader bootstraps itself by loading larger bootloader program from disk.

7. Bootloader: GRUB CIT 470: Advanced Network and System Administration

8. Slide #8 GRUB Boot Process Stage 1 (stored in MBR)‏ Detect the geometry and the accessing mode of the loading drive. Finds and runs stage 1.5. Stage 1.5 (stored at beginning of partition) Understands filesystem; loads stage 2 from filesystem. Stage 2 (stored in filesystem)‏ Displays menu of OS choices. Often displays boot splashscreen. Loads selected OS kernel.

9. CIT 470: Advanced Network and System AdministrationSlide #9 GRUB Installation At OS Install Time Most distributions install GRUB. Linux Install grub-install /dev/hda Native install Boot with CD and run grub. #>> root (hd0,0)‏ #>> setup (hd0)‏ #>> quit

10. CIT 470: Advanced Network and System AdministrationSlide #10 GRUB Boot Automatically boots default OS after timeout. Key sequences bring up –Menu of boot options (described in menu.lst)‏ –Edit kernel options (runlevel, other features)‏ –GRUB command shell A boot prompt password may be required before edit/shell access granted. –Can bypass OS security by specifying kernel options or accessing files from GRUB shell.

11. CIT 470: Advanced Network and System AdministrationSlide #11 Booting with GRUB Direct Boot Specify OS kernel image to load. Chainloading Specify another bootloader to load. Chainload NTLDR to boot MS Windows.

12. CIT 470: Advanced Network and System AdministrationSlide #12 Config: /boot/grub/menu.lst # timeout (sec) before booting default timeout 10 titleUbuntu, kernel 2.6.10-5-386 root (hd1,0)‏ kernel /boot/vmlinuz-2.6.10-5-386 root=/dev/hde1 ro quiet splash initrd /boot/initrd.img-2.6.10-5-386 boot titleWindows 2000 root (hd0,0)‏ makeactive chainloader +1

13. CIT 470: Advanced Network and System AdministrationSlide #13 GRUB Naming Convention GRUB uses BIOS hard disk numbers OS may not number disks identically to BIOS. Examples (hd0,0) First partition of first hard disk (hd1,2) Third partition of second hard disk.

14. Kernel Booting CIT 470: Advanced Network and System Administration

15. Initial RAMDisk Temporary filesystem used for booting. –Stored as /boot/initrd-VERSION –Loaded into memory by bootloader Contains drivers needed to mount root fs –RAID, LVM, NFS or other device drivers –Filesystem drivers Allows single kernel to be shipped by vendor –Drivers specific to your system on RAMdisk –Also supports hibernation for laptops CIT 470: Advanced Network and System Administration

16. Slide #16 Kernel Arguments Numeric arguments –Specify runlevel. – single also specifies single user mode Root device options –root= specifies which root device to use –ro, rw specify access type Console options –console=ttyS1, 9600 will use serial console Hardware options –Enable, disable specific hardware devices/features.

17. CIT 470: Advanced Network and System AdministrationSlide #17 Run Levels 0 – Shutdown 1 – Single user mode 2 – Multi-user, no networking, no GUI 3 – Multi-user, with networking, no GUI 4 – Unused 5 – Multi-user, networking, and GUI 6 – Reboot

18. Single User Mode Single user mode has –No GUI. –No network access. –Only one user (root) can use system. Why use single user mode? –Run fsck to fix filesystem corruption. –Backup files without filesystem active. –Fix problems without user interference. –May allow access to system without a password in case you have forgotten root’s password. CIT 470: Advanced Network and System Administration

19. Booting in Single User Mode 1.At GRUB prompt, select ‘a’ to append args 2.Append this argument to list: single 3.Hit return to complete argument changes 4.Select ‘b’ to boot the kernel Single-user mode differs from run level 1 in that run level 1 runs the scripts for run level 1, then enters single-user mode. CIT 470: Advanced Network and System Administration

20. What if you lost your root password? CIT 470: Advanced Network and System Administration 1.At GRUB prompt, select ‘a’ to append arguments 2.Append this argument to list: init=/bin/bash 3.Hit return to complete argument changes 4.Select ‘b’ to boot the kernel 5.At root prompt, remount / mount / -o rw,remount 6.Reset root password passwd 7.Power cycle system

21. CIT 470: Advanced Network and System Administration /etc/inittab # The default runlevel. id:2:initdefault: # Boot-time system configuration/initialization script. si::sysinit:/etc/init.d/rcS # What to do in single-user mode. ~~:S:wait:/sbin/sulogin # /etc/init.d executes the S and K scripts upon change l0:0:wait:/etc/init.d/rc 0 l1:1:wait:/etc/init.d/rc 1 l2:2:wait:/etc/init.d/rc 2 l3:3:wait:/etc/init.d/rc 3 l4:4:wait:/etc/init.d/rc 4 l5:5:wait:/etc/init.d/rc 5 l6:6:wait:/etc/init.d/rc 6 # What to do when CTRL-ALT-DEL is pressed. ca:12345:ctrlaltdel:/sbin/shutdown -t1 -a -r now

22. CIT 470: Advanced Network and System Administration rc Executed by init with runlevel as argument. Starts and stops services for each runlevel. /etc/rc#.d scripts –Symlinks to actual scripts in /etc/init.d –Stops services beginning with K* –Starts services beginning with S* –Executes in ASCII order.

23. CIT 470: Advanced Network and System Administration Scripts in runlevel 2 $ ls /etc/rc2.d S05vbesave S13gdm S20openntpd S89cron S08iptables S18hplip S20postfix S91apache2 S10acpid S18portmap S20powernowd S98usplash S10powernowd.early S19cupsys S20rsync S99acpi-support S10sysklogd S20apmd S20ssh S99rc.local S10syslog-ng S20argus-server S20xinetd S99rmnologin S11klogd S20hotkey-setup S21nfs-common S99stop-readahead S12dbus S20makedev S89anacron

24. CIT 470: Advanced Network and System AdministrationSlide #24 Example init.d script #! /bin/sh case "$1" in 'start') if [ -f /usr/local/sbin/sshd ]; then echo "starting SSHD daemon" /usr/local/sbin/sshd & fi ;; 'stop')‏ PID=`/usr/bin/ps -e -u 0 | /usr/bin/fgrep sshd | /usr/bin/awk '{print $1}'` if [ ! -z "$PID" ] ; then /usr/bin/kill ${PID} >/dev/null 2>&1 fi ;; *) echo "usage: /etc/init.d/sshd {start|stop}“ ;; esac

25. CIT 470: Advanced Network and System AdministrationSlide #25 Turning Services On/Off Add a new service Install startup script in /etc/init.d Create S symlinks in appropriate runlevels Create K symlinks in appropriate runlevels Prevent a service from starting on boot Remove S links from /etc/rc?.d/* Remove K links from /etc/rc?.d/*

26. CIT 470: Advanced Network and System AdministrationSlide #26 Red Hat Service Commands Starting or stopping a service service NAME [start,restart,stop] is equivalent to /etc/init.d/NAME [start,restart,stop] Enabling or disabling a service at boot time chkconfig --level # NAME is equivalent to ln –s /etc/init.d/NAME /etc/init.d/rc.d/rc#.d/S??name

27. Red Hat Service Configuration RH Linuxes use files in /etc/sysconfig VARIABLE=value format Documentation in RHEL manuals Examples desktop : select GNOME, KDE, XFCE desktop iptables : firewall configuration network-scripts/ifcfg-eth0 : eth0 cfg

28. /etc/sysconfig CIT 470: Advanced Network and System Administration

29. Slide #29 Shutdown shutdown –h now (or init 0 )‏ Offers time-delay option ( -h time ) Runs server stop scripts. Kill remaining processes. Flushes writes to disk. halt Kills processes. Flushes writes to disk ( sync ).

30. CIT 470: Advanced Network and System AdministrationSlide #30 Reboot reboot (or init 6 ) restarts system Ctrl-Alt-Del Defined in /etc/inittab ca:12345:ctrlaltdel:/sbin/shutdown -t1 -a -r now

31. CIT 470: Advanced Network and System AdministrationSlide #31 What's wrong with init? Performance –Starts services sequentially. –Shell scripts spawn lots of processes. Manual configuration –Order to start services determined manually. –i.e. network before authentication before nfs. Reliability –Init doesn’t monitor or restart services after boot. Hotplug hardware –Drives mounted at boot. –What about USB or network drives?

32. CIT 470: Advanced Network and System AdministrationSlide #32 Init Alternatives iniNG –Service config specifies dependencies. –need = system/initial net/all; –Starts services in parallel once dependencies met. launchd –Mac replacement for init, rc, cron, atd, inetd –Monitors services, starts on demand. Service Management Facility –Sun replacement for init with service monitoring.

33. CIT 470: Advanced Network and System Administration Upstart Event-based init replacement. Events –Hardware device has been added. –Filesystem has been mounted. –Time ( cron -replacement) –File has been modified. –Another job has begun or finished running. Backwards compatible with /etc/init.d scripts. Respawns services that are down.

34. Boot Process Summary CIT 470: Advanced Network and System Administration

35. Key Points Boot Steps 1.BIOS 2.Bootloader (GRUB) 3.Kernel 4.init init is PID 1, parent of all processes, started by kernel –Uses rc command to run all scripts in /etc.rcN.d dir where N is runlevel –RHEL: use chkconfig to configure, /etc/sysconfig for options Run levels 1 and Single user mode (use to fix problems) 3 = multiuser + network (servers) 5 = multiuser + network + GUI (workstations) CIT 470: Advanced Network and System Administration

36. Slide #36 References 1.Aeleen Frisch, Essential System Administration, 3 rd edition, O’Reilly, 2002. 2.M. Tim Jones, “Inside the Linux boot process,” http://www.ibm.com/developerworks/library/l-linuxboot/index.html, 2006. http://www.ibm.com/developerworks/library/l-linuxboot/index.html 3.M. Tim Jones, “Parallelize applications for faster Linux booting,” http://www.ibm.com/developerworks/linux/library/l-boot-faster/index.html, 2007. http://www.ibm.com/developerworks/linux/library/l-boot-faster/index.html 4.Evi Nemeth et al, UNIX System Administration Handbook, 3 rd edition, Prentice Hall, 2001. 5.Scott James Remnant, “Upstart in Universe,” http://www.netsplit.com/2006/08/26/upstart-in-universe/, 2006. http://www.netsplit.com/2006/08/26/upstart-in-universe/ 6.Starman, “Boot records revealed: MBR details,” http://mirror.href.com/thestarman/asm/mbr/index.html 7.“Extended boot record,” http://en.wikipedia.org/wiki/Extended_Boot_Record.http://en.wikipedia.org/wiki/Extended_Boot_Record 8.GRUB manual, http://www.gnu.org/software/grub/manual/grub.html 9.“How it works: Master Boot Record (MBR),” http://www.ata- atapi.com/hiwmbr.htmhttp://www.ata- atapi.com/hiwmbr.htm 10.“Replacement Init”, https://wiki.ubuntu.com/ReplacementInit