Chapter 2 Booting and Shutting Down

1. Chapter 2Booting and Shutting Down Kim Grempler (Sections 2.0 to 2.3) Leon Dague (Sections 2.4 to 2.7)

2. Bootstrapping • A.k.a. Booting • Kernel loaded into memory and executes • Initialization tasks performed • System available to users • Potential Problems when booting • Errors in configuration files, missing/unreliable equipment, or damaged filesystems • Boot configuration is first task of system administrator, on new system • Booting is hardware-dependent

3. Reference Chapters • Chapter 3: Root Account • Chapter 4: The Filesystem • Chapter 7: Devices and Drivers • Chapter 8: Serial Devices • Chapter 9: Installing a Boot program • Chapter 13: Configuring the Kernal • Chapter 31: Daemons

4. 2 Booting Modes • Automatic • Performs boot without external assistance • Manual • Automatic procedure until initialization scripts are run by operator • Single-user mode: most system processes not running and users unable to log in

5. Six Steps in Booting Process • Loading and initialization of the kernel • Device detection and configuration • Creation of spontaneous system processes • Operator intervention (single user boot only) • Execution of system startup scripts • Multi-user operation • **Admin. has little control of steps above. Boot configuration via editing system startup scripts**

6. Step 1: Loading and Initialization of the Kernal • Kernal (e.g., program) is loaded into memory to be executed • Pathname of kernal is vendor dependent • Example: /unix or /vmunix • 2-stage loading process • 1st: small boot program read into memory to enable kernal loading (outside domain of Unix) • 2nd: kernal runs tests to determine memory availability • kernels run in a fixed amount of memory and know what to reserve for internal storage and I/O buffers.

7. Step 2: Device Detection and Configuration • Kernal performs hardware check • General hardware device info is incorporated in kernal configuration • Locate and initialize each device • Acquire more info via drivers • If not found, will disable hardware • If hardware added, must reboot, to access

8. Step 3: Creation of Spontaneous System Processes • After basic initialization, kernel creates spontaneous processes in users space • Not created via normal UNIX fork mechanism • fork creates copy of the original process, with new ID, that is identical to the parent • BSD has 3 processes • Swapper - process 0; init - process1; pagedaemon - process 2 • ATT: varies • sched - process 0; init - process 1; various memory handlers • **Note- ONLY INIT USER PROCESS** • Kernal role complete; init handles processes for basic operations and UNIX daemons

9. Step 4: Operator Intervention (Single-User Boot Only) • init notified via command-line flag from kernel • init creates shell and waits for it to terminate (<control-d> or exit) before continuing on with rest of startup procedure • Always in bourne shell (e.g., sh) and runs as root with root partition mounted • Available programs located in /bin, /sbin, /etc, and /usr; ~ other filesystems must be mounted by operator • Daemons not available • fsck (checks and repairs filesystems) must be run by hand

10. Step 5: Execution of System Startup Scripts • The location, content, and organization of shell (e.g., sh) scripts vary from system to system • BSD: kept in /etc and names begin with rc • ATT: kept in /etc/init.d with links made to other directories such as /etc/rc0.d, /etc/rc1.d… • Examples of tasks performed in initialization scripts • Set computer name; Set time zone;fsck disk check; • Mount system’s disks; Remove files from /tmp • Configure network interfaces; • Start up daemons and network services; • Turn on accounting and quotas

11. Step 6: Multi-User Operation • To complete boot process and allow user access, init produces getty process on each workstation • BSD: init has only two states ~ single-user and multi-user • ATT: init has one single-user and several multi-user “run levels” to determine which system resources are enabled

12. Sample BSD Startup Scripts/etc/rc.boot • First rc script to run is /etc/rc.boot • The first two lines set HOME and PATH environment variables • Executes basic system commands during boot • hostname file in /etc for each network interface • enables IP networking on each interface • Reverse Address Resolution Protocol (RARP) • Find hostname from other machine on NW using hostconfig program and use NFS to mount filesystems • System Administrator intervene to fix problem

13. Sample BSD Startup Scripts/etc/rc.boot (cont.) • Address or hostname of default Internet gateway is read from /etc/defaultrouter • non-local NW connections up prior to more complicated routing in boot process • /usr filesystem read-only for system check to see if /fastboot exists • Yes: system shut down cleanly~ filesystems in consistent state • No: all filesystems listed in /etc/fstab checked in fsck • If disks check cleanly~ rc.boot runs /etc/rc.single

14. Sample BSD Startup Scripts/etc/rc.single • Commands in /etc/rc.single are executed at boot time even if not using single mode • Remounts / and /usr filesystems read/write • if not remounted~ system not able to come up • Cleans out /etc/mtabfile and adds entries for / and /usr • was previously mounted but not in mtab file because root filesystem not writable • /usr/kvm mounted~ clean up shared library cache

15. Sample BSD Startup Scripts/etc/rc.single • /etc/utmp file cleaned out • contains user list of current log ins • tzsetup command sets local time zone & status of daylight savings time (kernal is GMT) • loadkeys command sets keyboard mapping • rc.single exits~rc.boot exits • No problems in autoboot mode the next init process is /etc/rc • If problem~single-user (sh process) on console

16. Sample BSD Startup Scripts/etc/rc • /etc/rc is the main system startup up script in autoboot after rc.boot • if single-user: rc after shell is terminated • if root filesystems not writable~ rerun rc.single • clean up shared library cache • remove /fastboot file • /etc/passwd file edited ~system crashes • vipw and /etc/rc script make sure password file not destroyed at crash

17. Sample BSD Startup Scripts/etc/rc (cont.) • Enable quotas • /bin/ps -u cleans out the ps database (status of processes) • /etc/nologin created by shutdown to prevent logins during shutdown • executes rc.local script • swapon -a to make use of all swap partitions listed in etc/fstab • expreserve: looks in /tmp to find files that were edited when system went down

18. Sample BSD Startup Scripts/etc/rc (cont.) • Start standard system daemons (i.e., lpd,inetd, update, uushed)

19. Sample BSD Startup Scripts/etc/rc.local • /etc/rc.local contains commands for local system • portmap daemon maps RPC (remote procedure call) service numbers to the NW ports of appropriate servers • NIS (NW info service) Domain Name set from /etc/default domain • set subnet mask of all machines interfaces • default route reset~ if no default routing daemon run • list current configuration of NW interfaces on console

20. Sample BSD Startup Scripts/etc/rc.local (cont.) • All NFS filesystems mounted • named (server for Domain Name system) maps between hostnames and Internet addresses • Client side NFS daemon run (biod) • syslogd: responsible for managing log messages • save kernel core dump in /var/crash/hostname • Image saved on swap partition~ save image to real filesystem • Clean up temporary mail lock files and start sendmail

21. Sample BSD Startup Scripts/etc/rc.local (cont.) • Make machine NFS Server if filesystems need to be exported • Daemon to support diskless clients • rpc.statd and rpc.lockd manage advisory locks on NFS filesystems • Start automount daemon • 3rd party vendor install scripts • Appletalk protocol stack started • Licensed software add-ons

22. Sample ATT Startup Scripts • Leon Continue