Chapter 2 Booting and Shutting Down Kim Grempler Sections 2 0 to 2 3 Leon Dague Sections 2 4 to 2 7 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 Sample BSD Startup Scripts etc rc cont Start standard system daemons i e lpd inetd update uushed 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
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