Chapter 2 Booting and Shutting Down

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Chapter 2Booting and Shutting Down

• Kim Grempler (Sections 2.0 to 2.3)
• Leon Dague (Sections 2.4 to 2.7)

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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

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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

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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

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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

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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.

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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

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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

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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
  (ltcontrol-dgt 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

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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 systems disks Remove files from /tmp
• Configure network interfaces
• Start up daemons and network services
• Turn on accounting and quotas

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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

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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

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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

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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

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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 exitsrc.boot exits
• No problems in autoboot mode the next init
  process is /etc/rc
• If problemsingle-user (sh process) on console

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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

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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

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Sample BSD Startup Scripts/etc/rc (cont.)

• Start standard system daemons (i.e., lpd, inetd,
  update, uushed)

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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

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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

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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

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Sample ATT Startup Scripts

• Leon Continue