Booting and Shutting Down

This contains links to information used in the lectures.

Bootstrapping or Booting - A delicate phase
Automatic v Manual Booting
Manual boot needed when there are problems such as corrupted filesystem or incorrect configuration file
Single User v Multi User Mode

Bootstrapping procedure (typical)

Load and initialize kernel
- hardware loads bootstrap program from disk or network (configured in static RAM),
- bootstrap program loads kernel /vmunix (SunOS), /unix, /hp-ux (HP-UX 9.03), /stand/vmunix (HP-UX 10.0/Sys V)
- kernel performs memory tests
- HP-UX 10.0 example
  After checking the hardware, the process dependent startup code (PDC) gives the user the option to override the autoboot sequence by pressing the Esc key. At that point, a message resembling the following usually appears on the console.
```
           (c) Copyright. Hewlett-Packard Company. 1994.
           All rights reserved.

           PDC ROM rev. 130.0
           32 MB of memory configured and tested.

           Selecting a system to boot.
           To stop selection process, press and hold the ESCAPE key...
```
Device detection and configuration
- tries to locate and configure devices configured into kernel
- devices connected after boot time may not be accessible

Create spontaneous system processes (not created by forking)
These differ with OS. They will have parent process 0 usually. Only init is a real process, the others are portions of the kernel.

BSD (SunOS)
- swapper - process 0
- init - process 1
- pagedaemon - process 2
ATT
- sched - process 0
- init - process 1
- various memory handlers

HP-UX 9.03 (Condor)

     UID   PID  PPID  C    STIME TTY      TIME COMMAND
    root     0     0  0  Dec 31  ?        3:54 swapper
    root     1     0  0  Dec 29  ?        0:12 init
    root     2     0  0  Dec 29  ?        4:14 vhand
    root     3     0  0  Dec 29  ?        2:46 statdaemon
    root     7     0  0  Dec 29  ?        0:00 unhashdaemon
    root    10     0  0  Dec 29  ?        0:03 syncdaemon
    root     6     0  0  Dec 29  ?        0:00 sockregd

HP-UX 10.0 (Intrepid)

     UID   PID  PPID  C    STIME TTY       TIME COMMAND
    root     0     0  0  Dec 29  ?         0:10 swapper
    root     1     0  0  Dec 29  ?         0:00 init
    root     2     0  0  Dec 29  ?         1:09 vhand
    root     3     0  0  Dec 29  ?        28:20 statdaemon
    root     4     0  0  Dec 29  ?         0:58 unhashdaemon
    root     7     0  0  Dec 29  ?         0:00 ttisr
    root    32     0  0  Dec 29  ?         0:06 lvmkd
    root    33     0  0  Dec 29  ?         0:04 lvmkd
    root    34     0  0  Dec 29  ?         0:01 lvmkd
    root    12     0  0  Dec 29  ?         2:19 vx_sched_thread
    root    13     0  0  Dec 29  ?         4:33 vx_iflush_thread
    root    14     0  0  Dec 29  ?         1:53 vx_inactive_cache_thread
    root    15     0  0  Dec 29  ?         0:36 vx_delxwri_thread
    root    16     0  0  Dec 29  ?         0:18 vx_logflush_thread
    root    17     0  0  Dec 29  ?         0:03 vx_attrsync_thread
    root    18     0  0  Dec 29  ?         0:05 vx_inactive_thread
    root    19     0  0  Dec 29  ?         0:05 vx_inactive_thread
    root    20     0  0  Dec 29  ?         0:05 vx_inactive_thread
    ....
    root    35     0  0  Dec 29  ?         0:06 lvmkd
    root    36     0  0  Dec 29  ?         0:31 nvsisr
    root    37     0  0  Dec 29  ?         0:00 supsched
    root    38     0  0  Dec 29  ?         0:00 strmem
    root    39     0  0  Dec 29  ?         0:00 strweld

Operator intervention - manual boot
- init is notified and creates shell on console
- always sh
- normal root login but only root partition mounted (/bin, /sbin, /etc, etc) not /usr/bin usually
- no daemons (mail etc)
- fsck must be run by hand, if required
Startup scripts executed
Usually shell scripts run by sh spawned by init. What is run here is very OS specific. Two main varieties BSD and ATT. However HP-UX is a mixture of both.
- Variations
  - SunOS 4.1.2 (BSD) - scripts names starting rc in /etc
  - ATT - /etc/inittab with scripts in /etc/init.d with links to them in directories /etc/rc0.d, /etc/rc1.d etc., where 0, 1, etc. correspond to the run levels
  - HP-UX 10.0 - /etc/inittab with scripts in /sbin with links to them in directories /sbin/rc0.d etc.
  - HP-UX 9.03 - /etc/inittab with scripts in /etc similar to BSD
- Common actions:
  - Set name, time zone
  - Run fsck, mount disks, possibly remove /tmp files
  - Configure network interfaces
  - Start daemons
  - Turn on accounting and quotas
- SunOS 4.1.2 (BSD)
  The initialization scripts also use text files for site specific information. Do man rc for more detailed information.
  - rc.boot - first script run
  - rc.single - note that this is run even if the system intends to enter multiuser mode
  - rc - main script
  - rc.local - contains some non-local initializations too
  - rc.ip
- HP-UX 10.0 (ATT)
  The init daemon and command is a general process spawner. Its primary role is to create processes from a script stored in the file /etc/inittab.
  Init considers the system to be in a run level at any given time. A run level can be viewed as a software configuration of the system, where each configuration allows only a selected group of processes to exist. The processes spawned by boot init for each of these run levels are defined in the inittab file. Boot init can be in one of eight run levels, 0-6, and S or s. The run level is changed by having a privileged user run the init command.
  If S or s is entered, boot init goes into the single-user level. This is the only run level that does not require the existence of a properly formatted inittab file. If inittab does not exist or is improperly formatted, then by default the only legal run level that boot init can enter is the single-user level. The S level causes /dev/syscon to be linked to the user's terminal line rather than the default system console.
  Run level 2 is usually defined as the "normal" run level, containing all of the terminal processes and daemons that are spawned in the multiuser environment.
  The inittab file is composed of entries that are position-dependent and have the following format:
```
           id:rstate:action:process
```
  Each entry is delimited by a newline; however, a backslash (\) preceding a newline indicates a continuation of the entry. Up to 1024 characters per entry are permitted. Comments can be inserted in the process field by starting a "word" with a #.
  - id is the name of the entry. rstate defines the run level in which this entry is to be processed. Run levels correspond to a configuration of processes in the system where each process spawned by boot init is assigned one or more run levels in which it is allowed to exist. When boot init is requested to change run levels, all processes that do not have an entry in the rstate field for the target run level are sent the warning signal (SIGTERM) and allowed a 20-second grace period before being forcibly terminated by a kill signal (SIGKILL). If no run level is specified, the process is assumed to be valid for all run levels, 0 through 6.
  - action tells whether init should wait for the process to finish (wait), run it only once (once), restart it when it dies (respawn) or ignore it (off). There are many other actions also including (sysinit) entries which are executed before boot init tries to access the console and query the operator.
  - process is a sh command to be executed.
  One can change the meaning of run-levels but this is a bad idea.
  Files from intrepid running HP-UX 10.0.
  - /etc/inittab
  - /sbin/ioinitrc - start nfs daemons, then put user in shell or run ioinit
  - /sbin/bcheckrc - check file system
  - /sbin/lvmrc - logical volume manager
  - /sbin/rc - startup and shutdown sequencer script. This script sequences the scripts in the appropriate sequencer directories in alphabetical order as defined by the shell and invokes them as either startup or kill scripts. If a transition from a lower to a higher run level (i.e., init state) occurs, the start scripts for the new run level and all intermediate levels between the old and new level are executed. If a transition from a higher to a lower run level occurs, the kill scripts for the new run level and all intermediate levels between the old and new level are executed.
    The startup and shutdown scripts (referred to as startup scripts hereafter) exist in the /sbin/init.d directory, named after the subsystem they control.
    The contents of sequencer directories consist of symbolic links to startup scripts in /sbin/init.d. These symbolic links must follow a strict naming convention, as noted in the various fields of this example: /sbin/rc2.d/S060cron
    - The first character of a sequencer link name determines whether the script is executed as a start script (if the character is S), or as a kill script (if the character is K).
    - 060 - A three digit number is used for sequencing scripts within the sequencer directory. Scripts are executed by type (start or kill) in alphabetical order as defined by the shell.
    - cron - The startup script name must be the same name as the script to which this sequencer entry is linked. In this example, the link points to /sbin/init.d/cron
  - Listing of the directories /sbin/rc?.d. This shows the kill and startup scripts in the order they are executed in. Note that the kill scripts for level 1 tend to be the startup scripts for level 2 in reverse order and are usually links to the same file in /sbin/init.d.
  - Listing of the directory /sbin/rc1.d. This shows the symbolic links to files in /sbin/init.d.
  - Startup/kill script for httpd
Run man init, and man inittab for more details.
Multiuser Operation init runs getty to allows logins on terminals
HP-UX 10.0 boot sequence details
Exercise: lookup the manual pages on boot, pdc, isl, hpux on HP-UX 10.0

Boot Problems Hardware problems Before calling hardware maintenance : Check power supply to each component (cord/switch) Check cables, (SCSI, ethernet etc.) Check fault lights Recycle power on all components If the kernel gets to probing devices and one doesn't appear then it is broken or improperly connected Try to run hardware diagnostics Defective boot blocks Many Unix systems read a boot block first before the kernel. If this is damaged try to boot from distribution media (or another disk). Try to reinstall the boot block. Damaged filesystems Damage may be : Soft: scrambled or lost information on disk Hard: disk head crash Solutions : Soft: If have an alternative root partition try to boot from it If the problem is less severe try to boot into single user mode, then use fsck and hope it will fix the problem. In particular, if you get messages about inodes, superblock, maps or filesystems, this may solve the problem. If you system allows booting from distribution media, do that. Mount the other filesystems, dump them and reload the operating system. Good idea to disconnect other disks to minimize risk. Hard: cry a lot, pray you have backups, buy a new disk, call a commercial recovery service Improperly configured kernel This is only likely to happen after a kernel rebuild. Make sure to keep the old kernel where you can boot from it. Errors in startup scripts This is the most common problem. Fix it as one would any other shell script. Reboot from scratch after each change - the script may fail otherwise. Rebooting and shutting down Blast with shotgun or other projectile weapon - well speaks for itself Shut off power - for fires/floods etc. only Not advised. Unix is not DOS (well except for HP 712s maybe). Crashing the system can leave the filesystem in an inconsistent state, and may damage disks. Send init a TERM signal - not advised Effects are unpredictable and often nasty. BSD kills user processes, daemons, gettys and leaves the system in single-user mode. Other Unixes may not. Kill init - not advised Killing init will cause a panic or reboot. shutdown - the approved way The most general approved way. (Note: to get the correct manpage on HP-UX you need to type man 1m shutdown.) Arguments vary with OS and include: Waiting a period in secs. Messages are sent to logged in users. secs (BSD, SunOS, HP-UX 9 and 10) or -gsecs (Solaris/IRIX) Indicate fast reboot (no fsck) (-f on BSD/SunOS systems) Halt (-i0 Solaris/IRIX, -h others), Reboot (-i6 Solaris/IRIX, -r others), Go to single-user (-iS Solaris/IRIX only) halt - halt the system Does not exist on HP-UX. Called by shutdown -h to kill non-essential processes, execute sync, wait for writes to complete, halt the kernel. halt -n does not sync. Used after repairs with fsck to prevent overwriting. reboot - reboot the system Causes the system to reboot. Called by shutdown -r. telinit - Change init run level On some systems with multi-level init (not HP-UX). Paul A. Farrell Wednesday, January 17, 1996