Assignment

Read Chapters 11, 12, 13, and 15 in LAH. Read 4, 5, and 6 in WS2k8.

Booting Unix

• Steps in the typical Unix boot process
• The initial bootstrap program resides in firmware somewhere (e.g., the Sun "monitor", PC BIOS mode, [U]EFI (also see this article)
• ``man grub?'' on Linux

UNIX/Linux Kernel initialization

• You can see running monologue from various kernel routines, mostly dealing with the kernel and device drivers recognizing the hardware of the system. (You may have to use CTRL-ALT-F1 / CTRL-ALT-F2} / etc. to find the virtual terminal output. Also, if you are coming up with X enabled, you may have to click on a button labeled something like ``details'' to see more, or perhaps the "Esc" key.)
• Often logged in /var/adm/messages (or /var/log/messages, or perhaps /var/log/boot.log) and typically the system console and usually accessible via dmesg --- but, dmesg is not available on all UNIXes
• Very system-specific but with experience you should be able to scan a series of boot messages and spot problems.

UNIX/Linux Kernel initialization (old-ish 2.4)

Example dmesg outputs:

Linux version 2.4.21-37.EL (centos@sillage.bis.pasteur.fr) 
   (gcc version 3.2.3 20030502 (Red Hat Linux 3.2.3-52)) #1 
   Wed Sep 28 14:14:23 EDT 2005
BIOS-provided physical RAM map:
 BIOS-e820: 0000000000000000 - 00000000000a0000 (usable)
 BIOS-e820: 00000000000f0000 - 0000000000100000 (reserved)
 BIOS-e820: 0000000000100000 - 000000001f771000 (usable)
 BIOS-e820: 000000001f771000 - 000000001f773000 (ACPI NVS)

UNIX/Linux Kernel initialization (old-ish 2.4)

 BIOS-e820: 000000001f773000 - 000000001f794000 (ACPI data)
 BIOS-e820: 000000001f794000 - 000000001f800000 (reserved)
 BIOS-e820: 00000000fec00000 - 00000000fec10000 (reserved)
 BIOS-e820: 00000000fee00000 - 00000000fee10000 (reserved)
 BIOS-e820: 00000000ffb00000 - 0000000100000000 (reserved)
0MB HIGHMEM available.
503MB LOWMEM available.
[ ... ]
Kernel command line: ro root=LABEL=/
Initializing CPU#0

UNIX/Linux Kernel initialization (old-ish 2.4)

Detected 2399.594 MHz processor.
Console: colour VGA+ 80x25
Calibrating delay loop... 4784.12 BogoMIPS
[ ... ]
Memory: 500836k/515524k available (1545k kernel code, 
    12128k reserved, 1073k data, 164k init, 0k highmem)
[ ... ]
CPU: Trace cache: 12K uops, L1 D cache: 8K
CPU: L2 cache: 512K

UNIX/Linux Kernel initialization (old-ish 2.4)

Intel machine check architecture supported.
Intel machine check reporting enabled on CPU#0.
CPU:     After generic, caps: bfebfbff 00000000 00000000 00000000
CPU:             Common caps: bfebfbff 00000000 00000000 00000000
CPU: Intel(R) Pentium(R) 4 CPU 2.40GHz stepping 07
[ ... ] 
Linux NET4.0 for Linux 2.4
[ ... ] 

UNIX/Linux Kernel initialization (old-ish 2.4)

hda: WDC WD800BB-75CAA0, ATA DISK drive
blk: queue c041c900, I/O limit 4095Mb (mask 0xffffffff)
hdc: LG CD-ROM CRN-8245B, ATAPI CD/DVD-ROM drive
ide0 at 0x1f0-0x1f7,0x3f6 on irq 14
ide1 at 0x170-0x177,0x376 on irq 15
hda: attached ide-disk driver.
hda: host protected area => 1
hda: setmax LBA 156301488, native  156250000

UNIX/Linux Kernel initialization (old-ish 2.4)

hda: 156250000 sectors (80000 MB) w/2048KiB Cache, 
    CHS=9726/255/63, UDMA(100)
ide-floppy driver 0.99.newide
Partition check:
 hda: hda1 hda2 hda3
ide-floppy driver 0.99.newide

UNIX/Linux Kernel initialization (old-ish 2.4)

[ ... ] 
EXT3-fs: mounted filesystem with ordered data mode.
Freeing unused kernel memory: 164k freed
[ ... ] 
EXT3 FS 2.4-0.9.19, 19 August 2002 on ide0(3,2), internal journal
Adding Swap: 1044216k swap-space (priority -1)

UNIX/Linux Kernel initialization (old-ish 2.4)

kjournald starting.  Commit interval 5 seconds
EXT3 FS 2.4-0.9.19, 19 August 2002 on ide0(3,1), internal journal
EXT3-fs: mounted filesystem with ordered data mode.
[ ... ] 

UNIX/Linux Kernel initialization (2.6)

[    0.000000] Initializing cgroup subsys cpuset
[    0.000000] Initializing cgroup subsys cpu
[    0.000000] Linux version 2.6.40.4-5.fc15.x86_64 (mockbuild@x86-10.phx2.fedoraproject.org) (gcc version 4.6.0 20110603 (Red Hat 4.6.0-10) (GCC) ) #1 SMP Tue Aug 30 14:38:32 UTC 2011
[    0.000000] Command line: ro root=UUID=a34a9b1e-82f6-4d91-a407-f5a769ed09b8 rd_NO_LUKS rd_NO_LVM rd_NO_MD rd_NO_DM LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 KEYTABLE=us rhgb quiet
[    0.000000] BIOS-provided physical RAM map:
[    0.000000]  BIOS-e820: 0000000000000000 - 000000000009f000 (usable)
[    0.000000]  BIOS-e820: 000000000009f000 - 00000000000a0000 (reserved)
[    0.000000]  BIOS-e820: 00000000000f0000 - 0000000000100000 (reserved)
[    0.000000]  BIOS-e820: 0000000000100000 - 000000007fed0000 (usable)
[    0.000000]  BIOS-e820: 000000007fed0000 - 000000007fed3000 (ACPI NVS)
[    0.000000]  BIOS-e820: 000000007fed3000 - 000000007fee0000 (ACPI data)
[    0.000000]  BIOS-e820: 000000007fee0000 - 000000007ff00000 (reserved)
[    0.000000]  BIOS-e820: 00000000f0000000 - 00000000f4000000 (reserved)
[    0.000000]  BIOS-e820: 00000000fec00000 - 0000000100000000 (reserved)
[    0.000000] NX (Execute Disable) protection: active
[    0.000000] DMI 2.4 present.
[    0.000000] DMI: Dell Inc OptiPlex 740/0TT708, BIOS 1.1.8  06/08/2007

UNIX/Linux Kernel initialization (2.6)

[    0.000000] Memory: 2037512k/2095936k available (4680k kernel code, 452k absent, 57972k reserved, 6905k data, 936k init)
[    0.000000] SLUB: Genslabs=15, HWalign=64, Order=0-3, MinObjects=0, CPUs=2, Nodes=1
[    0.000000] Hierarchical RCU implementation.
[    0.000000] 	RCU dyntick-idle grace-period acceleration is enabled.
[    0.000000] NR_IRQS:16640 nr_irqs:512 16
[    0.000000] spurious 8259A interrupt: IRQ7.
[    0.000000] Console: colour VGA+ 80x25
[    0.000000] console [tty0] enabled
[    0.000000] allocated 16777216 bytes of page_cgroup
[    0.000000] please try 'cgroup_disable=memory' option if you don't want memory cgroups
[    0.000000] hpet clockevent registered
[    0.000000] Fast TSC calibration using PIT
[    0.000000] Detected 2605.321 MHz processor.
[    0.000000] Marking TSC unstable due to TSCs unsynchronized
[    0.001007] Calibrating delay loop (skipped), value calculated using timer frequency.. 5210.64 BogoMIPS (lpj=2605321)
[    0.001012] pid_max: default: 32768 minimum: 301
[    0.001043] Security Framework initialized
[    0.001062] SELinux:  Initializing.
[    0.001071] SELinux:  Starting in permissive mode

UNIX/Linux Kernel initialization (2.6)

[    0.001383] Dentry cache hash table entries: 262144 (order: 9, 2097152 bytes)
[    0.002806] Inode-cache hash table entries: 131072 (order: 8, 1048576 bytes)
[    0.003288] Mount-cache hash table entries: 256
[    0.003474] Initializing cgroup subsys cpuacct
[    0.003480] Initializing cgroup subsys memory
[    0.003498] Initializing cgroup subsys devices
[    0.003501] Initializing cgroup subsys freezer
[    0.003503] Initializing cgroup subsys net_cls
[    0.003506] Initializing cgroup subsys blkio
[    0.003516] Initializing cgroup subsys perf_event
[    0.003552] tseg: 007ff00000
[    0.003555] CPU: Physical Processor ID: 0
[    0.003557] CPU: Processor Core ID: 0
[    0.003559] mce: CPU supports 5 MCE banks
[    0.003573] using AMD E400 aware idle routine
[    0.003913] ACPI: Core revision 20110413
[    0.008011] ftrace: allocating 24446 entries in 96 pages
[    0.009647] ..TIMER: vector=0x30 apic1=0 pin1=2 apic2=-1 pin2=-1
[    0.019888] CPU0: AMD Athlon(tm) 64 X2 Dual Core Processor 5000+ stepping 02
[    0.019998] Performance Events: AMD PMU driver.
[    0.019998] ... version:                0
[    0.019998] ... bit width:              48
[    0.019998] ... generic registers:      4
[    0.019998] ... value mask:             0000ffffffffffff
[    0.019998] ... max period:             00007fffffffffff
[    0.019998] ... fixed-purpose events:   0
[    0.019998] ... event mask:             000000000000000f

UNIX/Linux Kernel initialization (2.6)

[    0.251377] Trying to unpack rootfs image as initramfs...
[    0.602091] Freeing initrd memory: 14776k freed
[    0.611303] Simple Boot Flag at 0x3a set to 0x80
[    0.611741] Intel AES-NI instructions are not detected.
[    0.611954] audit: initializing netlink socket (disabled)
[    0.611970] type=2000 audit(1315925247.610:1): initialized
[    0.639163] HugeTLB registered 2 MB page size, pre-allocated 0 pages
[    0.655096] VFS: Disk quotas dquot_6.5.2
[    0.655152] Dquot-cache hash table entries: 512 (order 0, 4096 bytes)
[    0.655753] msgmni has been set to 4008
[    0.655828] SELinux:  Registering netfilter hooks
[    0.656341] alg: No test for stdrng (krng)
[    0.656352] NET: Registered protocol family 38
[    0.656415] Block layer SCSI generic (bsg) driver version 0.4 loaded (major 253)

UNIX/Linux Kernel initialization (2.6)

[    1.023889] device-mapper: uevent: version 1.0.3
[    1.023976] device-mapper: ioctl: 4.20.0-ioctl (2011-02-02) initialised: dm-devel@redhat.com
[    1.024056] cpuidle: using governor ladder
[    1.024059] cpuidle: using governor menu
[    1.024497] EFI Variables Facility v0.08 2004-May-17
[    1.024683] usbcore: registered new interface driver usbhid
[    1.024685] usbhid: USB HID core driver
[    1.024770] ip_tables: (C) 2000-2006 Netfilter Core Team
[    1.024786] TCP cubic registered
[    1.024788] Initializing XFRM netlink socket
[    1.024800] NET: Registered protocol family 17
[    1.024820] Registering the dns_resolver key type
[    1.024940] PM: Hibernation image not present or could not be loaded.
[    1.024959] registered taskstats version 1
[    1.031818] IMA: No TPM chip found, activating TPM-bypass!
[    1.032171]   Magic number: 11:714:788
[    1.032273] rtc_cmos 00:04: setting system clock to 2011-09-13 14:47:28 UTC (1315925248)
[    1.032316] Initializing network drop monitor service
[    1.034569] Freeing unused kernel memory: 936k freed
[    1.035030] Write protecting the kernel read-only data: 10240k
[    1.041589] Freeing unused kernel memory: 1444k freed
[    1.049947] Freeing unused kernel memory: 1688k freed

UNIX/Linux Kernel initialization (2.6)

[    1.090909] dracut: dracut-009-12.fc15
[    1.100001] dracut: rd.luks=0: removing cryptoluks activation
[    1.102866] dracut: rd.lvm=0: removing LVM activation
[    1.109223] udev[128]: starting version 167
[    1.144994] [drm] Initialized drm 1.1.0 20060810
[    1.163906] [drm] radeon defaulting to kernel modesetting.
[    1.163910] [drm] radeon kernel modesetting enabled.
[    1.165250] ACPI: PCI Interrupt Link [APC5] enabled at IRQ 16
[    1.165277] radeon 0000:03:00.0: PCI INT A -> Link[APC5] -> GSI 16 (level, low) -> IRQ 16
[    1.165283] radeon 0000:03:00.0: setting latency timer to 64
[    1.165543] [drm] initializing kernel modesetting (RV515 0x1002:0x7183 0x1028:0x0D02).
[    1.165564] [drm] register mmio base: 0xFDDF0000
[    1.165566] [drm] register mmio size: 65536
[    1.167721] ATOM BIOS: RV516
[    1.167744] [drm] Generation 2 PCI interface, using max accessible memory
[    1.167750] radeon 0000:03:00.0: VRAM: 256M 0x0000000000000000 - 0x000000000FFFFFFF (256M used)
[    1.167753] radeon 0000:03:00.0: GTT: 512M 0x0000000010000000 - 0x000000002FFFFFFF

Linux booting

Linux provides a flexible multi-operating system boot loader named grub (GRand Unified Bootloader) that can be used to boot different operating systems. Like Windows bootloaders, it can also sit on the Master Boot Record (MBR) of the boot device and transfer control to specific operating system kernels depending on either a user type-in or a default. Grub's behavior is controlled by /boot/grub/grub.conf.

Previously, there was lilo, which is still seen occasionally, and even older, the loadlin program which used DOS to boot Linux.

Linux booting

Here's a grub configuration file on a Fedora 11 machine with a choice of three different kernels:

# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE:  You have a /boot partition.  This means that
#          all kernel and initrd paths are relative to /boot/, eg.
#          root (hd0,0)
#          kernel /vmlinuz-version ro root=/dev/mapper/luks-67331215-2e69-4e48-85b6-f9600f5aaa7c
#          initrd /initrd-version.img
#boot=/dev/sda
default=0
timeout=0
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
#
title Fedora (2.6.30.5-43.fc11.x86_64)
root (hd0,0)
kernel /vmlinuz-2.6.30.5-43.fc11.x86_64 ro root=/dev/mapper/luks-67331215-2e69-4e48-85b6-f9600f5aaa7c rhgb quiet
initrd /initrd-2.6.30.5-43.fc11.x86_64.img
#
title Fedora (2.6.29.6-217.2.16.fc11.x86_64)
root (hd0,0)
kernel /vmlinuz-2.6.29.6-217.2.16.fc11.x86_64 ro root=/dev/mapper/luks-67331215-2e69-4e48-85b6-f9600f5aaa7c rhgb quiet
initrd /initrd-2.6.29.6-217.2.16.fc11.x86_64.img
#
title Fedora (2.6.29.6-217.2.8.fc11.x86_64)
root (hd0,0)
kernel /vmlinuz-2.6.29.6-217.2.8.fc11.x86_64 ro root=/dev/mapper/luks-67331215-2e69-4e48-85b6-f9600f5aaa7c rhgb quiet
initrd /initrd-2.6.29.6-217.2.8.fc11.x86_64.img

Grub from Debian Box

Here's a grub configuration file from a Debian Squeeze machine with two boot-up choices:

#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
#

### BEGIN /etc/grub.d/00_header ###
if [ -s $prefix/grubenv ]; then
  load_env
fi
set default="0"
if [ "${prev_saved_entry}" ]; then
  set saved_entry="${prev_saved_entry}"
  save_env saved_entry
  set prev_saved_entry=
  save_env prev_saved_entry
  set boot_once=true
fi

function savedefault {
  if [ -z "${boot_once}" ]; then
    saved_entry="${chosen}"
    save_env saved_entry
  fi
}

function load_video {
  insmod vbe
  insmod vga
  insmod video_bochs
  insmod video_cirrus
}

insmod part_msdos
insmod ext2
set root='(hd0,msdos1)'
search --no-floppy --fs-uuid --set bb37e57f-0535-4a67-8f1d-f11cdd6098f3
if loadfont /usr/share/grub/unicode.pf2 ; then
  set gfxmode=640x480
  load_video
  insmod gfxterm
fi
terminal_output gfxterm
insmod part_msdos
insmod ext2
set root='(hd0,msdos1)'
search --no-floppy --fs-uuid --set bb37e57f-0535-4a67-8f1d-f11cdd6098f3
set locale_dir=($root)/boot/grub/locale
set lang=en
insmod gettext
set timeout=5
### END /etc/grub.d/00_header ###

### BEGIN /etc/grub.d/05_debian_theme ###
set menu_color_normal=cyan/blue
set menu_color_highlight=white/blue
### END /etc/grub.d/05_debian_theme ###

### BEGIN /etc/grub.d/10_linux ###
menuentry 'Debian GNU/Linux, with Linux 2.6.32-5-amd64' --class debian --class gnu-linux --class gnu --class os {
	insmod part_msdos
	insmod ext2
	set root='(hd0,msdos1)'
	search --no-floppy --fs-uuid --set bb37e57f-0535-4a67-8f1d-f11cdd6098f3
	echo	'Loading Linux 2.6.32-5-amd64 ...'
	linux	/boot/vmlinuz-2.6.32-5-amd64 root=UUID=bb37e57f-0535-4a67-8f1d-f11cdd6098f3 ro  quiet
	echo	'Loading initial ramdisk ...'
	initrd	/boot/initrd.img-2.6.32-5-amd64
}
menuentry 'Debian GNU/Linux, with Linux 2.6.32-5-amd64 (recovery mode)' --class debian --class gnu-linux --class gnu --class os {
	insmod part_msdos
	insmod ext2
	set root='(hd0,msdos1)'
	search --no-floppy --fs-uuid --set bb37e57f-0535-4a67-8f1d-f11cdd6098f3
	echo	'Loading Linux 2.6.32-5-amd64 ...'
	linux	/boot/vmlinuz-2.6.32-5-amd64 root=UUID=bb37e57f-0535-4a67-8f1d-f11cdd6098f3 ro single 
	echo	'Loading initial ramdisk ...'
	initrd	/boot/initrd.img-2.6.32-5-amd64
}
### END /etc/grub.d/10_linux ###

### BEGIN /etc/grub.d/20_linux_xen ###
### END /etc/grub.d/20_linux_xen ###

### BEGIN /etc/grub.d/30_os-prober ###
### END /etc/grub.d/30_os-prober ###

### BEGIN /etc/grub.d/40_custom ###
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.
### END /etc/grub.d/40_custom ###

### BEGIN /etc/grub.d/41_custom ###
if [ -f  $prefix/custom.cfg ]; then
  source $prefix/custom.cfg;
fi
### END /etc/grub.d/41_custom ###

UNIX/Linux init and bootup scripts

• UNIX/Linux operating systems generally use some series of programs and/or scripting that are started at boot time. Currently, most of these scripts are plain shell script text files. However, this is an area of active research, and better dependency handling regimes are in the works.
• Old-style BSD-based systems used a simple naming convention of /etc/rc*. This simplistic version of startup scripts is rare these days. More common are the System V startup scripts (with many variations).
• SystemV bootup scripts allow for more complex script configurations (the scripts are ``buried'' in directories of /etc/ rather than just being all in one directory). The init process starts the rc { } file processing.
• But maybe what we want instead is more like the daemontools approach. Instead of "dependencies", maybe we should make daemons that are smart enough to fail gracefully until a needed service is available.

UNIX/Linux bootup scripts

• /etc/inittab is the master config file for init — but it doesn't have much when you are using systemd on Fedora 15.

# inittab is no longer used when using systemd.
#
# ADDING CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.
#
# Ctrl-Alt-Delete is handled by /etc/systemd/system/ctrl-alt-del.target
#
# systemd uses 'targets' instead of runlevels. By default, there are two main targets:
#
# multi-user.target: analogous to runlevel 3
# graphical.target: analogous to runlevel 5
#
# To set a default target, run:
#
# ln -s /lib/systemd/system/.target /etc/systemd/system/default.target
#

• This file controls which bootup scripts will be executed by init, but not by systemd!
• The traditional scripts are divided into ``run-levels'', which determine what sort of booting you are doing (multi-user, single-user, shutdown, specialty boot, etc.). The ``man'' page for ``init'' (``man init'') explains the run level numbering.

UNIX/Linux bootup scripts

The idea for init is that soft-links that start with a capital ``S'' are executed at startup; soft-links with a leading capital ``K'' are executed at shutdown (you can see this behavior in /sbin/rc2 on Solaris and /etc/rc.d/rc on RedHat).

The Linux init package usually includes a utility named runlevel that you can run to determine the current machine's run level.

UNIX/Linux init

CentOS 3.6 Linux /etc/inittab

#
# inittab       This file describes how the INIT process 
#               should set up
#               the system in a certain run-level.
#
# Author:       Miquel van Smoorenburg, 
#               
#               Modified for RHS Linux by Marc Ewing and 
#               Donnie Barnes
#
# Default runlevel. The runlevels used by RHS are:
#   0 - halt (Do NOT set initdefault to this)
#   1 - Single user mode
#   2 - Multiuser, without NFS (The same as 3, if you do not have networking)
#   3 - Full multiuser mode
#   4 - unused
#   5 - X11
#   6 - reboot (Do NOT set initdefault to this)
# 
id:5:initdefault:

# System initialization.
si::sysinit:/etc/rc.d/rc.sysinit

l0:0:wait:/etc/rc.d/rc 0
l1:1:wait:/etc/rc.d/rc 1
l2:2:wait:/etc/rc.d/rc 2
l3:3:wait:/etc/rc.d/rc 3
l4:4:wait:/etc/rc.d/rc 4
l5:5:wait:/etc/rc.d/rc 5
l6:6:wait:/etc/rc.d/rc 6

# Trap CTRL-ALT-DELETE
ca::ctrlaltdel:/sbin/shutdown -t3 -r now

# When our UPS tells us power has failed, assume we have a few minutes
# of power left.  Schedule a shutdown for 2 minutes from now.
# This does, of course, assume you have powerd installed and your
# UPS connected and working correctly.  
pf::powerfail:/sbin/shutdown -f -h +2 "Power Failure; System Shutting Down"

# If power was restored before the shutdown kicked in, cancel it.
pr:12345:powerokwait:/sbin/shutdown -c "Power Restored; Shutdown Cancelled"


# Run gettys in standard runlevels
1:2345:respawn:/sbin/mingetty tty1
2:2345:respawn:/sbin/mingetty tty2
3:2345:respawn:/sbin/mingetty tty3
4:2345:respawn:/sbin/mingetty tty4
5:2345:respawn:/sbin/mingetty tty5
6:2345:respawn:/sbin/mingetty tty6

# Run xdm in runlevel 5
x:5:respawn:/etc/X11/prefdm -nodaemon

UNIX/Linux init

Solaris 9 /etc/inittab

ap::sysinit:/sbin/autopush -f /etc/iu.ap
ap::sysinit:/sbin/soconfig -f /etc/sock2path
fs::sysinit:/sbin/rcS sysinit             >/dev/msglog 2<>/dev/msglog /dev/msglog 2<>/dev/msglog
sS:s:wait:/sbin/rcS                       >/dev/msglog 2<>/dev/msglog /dev/msglog 2<>/dev/msglog /dev/msglog 2<>/dev/msglog /dev/msglog 2<>/dev/msglog /dev/msglog 2<>/dev/msglog /dev/msglog 2<>/dev/msglog /dev/msglog 2<>/dev/msglog /dev/msglog 2<>/dev/msglog /dev/msglog 2<>/dev/msglog /dev/msglog 2<>/dev/msglog 
  

UNIX bootup scripts

Notice the location of the actual init shell scripts can vary (/etc, /etc/rc.d, etc.), even between different versions of UNIX. For instance, Solaris: /etc/rc?.d (/etc/rc2.d is typical), CentOS Linux: /etc/rc.d

UNIX/Linux Controlling init link sprawl

On some systems, you can use chkconfig to control the maze of links.

# chkconfig --list   # show what is on and what is off for runlevels
anacron        	0:off	1:off	2:on	3:on	4:on	5:on	6:off
atd            	0:off	1:off	2:off	3:on	4:on	5:on	6:off
atieventsd     	0:off	1:off	2:off	3:off	4:off	5:on	6:off
auditd         	0:off	1:off	2:on	3:on	4:on	5:on	6:off
autofs         	0:off	1:off	2:off	3:on	4:on	5:on	6:off

# chkconfig --level 2345 sendmail on    # have sendmail start 2345

# chkconfig --del sendmail      # remove sendmail from chkconfig management
# chkconfig --add sendmail      # add sendmail to chkconfig management

A sample init script

The current Fedora 15 init script for ntpd

The systemd man page

A version of the systemd(1) man page

Typical problems with UNIX booting

• Error in startup scripts (much more common problem on established servers than rather newly installed servers, and generally happens when a sysadmin has made some sort of change)
• The monitor/BIOS can't find bootblock or bootloader (much more likely during install)
• Kernel won't load or recognize your hardware (much more likely during install)
• Can't find swap partition(s) (very much more likely during install)
• Damaged root (and/or /usr or maybe even /var) file system (not seen as often these days due to good journaling file systems such as ext3)

Upshot

• You should know BASH syntax, so you can figure out what went wrong during boot.
• Occasionally you may wish to customize the shell scripts to either modify the ``out of the box'' behavior of the boot process or to add your own daemon startups.
• Traditionally, best practice has been widely considered to keep all of your local customizations in separate shell scripts (e.g., /etc/rc.local is a good place on Linux machines, /etc/rc.d/S99local Solaris). However, with systems governed by chkconfig, it's best to use its scheme.

Upshot

Beware that many versions of UNIX/Linux choose to use symbolic links between a common script directory and the particular runlevel directory. Treat any modifications to the startup shell scripts as you would any other program -- edit, test (reboot), document, debug until it works.

Upshot

In a major site, you may find that weekly reboots at an off time (such as early on Sunday morning) are automatically done to discover any bad interactions among boot modifications that might have been made recently.

Windows Server 200x Server booting

• Windows Server 200x, Linux, and Solaris on x86/x64 can run on the same exact hardware, so at the earliest levels of booting both follow the same path through the hardware and firmware initialization (CMOS settings for boot device, loading up the boot loader from the boot disk, etc.)
• Being a proprietary operating system, much of the internal machinations of Windows are not as apparent. Also, they are difficult to debug if there's a problem, since most of these steps are not visible.

Windows Server 2003-specific booting

• Steps in Windows boot process (good description in William Boswell's Inside Windows Server 2003):
• For x64,
• EFI (Extensive Firmware Interface) now finds the bootstrap loader IA64ldr which finds the basic NT kernel NTOSKRN.EXE
• For x86,
• POST hands off via INT 13h which looks for bootable device, then loads MBR (Master Boot Record)
• MBR scans the partition table to find sector/offset, and loads the first 512 byte sector into 0x7c00 and executes it; it searches for Ntldr
• Ntldr initializes video hardware, puts the screen in 80x25 mode; searches for Boot.ini (not necessary to find though since defaults exists); finally finds and executes NTDETECT.COM
• C:$\backslash$WINNT$\backslash$SYSTEM32$\backslash$NTDETECT.COM finds the kernel (NTOSKRNL.EXE)
• NTOSKRNL.EXE extracts system information from the system's Registry database and then it:
• Loads HAL.DLL (hardware abstraction) and BOOTVID.DLL (video)
• Loads Session manager SMSS.EXE, which starts many services (WINLOGON.EXE, local security authority LSASS.EXE, printing) and loads SCREG.EXE to load other devices and services
• The system information includes HAL (Hardware Abstraction Layer) and the system hive from the Registry (chapter 4 in W2K3).

Win2Kx booting happens ``behind the scenes''

• You can modify that somewhat by editing C:$\backslash$BOOT.INI for 2003 (examples are from Microsoft, at http://support.microsoft.com/kb/323427):

[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows .NET Standard Server" /fastdetect

Win2K booting happens ``behind the scenes''

Notice the ``boot loader'' stanza used to specify the loader behavior and give the default operating system while the ``operating systems'' stanza gives the choices for operating system. To boot Win2K3 or XP, for example, you could use:

[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows .NET Standard Server" /fastdetect
multi(0)disk(1)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP Professional" /sos

Win2K3 booting happens ``behind the scenes''

You can place many options such as /sos in the boot.ini file (sos means display device driver names as they load).

Here is a quick list of the ones for 2003 (from http://support.microsoft.com/kb/833721)

Win2K3 booting happens ``behind the scenes''

• /basevideo -- forces the system into base video VGA mode, at 640x480 with 16 colors
• /baudrate=NUMBER
• /crashdebug
• /debug
• /debugport=COMNUMBER
• /maxmem=NUMBER
• /noguiboot
• /nodebug
• /numproc=NUMBER
• /pcilock
• /fastdetect:COMNUMBER
• /sos -- displays device driver name as they are loaded
• /PAE
• /HAL=FILENAME
• /kernel=FILENAME
• /bootlog -- turn on boot logging
• /burnmemory=NUMBER
• /3GB
• /safeboot:PARAMETER -- where parameter can be ``minimal'', ``network'', ``minimal(alternateshell)''; for instance, to boot in safe mode with just a command prompt, use /safeboot:minimal(alternateshell) /sos /bootlog /noguiboot
• /userva
• /redirect
• /channel

Win2k8 is worse

In Windows 2008, Microsoft eliminated the boot.ini file. Now only ``magic'' commands will let you modify boot parameters. Microsoft's bcdedit.exe or EasyBCD will let you do things such as set up multi-boot.

Look at for a short summary of the boot sequence for W2k8, Vista, and Windows 7.

To Quote MICROSOFT

What is the BCD store?

The Boot Configuration Data (BCD) store contains boot configuration parameters and controls how the operating system is started in Microsoft® Windows Vista® and Microsoft® Windows Server® 2008 operating systems. These parameters were previously in the Boot.ini file (in BIOS-based operating systems) or in the nonvolatile RAM (NVRAM) entries (in Extensible Firmware Interface–based operating systems). You can use the Bcdedit.exe command-line tool to affect the Windows® code which runs in the pre-operating system environment by adding, deleting, editing, and appending entries in the BCD store. Bcdedit.exe is located in the WindowsSystem32 directory of the Windows Vista partition.

[From http://technet.microsoft.com/en-us/library/cc721886.aspx]

Final word on booting

Since the boot loading process is reasonably common to various platforms, many boot loaders can handle different operating systems. You can, for instance, use grub to boot up Linux, Win2K, WinXP (and occasionally Vista, though by default Vista is not going to like a non-Windows MBR), and so forth; you can also use some third-party software, such as Neosmart EasyBCD. (The last works particularly well with Vista and Linux dual-booting.)

None of these are perfect. So far, Neosmart EasyBCD seems to be a good choice, but who knows what will break next!?