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)
- See ``man eeprom'', ``man monitor'' on Suns
- ``man grub'' on Linux (grub is covered in more detail below)
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 (dmesg is not available on all UNIXes, alas)
- Tend to be 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)
Initializing cgroup subsys cpuset
Linux version 2.6.24.5-85.fc8 (mockbuild@xenbuilder2.fedora.redhat.com) (gcc version 4.1.2 20070925 (Red Hat 4.1.2-33)) #1 SMP Sat Apr 19 11:18:09 EDT 2008
Command line: ro root=/dev/VolGroup00/LogVol00 rhgb quiet
BIOS-provided physical RAM map:
BIOS-e820: 0000000000000000 - 0000000000095000 (usable)
BIOS-e820: 0000000000095000 - 00000000000a0000 (reserved)
UNIX/Linux Kernel initialization (2.6)
ACPI: RSDP 000F99E0, 0014 (r0 ACPIAM)
ACPI: RSDT BFFA0000, 0048 (r1 ACRSYS ACRPRDCT 20070721 MSFT 97)
ACPI: FACP BFFA0200, 0084 (r2 072107 FACP1408 20070721 MSFT 97)
ACPI: DSDT BFFA05C0, 5BCE (r1 1AAAA 1AAAA000 0 INTL 20051117)
ACPI: FACS BFFAE000, 0040
ACPI: APIC BFFA0390, 006C (r1 072107 APIC1408 20070721 MSFT 97)
UNIX/Linux Kernel initialization (2.6)
ACPI: PM-Timer IO Port: 0x808
ACPI: Local APIC address 0xfee00000
ACPI: LAPIC (acpi_id[0x01] lapic_id[0x00] enabled)
Processor #0 (Bootup-CPU)
ACPI: LAPIC (acpi_id[0x02] lapic_id[0x01] enabled)
Processor #1
ACPI: LAPIC (acpi_id[0x03] lapic_id[0x02] enabled)
Processor #2
ACPI: LAPIC (acpi_id[0x04] lapic_id[0x03] enabled)
Processor #3
UNIX/Linux Kernel initialization (2.6)
SMP: Allowing 4 CPUs, 0 hotplug CPUs
PERCPU: Allocating 42248 bytes of per cpu data
Built 1 zonelists in Node order, mobility grouping on. Total pages: 774141
Policy zone: DMA32
Kernel command line: ro root=/dev/VolGroup00/LogVol00 rhgb quiet
Initializing CPU#0
PID hash table entries: 4096 (order: 12, 32768 bytes)
hpet clockevent registered
TSC calibrated against HPET
time.c: Detected 2393.996 MHz processor.
Console: colour VGA+ 80x25
console [tty0] enabled
Checking aperture...
UNIX/Linux Kernel initialization (2.6)
Memory: 3092116k/3145344k available (2491k kernel code, 52800k reserved, 1390k data, 332k init)
SLUB: Genslabs=12, HWalign=64, Order=0-1, MinObjects=4, CPUs=4, Nodes=1
Calibrating delay using timer specific routine.. 4790.59 BogoMIPS (lpj=2395297)
Security Framework initialized
SELinux: Initializing.
SELinux: Starting in permissive mode
selinux_register_security: Registering secondary module capability
UNIX/Linux Kernel initialization (2.6)
Booting processor 1/4 APIC 0x1
Initializing CPU#1
Calibrating delay using timer specific routine.. 4787.75 BogoMIPS (lpj=2393876)
CPU: L1 I cache: 32K, L1 D cache: 32K
CPU: L2 cache: 4096K
CPU 1/1 -> Node 0
CPU: Physical Processor ID: 0
CPU: Processor Core ID: 1
Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz stepping 0b
checking TSC synchronization [CPU#0 -> CPU#1]: passed.
UNIX/Linux Kernel initialization (2.6)
ata6: SATA link down (SStatus 0 SControl 300)
scsi 0:0:0:0: Direct-Access ATA Hitachi HDT72505 V56O PQ: 0 ANSI: 5
sd 0:0:0:0: [sda] 976773168 512-byte hardware sectors (500108 MB)
sd 0:0:0:0: [sda] Write Protect is off
sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00
sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
sd 0:0:0:0: [sda] 976773168 512-byte hardware sectors (500108 MB)
sd 0:0:0:0: [sda] Write Protect is off
sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00
sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
sda: sda1 sda2 sda3 sda4 < sda5 sda6 >
sd 0:0:0:0: [sda] Attached SCSI disk
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
UNIX/Linux init and bootup scripts
- UNIX/Linux operating systems 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.
UNIX/Linux bootup scripts
- /etc/inittab is the master config file for init
- This file controls which bootup scripts will be executed
- The 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 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 includes a nifty 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 startup 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
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 and are difficult to learn. 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''
[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.
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. The ancient Partition Magic usually works for XP/2003, but there are many reports of issues with Vista; Neosmart EasyBCD seems so far to be a good choice for Vista/Linux dualboot.
