Apache Web Hosting, Affordable, PHP5, Comcast - Linux Blog

Chapter 8 . Understanding the Boot Process 305 Page cache hash table entries: 16384 (order 4, 64k) VFS: Diskquotas version dquot_6.4.0 initialized CPU: Intel Pentium III (Coppermine) stepping 03 Checking 386/387 coupling… OK, FPU using exception 16 error reporting. Checking hlt instruction… OK. POSIX conformance testing by UNIFIX mtrr: v1.35a (19990819) Richard Gooch (rgooch@atnf.csiro.au) PCI: PCI BIOS revision 2.10 entry at 0xfd9de PCI: Using configuration type 1 PCI: Probing PCI hardware PCI: Enabling memory for device 00:78 PCI: Enabling memory for device 00:80 Linux NET4.0 for Linux 2.2 Understanding Runlevels and init Objective 2.6 Boot, Initialization, Shutdown, Run Levels Change runlevels and shutdown or reboot system. Securely change the run- level of the system, specifically to single user mode, halt (shutdown) or reboot. Make sure to alert users beforehand, and properly terminate processes. Involves using the commands: shutdown, init The Linux boot process is very customizable, but can differ between distributions in the details. To understand the boot process and how to troubleshoot and debug it, you need to be familiar with the concept of runlevels and the init process. Using runlevels A Linux system can be configured to have several different configurations or states. These different states are known as runlevels, and there are seven of them, numbered 0 through 6. Runlevels 7 through 9 are valid, but unused because traditional UNIX operating systems did not support them. To see which runlevel the system is currently in, use the runlevel command. For example: debian~# runlevel N 2 The N in this example specifies that the system was booted to this runlevel and that there was no previous runlevel. On most distributions the runlevel dictates the configuration of the system. One runlevel may be for text mode and another for GUI mode. Separate runlevels are sometimes used to have network and nonnetwork configurations. Table 8-5 lists the standard runlevel uses for Red Hat and its variants. Exam Tip To see which runlevel the system is currently in, just type runlevel.
We recommend cheap and reliable webhost to host and run your web applications: Coldfusion Web Hosting services.

304 Part II . Getting Around in Linux Table 8-4 (continued) Option Function -r Changes the perceived root when installing LILO in a troubleshooting situation. -R Specifies a command to run the next time the boot loader is executed, after which the command is erased. Used with reboot scripts. -s Saves the existing boot sector to the specified filename. -S Saves the existing boot sector to the specified filename, and overwrites an existing file if it exists. -t Enables test mode. Use with the -v parameter to display what LILO would do if installed. -T Prints out system information for the requested option. See the lilo man page for a list of the options. -u Uninstalls LILO from the specified device. -U Uninstalls LILO from the specified device, but does not perform a time stamp check. -v Increases the verbosity of information displayed. Up to five -v parameters can be added to further increase the amount of information displayed. -V Displays the LILO version number. -q Prints information contained in the map file telling which images LILO will boot, as well as other information from lilo.conf. Viewing boot messages During the boot process the messages displayed to the console are saved to a log file, usually named /var/log/dmesg. To view this log you can either display the log file or use the dmesg command. Below is an example of the result of the use of this command: Linux version 2.2.16-22 (root@porky.devel.redhat.com) (gcc version egcs-2.91.66 19990314/Linux (egcs-1.1.2 release)) #1 Tue Aug 22 16:49:06 EDT 2000 Detected 579006 kHz processor. Console: colour VGA+ 80×25 Calibrating delay loop… 1048.58 BogoMIPS Memory: 46712k/49152k available (1048k kernel code, 412k reserved, 916k data, 64 k init, 0k bigmem) Dentry hash table entries: 262144 (order 9, 2048k) Buffer cache hash table entries: 65536 (order 6, 256k)
We would like to recommend you tested and proved virtual web hosting services, which you will surely find to be of great quality.

Chapter 8 . Understanding the Boot Process 303 Installing and updating LILO Any time that you modify the lilo.conffile or install a new kernel, you must reinstall the LILO boot sector. To simply reinstall LILO using the existing lilo.conf file, just type lilo at the prompt. Many of the entries in the lilo.conf file can be specified on the lilo command line. Table 8-4 lists all of the possible command-line options for lilo. Whenever a change is made to /etc/lilo.conf, you must remember to rerun lilo to install the new boot sector. Exam Tip Table 8-4 lilo Options Option Function -c Enables map compaction so that read requests from adjacent sectors are combined into one. -C Uses a different configuration file instead of the standard /etc/lilo.conf. -d Specifies the amount of time in tenths of seconds to wait before booting the default kernel image. -D Uses the specified kernel label as the default image. -f Uses a different disk-tab file instead of the default /etc/disktab. -i Uses a different boot loader file instead of the default /boot/boot.b. -I Prints the kernel image path for the requested label. -l Generates linear addresses instead of sector/head/cylinder addresses. -L Generates 32-bit LBA addresses, so that a drive with more than 1024 cylinders can be accessed. -m

302 Part II . Getting Around in Linux This entry causes LILO to install the specified file to the boot sector. prompt delay=100 timeout=100 These lines tell LILO to display a boot prompt and wait 10 seconds (100 tenths) before booting to the default image. If someone presses a key, it will cancel the delay option. If a person does not press a key for 10 seconds after that, the timeout option will boot the default image. vga=normal This line tells LILO to boot in normal VGA mode, which is 80 columns by 25 lines. default=Linux2.4 This line sets the default boot image, which will be configured in the next section. image=/boot/vmlinuz-2.2.17-reiser label=Linux read-only append= mem=256M hdd=ide-scsi This is the first image block. It instructs LILO to boot the kernel file named /boot/vmlinuz-2.2.17-reiser. This block is named Linux in the boot menu. The root file system will be mounted read-only when the system first boots, so that it can be checked with fsck. It will later be remounted as read/write by a startup script. The string mem=256M hdd=ide-scsi is passed to the kernel at boot. This string tells the kernel that the system has 256MB of RAM installed and configures /dev/hdd as an IDE drive using SCSI emulation, which is required for IDE CD-R drives. image=/boot/vmlinuz-2.4.0-test10 label=Linux2.4 read-only append= hdd=ide-scsi This is another image block, which is used to test a new kernel. The rest of the options are the same as the previous example. other=/dev/hda4 label=Windows restricted This block is used to boot another operating system, and in this case, Windows. The other directive tells LILO to use the boot information contained in the /dev/hda4 boot block. The restricted entry tells LILO to not accept any boot parameters on this entry.
From our experience, we can recommend PHP Web Hosting services, if you need affordable webhost to host and run your web application.

Chapter 8 . Understanding the Boot Process 301 Entry Function password=
Password-protects this image at boot. restricted Requires the password option above to be used only if a kernel parameter is passed at boot. This will stop someone from changing the root device at boot or booting to single- user mode. append= Passes the specified string to the kernel during boot, just as if you had entered it at the boot prompt. initrd= Specifies the initial RAM disk image to use at boot. literal= Like append, but removes all other options. ramdisk= Specifies the size of the optional RAM disk. read-only Specifies that the root file system should be mounted read- only, so that it can be checked with fsck. read-write Specifies that the root file system should be mounted read/write. root= Specifies the device to be used as the root file system. vga= Enables the use of the VGA graphics mode during boot. optional Does not use the image if it is not available when LILO is installed. Useful for testing new kernels that may not always be there. The following is an example of a /etc/lilo.conf file, with explanations. # Support LBA for large hard disks. # lba32 This line enables LBA mode, which allows LILO to boot from a hard drive with more than 1024 cylinders. boot=/dev/hda This line tells LILO to install itself to the master boot record of /dev/hda. If a partition is specified, such as /dev/hda3, it will install itself into the boot block of the partition. root=/dev/hda3 This line specifies that the root volume is to be mounted from /dev/hda3. install=/boot/boot.b
We highly recommend you visit web and email hosting services if you need stable and cheap web hosting platform for your web applications.

300 Part II . Getting Around in Linux Table 8-2 (continued) Entry Function linear Generates linear addresses instead of sector/head/cylinder addresses. This is required for some SCSI disks. lock Tells LILO to remember the last boot command line and use it as the default until another is manually entered. map=

Chapter 8 . Understanding the Boot Process 299 Table 8-2 Global lilo.conf Entries Entry Function backup= Copies the original boot sector to the specified backup file. boot= Specifies the name of the disk device or partition that the new boot record is written to. If this entry is omitted, the new boot sector will be written to the current root partition. change-rules Specifies boot-time changes to the partition type numbers. See the lilo.conf man page for more information. compact Causes LILO to try to merge read requests for adjacent disk sectors into a single request. This can greatly speed up booting from a floppy disk. default= Defines the default boot image to use. If this is omitted, the first boot entry listed will be used as the default. delay= Causes LILO to wait the specified number of tenths of seconds before booting the default image. disk= Lets you specify nonstandard parameters for the specified disk. disktab= Specifies the location of the disk parameter file. This file was once used to hold disk geometry information. The use of disk tabs is now discouraged. fix-table Lets LILO adjust the sector/head/cylinder relationship to the linear addresses on the disk drive. This is sometimes used with other operating systems that do not convert the information the same way as LILO. force-backup= Has the same function as the backup entry, but overwrites an existing file if it exists. ignore-table Instructs LILO to ignore corrupt partition table information. install= Tells LILO which boot loader to install, either the text mode or the menu mode. lba32 Generates 32-bit logical block addresses instead of sector/head/cylinder addresses. This allows booting from disks with more than 1024 cylinders. Continued
We recommend cheap and reliable webhost to host and run your web applications: Coldfusion Web Hosting services.

298 Part II . Getting Around in Linux Table 8-1 Kernel Parameters Parameter Function init= Sets the initial command to be run by the kernel. By default this is init. nfsaddrs= Sets the NFS boot address, which is used for network booting. nfsroot= Sets the NFS root name, which is used for network booting. no387 Disables the use of the math coprocessor on the CPU. Math Coprocessor Emulation must be enabled in the kernel for this to work. no-hlt Instructs Linux to not use the hlt CPU instruction, which is broken on some older chips. root= Changes the root file system device to the one specified. For example, to mount a floppy disk as the root file system you would use root=/dev/fd0. ro Mounts the root file system read-only so that fsck can fix any errors on the disk. rw Mounts the root file system read/write. This is the default. reserve= Stops a driver from probing the specified IO port region. Some hardware reacts badly to this scanning. mem= Tells the kernel the amount of RAM installed in the system. panic=N Tells the kernel to reboot N seconds after a kernel panic. A kernel panic occurs when a nonrecoverable error happens in the kernel and the entire machine crashes. reboot=[warm|cold] [,[bios|hard]] Sets the type of reboot used when the system is instructed to restart. nosmp Disables SMP support. maxcpus=N Sets the maximum number of CPUs used to N. Configuring LILO LILO is easily configurable through its configuration file, /etc/lilo.conf. The lilo.conf file has many different entries to dictate where and how LILO is installed and how it accesses the operating systems installed on the system. Table 8-2 lists the global entries and Table 8-3 lists the per-image entries.
We recommend high quality webhost to host and run your jsp application: christian web host services.

Chapter 8 . Understanding the Boot Process 297 This chapter covers the installation of the LILO boot manager and the processes the system goes through during startup. These processes set up the system and allow you to customize what happens during booting. Troubleshooting information is also covered that will help should the system not boot. Using LILO Objective 2.6 Boot, Initialization, Shutdown, Run Levels Boot the system. Guide the system through the booting process, including giving options to the kernel at boot time, and check the events in the log files. Involves using the commands: dmesg (lilo). Involves reviewing the files: /var/log/messages, /etc/lilo.conf, /etc/conf.modules | /etc/modules.conf 2.2 Linux Installation and Package Management Install a boot manager. Select, install and configure a boot loader at an appropriate disk location. Provide alternative and backup boot options (like a boot floppy disk). Involves using the command: lilo. Involves editing the file: /etc/lilo.conf. LILO, the Linux Loader, is the most popular boot manager and has been used for many years. Other boot managers have come out that provide other features, but LILO is still the standard that almost all distributions use. LILO is usually installed to the master boot record (MBR) of a hard disk. This is the place on a hard disk where the system s BIOS looks for the operating system s boot information. LILO can also be installed to the boot sector of a partition, instead of the MBR for the entire drive. This is done when another primary boot manager is used, which will then execute LILO when Linux is booted. When the system boots and executes LILO, you will see a boot prompt that looks like this: LILO: Pressing the Tab key will list the possible boot selections. Pressing the Enter key will boot the default selection that was configured. You can pass parameters to the kernel by appending them after the boot selection name. If a parameter is not interpreted by the kernel, it is then checked as an environment variable. Environment variables should be in the form of variable=value. Finally, if the parameter is not recognized by the kernel and is not in the form of an environment variable, it is passed on to the boot process, which is usually init. Table 8-1 lists the possible kernel parameters. Exam Tip If Linux does not see all the RAM installed in your system, tell it the correct amount using the mem= boot parameter.
Go visit our java server pages services for a reliable, lowcost webhost to satisfy all your needs.

296 Part II . Getting Around in Linux CHAPTER PRE-TEST 1. Which process always has a process ID of 1? 2. Which type of startup system do Red Hat and Debian use? 3. Which commands are used to change the runlevel? 4. Which file configures the init process? 5. Which file is displayed to console users before the login prompt? 6. How would you tell init to not run any scripts when the system starts? 7. What does it mean when the LILO prompt displays only LIL? 8. Which boot parameter tells the kernel the amount of RAM installed in the system? 9. Which file is used to configure LILO? 10. Which runlevel is used to reboot the system? . Answers to these questions can be found at the end of the chapter. .
From our experience, we are can tell you that you can find a reliable and cheap webhost service at Java Web Hosting services.