The document provides information about the boot process on Linux systems from BIOS to kernel loading. It discusses:
- The boot sequence from BIOS performing self-test to loading the master boot record from the boot drive, then the boot loader (LILO or GRUB), and finally the kernel.
- How LILO and GRUB allow selecting operating systems and passing options to the kernel like the root filesystem.
- Common boot loader characteristics and how GRUB uses device names differently than Linux.
- How to recover from a failed boot by booting from removable media and reinstalling LILO or GRUB in the master boot record.
- Common kernel parameters and where to
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in this ppt there are talkin about the Linux directory structure. special focus on the why we have such type of directory and that is explain slide by slide
The Superuser: Root
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Linux directory structure by jitu mistryJITU MISTRY
in this ppt there are talkin about the Linux directory structure. special focus on the why we have such type of directory and that is explain slide by slide
The Superuser: Root
Disks and Partitions
Making New Partitions
Mounting Filesystems
Mounting a Filesystem: mount
Mounting Other Filesystems
Unmounting a Filesystem: umount
Sample /etc/fstab
Filesystem Types
Part 4 of 'Introduction to Linux for bioinformatics': Managing data Joachim Jacob
This is part 4 of the training session 'Introduction to Linux for bioinformatics'. We shows basics of data management, and tips for handling big data effectively. Interested in following this training session? Please contact me at http://www.jakonix.be/contact.html
Goes into details about the prior knowledge required to design a file system. Concludes with a demo that explains how these concepts are used by Second Extended File System (ext2fs) A demo is also provided.
Presented at Florence, Italy on 6th December 2017
This presentation examines the way files are stored in Linux following the File System Hierarchy. It also addresses the recent proposals by Fedora to change this to merge bin directories.
Transcript: Selling digital books in 2024: Insights from industry leaders - T...BookNet Canada
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Link to video recording: https://bnctechforum.ca/sessions/selling-digital-books-in-2024-insights-from-industry-leaders/
Presented by BookNet Canada on May 28, 2024, with support from the Department of Canadian Heritage.
Builder.ai Founder Sachin Dev Duggal's Strategic Approach to Create an Innova...Ramesh Iyer
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- Essentials of FME Parameters: Understand the pivotal role of parameters, including Reader/Writer, Transformer, User, and FME Flow categories. Discover how they are the key to unlocking automation and optimization within your workflows.
- Practical Applications in FME Form: Delve into key user parameter types including choice, connections, and file URLs. Allow users to control how a workflow runs, making your workflows more reusable. Learn to import values and deliver the best user experience for your workflows while enhancing accuracy.
- Optimization Strategies in FME Flow: Explore the creation and strategic deployment of parameters in FME Flow, including the use of deployment and geometry parameters, to maximize workflow efficiency.
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Don’t miss this opportunity to elevate your FME expertise and drive your projects to new heights of efficiency.
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Paper presented at SYNERGY workshop at AVI 2024, Genoa, Italy. 3rd June 2024
https://alandix.com/academic/papers/synergy2024-epistemic/
As machine learning integrates deeper into human-computer interactions, the concept of epistemic interaction emerges, aiming to refine these interactions to enhance system adaptability. This approach encourages minor, intentional adjustments in user behaviour to enrich the data available for system learning. This paper introduces epistemic interaction within the context of human-system communication, illustrating how deliberate interaction design can improve system understanding and adaptation. Through concrete examples, we demonstrate the potential of epistemic interaction to significantly advance human-computer interaction by leveraging intuitive human communication strategies to inform system design and functionality, offering a novel pathway for enriching user-system engagements.
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Pradeep Chinnala, Senior Consultant Automation Developer @WonderBotz and UiPath MVP
Deepak Rai, Automation Practice Lead, Boundaryless Group and UiPath MVP
2. Exam Objectives
Key Knowledge Areas
Provide common commands to the boot loader and options to the kernel at boot time.
Demonstrate knowledge of the boot sequence from BIOS to boot completion.
Check boot events in the log files.
Objective 1: System Architecture
Boot the system Weight: 3
Terms and Utilities
/var/log/messages
dmesg
BIOS
bootloader
kernel
init
2
3. Boot the system
Boot process for PCs:
Boot overview
1. When PC is turned on, BIOS (Basic Input Output Service) performs a selftest;
2. When machine passes self test, BIOS loads Master Boot Record;
usually from first 512-byte sector of the boot drive.
This is usually the 1st hard drive on system, may also be diskette, CD, USB key.
3. For a hard drive, MBR loads a stage 1 boot loader;
Which is either LILO or GRUB stage1 boot loader on a Linux system.
This is another 512-byte, single-sector record.
4. stage 1 boot loader loads a sequence of records called stage 2 boot loader
(or sometimes the stage 1.5 loader).
5. stage 2 loader loads the operating system.
For Linux, this is the kernel, and possibly an initial RAM disk (initrd).
3
4. Boot the system
When BIOS has finished starting up, it loads first sector of boot disk into memory,
and runs the code it finds there.
On a floppy disk, boot sector is the first sector, and that‘s the whole story.
Boot with floppy
4
Floppy disk boot sector (“logical” layout)Ex:
5. Boot the system
For hard disks, the first sector of the disk (/dev/hda) is the partition sector.
•This usually contains a program that loads the boot sector from the “active” partition.
•This first sector is known as MBR (Master boot record).
Boot with disk
5
Each partition on a hard disk has its own boot sector.Ex:
MSoft operating systems (FDISK /MBR in MSDOS) install a partition sector loader to do the following:
• Check which partition is marked as “active”.
• Load the sector from the start of that partition and run it.
6. Boot the system
Linux boot loaders have characteristics in common:
boot loaders characteristics
6
The code stored on the boot sector or the partition sector is just the first stageloader.
This means that its not responsible for loading the operating system, but only for loading boot loader into memory.
•The boot loader can be configured to load other operating systems.
- When loading other operating systems, the boot loader may load them into
memory,
- or call that operating system's own boot loader.
•Interactively enter options to be passed to the kernel to be loaded.
- Kernel options are used, to indicate where the root filesystem is (root=/dev/hda3),
- and can be used for debugging (init=/bin/sh).
Chain loading
Occurs when the boot manager that is located in the master boot record (MBR)
loads the boot loader that is in a partition boot record.
7. Boot the system
stage 2 loaders used in LILO and GRUB allow to choose from several operating
systems or versions to load. However, LILO and GRUB differ significantly
Linux boot loaders
7
With LILO, a change to the system requires use of command to recreate LILO boot setup
whenever there’s changes to kernel or other changes to the system.
With GRUB, can accomplish changes with a configuration text file that can be edited.
With GRUB 2 also requires a rebuild from a configuration file normally stored in /etc.
During Linux installation, you will usually specify either LILO or GRUB manager.
If chosing GRUB, then you may not have LILO installed.
8. Boot the system
Installing another operating system can overwrite the MBR.
Some systems like DOS and Windows, always install their own MBR.
Recovery
8
Boot from floppy into the Linux system and rerun lilo or grub-install.
Linux distributions can also boot the Linux in recovery mode.
In recovery mode the root file system on the hard drive could not be mounted or mounted
in recovery mode.
Use chroot cmd to make the recovery mount point become the root (/) directory.
Then run lilo or grub-install to reinstall the MBR.
10. Boot the system
Recovery
10
With prompt in recovery u can create a mount point (/mnt/sysimage), mount /dev/sda6,
chroot into the mounted system. cat /etc/issue commands show effect of chroot cmd.
Ex: root@yourcomp:~# mkdir /mnt/sysimage
root@yourcomp:~# mount /dev/sda6 /mnt/sysimage
root@yourcomp:~# cd /mnt/sysimage
root@yourcomp:~# mount -t proc none proc/
root@yourcomp:~# mount -t sysfs none sys/
root@yourcomp:~# mount -o bind /dev dev/
root@yourcomp:~# cat /etc/issue
Ubuntu 9.10 n l
root@yourcomp:~# chroot /mnt/sysimage
root@yourcomp:~#
sh-3.00# chroot /mnt/sysimage
[root@yourcomp /]# cat /etc/issue
Fedora release 8 (Werewolf)
Kernel r on an m
[root@yourcomp /]# grub-install /dev/fd0
Installation finished. No error reported.
This is the contents of the device map /boot/grub/device.map.
Check if this is correct or not. If any of the lines is incorrect,
fix it and re-run the script `grub-install'.
(fd0) /dev/fd0
(hd0) /dev/sda
[root@yourcomp /]#
11. Boot the system
Kernel parameters
11
LILO and GRUB allow to edit cmdline that is passed to kernel when it boots.
Kernel boot parameters are used to override the hardware config parameters detected by the kernel.
Ex: root@yourcomp:~# cat /proc/cmdline
ro root=/dev/hda1 apm=off
Format parameters supplied are:
- single word; - format name=value; format name=value1,value2,value3.
Each name identifies which part of the kernel receives the option.
Default kernel command line always specifies the root filesystem, mounted ro read-only
12. Boot the system
Kernel parameters
12
Kernel cmdline Parameters used:
•single – boot into single user mode (with root password)
•emergency – boot into a shell (newer versions of init require the root password)
•1, 2, 3, 4, 5, 6 – boot into a specific runlevel.
cmdline parameters not used by kernel as environment variables to load the usual daemons,
are passed onto init process program ( /sbin/init).
bootparam(7) man page discusses the boot parameters in detail.
file /usr/src/linux/Documentation/kernelparameters.txt is a complete reference.
Ex: root@yourcomp:~# man bootparam
root@yourcomp:~# less /usr/src/linux/Documentation/kernel-parameters.txt
13. Boot the system
Kernel parameters
13
boot parameters used:
•root=/dev/hda1: change the root filesystem during bootup
•init=/sbin/init: kernel boot will run /sbin/init.
troubleshooting parameter is init=/bin/bash which runs an interactive shell instead of /sbin/init.
•mem=32M: limit the amount of memory to specified. kernel does not attempt to check memory actually present
•Noinitrd: don't execute /linuxrc on initial root disk image supplied by boot loader.
avoid the behaviour of initial root disk loading modules required for booting (filesystem support).
•Config devices compiled in Kernel with IO and IRQ settings in format: device=irq,iobase
•rdev cmd: used to modify a kernel image to not require boot options for:
- root device (rdev /boot/vmlinuz "/dev/hda7 "),
- VGA mode (vidmode /boot/vmlinuz "788"),
- Readonly/Readwrite root filesystem (rootflags ...)
•vga=value: changes display mode of VGA adapter
VESA graphics modes support:
Color depth 640x480 800x600 1024x768 1280x1024
8 bits 256 colours 769 771 773 775
15 bits 32768 colours 784 787 790 793
16 bits 65535 colours 785 788 791 794
24 bits 16.7 Million 786 789 792 795
14. Boot the system
Kernel parameters with LILO
14
To control booting using LILO, interrupt boot process using:
1.Press Shift: To obtain prompt, Shift before LILO begins booting if there’s no timeout specified in
lilo.conf.
2.Enter a password: lilo.conf can specify that password must be entered to change boot parameters.
LILO allows configuring the boot sequence in following ways:
1.Select kernel to boot or boot image to load: By typing it's name (press Tab to see list), or by
selecting it from a menu.
2.Add options to the kernel command line (you can't remove option that are already there)
LILO: linux root=/dev/fd0 rw init=/bin/bash
15. Boot the system
Kernel parameters with GRUB
15
GRUB's is free cross platform, so it does not follow Linux hard disk convention naming.
(fd0) – /dev/fd0
(hd0) – /dev/hda (SCSI = sd0)
(hd0,1) – /dev/hda2 (2nd
partition of 1st
disk)
To boot Linux, it is required that GRUB knows:
1.where are the files found (root);
2.where is the kernel found (kernel);
3.where is the initial root disk (initrd), that contain vital system modules (filesystem or SCSI controller).
The boot command tells GRUB to boot.
Ex: root (hd0,0) # source of grub files is
/dev/hda1
kernel /boot/vmlinuz root=/dev/hda1 # load a kernel
initrd /boot/initrd # load an initial root disk
boot # boot up
16. Boot the system
Kernel parameters with GRUB
16
GRUB commands that are in /etc/grub.conf, can be typed when the system boots.
Newer versions of GRUB print helpful menus, for the key-presses:
• p – enter a password
• c – start the GRUB command line (type GRUB configuration yourself)
• e – edit a GRUB configuration line
• a – modify kernel arguments before booting
• o – open a new line for configuration commands
• d – remove the selected line from the configuration
• b – boot the system
• Escape – return to the menu
17. Boot the system
Boot messages
17
When Linux kernel boots, each subsystem is initialised in a predetermined order.
The messages generated by each subsystem are generally displayed on the console.
And are also recorded in 2 places:
Ex:
yourname@yourcomp~> grep "^Apr.*d:" /var/log/messages|tail -n 14
Apr 2 15:36:50 lyrebird kernel: hdd: attached ide-scsi driver.
Apr 2 15:36:26 lyrebird rc.sysinit: Setting hostname lyrebird: succeeded
Apr 2 15:36:26 lyrebird rc.sysinit: Initializing USB keyboard: succeeded
Apr 2 15:36:55 lyrebird sshd: succeeded
Apr 2 15:36:57 lyrebird crond: crond startup succeeded
Listing daemon status messages after a reboot.
1.kernel message (ring) buffer – kernel keeps 16k of messages, displayed by dmesg command.
redirect output to a file for later analysis or forward it to a kernel developer for debugging purposes
2.syslogd records timestamped kernel messages to /var/log/messages.
• After system starts /sbin/init, kernel logs events in the ring buffer,
but processes use the syslog daemon to log messages, usually in /var/log/messages.
• Each syslog line has a timestamp, and the file persists between system restarts.
This file is where you should first look for errors that occurred during the init scripts stage of booting.