Linux Boot and kernel management

system boot and kernel management

Linux composition

Linux:kerne+rootfs (Application)

Kernel: Process management, memory management, network management, drivers, file systems, security features

Roots: Programs and GLIBC

Function: Equivalent to a collection of commands

Libraries: function sets, functions, calling interfaces (header file is responsible for description)

Procedure call: Procedure, no return value

Functions Call: function

Program: Binary Execution file

Kernel design:

Single core (monolithic kernel): Linux

Integrate all functions into one program

Microkernel (micro kernel): Windows,solaris

Each feature is implemented using a separate subsystem

Kernel

Linux kernel Features:

Support modularity:. KO (Kernel object)

Such as: File system, hardware driver, network protocol, etc.

Supports automated loading and unloading of kernel modules

Part:

Core files:/boot/vmlinuz-version-release (storing some of the most important files)

RAMDisk: Auxiliary pseudo-File system

Centos5;/boot/initrd-version-release.img

Centos6,7:/boot/initramfs-version-release.img

Module files:/lib/modules/version-release (most function modules)

/lib/modules (storage of most drives)

CENTOS6 startup process

Post Power-up check →mbr boot →grub→ load kernel

Start the process:

Post:power-on-self-test

ROM (Read only): BIOS, save the computer system important basic input and output programs, power will run these programs, System Information settings, power on the self-test program, etc.

RAM (does not represent memory here): Power loss does not lose data in RAM because the motherboard has a battery and the order of adjustment in the BIOS is saved here

Find the boot device in order, the first device with a boot program is the boot device (can be adjusted in the BIOS)

Bootloader: Boot loader (a program used to start the computer), boot program

Windows:ntloader, just start the OS and just start Windows

Linux: Early use of Lilo (Linux loader can only be used to boot Linux) to boot Linux,grub boot Linux can also boot Windows

Grub:grand Unified Bootloader

GRUB 0.X: Old version

Mbr:

446:bootloader (first stage of Grub), 64: Partition table, 2:55AA

Grub:

Primary boot loader:1st Stage (first phase of grub)

1.5 Stage (the file system driver used to read the boot partition) both are stored in binary mode

Read file system driver, use Initramfs-version-release file to read file system driver;

CENTOS5 RAMDisk: Simulates a disk and converts the emulated disk to a file system and then to a disk

CENTOS6 Ramfs: Directly to a file system to access the disk through the file system

System initialization

Post-->bootsequence (BIOS)-->bootloader (MBR)-->kernel (RAMDisk)-->rootfs (read-only)-->init (SYSTEMD)

RAMDisk File creation:

MKINITRD "filename (preferably formerly known as) ' Uname-r '. img" ' Uname-r ' (re-authoring RAMDisk file for the kernel currently in use)

Types of init programs

Sysv:init,centos 5 ago

Configuration file/etc/inittab

Upstart:init,centos6

Configuration files:/etc/inittab,/etc/init/*.conf

SYSTEMD:SYSTEMD, CentOS 7

Configuration file:/usr/lib/systemd/system

/etc/systemd/system

Boot START process:

Post

MBR boot loader Grub

/boot/vmlinxz

/boot/initramfs.

/sbin/init

/etc/inittab

/etc/rcn.d/-/etc/init.d/xxx

/etc/rc.d/rc.local

Login

Mode (adjust the boot mode in/etc/inittab):

0: Turn off the machine

1: Single-user mode

2: Multi-user mode, no NFS function

3: Multi-user mode (almost the same as 2, and the character interface)

4: Not used, temporarily useless

5: Graphical interface

6: Restart

Default Level: 3,5

Toggle Level: Init #

View level: RunLevel

Configuration file for Centos 5:/etc/inittab

NTSYSV viewing boot-up programs

Chkconfig--list "program name"

--add added to the boot-up service

"Program name" on boot start

--del "program name" Delete Service boot start

(1) Default mode definition

(2) System initialization script

(3) script corresponding to the running mode

/etc/rc#.d/a series of start-up files in the beginning of S, the lower the number, the highest priority of the boot;

Also holds a series of stop files at the beginning of K, the smaller the value, the higher the priority of the shutdown

/etc/rc#.d/s99local function is to write the boot to do things

The content in/etc/rc.d/rc.local is started as the server boots up

Services managed by xinetd

Transient: Service is managed by the XINETD process

The incoming request was first XINETD agent

Configuration files:/etc/xinetd.conf,/etc/xinetd.d/<servicename>

When the Vmlinux file in the/boot directory is lost, you can use the disc rescue mode to rename the Vmlinux under Isolinux in the disc and copy it to the/boot directory.

cp/mnt/cdrom/isolinux/vmlinux/mnt/sysimage/vmlinux-' Uname-r ' can

Enter rescue mode execution when the/boot directory is lost

Rpm-ivh/mnt/cdrom/package/kernel-xxxxxx--force--root=/mnt/sysimage/

Grub Legacy

Grub

Stage1:mbr

Stage1_5 (1.5 stage): Sector after MBR

GRUB.CONF (Grub configuration file)

The location of the root partition is indicated in/etc/grub.conf, a sequence of processes can be found after the root file is found, and then started

Installing GRUB

(1) Grub-install

Install Grub Stage1 and stage1_5 to/dev/disk disk and copy grub-related files to the Dir/boot directory

Grub-install [--root-directory=dir] (Specifies the parent directory for the location of the grub installation)/dev/disk 440-byte repair method GRUB-INSTALL/DEV/SDA

(2) Grub (Interactive command, HD writes the first hard drive of the boot mount point, hd0,0 is the number one partition of the first hard drive)

Root (hd#,#)

Setup (hd#)

Crack root password (must be in front of server)

(1) When the selection menu appears during startup, enter "a" in the rear input 1 to enter single user mode

(2) After entering passwd root to set a new password

(3) Append "Password Fang" to the/etc/grub.conf file to add the single-user mode to the plaintext password

Grub-md5-crypt can generate a random MD5 password, copy the generated random password to the/etc/grub.conf password followed by entering single-user mode encryption

Grub-crypt generates random passwords and copies the generated random passwords to password-encrypted in/etc/grub.conf

Start Password:/etc/grub.conf Start menu Add password-encrypted "generated random password" can be added with password to start

Configuration file:/boot/grub/grub.conf

default=#: Sets the default Startup menu item;

timeout=#: Specifies the duration of the menu item Wait option selection

Splashimage (hd#,#)/path/xpm_file: Menu background image

Password: Start menu edit Set Password

Hiddenmenu: Hide Menu

Title: Defining the menu item title

Root (hd#,#): Find the device partition where the Stage2 and kernel files reside;

Kernel: Root kernel "Kernel pack location" for Grub

INITRD "kernel-matched Ramfs file"

/proc directory:

Storing a series of process files

Parameters: Read-only: Output information

/proc/sys

Sysctl-a: All the settings that are in effect

SYSCTL-W: Modifies a specified row of data, the modified data is stored in memory, and is restored after a reboot

Sysctl-p: Read the/etc/sysctl.conf file, is the modification to take effect, when there is no line in the file, it will be synchronized with the definition in the NEI

Common parameters:

Net.ipv4.forward: Whether the management routing function turns on 0 on, 1 is off

Net.ipv4.icmp_echo_ignore_all: Do not allow other hosts to ping themselves

Vm.drop_caches: To change this value to 1 is to free the cache memory

/sys directory:

Storage of a range of key hardware-related content

Compiling the installation kernel

Kernel components:

Kernel, kernel core, typically in the/boot directory, named Vmlinuz-version-release

Kernel object: Kernel objects, typically placed in/lib/modules/version-release

[]:not Set (not enabled)

[M]:m (exists as a module, and is a standalone file)

[*]:y (stored in Vmlinuz, not stand-alone file)

Kernel version

In-run kernel:

uname command:

Uname-print System Information

uname [OPTION] ...

-N: Display host name

-R: Display Version-release

-A: Show All information

Kernel module Commands:

Lsmod displaying modules that have already been loaded

The content displayed is from:/proc/modules file

Modinfo command:

Display detailed description of the module

Modinfo [-K kernel] [modulename|filename]

-N: Show only module file path

-P: Display module parameters

-a:author author

-d:description description

-l:license

Example: Lsmod | grep Xfs;modinfo XFS to see if XFS modules are running and view details

modprobe command (automatically resolves dependencies):

Loading or unloading kernel modules

Modprobe

-R: Unload the module, and there is a dependency between the modules, and after the drive disappears, the hardware disappears.

Configuration file:/etc/modprobe.conf or/etc/modprobe.d/*.conf

Depmod command:

To set dependencies between modules

To mount or unload a kernel module:

Insmod command: Specifies the module file and does not automatically resolve the dependent module

insmod [filename] [module options]

Insmod ' Modinfo-n exportfs ' (The execution results in the anti-apostrophe are loaded with insomod)

Rmmod command: Uninstalling the module

Rmmod [ModuleName]

Compiling the kernel

1 Download the kernel file to be compiled from www.kernel.org

2 Installing the Development Tools Group

3. config: Prepare the text configuration file, you can modify the existing config-3.10.0-693.el7.x86_64 file on the system to the. config file editing

4 Make Menuconfig: Configure kernel options, this command is a menu, the menu "--->" after the description of the sub-menu

[]:not Set (not enabled)

[M]:m (exists as a module, and is a standalone file)

[*]:y (stored in Vmlinuz, not stand-alone file)

5 Make [-j #] (-j Specifies the number of CPU cores) will generate a compiled version of the directory under/lib

6 Make Modules_install: Install the module, which is equivalent to installing the Lib/modules directory

7 make install: Install kernel-related files

Linux Boot and kernel management