System failure and its recovery

I. System start-up

1. System Startup process

Power-on------->bios (read-only storage on motherboard) function, hardware detection, activation hardware)

Grub System boot (grub boot divided into two stages)

1) Stage 1 MBR (Master boot record) master boot record on hard disk track, one sector, 446 bytes

2) Phase 2 Grub File boot phase

By the file/boot/grub2/grub.cfg control process, specify the/boot partition location-load the kernel-and start the system initialization process-->grub2-mkconfig

2. Kernel Boot phase

Detect hardware devices--device driver initialization---load/read-only mount initialization process systemd--> kernel file is missing please reinstall kernel

3.SYSTEMD initialization

Enable SELinux and systemd-tools--> load kernel parameters-load system clock, keyboard, host name--read/write mount/File system--Activate RAID,LVM device--activate system quota-- Start all service scripts in Multi-user.target.wants--Enable Virtual Console--start graphics
Two. System startup error Recovery

1./boot/gurb Error in Boot program

Destroy/dev/vda First 446 bytes boot: dd if=/dev/zero if=/dev/vda bs=446 count=1 (boot partition where mount is destroyed)

SELinux kernel-level enhanced firewall

Boot not bootable program

Turn off the virtual machine, add the ISO image disc, boot from the CD drive

Troubleshooting #系统修复

Rescue a Res Hat Enterprise Linux system #选择挽救模式 (second item of menu)

1. Continuation 2. Read-only 3 Skip Select first item

Chroot/mnt/sysimage

GRUB2-INSTALL/DEV/SDA #根据实际boot分区挂载

Execute two exit exit from hard drive, restore success

2. boot file/boot/grub2/grub.cfg missing

When the system does not restart
Grub > Set root= ' hd0,msdos1 ' position is not fixed, specify/boot partition
Grub > linux16/boot/vmlinuz-3.10.0-123.e17.x86_64 ro root=/dev/vda1 The device name of the root partition
Grub > Initrd16/boot/initramfs-3 .... tab-Padded
Grub > Boot

Note: You can allow the system to start normally, but temporarily, you will need to do the following:

Grub2-mkconfig >/boot/grub2/grub.cfg

3. Kernel loss

Simulation Problem rm-rf/boot/vmlinuz-3.10 ..... .....

.

Go to rescue mode

Go to rescue mode

Chroot/mnt/sysimage to mount the root partition on the hard disk

MKDIR/RHEL7 Establishment Directory

MOUNT/DEV/SR0/RHEL7 Mount the disc

Cd/rhel7/packages into the Packages of the disc

CP kernel-3.10.0-123.e17 .../mnt copy the kernel to MNT

Cd/mnt into the MNT

Rpm2cpio kernel-3.10 ... rpm |cpio-id compress kernel using cpio format and unzip

CD boot into the boot directory of the split build

Copy the missing kernel files back

CP vmlinuz-3.10 ..../boot

Exit two times

4) when the/boot partition is deleted

1 "Recover Corrupted boot boot bootloader

2> Recovering the kernel

3> Restore Initialization files

4> Restore boot file/boot/grub2/grub.cfg, you only need to execute Grub2-mkconfig >/boot/grub2/grub.cfg at this time

5) Loss of initialization file

Initramfs-3.10.0-123.el7.x86_64.img #初始化文件

Enter Rescue mode

Chroot/mnt/sysimage

mkinitrd/boot/initramfs-$ (UNAME-R). IMG $ (UNAME-R)

Execute two exit, boot success from hard drive

6. Flash Back

Boot from CD into rescue mode

Chroot/mnt/sysimage

Cp/bin/bash/mnt/sysimage/bin/bash

Exit exits

Note: In case of system startup error recovery, except the boot file/boot/grub2/grub.cfg loss does not require the CD boot into the rescue mode, all other situations need to boot from the CD into the rescue mode

################################ #附录 ####################################

The boot is tampered with.

Error formation

Systemctl Set-default Reboot.target

Solution Solution
Press the up and down keys in the power on option to stop reading seconds
Press E to enter edit mode
Select Kernel Boot Line
Linux16/vmlinuz-xxxxxxxxxx ro xxxxxxxxxxxxxx changed to:

Inux16/vmlinuz-xxxxxxxxxxx RW Rd.break

CTRL +X
Chroot/sysroot
Rm-rf/etc/systemd/system/default.target
Ln-s/lib/systemd/system/graphical.target/etc/systemd/system/default.target
Exit

Forgot root password

Press the up and down keys in the power on option to stop reading seconds

Press E to enter edit mode

Select Kernel Boot Line

Linux16/vmlinuz-xxxxxxxxxx ro xxxxxxxxxxxxxx changed to:

Linux16/vmlinuz-xxxxxxxxxxx RW Rd.break

chroot/sysroot/

Touch/.autorelabel