RHEL7 Boot boot Process repair

First, the MBR and partition tables are backed up, and the backed up MBR files are stored in an FTP or USB flash drive, backup kernel file installation package

[[email protected] ~] #dd  if=/dev/sda of=/root/mbr bs=512 count=1[[email  Protected] ~]# cd /boot[[email protected] boot]# lsconfig-3.10.0-123.el7.x86_64                               symvers-3.10.0-123.el7.x86_64.gzgrub2                                                        system.map-3.10.0-123.el7.x86_64initramfs-0-rescue-9e0bb12a92ad483499d77d78010474c1.img   vmlinuz-0-rescue-9e0bb12a92ad483499d77d78010474c1initramfs-3.10.0-123.el7.x86_64.img                       vmlinuz-3.10.0-123.el7.x86_64[[email protected]  boot]# rpm -qf vmlinuz-3.10.0-123.el7.x86_64 kernel-3.10.0-123.el7.x86_64

In the installation CD,

KERNEL-3.10.0-123.EL7.X86_64.RPM Package for Backup

Second, the simulation system MBR and Boot folder is missing, this step does not operate when the boot is repaired

[[email protected] boot]# dd If=/dev/zero OF=/DEV/SDA bs=512 count=1[[email protected] boot]# rm-rf/boot/*

Third, repair start : Mount the CD or boot from PXE, into the rescue mode

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Configure an IP address for the local network adapter, and then download the MBR on the FTP to the local

#ifconfig eno33554960 192.168.0.102 netmask 255.255.255.0#ftp 192.168.0.99#get mbr#bye#dd if=mbr OF=/DEV/SDA

This restores the MBR and the partition table

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Press Exit,exit, restart the computer, re-enter the rescue mode, the system has been able to identify the partition table, the root mount to the/mnt/sysimage

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Re-switch the root back/, then reinstall Grub, reinstall the kernel file

Sh-4.2#chroot/mnt/sysimagebash-4.2#grub2-install/dev/sdabash-4.2#ifconfig eno33554960 192.168.0.102 netmask 255.255.255.0bash-4.2#ftp 192.168.0.99bash-4.2#get KERNEL-3.10.0-123.EL7.X86_64.RPMBASH-4.2#RPM-IVH--force kernel-3.10.0-123.el7.x86_64.rpm

Restart the computer, proceed to rescue mode, regenerate the grub.cfg configuration file

Bash-4.2#grub2-mkconfig >/boot/grub2/grub.cfgbash-4.2#syncbash-4.2#exitexit

The system will automatically restart two times, after the boot is complete, the system repair is complete, can log on the system normally

If only the grub.cfg file is missing, you can manually enter the start command at the Grub command prompt and use Grub2-mkconfig >/boot/grub2/after the boot is complete Grub.cfg to repair the Grub.cfg file, when starting to partition the hard disk, root=/dev/sda1 if the logical volume, the root of the volume group name and not the same, here/dev/mapper/rhel-root for example

Grub> set root= ' hd0,msdos1 ' grub> linux16/vmlinuz-3.10.0-123.el7.x86_64 root=/dev/mapper/rhel-root rogrub> initrd16/initramfs-3.10.0-123.el7.x86_64.imggrub> Boot

Use Grub2-mkconfig to repair grub configuration files after booting to the desktop

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

The system boots properly after rebooting

RHEL7 Boot boot Process repair