01-04

Working with boot

Task:

• Get to system without password
• On the system installed on LVM rename Volume Group
• Add module to initrd
• *Additional - configure system without separated /boot, only with LVM
  • Patched grub at: https://yum.rumyantsev.com/centos/7/x86_64/
  • PV must be inited with --bootloaderareasize 1m

Description:

How to login without a password:

Simple way

1. Start the system and, on the GRUB 2 boot screen, press the e key for edit.
2. Remove the rhgb and quiet parameters from the end, or near the end, of the linux16 line, or linuxefi on UEFI systems. It will look like:

linux16 /vmlinuz<version> root=<lvm_path> rw single init=/bin/bash 
linux16 /vmlinuz<version> root=<lvm_path> rw single init=/bin/sh

3. Press ctrl + x to boot the system wuth the changed parameters.
4. Try to change passwords

passwd username

Selinux way

1. Start the system and, on the GRUB 2 boot screen, press the e key for edit.
2. Remove the rhgb and quiet parameters from the end, or near the end, of the linux16 line, or linuxefi on UEFI systems. Add the following parameters at the end of the linux line on 64-Bit IBM Power Series, the linux16 line on x86-64 BIOS-based systems, or the linuxefi line on UEFI systems:

rd.break enforcing=0

It will look like:

linux16 /vmlinuz<version> root=<lvm_path> ro rd.break enforcing=0

3. Add the following parameters at the end of the linux line on 64-Bit IBM Power Series, the linux16 line on x86-64 BIOS-based systems, or the linuxefi line on UEFI systems:

rd.break enforcing=0

Adding the enforcing=0 option enables omitting the time consuming SELinux relabeling process.

The initramfs will stop before passing control to the Linux kernel, enabling you to work with the root file system. Note that the initramfs prompt will appear on the last console specified on the Linux line.

3. Press ctrl + x to boot the system wuth the changed parameters. With an encrypted file system, a password is required at this point. However the password prompt might not appear as it is obscured by logging messages. You can press the Backspace key to see the prompt. Release the key and enter the password for the encrypted file system, while ignoring the logging messages.

The initramfs switch_root prompt appears.

4. The file system is mounted read-only on /sysroot/. You will not be allowed to change the password if the file system is not writable.

Remount the file system as writable:

switch_root:/# mount -o remount,rw /sysroot

5. The file system is remounted with write enabled.

Change the file system's root as follows:

switch_root:/# chroot /sysroot

The prompt changes to sh-4.2#. 6. Now chage the password! Enter the passwd command and follow the instructions displayed on the command line to change the root password. 7. The most important step: Updating the password file results in a file with the incorrect SELinux security context. To relabel all files on next system boot, enter the following command:

sh-4.2# touch /.autorelabel

8. Remount the file system as read only:

sh-4.2# mount -o remount,ro /

9. Exit twice
10. Now on login use your new password.

From: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/system_administrators_guide/sec-terminal_menu_editing_during_boot#sec-Changing_and_Resetting_the_Root_Password

How to:

$ vagrant up
$ vagrant halt
$ vm_id=$(vboxmanage list vms | grep 01-04 | awk '{print $2}' | tr -d [{}])
$ vboxmanage startvm $vm_id

# yum will see the picture at vbox window