25.8. Using rescue mode

Procedure

1. Boot the system from either minimal boot media, or a full installation DVD or USB drive, and wait for the boot menu to be displayed.
2. From the boot menu, either select Troubleshooting > Rescue a Red Hat Enterprise Linux system option, or append the inst.rescue option to the boot command line. To enter the boot command line, press the Tab key on BIOS-based systems or the e key on UEFI-based systems.

3. Optional: If your system requires a third-party driver provided on a driver disc to boot, append the inst.dd=driver_name to the boot command line:

   inst.rescue inst.dd=driver_name

4. Optional: If a driver that is part of the Red Hat Enterprise Linux distribution prevents the system from booting, append the modprobe.blacklist= option to the boot command line:

   inst.rescue modprobe.blacklist=driver_name

5. Press Enter (BIOS-based systems) or Ctrl+X (UEFI-based systems) to boot the modified option. Wait until the following message is displayed:

   The rescue environment will now attempt to find your Linux installation and mount it under the directory: /mnt/sysroot/. You can then make any changes required to your system. Choose 1 to proceed with this step. You can choose to mount your file systems read-only instead of read-write by choosing 2. If for some reason this process does not work choose 3 to skip directly to a shell.
   
   1) Continue
   2) Read-only mount
   3) Skip to shell
   4) Quit (Reboot)

   If you select 1, the installation program attempts to mount your file system under the directory /mnt/sysroot/. You are notified if it fails to mount a partition. If you select 2, it attempts to mount your file system under the directory /mnt/sysroot/, but in read-only mode. If you select 3, your file system is not mounted.

   For the system root, the installer supports two mount points /mnt/sysimage and /mnt/sysroot. The /mnt/sysroot path is used to mount / of the target system. Usually, the physical root and the system root are the same, so /mnt/sysroot is attached to the same file system as /mnt/sysimage. The only exceptions are rpm-ostree systems, where the system root changes based on the deployment. Then, /mnt/sysroot is attached to a subdirectory of /mnt/sysimage. Use /mnt/sysroot for chroot.

6. Select 1 to continue. Once your system is in rescue mode, a prompt appears on VC (virtual console) 1 and VC 2. Use the Ctrl+Alt+F1 key combination to access VC 1 and Ctrl+Alt+F2 to access VC 2:

   sh-4.2#

7. Even if your file system is mounted, the default root partition while in rescue mode is a temporary root partition, not the root partition of the file system used during normal user mode (multi-user.target or graphical.target). If you selected to mount your file system and it mounted successfully, you can change the root partition of the rescue mode environment to the root partition of your file system by executing the following command:

   sh-4.2# chroot /mnt/sysroot

   This is useful if you need to run commands, such as rpm, that require your root partition to be mounted as /. To exit the chroot environment, type exit to return to the prompt.

8. If you selected 3, you can still try to mount a partition or LVM2 logical volume manually inside rescue mode by creating a directory, such as /directory/, and typing the following command:

   sh-4.2# mount -t xfs /dev/mapper/VolGroup00-LogVol02 /directory

   In the above command, /directory/ is the directory that you created and /dev/mapper/VolGroup00-LogVol02 is the LVM2 logical volume you want to mount. If the partition is a different type than XFS, replace the xfs string with the correct type (such as ext4).

9. If you do not know the names of all physical partitions, use the following command to list them:

   sh-4.2# fdisk -l

   If you do not know the names of all LVM2 physical volumes, volume groups, or logical volumes, use the pvdisplay, vgdisplay or lvdisplay commands.

Procedure

1. Change the root directory to the /mnt/sysroot/ directory:

   sh-4.2# chroot /mnt/sysroot/

2. Execute sos report to generate an archive with system configuration and diagnostic information:

   sh-4.2# sos report

   sos report prompts you to enter your name and the case number you received from Red Hat Support. Use only letters and numbers because adding any of the following characters or spaces could render the report unusable: # % & { } \ < > > * ? / $ ~ ' " : @ + ` | =

3. Optional: If you want to transfer the generated archive to a new location by using the network, it is necessary to have a network interface configured. In this scenario, use the dynamic IP addressing as no other steps are required. However, when using static addressing, enter the following command to assign an IP address (for example 10.13.153.64/23) to a network interface, for example dev eth0:

   bash-4.2# ip addr add 10.13.153.64/23 dev eth0

4. Exit the chroot environment:

   sh-4.2# exit

5. Store the generated archive in a new location, from where it can be easily accessible:

   sh-4.2# cp /mnt/sysroot/var/tmp/sos report new_location

6. For transferring the archive through the network, use the scp utility:

   sh-4.2# scp /mnt/sysroot/var/tmp/sos report username@hostname:sos report

Procedure

1. Change the root partition:

   sh-4.2# chroot /mnt/sysroot/

2. Reinstall the GRUB2 boot loader, where the install_device block device was installed:

   sh-4.2# /sbin/grub2-install install_device

   重要

   Running the grub2-install command could lead to the machine being unbootable if all the following conditions apply:

   • The system is an AMD64 or Intel 64 with Extensible Firmware Interface (EFI).
   • Secure Boot is enabled.

   After you run the grub2-install command, you cannot boot the AMD64 or Intel 64 systems that have Extensible Firmware Interface (EFI) and Secure Boot enabled. This issue occurs because the grub2-install command installs an unsigned GRUB2 image that boots directly instead of using the shim application. When the system boots, the shim application validates the image signature, which when not found fails to boot the system.

3. Reboot the system.

Procedure

1. To add a new driver using dnf:

   1. Make the RPM package that contains the driver available. For example, mount a CD or USB flash drive and copy the RPM package to a location of your choice under /mnt/sysroot/, for example: /mnt/sysroot/root/drivers/.

   2. Change the root directory to /mnt/sysroot/:

      sh-4.2# chroot /mnt/sysroot/

   3. Use the dnf install command to install the driver package. For example, run the following command to install the xorg-x11-drv-wacom driver package from /root/drivers/:

      sh-4.2# dnf install /root/drivers/xorg-x11-drv-wacom-0.23.0-6.el7.x86_64.rpm

      注記

      The /root/drivers/ directory in this chroot environment is the /mnt/sysroot/root/drivers/ directory in the original rescue environment.

   4. Exit the chroot environment:

      sh-4.2# exit

2. To remove a driver by using dnf:

   1. Change the root directory to the /mnt/sysroot/ directory:

      sh-4.2# chroot /mnt/sysroot/

   2. Use the dnf remove command to remove the driver package. For example, to remove the xorg-x11-drv-wacom driver package, run:

      sh-4.2# dnf remove xorg-x11-drv-wacom

   3. Exit the chroot environment:

      sh-4.2# exit

      If you cannot remove a malfunctioning driver for some reason, you can instead blocklist the driver so that it does not load at boot time.

   4. When you have finished removing drivers, reboot the system.