Method 1 - using bootable installation media (DVD or ISO)
## For physical servers, insert the bootable installation DVD, for VMs, select the bootable installation ISO as optical drive
## in our case, we are using the RHEL 6.2 installation boot DVD
Once booted from the optical drive, select Rescue Installed system
Select the keyboard and click OK
Select Local CD/DVD and then click OK
Select network option accordingly, in our case, we did not require netowrk, so selected No
Select Continue
Click OK
Take note the system being recovered is not mounted under /mnt/sysimage, click OK
Select shell Start shell
## run df command to see the filesystem mounted under /mnt/sysimage
## run the following to change system root to /mnt/sysimage
bash-4.1# chroot /mnt/sysimage
## perform the recovery accordingly e.g. to change root password
bash-4.1# passwd root
Method 2 - boot current system into single user mode
## If we don't have bootable installation media, try to boot to single user mode
At this screen, press any key to enter Grub menu
Press a to append to the kernel arguments for this menu entry
Add a space and then single selinux=0 to the end of the line, then press Enter to accept the changes
The system will boot into single user mode and shell prompt presented without need to login.
## proceed to perform the recovery or troubleshooting
RHEL 7
Method 1 - using bootable installation media (DVD or ISO)
## For physical servers, insert the bootable installation DVD, for VMs, select the bootable installation ISO as optical drive
Once booted from optical drive, select Troubleshooting
Select Rescue a Red Hat Enterprise Linux system
Select Continue
## The system's root filesystem is not mounted as /mnt/sysimage and you will be presented with the following prompt
sh-4.2#
## make that the root environment by
sh-4.2# chroot /mnt/sysimage
## You can now proceed with the recovery or troubleshooting, e.g. to change root password
sh-4.2# passwd root
Method 2 - edit grub menu
Boot the system
At the GRUB menu, press e
At the grub editor, use the arrow keys to look for the line that starts with linux16
Move the cursor to the end of that line
Add to the end of the line: rd.break enforcing=0
Press Ctrl-x to save
## You will be presented with the following prompt
switch_root:/#
## type the following to mount rhe root filesystem of the system being recovered
switch_root:/# mount -o remount,rw /sysroot
switch_root:/# chroot /sysroot
## the prompt will change to
sh-4.2#
## you can perform the troubleshooting or recovery accordingly
## e.g. to change the root password
sh-4.2# passwd root
sh-4.2# exit
switch_root#: exit • system will then boot to normal multi user mode login as root with the new password
• at this point /etc/shadow file will have lost it's SELinux label, need to put it back
# ls -ldZ /etc/shadow ----------. root root system_u:object_r:unlabeled_t:s0 /etc/shadow
# restorecon /etc/shadow
# ls -ldZ /etc/shadow ----------. root root system_u:object_r:shadow_t:s0 /etc/shadow
