Note: This is a critical RHCSA 7 exam objective (if you can’t take control of a VM through a reboot at the
beginning of the exam, you will fail it entirely).
Presentation
In RHEL
7, the procedure to get access to a system during the boot
process and modify the root password has changed because of the adoption
of Systemd.
There were several procedures floating around to recover
the root password. Some were working with physical servers but not with virtual
machines, some the other way around.
The following procedure works all the time.
Procedure
At the beginning of the boot process,
at the GRUB 2 menu, type the e key
to edit.
Then, go to the kernel line (the line
starting with linux16) and add the following statements at the
end:
rd.break enforcing=0
Caution: The keys to press are
those of a US keyboard (querty).
Note: rd.break asks for a break at an early stage of the boot process. enforcing=0 puts the system into SELinux Permissive mode. Don’t confuse with selinux=0 that completely disables SELinux.
Note: rd.break asks for a break at an early stage of the boot process. enforcing=0 puts the system into SELinux Permissive mode. Don’t confuse with selinux=0 that completely disables SELinux.
Press Ctrl
x to resume the boot process.
Then, mount the /sysroot partition
as read/write:
switch_root:/# mount –o remount,rw /sysroot
Execute the chroot command
on the /sysroot partition:
switch_root:/# chroot /sysroot
Change the root password:
sh-4.2# passwd root
Changing password for user root.
New passwd: mypassword
Retype new password: mypassword
passwd: all authentication token updated successfully.
sh-4.2# exit
exit
switch_root:/# exit
logout
Connect to your server at the console
(don’t reboot now!) with the root user and the new password:
...
[ OK ] Started Network Manager Script Dispatcher Service.
[ OK ] Started Crash recovery kernel arming.
[ OK ] Reached target Multi-User System.
CentOS Linux 7 (Core)
Kernel 3.10.0-229.14.1.el7.x86_64 on an x86_64
vm login: root
Password: mypassword
