How to reset the root password on Linux
The scenario is that you forgot your user password with which you usually access Linux or the root password, if there is one set.
For this usecase we are using a rescue CD like SystemRescueCD or Mariposa Rescue Disk for troubleshooting, but the approach is similar, independent from the distribution or live-CD that you use.
In case you do not know how to boot from the rescue CD, check the articles about Ventoy or Rufus.
Boot your RescueCD and switch to root.
su - root
Find out the root logical volume.
lsblk -io KNAME,TYPE,SIZE,MODEL
The output is something like the following:
KNAME TYPE SIZE MODEL
sda disk 465,8G Samsung SSD 870 EVO 500GB
sda1 part 487M
sda2 part 55,9G
sda3 part 29,8G
sda4 part 1K
sda5 part 379,6G Then, in order to be really sure how the partitions have been mounted, enter:
less /etc/fstab
The output is something like the following:
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
#
# / was on /dev/sda2 during installation
UUID=[...] / ext4 errors=remount-ro 0 1
# /boot was on /dev/sda1 during installation
UUID=[...] /boot ext4 defaults 0 2
# /home was on /dev/sda5 during installation
UUID=[...] /home ext4 defaults 0 2
# swap was on /dev/sda3 during installation
UUID=[...] none swap sw 0 0
Alternatively you can enter the following command:
sudo lshw -class disk
The output is something like the following:
*-disk:0
description: ATA Disk
product: Samsung SSD 870
physical id: 0
bus info: scsi@2:0.0.0
logical name: /dev/sda
version: 1B6Q
serial: [...]
size: 465GiB (500GB)
capabilities: partitioned partitioned:dos
configuration: ansiversion=5 logicalsectorsize=512 sectorsize=512 signature=[...]
and then:
sudo fdisk -l /dev/sda
The output is something like the following:
Disk /dev/sda: 465,76 GiB, 500107862016 bytes, 976773168 sectors
Disk model: Samsung SSD 870
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: [...]
Device Boot Start End Sectors Size Id Type
/dev/sda1 * 2048 999423 997376 487M 83 Linux
/dev/sda2 999424 118185983 117186560 55,9G 83 Linux
/dev/sda3 118185984 180686847 62500864 29,8G 83 Linux
/dev/sda4 180688894 976771071 796082178 379,6G 5 Extended
/dev/sda5 180688896 976771071 796082176 379,6G 83 Linux
In this case, /dev/sda2 is our root logical volume.
Create an directory to which you can mount the root logical volume: mkdir /mnt/root
Mount the logical volume: mount /dev/sda2 /mnt/root
Change the root directory from SystemRescueCD to the one that just mounted:
chroot /mnt/root /bin/bash
Reset the root or user password: passwd root or passwd user1
You will be prompted to enter an new password.
Reboot.
exit
reboot
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