Mereset password linux dapat dilakukan dengan beberapa cara. Silahkan pilih salah satu cara berikut yang sesuai.

A. ROOT SHELL METHOD 1

1. Reboot to grub menu
   1. If Ubuntu is the only operating system on your computer, to get the boot menu to show, you have to hold down the Shift key during bootup.
   2. If you have a dual or multi-boot, the boot menu should appear without the need to hold down the shift key.
2. From the boot menu, select recovery mode and hit Enter.
3. You’ll be presented with a few options. Select the Drop to root shell prompt option and then press Enter.
4. Once you’re at the root shell prompt, if you have forgotten your username as well, type​ –
   ls /home
   This will list all the user accounts in your system.
5. To reset the password, type passwd username where username is the username you want to reset, for example –
   passwd ubuntuuser
6. You’ll then be prompted for a new password. Type your new password and then hit Enter. NOTE: When you type the password, nothing will appear to indicate your typing. You’ll be prompted to retype the password. Repeat your password and hit Enter again.
7. Now the password should be reset. Type exit to return to the recovery menu.
8. After you get back to the recovery menu, select resume normal boot, and your new password should work now.

B. ROOT SHELL METHOD 2

1. Reboot your computer. Follow Step 1 in Option 1 above for a single or dual boot system.
2. Highlight your image and press E to edit.
3. Find the line starting with “linux” and append rw init=/bin/bash at the end of that line.
4. Press Ctrl + X to boot.
5. Type in passwd username.
6. Set your password as in OPTION 1 above and restart your PC. Your new password should work now.

C. LIVE DISC OR USB

1. Boot to the Live Ubuntu media.
2. From the menu, open a terminal.
3. Find out the device name for your primary disk. sudo fdisk-l will list all partitions. Derive your partition from the list. We’re looking for something like /dev/sda1 (which it will likely be)
4. Mount this somewhere so we can use it: (Assuming our primary partition is at /dev/sda1)
   sudo mount /dev/sda1 /mnt
5. Cross-mount things from the Live install so we can “use” the mounted disk (just copy and paste):
   for d in dev sys run proc; do sudo mount –bind /$d /mnt/$d; done
6. Become root on the system by running –
   sudo chroot /mnt
   (You can now do anything root can on the real install)
7. Set the password for the account with: passwd username
8. Reboot and you are done.

Sumber:
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