来源于：Reset Root Password in Oracle Linux 7 (文档 ID 1954652.1)
注意：本文章也适用于RHEL7.x
APPLIES TO:
Linux OS - Version Oracle Linux 7.0 and later
Linux x86
Linux x86-64
GOAL
How to reset root password in Oracle linux 7
SOLUTION
1. While booting GRUB 2 Edit Menu Option (by pressing E)
2. Select the line starts with linux16******* (append "rd.break" at the end of the line), e.g.:
linux16 **** rd.break
3. Press ctrl+x to boot or start.
4. First we will remount the sysroot file system in read and write mode and then use chroot to got into a chroot jail:
# mount -o remount,rw /sysroot
# chroot /sysroot5. Type passwd command in the command line and press same password twice for reset root password:
# passwd
6. Make sure that all unlabel files ( including shadow ) get relabeled during booting:
# touch /.autorelabel
7. Type the command to sync:
# sync
8. Type twice exit command to leave & logout.
9. The system will apply some SELinux contexts and reboot.