linux + why I cant change the passwd

Question

I have redhat 6.x version

I am trying to change the passwd from single user mode but I get the following

passwd root
changing password for user root
passwd: permission denied 

then I try to verify filesystem is mounted in read/write

 mount -o remount,rw /

but I get permission denied again when typing passswd root

please help me to understand why I get permission denied from single user mode?

Answer 1

Have you checked your /etc/passwd and /etc/shadow files?

grep root /etc/passwd /etc/shadow

Have you attempted editing /etc/shadow (with nano or vim)? You can manually remove root's password, and save.

Answer 2

Edit the kernel booting options, change ro init=/sysroot/bin/sh to rw init=/sysroot/bin/sh and boot CentOS. When logged in, follow these commands:

chroot /sysroot
passwd root
touch /.autorelabel
reboot

You now should be able to loggin as root user.

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