Cannot change root password

Technical Subjects
1

Hello i am trying to Change password on RG500U-EA

I am facing the following error? Any idea why this is read-only?

root@udx710-module:/bin # passwd
Changing password for root
New password:
Retype password:
passwd: /etc/passwd: Read-only file system
passwd: can’t update password file /etc/passwd

2

mount -o rw,remount /

3

@Bean.Wang-Q Thank you!