How to change files under linux maintenance mode

When system boots into maintenance, it mounts / as read only mode. When you want to fix it, it doesn't allow writing. Here is a way to fix without envolving recue CD booting.

mount -o remount,rw /

Now, you have write permission to / file system.

For other types of booting problems, for example, driver issue, rpm issue, which cause system can't boot, take a look this article

https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Installation_Guide/ap-rescuemode.html#s1-rescuemode-booting-single