Comment by IcePic

Then again, on a recent linux system, the non-ability to write to the file might be permissions. Or an immutable attr, or selinux, or apparmor, or setfacl flags or a RO mount where it lies. As soon as you decide to print out the solution to "can't write to: X" you are in for a page full of advice on what to look for. Perhaps the disk was full, perhaps uid was wrong, perhaps the 5% reserved-for-root-only kicked in. You'd end up writing a unix sysadmin guide, and then perhaps the parent dir had too strict perms to allow you to write to a file in it...