You might want to check the directory's file attributes using `lsattr` - if ...

You might want to check the directory's file attributes using `lsattr` - if "immutable" is set, you'll have to specifically unset that flag in order for anyone to be able to make changes to that inode.

You should also check the underlying filesystem and its (current) mount options in /proc/mounts. There are many possible causes for a problem like this, maybe read-only re-mounting or some changes in the network (for a network-enabled filesystem, of course) could have led to what you are experiencing.

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