“Operation not supported” – extended attributes, getfattr, setfattr

When using getfattr and setfattr on a filesystem that you’re sure about extended attributes is supported (i.e. ext4, reiserfs, btrfs) and get “Operation not supported” errors like this…

# touch test.txt
# setfattr --name test --value 42 test.txt
setfattr: test.txt: Operation not supported
# getfattr --name test test.txt
test.txt: test: Operation not supported

… then make sure you’re using the “user” namespace (the name of the attribute is prefixed with user.), like this:

# setfattr --name user.test --value 42 test.txt
# getfattr --name user.test test.txt
# file: test.txt
user.test="42"

And please don’t ask me why I’m posting this.