When running (on linux different ubuntu variations):
>ln -s dir_1 symlink_dir >ln -s dir_2 symlink_dir
It fails without telling that it fails. But if you do the same thing on a file instead or, add v to the option it does tell you that it fails:
>ln -s file_1 symlinkg_file >ln -s file_2 symlinkg_file
>ln -sv dir_1 symlink_dir >ln -sv dir_2 symlink_dir
It fails with the error msg:
ln: failed to create symbolic link
For me this seems to be a very strange behaviour? Is there a reason for this?