MySQL Error 1215: Cannot add foreign key constraint

Check that both tables have the same engine type, so there isn’t a mix of for example MyISAM and InnoDB.

rm unable to delete file even as root or sudo [Solved]

When it is not possible to delete a file using rm even when logged in as root or by using sudo, check the file attributes with:

lsattr filename.ext

If it has the “i” attribute, this is preventing the file from being deleted, even by super users. When you have verified the reason for this and still want to delete the file then remove the “i” attribute with:

chattr -i filename.ext

Then delete the file using rm as you normally would.