adduser : {user : string, passwd : string option} -> string option,
passwd : {user : string, passwd : string} -> string option,
createdb : {user : string, dbname : string} -> string option,
adduser : {user : string, passwd : string option} -> string option,
passwd : {user : string, passwd : string} -> string option,
createdb : {user : string, dbname : string} -> string option,