OK, so you have not installed Virtuoso but compiled from source, in which case the standard “isql” file is called “isql-v” for a default Ubuntu installation which you performed as their is already another tool called “isql” which is available as a debian package, so we rename ours such as to not conflict with it. So use the isql-v program which is also documented in our official Virtuoso Open Source documentation when building on Ubuntu .