sqlite3_system_errno —
Low-level system error code
int
sqlite3_system_errno(sqlite3*);
Attempt to return the underlying operating system error code or error number
  that caused the most recent I/O error or failure to open a file. The return
  value is OS-dependent. For example, on unix systems, after sqlite3_open_v2()
  returns SQLITE_CANTOPEN, this interface could be called to get back the
  underlying "errno" that caused the problem, such as ENOSPC, EAUTH,
  EISDIR, and so forth.