How do I stop AutoCAD from opening multiple sessions?

The usual cause is the SDI system variable. With SDI 1 (single document interface), AutoCAD holds one drawing per session, so opening another drawing from Windows Explorer, or double-clicking one in Hurricane, starts a whole new AutoCAD session. With SDI 0, new drawings open as tabs in the session that is already running.

Fix: set SDI back to 0

Type this at the AutoCAD command line:

SDI
0

Why Hurricane uses SDI 1, and how to have both

For batch processing it is best to run with SDI set to 1, one drawing at a time. You do not have to leave it that way: on Hurricane's Settings tab, set the PreBatch command to SDI 1 and the PostBatch command to SDI 0. SDI is then 1 only while a Hurricane script runs, and AutoCAD goes back to opening drawings in one session afterward.

Going the other way, AutoCAD will not switch to SDI 1 while more than one drawing is open. If a batch stops with "Cannot set SDI to that value", close all drawings but one; see this FAQ.

AutoCAD R14 (legacy)

AutoCAD R14 can only load one drawing at a time, so double-clicking a drawing in Windows Explorer starts a second instance. You can avoid this by setting R14 up as a DDE application, so drawings opened from Explorer use the existing session (shortcuts on the desktop or Start menu still start new sessions):

1. In the Windows Explorer menu bar, select View > Options.
2. Select the File Types tab.
3. From the list, select AutoCAD Drawing and click Edit.
4. In the Actions list, select Open, then Edit.
5. Select Use DDE.
6. In the DDE Message field, enter: [_FILEOPEN "%1" ] (include the single space before and after the quotation marks).
7. In the Application field, enter: AutoCAD.R14.DDE
8. In the Topic field, enter: SYSTEM
9. Click OK, then Close twice to exit the Options dialog box.

Related

• AutoCAD SDI system variable: one drawing at a time
• When I double-click on a file in Hurricane, another AutoCAD session is started
• I get "Cannot set SDI to that value"