Troubleshooting ODBC connections
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## Troubleshooting ODBC connections

Supposing everything compiles and installs without trouble, how do you know if your ODBC setup works? Or, if you know it doesn't, what then?

First, try to connect with tsql. If you're intending to use `freetds.conf`, exercise it with tsql -S `servername`. If not, use TDSVER=auto tsql -H `hostname` -p `port`

If tsql works and isql doesn't, you've isolated the problem to the ODBC setup. FreeTDS might have some interoperability problems, but mere connection to the database isn't one of them! If tsql doesn't work, turn on logging with `TDSDUMP`. The log will tell you what TCP/IP name (and address) FreeTDS is attempting to connect to, and what version of the TDS protocol it's using.

### With iODBC

`iODBC` comes with a sample command line query program called odbctest, located in the `iodbc/samples` directory. Using this program you can get a listing of DSNs, connect, and issue queries.

| Tip
For debugging purposes, you may wish to link a program such as odbctest directly to FreeTDS instead of to the driver manager. [15] To do so, compile and install the `ODBC` driver with `iODBC` as normal [16], then compile and link the program: Example 4.7. Compile `odbctest` without a driver manager.
    	$ make odbctest.o
    	$ gcc -g -o odbctest odbctest.o /usr/local/freetds/lib/libtdsodbc.a
Now you can run gdb or another debugger and set breakpoints on functions in the library without the driver manager getting in the way.

### With unixODBC

Try isql -v `dsn` `username` `password`, and have a look at the log. See if the right address and TDS version are being used. Adjust to taste.

#### Use osql

The osql utility is a Bourne shell script that checks your ODBC configuration. If it approves, it invokes the `unixODBC` isql utility. Cf. man osql for details on its use.

Example 4.8. Use osql to test the ODBC setup.

    	$ osql -S machine -U mr_ed -P hayseed
    	looking for odbc.ini and odbcinst.ini in /usr/local/etc
    	reading "/usr/home/mr_ed/.odbc.ini"
    	[machine] found in "/usr/home/mr_ed/.odbc.ini"
    	found this section:
    	[machine]
    	Database = testdb
    	Servername = machine
    	Trace           = Yes
    	TraceFile       = /tmp/unixodbc.trace

    	looking for driver for DSN [machine]
    	no driver mentioned for [machine] in .odbc.ini
    	looking for driver for DSN [default]
    	driver "FreeTDS" found for [default] in .odbc.ini
    	found driver named "FreeTDS"
    	FreeTDS is not a readable file
    	looking for entry named [FreeTDS] in /usr/local/etc/odbcinst.ini
    	driver "/usr/local/lib/libtdsodbc.so" found for [FreeTDS] in odbcinst.ini
    	/usr/local/lib/libtdsodbc.so is a readable file
    	Using ODBC-Combined strategy
    	FreeTDS servername is "machine" (from /usr/home/mr_ed/.odbc.ini)
    	looking for [machine] in /usr/home/mr_ed/.freetds.conf
    	"/usr/home/mr_ed/.freetds.conf" is a readable file
    	found this section:
    	[machine]
    	host = machine.example.com
    	port = 2500
    	tds version = 7.1

    	machine.example.com has address 10.82.32.177

    	DSN: machine
    	Driver: /usr/local/lib/libtdsodbc.so
    	Server's hostname: machine.example.com
    	Address: 10.82.32.177

    	Attempting connection as mr_ed ...
    	+ exec isql machine mr_ed hayseed -v
    	+---------------------------------------+
    	| Connected!                            |
    	|                                       |
    	| sql-statement                         |
    	| help [tablename]                      |
    	| quit                                  |
    	|                                       |
    	+---------------------------------------+
    	SQL>

The reader is here advised that the isql that comes with many versions of `unixODBC` will truncate text and surprise in other ways without warning. If it behaves strangely, try FreeTDS's bsqlodbc before you decide you've found a FreeTDS bug.

[15] Why? Once the program is started in the debugger, the driver entry points become viable breakpoints. Because the DM loads the driver dynamically with `dlopen(3)`, no driver addresses even exist until the runtime linker loads it.

[16] When linking directly to FreeTDS you still need the Driver Manager's header files.

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