Performing an In-Place Downgrade

Downgrade Adaptive Server 15.7 SP100 to versions 15.5, 15.5 ESDs, 15.7, and 15.7 ESDs in place using the same installation directory the upgrade was performed from.

When downgrading from Adaptive Server version 15.7 SP100 to version 15.5 ESD #4, you can perform the downgrade to the same Sybase installation directory where version 15.7 resides.

Note: Although in-place downgrades are allowed, you have less risk of experiencing problems if you save all the data externally and perform a clean downgrade.

Back up the entire contents of the current operating system's $SYBASE directory in case you need to revert back to it.
Place a database (@db_name) in single-user mode.
Run sp_downgrade 'prepare' to validate the readiness of Adaptive Server 15.7 for the downgrade:
```
sp_downgrade 'prepare', @toversion = '155'
```
Perform any manual changes sp_downgrade 'prepare' identifies for your downgrade, and repeat the command until it displays no additional requirements.
Note: Before you proceed, make sure you understand the implications of any sp_downgrade warnings displays before you proceed.
Run sp_downgrade 'downgrade':
```
sp_downgrade 'downgrade', @toversion = '155, @override=1
```
Once you successfully perform sp_downgrade 'downgrade', you cannot have any activity on the 15.7 server.
Run checkpoint, then immediately issue the shutdown command to shut down the 15.7 server.
(Optional) Make OS copies of any existing Adaptive Server device files.
Install the Adaptive Server version 15.5 EBF 18661 SMP ESD #4 binary overlay via ./setup, which starts InstallAnywhere in GUI mode.

Note: At the end of the InstallAnywhere installation process, do not select Configure a Server.
Do not modify the RUN_server file, since the location of the files referenced in the file do not change in this downgrade method.
Start Adaptive Server.

If you see error messages in the error log, perform post-downgrade tasks.

If you start a downgraded server using the 15.7 configuration file, the new options generate an Unknown parameter message. The unknown options are reported the first time you restart the server. You can ignore these messages; the configuration file is rewritten without the unknown options.