Recovering from a system hang

A system can hang because your hardware I/O or software are experiencing problems. When data is retrieved from a disk, certain errors can stop the retrieval process; rather than performing a data recovery, the system may hang.

If you can still use the keyboard, but the operating system does not respond or if the disk activity light is not illuminated, the problem is probably due to a software hang.

To recover from a system hang, you must reboot your system by pressing the reset button or <Ctrl><Alt><Del>. If you were working in an application such as vi, the application might have saved a backup file automatically. You can retrieve this file after you reboot your system.

Hardware hang

Check the following if your disk activity lights are on:

• SCSI bus parity checking/generation -- This must be enabled or disabled for all devices on the bus. If all of your devices support SCSI parity, enable this for all devices. If not all of your devices support SCSI parity, disable it for all devices.

• Terminator power -- Make sure the SCSI bus is terminated correctly; each end of the SCSI chain must contain terminators.

• Cabling -- Make sure your cable and connectors are in good condition and that the spacing between devices is correct.

• Bus device order -- Order is important, especially if you are mixing SCSI 1 and SCSI 2 devices.

Software hang

Software hangs may be caused by applications that consume memory without freeing it. Check the following if hangs occur frequently:

• Check your third-party software. It might contain a driver that is not compatible with UnixWare.

• Disable the desktop and try to re-create the hang while your local system is in text mode. Sometimes the messages are displayed on the console.

• Check for adequate swap space two times the amount of RAM.

See ``Changing swap space size'' for information on swap space and tuning system parameters.