Some physical Input/Output error has occurred. If the process was writing a file at the time, data corruption is possible.
First, find out which device is experiencing the I/O error. If the device is a tape drive, make sure a tape is inserted into the drive. When this error occurs with a tape in the drive, it is likely that the tape contains an unrecoverable bad spot.
If the device is a floppy drive, an unformatted or defective diskette could be at fault. Format the diskette, or obtain a replacement.
If the device is a hard disk drive, you might need to run fsck(1M) and possibly even reformat the disk.
In some cases this error might occur on a call following the one to which it actually applies.
The symbolic name for this error is EIO, errno=5.