Additional District and Sessions judge G K Sinha passed the order sentencing the six after finding them guilty in the murder of one Ganesh Saut, in May 1986.
The court also slapped a fine of Rs 20,000 on each.
According to the prosecution, Saut was murdered with a sharp weapon by Jairam Yadav, Puran Yadav, Jamun Yadav, Jitan Yadav, Damodar Yadav and his son Gopal Yadav at Simrikola village under Banka police station area on May 18, 1986 owing to a land dispute.