GECOS

GECOS is the name of a field in the Unix and Unix-like operating system password file, /etc/passwd. It is the fifth field in the standard passwd entry and is traditionally used to store the user’s personal information. In many implementations this field contains a comma-separated list, with the first element typically representing the user’s full name, followed by optional details such as office location, work phone, and home phone. The GECOS field is part of the legacy interface for user account data and is not typically required for authentication; it is mainly used to provide user information to programs that display account details, such as finger, and to login prompts that show the user’s full name.

Origin and naming: The term GECOS is historically associated with early computing environments and is widely described as deriving from the General Electric Comprehensive Operating System, reflecting the field’s origins in older time-sharing and workstation systems. The exact expansion and origin are sometimes described differently in historical sources, but the convention of the field name has persisted in Unix variants as a holder for “comment” or user information.

Usage and compatibility: On modern systems, GECOS is stored in the passwd structure as pw_gecos and can be viewed with commands such as getent passwd username or finger username. It can be edited by utilities like chfn or usermod, depending on system policy. While often populated with a user’s full name, its content is largely informational and not used for authentication.