CurrentGroup looks up the current user's group by their primary group id's entry in /etc/passwd.

CurrentUser looks up the current user by their user id in /etc/passwd.

GetExecUser parses a user specification string (using the passwd and group readers as sources for /etc/passwd and /etc/group data, respectively).

GetExecUserFile is a wrapper for GetExecUser.

LookupGid looks up a group by its group id in /etc/group.

LookupGroup looks up a group by its name in /etc/group.

LookupUid looks up a user by their user id in /etc/passwd.

LookupUser looks up a user by their username in /etc/passwd.

The current operating system does not provide the required data for user lookups.