GROUP(5) File Formats Manual GROUP(5)

groupformat of the group permissions file

The file ⟨/etc/group⟩ consists of newline separated ASCII records, one per group, containing four colon ‘:’ separated fields. These fields are as follows:

Name of the group.
Group's encrypted password.
The group's decimal ID.
Group members.

The group field is the group name used for granting file access to users who are members of the group. The gid field is the number associated with the group name. They should both be unique across the system (and often across a group of systems) since they control file access. The passwd field is an optional encrypted password. This field is rarely used and an asterisk is normally placed in it rather than leaving it blank. The member field contains the names of users granted the privileges of group. The member names are separated by commas without spaces or newlines. A user is automatically in a group if that group was specified in their /etc/passwd entry and does not need to be added to that group in the /etc/group file.

Processes generally find group records using one of the getgrent(3) family of functions. On Mac OS X, these functions interact with the DirectoryService(8) daemon, which reads the /etc/group file as well as searching other directory information services to determine groups and group membership.


passwd(1), setgroups(2), crypt(3), getgrent(3), initgroups(3), passwd(5), DirectoryService(8)

The passwd(1) command does not change the group passwords.

A group file format appeared in Version 6 AT&T UNIX.

July 18, 1995 Mac OS X