GROUP(5) File Formats and Configurations GROUP(5)

NAME

group - group file

DESCRIPTION

The group file is a local source of group information. The group file
can be used in conjunction with other group sources, including the
NIS maps group.byname and group.bygid, or group information stored on
an LDAP server. Programs use the getgrnam(3C) routines to access this
information.


The group file contains a one-line entry for each group recognized by
the system, of the form:


groupname:password:gid:user-list


where

groupname
The name of the group. A string consisting of lower case
alphabetic characters and numeric characters. Neither a
colon (:) nor a NEWLINE can be part of a groupname. The
string must be less than MAXGLEN-1, usually 8,
characters long.


gid
The group's unique numerical ID (GID) within the system.


user-list
A comma-separated list of users allowed in the group.


The maximum value of the gid field is 2147483647. To maximize
interoperability and compatibility, administrators are recommended to
assign groups using the range of GIDs below 60000 where possible.


If the password field is empty, no password is demanded. During user
identification and authentication, the supplementary group access
list is initialized sequentially from information in this file. If a
user is in more groups than the system is configured for,
{NGROUPS_MAX}, a warning will be given and subsequent group
specifications will be ignored.


Malformed entries cause routines that read this file to halt, in
which case group assignments specified further along are never made.
To prevent this from happening, use grpck(8) to check the /etc/group
database from time to time.


If the number of characters in an entry exceeds 2047, group
maintenance commands, such as groupdel(8) and groupmod(8), fail.


Previous releases used a group entry beginning with a `+' (plus sign)
or `-' (minus sign) to selectively incorporate entries from a naming
service source (for example, an NIS map or data from an LDAP server)
for group. If still required, this is supported by specifying group:
compat in nsswitch.conf(5). The compat source may not be supported in
future releases. Possible sources are files followed by ldap. This
has the effect of incorporating information from an LDAP server after
the group file.

EXAMPLES

Example 1: Example group File.

The following is an example of a group file:


root::0:root
stooges:q.mJzTnu8icF.:10:larry,moe,curly


and the sample group entry from nsswitch.conf:


group: files ldap


With these entries, the group stooges will have members larry, moe,
and curly, and all groups listed on the LDAP server are effectively
incorporated after the entry for stooges.


If the group file was:


root::0:root
stooges:q.mJzTnu8icF.:10:larry,moe,curly
+:


and the group entry from nsswitch.conf:


group: compat


all the groups listed in the NIS group.bygid and group.byname maps
would be effectively incorporated after the entry for stooges.

SEE ALSO

groups(1), newgrp(1), getgrnam(3C), initgroups(3C), unistd.h(3HEAD),
nsswitch.conf(5), groupadd(8), groupdel(8), groupmod(8), grpck(8)


System Administration Guide: Basic Administration

March 11, 2025 GROUP(5)