freebsd-dev/share/man/man5/group.5

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.\"     From: @(#)group.5	8.3 (Berkeley) 4/19/94
.\" $FreeBSD$
.\"
.Dd September 29, 1994
.Dt GROUP 5
.Os
.Sh NAME
.Nm group
.Nd format of the group permissions file
.Sh DESCRIPTION
The file
.Aq Pa /etc/group
consists of newline separated
.Tn ASCII
records, one per group, containing four colon
.Ql \&:
separated fields.
These fields are as follows:
.Bl -tag -width password -offset indent -compact
.It group
Name of the group.
.It passwd
Group's
.Em encrypted
password.
.It gid
The group's decimal ID.
.It member
Group members.
.El
.Pp
Lines whose first non-whitespace character is a pound-sign (#)
are comments, and are ignored.
Blank lines that consist 
only of spaces, tabs or newlines are also ignored.
.Pp
The
.Ar group
field is the group name used for granting file access to users
who are members of the group.
The
.Ar 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
.Ar passwd
field
is an optional
.Em encrypted
password.
This field is rarely used
and an asterisk is normally placed in it rather than leaving it blank.
The 
.Ar member
field contains the names of users granted the privileges of
.Ar 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
.Pa /etc/passwd
entry and does not need to be added to that group in the
.Pa /etc/group file.
.\" .Pp
.\" When the system reads the file
.\" .Pa /etc/group
.\" the fields are read into the structure
.\" .Fa group
.\" declared in
.\" .Aq Pa grp.h :
.\" .Bd -literal -offset indent
.\" struct group {
.\"	char    *gr_name;        /* group name */
.\"	char    *gr_passwd;      /* group password */
.\"	int     gr_gid;          /* group id */
.\"	char    **gr_mem;        /* group members */
.\" };
.\" .Ed
.Sh YP/NIS INTERACTION
The
.Pa /etc/group
file can be configured to enable the YP/NIS group database.
An entry whose
.Ar name
field consists of a plus sign (`+') followed by a group name, will be
replaced internally to the C library with the YP/NIS group entry for the
named group.  An entry whose
.Ar name
field consists of a single plus sign with no group name following,
will be replaced with the entire YP/NIS
.Dq Li group.byname
map.
.Pp
If the YP/NIS group database is enabled for any reason, all reverse
lookups (i.e.,
.Fn getgrgid )
will use the entire database, even if only a few groups are enabled.
Thus, the group name returned by
.Fn getgrgid
is not guaranteed to have a valid forward mapping.
.Sh LIMITS
There are various limitations which are explained in
the function where they occur; see section
.Sx SEE ALSO .

In older implementations, 
a group cannot have more than 200 members.
The maximum line length of
.Pa /etc/group
is 1024 characters.
Longer lines will be skipped.
This limitation disappeared in
.Fx 3.0 .
Older binaries that are statically linked, depend on old
shared libraries, or non-FreeBSD binaries in compatibility mode
may still have this limits.
.Sh FILES
.Bl -tag -width /etc/group -compact
.It Pa /etc/group
.El
.Sh SEE ALSO
.Xr passwd 1 ,
.Xr setgroups 2 ,
.Xr crypt 3 ,
.Xr getgrent 3 ,
.Xr initgroups 3 ,
.Xr yp 4 ,
.Xr passwd 5
.Sh BUGS
The
.Xr passwd 1
command does not change the
.Nm group
passwords.
.Sh HISTORY
A
.Nm
file format appeared in
.At v6 .
The YP/NIS functionality is modeled after
.Tn SunOS
and first appeared in
.Tn FreeBSD
1.1.
Support for comments first appeared in
.Fx 3.0 .