/etc/security/group.conf is in libpam-modules 1.1.3-7ubuntu2.3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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# This is the configuration file for the pam_group module.
#
#
# *** Please note that giving group membership on a session basis is
# *** NOT inherently secure. If a user can create an executable that
# *** is setgid a group that they are infrequently given membership
# *** of, they can basically obtain group membership any time they
# *** like. Example: games are allowed between the hours of 6pm and 6am
# *** user joe logs in at 7pm writes a small C-program toplay.c that
# *** invokes their favorite shell, compiles it and does
# *** "chgrp play toplay; chmod g+s toplay". They are basically able
# *** to play games any time... You have been warned. AGM
#
#
# The syntax of the lines is as follows:
#
# services;ttys;users;times;groups
#
# white space is ignored and lines maybe extended with '\\n' (escaped
# newlines). From reading these comments, it is clear that
# text following a '#' is ignored to the end of the line.
#
# the combination of individual users/terminals etc is a logic list
# namely individual tokens that are optionally prefixed with '!' (logical
# not) and separated with '&' (logical and) and '|' (logical or).
#
# services
# is a logic list of PAM service names that the rule applies to.
#
# ttys
# is a logic list of terminal names that this rule applies to.
#
# users
# is a logic list of users or a netgroup of users to whom this
# rule applies.
#
# NB. For these items the simple wildcard '*' may be used only once.
# With netgroups no wildcards or logic operators are allowed.
#
# times
# It is used to indicate "when" these groups are to be given to the
# user. The format here is a logic list of day/time-range
# entries the days are specified by a sequence of two character
# entries, MoTuSa for example is Monday Tuesday and Saturday. Note
# that repeated days are unset MoMo = no day, and MoWk = all weekdays
# bar Monday. The two character combinations accepted are
#
# Mo Tu We Th Fr Sa Su Wk Wd Al
#
# the last two being week-end days and all 7 days of the week
# respectively. As a final example, AlFr means all days except Friday.
#
# Each day/time-range can be prefixed with a '!' to indicate "anything
# but"
#
# The time-range part is two 24-hour times HHMM separated by a hyphen
# indicating the start and finish time (if the finish time is smaller
# than the start time it is deemed to apply on the following day).
#
# groups
# The (comma or space separated) list of groups that the user
# inherits membership of. These groups are added if the previous
# fields are satisfied by the user's request
#
# For a rule to be active, ALL of service+ttys+users must be satisfied
# by the applying process.
#
#
# Note, to get this to work as it is currently typed you need
#
# 1. to run an application as root
# 2. add the following groups to the /etc/group file:
# floppy, play, sound
#
#
# Here is a simple example: running 'xsh' on tty* (any ttyXXX device),
# the user 'us' is given access to the floppy (through membership of
# the floppy group)
#
#xsh;tty*&!ttyp*;us;Al0000-2400;floppy
#
# another example: running 'xsh' on tty* (any ttyXXX device),
# the user 'sword' is given access to games (through membership of
# the sound and play group) after work hours.
#
#xsh; tty* ;sword;!Wk0900-1800;sound, play
#xsh; tty* ;*;Al0900-1800;floppy
#
# yet another example: any member of the group 'admin' running
# 'xsh' on tty*, is granted access (at any time) to the group 'plugdev'
#
#xsh; tty* ;%admin;Al0000-2400;plugdev
#
# End of group.conf file
#
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