Unix group management and file sharing

Overview: 

Unix groups are a useful way for multiple users to share files.

This document describes unix group creation and management.

Group Creation

If you wish to share files with another user, unix groups are a useful way to accomplish this. Unix groups must be created by a system administrator. If you wish to have a unix group created, send an email to labstaff@cs.rochester.edu.

Include the following in your group request email:
Group Name --  Desired group name (8 character max)
Group Administrator(s) --  Name of the administrator(s) for this group
Initial group members --  Whom to initially add to the group
Group Purpose --  Reason you are requesting a new group

Include your desired group name (8 character max), the purpose of the group, the administrator of the group and the initial group members. A group may have multiple administrators if desired. If the group is approved, it will be created and distributed throughout our network as part of our overnight system update.

Group Administration

Once the group has been created by a system administrator, the group administrator can manage additions and deletions of group members. To manage a group, connect to the machine master.cs.rochester.edu via ssh and use the "gpasswd" program. There is a man page available, but the key options are "-a" to add members to a group and "-d" to remove members from a group. Note: the group password options discussed in the man page are currently non-functional. Any updates made by a group administrator will be distributed as part of our hourly system update.

Examples:
Add a user (joe) to a group (specialproj)

gpasswd -a joe specialproj

Remove a user (bob) from a group (cs108)

gpasswd -d bob cs108

Group Limitations

Unix has a built in limit of 16 active groups. If a user is a member of more than 16 groups, only the first 16 in numerical gid order will be active. If a user wishes to use one of the groups beyond the 16, the "newgrp" command should be run specifying which group the user wishes to work in.