Q. Can You tell me more about Linux /etc/group file?
A. /etc/group is a text file which defines the groups to which users belong under Linux and UNIX operating system. Under Unix / Linux multiple users can be categorized into groups. Unix file system permissions are organized into three classes, user, group, and others. The use of groups allows additional abilities to be delegated in an organized fashion, such as access to disks, printers, and other peripherals. This method, amongst others, also enables the Superuser to delegate some administrative tasks to normal users.
/etc/group file
It stores group information or defines the user groups i.e. it defines the groups to which users belong. There is one entry per line, and each line has the format (all fields are separated by a colon (:)
Consider following /etc/group line:
cdrom:x:24:vivek,student13,raj _____ _ _ _____ | | | | | | | | 1 2 3 4
- group_name: It is the name of group. If you run ls -l command, you will see this name printed in the group field.
- Password: Generally password is not used, hence it is empty/blank. It can store encrypted password. This is useful to implement privileged groups.
- Group ID (GID): Each user must be assigned a group ID. You can see this number in your /etc/passwd file.
- Group List: It is a list of user names of users who are members of the group. The user names, must be separated by commas.
More about a user groups
Users on Linux systems are assigned to one or more groups for following reasons:
- To share files or other resource with a small number of users
- Ease of user management
- Ease of user monitoring
- Group membership is perfect solution for large Linux (UNIX) installation.
- Group membership gives you or your user special access to files and directories or devices which are permitted to that group
Consider following figure (Click to enlarge)
User tom is part of both 'Web developers' and 'Sales' group. So tom can access files belongs to both groups.
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- Last Updated: 11/19/08



{ 9 comments… read them below or add one }
On the money. The detail was clear and straight forward. I quickly found the answer to the problem that we were facing in our production test environment.
Clear and good.
wonderful
perfect!! just what i need ;)
Great, Thanks!
But one more question remains:
Does /etc/group allow wildcards (probably not) or is it possible to allow all group members of one group to be part of another?
I have the problem, that different linux installations (which are all needed unfortunately) provide different groups and user authentification is central from NIS …
Will a blank line in the /etc/group file cause a system read problem? I know on some UNIX platforms, a blank line in the password file causes problems. Thanx
It may cause a problem. It is better to remove a blank line. But I never tested it… YMMV.
Can a group be a member of another group?
What is the default permission for /etc/group