Novell LINUX ENTERPRISE SERVER 10 SP2 - INSTALLATION AND ADMINISTRATION Installation Manual page 380

loss of data. Because under normal circumstances only root can delete system files or
format hard disks, the threat from the Trojan horse effect or from accidentally entering
destructive commands can be significantly reduced.
18.2.1 File System Permissions
Basically, every file in a Linux file system belongs to a user and a group. Both of these
proprietary groups and all others can be authorized to write, read, or execute these files.
A group, in this case, can be defined as a set of connected users with certain collective
rights. For example, call a group working on a certain project project3. Every user
in a Linux system is a member of at least one proprietary group, normally users.
There can be as many groups in a system as needed, but only root is able to add
groups. Every user can find out, with the command groups, of which groups he is a
member.
File Access
The organization of permissions in the file system differs for files and directories.
File permission information can be displayed with the command ls -l. The
output could appear as in Example 18.1, "Sample Output Showing File Permissions"
(page 362).
Example 18.1 Sample Output Showing File Permissions
-rw-r----- 1 tux project3 14197 Jun 21
As shown in the third column, this file belongs to user tux. It is assigned to the
group project3. To discover the user permissions of the Roadmap file, the first
column must be examined more closely.
-
Type
This column consists of one leading character followed by nine characters grouped
in threes. The first of the ten letters stands for the type of file system component.
The hyphen (–) shows that this is a file. A directory (d), a link (l), a block device
(b), or a character device could also be indicated.
362 Installation and Administration
rw-
Users Permissions
15:03 Roadmap
r--
Group Permissions
---
Permissions for Other
Users