2.7. Security and Users

SUSE LINUX – Administration Guide Chapter 2. System Configuration with YaST / 2.7. Security and Users
	2.6. Network Services		2.8. System

A basic aspect of Linux is its multiuser capability. Consequently, several users can work independently on the same Linux system. Each user has a user account identified by a login name and a personal password for logging in to the system. All users have their own home directories where personal files and configurations are stored.

2.7.1. User Administration

After you select to edit users, YaST provides an overview of all local users in the system. If you are part of an extensive network, click ‘Set Filter’ to list all system users (for example, root) or NIS users. You can also create user-defined filter settings. Instead of switching between individual user groups, combine them according to your needs. To add new users, fill in the required blanks in the following screen. Subsequently, the new user can log in to the host with the login name and password. The user profile can be fine-tuned with ‘Details’. You can manually set the user ID, the home directory, and the default login shell. Assign the new user to specific groups. Configure the validity of the password in ‘Password Settings’. Click ‘Edit’ to change these settings whenever necessary. To delete a user, select the user from the list and click ‘Delete’.

For advanced network administration, use ‘Expert Options’ to define the default settings for the creation of new users. Select the authentication method (NIS, LDAP, Kerberos, or Samba) and the algorithm for the password encryption. These settings are relevant for large networks.

Figure 2.14. User Administration

2.7.2. Group Administration

Start the group administration module from the YaST Control Center or click ‘Groups’ in the user administration. Both dialogs have the same functionality, allowing you to create, edit, or delete groups.

YaST provides a list of all groups. To delete a group, select it from the list (the selected line is highlighted dark blue) and click ‘Delete’. Under ‘Add’ and ‘Edit’, enter the name, group ID (gid), and members of the group in the respective YaST screen. If desired, set a password for the change to this group. The filter settings are the same as in the ‘User Administration’ dialog.

Figure 2.15. Group Administration

2.7.3. Security Settings

In ‘Local Security Configuration’, which can be accessed under ‘Security&Users’, select one of the following four options: Level 1 is for stand-alone computers (preconfigured). Level 2 is for workstations with a network (preconfigured). Level 3 is for a server with a network (preconfigured). Use ‘Custom Settings’ for your own configuration.

If you click one of the first three items, incorporate one of the levels of preconfigured system security options. To do this, simply click ‘Finish’. Under ‘Details’, access the individual settings that can be modified. If you choose ‘Custom settings’, proceed to the different dialogs with ‘Next’. Here, find the default installation values.

‘Password Settings’

For new passwords to be checked by the system before they are accepted, mark ‘Checking new passwords’ and ‘Plausibility test for password’. Set the minimum and maximum length of passwords for newly created users. Define the period for which the password should be valid and how many days in advance an expiration alert should be issued when the user logs in to the text console.

‘Boot Settings’

Specify how the key combination Ctrl-Alt-Del should be interpreted by selecting the desired action. Usually, this combination, entered in the text console, causes the system to reboot. Do not modify this setting unless your machine or server is publicly accessible and you are afraid someone could carry out this action without authorization. If you select ‘Stop’, this key combination causes the system to shut down. With ‘Ignore’, this key combination is ignored.

Specify the ‘Shutdown Behavior of KDM’ by granting permission to shut down the system from the KDE display manager, the graphical login of KDE. Give permission to ‘Only root’ (the system administrator), ‘All users’, ‘Nobody’, or ‘Local users’. If ‘Nobody’ is selected, the system can only be shut down via the text console.

‘Login Settings’

Typically, following a failed login attempt, there is a waiting period lasting a few seconds before another login is possible. This makes it more difficult for password sniffers to log in. Optionally activate ‘Record failed login attempts’ and ‘Record successful login attempts’. If you suspect someone is trying to discover your password, check the entries in the system log files in /var/log. With ‘Allow remote graphical login’, other users are granted access to your graphical login screen via the network. Because this access possibility represents a potential security risk, it is inactive by default.

‘Add User Settings’

Every user has a numerical and an alphabetical user ID. The correlation between these is established via the file /etc/passwd and should be as unique as possible. Using the data in this screen, define the range of numbers assigned to the numerical part of the user ID when a new user is added. A minimum of 500 is suitable for users. Proceed in the same way with the group ID settings.

‘Miscellaneous Settings’

For ‘Setting of file permissions’, there are three selection options: ‘Easy’, ‘Secure’, and ‘Paranoid’. The first one should be sufficient for most users. The YaST help text provides information about the three security levels.

The setting ‘Paranoid’ is extremely restrictive and can serve as the basic level of operation for system administrator settings. If you select ‘Paranoid’, remember that some programs might not work or not work correctly, because users no longer have the permissions to access certain files. In this dialog, also define which user should start the updatedb program.

This program, which automatically runs on a daily basis or after booting, generates a database (locatedb) in which the location of each file on your computer is stored. If you select ‘Nobody’, any user can find only the paths in the database that can be seen by any other (unprivileged) user. If root is selected, all local files are indexed, because the user root, as superuser, may access all directories. Finally, make sure the option ‘Current directory in root's path’ is deactivated (default).

Press ‘Finish’ to complete your security configuration.

Figure 2.16. Security Settings

2.7.4. Firewall

Use this module to configure SuSEfirewall2 to protect your machine against attacks from the Internet. Detailed information about SuSEfirewall2 can be found in 27.1. “Masquerading and Firewalls”.

	Automatic Activation of the Firewall
YaST automatically starts a firewall with suitable settings on every configured network interface. You only need to start this module if you want to reconfigure the firewall with custom settings or deactivate it.