Controlling Access to Files

The Solaris OS is a multiuser environment. In a multiuser environment, all the users who are logged in to a system can read files that belong to other users. With the appropriate file permissions, users can also use files that belong to other users. For more discussion, see Chapter 7, Controlling Access to Files (Tasks). For step-by-step instructions on setting appropriate permissions on files, see Protecting Files (Task Map).

Protecting Files With Encryption

You can keep a file secure by making the file inaccessible to other users. For example, a file with permissions of 600 cannot be read except by its owner and by superuser. A directory with permissions of 700 is similarly inaccessible. However, someone who guesses your password or who discovers the root password can access that file. Also, the otherwise inaccessible file is preserved on a backup tape every time that the system files are backed up to offline media.

The Solaris Cryptographic Framework provides digest, mac, and encrypt commands to protect files. For more information, see Chapter 13, Solaris Cryptographic Framework (Overview).

Using Access Control Lists

ACLs, pronounced “ackkls,” can provide greater control over file permissions. You add ACLs when traditional UNIX file protections are not sufficient. Traditional UNIX file protections provide read, write, and execute permissions for the three user classes: owner, group, and other. An ACL provides finer-grained file security.

ACLs enable you to define the following file permissions:

• Owner file permissions

• File permissions for the owner's group

• File permissions for other users who are outside the owner's group

• File permissions for specific users

• File permissions for specific groups

• Default permissions for each of the previous categories

For more information about using ACLs, see Using Access Control Lists to Protect Files.

Sharing Files Across Machines

A network file server can control which files are available for sharing. A network file server can also control which clients have access to the files, and what type of access is permitted for those clients. In general, the file server can grant read-write access or read-only access either to all clients or to specific clients. Access control is specified when resources are made available with the share command.

The /etc/dfs/dfstab file on the file server lists the file systems that the server makes available to clients on the network. For more information about sharing file systems, see Automatic File-System Sharing in System Administration Guide: Network Services.

Restricting root Access to Shared Files

In general, superuser is not allowed root access to file systems that are shared across the network. The NFS system prevents root access to mounted file systems by changing the user of the requester to the user nobody with the user ID 60001. The access rights of user nobody are the same as those access rights that are given to the public. The user nobody has the access rights of a user without credentials. For example, if the public has only execute permission for a file, then user nobody can only execute that file.

An NFS server can grant superuser capabilities on a shared file system on a per-host basis. To grant these privileges, use the root=hostname option to the share command. You should use this option with care. For a discussion of security options with NFS, see Chapter 6, Accessing Network File Systems (Reference), in System Administration Guide: Network Services.