System Administration Guide: Security Services

Controlling Access to Files

The Solaris operating environment is a multiuser environment. In a multiuser environment, all the users who are logged in to a machine can read files that belong to other users. With the appropriate file permissions, users can also use files that belong to other users. Table 2–3 describes the commands for file system security. For step-by-step instructions on securing files, see Chapter 4, Securing Files (Tasks).

Commands for File System Security

This table describes the commands for monitoring and securing files and directories.

Table 2–3 Commands for File System Security


Command	Description	Man Page
`ls`	Lists the files in a directory and information about the files.	ls(1)
`chown`	Changes the ownership of a file.	chown(1)
`chgrp`	Changes the group ownership of a file.	chgrp(1)
`chmod`	Changes permissions on a file. You can use either symbolic mode, which uses letters and symbols, or absolute mode, which uses octal numbers, to change permissions on a file.	chmod(1)

File Encryption

You can keep a file secure by making the file inaccessible to other users. For example, a file with permission 600 cannot be read except by its owner and the superuser. A directory with permissions 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 machine files are backed up to tape.

Fortunately, an additional layer of security is available to all users of Solaris software in the United States, the Solaris Encryption Kit. The encryption kit includes the crypt command, which scrambles the data to disguise the text. For more information, see the crypt(1) man page.

Access Control Lists (ACLs)

ACLs, pronounced “ackkls”, can provide greater control over file permissions. You add ACLs when the traditional UNIX file protection in the Solaris operating environment is not sufficient. The traditional UNIX file protection provides 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
Owner's group file permissions
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 step–by–step instructions on using ACLs, see Using Access Control Lists (ACLs).

The following table lists the commands for administering ACLs on files or directories.

Table 2–4 Access Control List (ACL) Commands


Command	Description	Man Page
`setfacl`	Sets, adds, modifies, and deletes ACL entries	setfacl(1)
`getfacl`	Displays ACL entries	getfacl(1)

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: Resource Management and 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 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 privileges 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.