Unix security

Unix security refers to the means of securing a Unix or Unix-like operating system.

Permissions
A core security feature in these systems is the file system permissions. All files in a typical Unix filesystem have permissions set enabling different access to a file. Unix permissions permit different users access to a file with different privilege (e.g., reading, writing, execution). Like users, different user groups have different permissions on a file.

User groups
Many Unix implementations add an additional layer of security by requiring that a user be a member of the wheel user privileges group in order to access the  command.

Root access
Most Unix and Unix-like systems have an account or group which enables a user to exact complete control over the system, often known as a root account. If access to this account is gained by an unwanted user, this results in a complete breach of the system. A root account however is necessary for administrative purposes, and for the above security reasons the root account is seldom used for day to day purposes (the sudo program is more commonly used), so usage of the root account can be more closely monitored.

Passwords
Selecting strong passwords and guarding them properly are important for Unix security.

On many UNIX systems, user and password information, if stored locally, can be found in the   and   file pair.

Patching
Operating systems, like all software, may contain bugs in need of fixing or may be enhanced with the addition of new features; many UNIX systems come with a package manager for this. Patching the operating system in a secure manner requires that the software come from a trustworthy source and not have been altered since it was packaged. Common methods for verifying that operating system patches have not been altered include the use of the digital signature of a cryptographic hash, such as a SHA-256 based checksum, or the use of read-only media.

Viruses and virus scanners
There are viruses and worms that target Unix-like operating systems. In fact, the first computer worm—the Morris worm—targeted Unix systems.

There are virus scanners for UNIX-like systems, from multiple vendors.

Firewalls
Network firewall protects systems and networks from network threats which exist on the opposite side of the firewall. Firewalls can block access to strictly internal services, unwanted users and in some cases filter network traffic by content.

iptables
iptables is the current user interface for interacting with Linux kernel netfilter functionality. It replaced ipchains. Other Unix like operating systems may provide their own native functionality and other open source firewall products exist.

General

 * Practical UNIX and Internet Security, Simson Garfinkel and Gene Spafford, O'Reilly & Associates, 2003.