Linux (and other Unix-like systems) have a multi-tier security that permits user root any system-wide changes. Regular users can be limited: where they can save files, what hardware they can access, their memory usage, applications, disk usage (quota), and the range of priority settings they can apply, can all be specified to provide sufficient freedoms. If necessary they must become root. (See su or sudo). There are also group accounts management, and file and directory permissions.

Linux security software examples include for:

• Authentication modules, PAM and OPIE;
• System logging, Syslog;
• Network services, TCP wrappers, port mappers, and xinetd;
• The shell, ssh.
• Security auditing, Crack, Tiger and Tripwire;
• Cryptographic software, TCFS;
• Packet filtering, iptables;
• Privilege delegation, CaclMgr, sudo.

Most Linux software applications are open standard and open source. For example any application may extend its own authentication, configuration and logging over to PAM or Syslog.