Maintaining a secure environment on Unix and Unix-like operating systems is dependent on design concepts of these operating systems, but vigilance through user and administrative techniques is important to maintain security also.

There are a few security concepts in the Unix-like systems:

• Permission: A core security feature in these systems is the permissions system. All files in a typical Unix-style filesystem have permissions set enabling different access to a file.
• User groups: Users under Unix-like operating systems often belong to managed groups with specific access permissions.

In the following table, some important security tips are listed:

General security tips

• Avoid doing your regular jobs when you are logged in as root.
• Check log files to find suspicious activities.
• Install and execute the Bastille Linux hardening tool.
• Configure sudo (superuser do) to execute privileged commands as a normal user instead of using su.
• Use strong and encrypted password to protect your system and data.
• Disable crtl+alt+del shutdowns by any other user than root - Securing /etc/passwd by using "shadow" passwords (encrypted)

File security

• Audit system for unauthorized use of setuid and setgid
• Reduce unnecessary world-writable files
• Locate all files that have no owner or group - they may be created by an intruder.
• Use tools such as Tripwire to monitor file integrity

Kernel security

• Password-protect LILO to require authorization.
• Use OpenWall kernel patch to prevent buffer overflows, restrict information in /proc available to normal users, and other changes.
• icmp_echo_ignore_all: Ignore all ICMP ECHO requests. This option prevents ping flood.
• icmp_echo_ignore_broadcasts: Ignore ICMP echo requests with a broadcast/multicast destination address.
• tcp_syncookies: Protection from the SYN Attack. Send syncookies when the SYN backlog queue of a socket overflows.
• rp_filter: Determines if source address verification is enabled. This option may prevent IP spoofing attacks against the internal network.
• secure_redirects: Accept ICMP redirect messages only for gateways listed in default gateway list.
• log_martians: Log packets with impossible addresses to kernel log.

Networking security

• Using SSH (secure shell) or OpenSSH to replace telnet, ftp, rsh, and rlogin should be standard practice.
• Disable any network services or open ports you do not require for your server to work properly.
• Use firewall to enhance the security provided by tcpd (tcp wrapper)
• Install nmap to determine potential communication channels remotely.

System backup and up-to-date

• Backup system, applications and data periodically
• Check your backups of user and system files regularly to make sure they are useful.
• Keep system and application updated