LPI Linux Certification in a Nutshell, 2nd Edition

Security (Topic 1.114)

Objective 1: Perform Security Administration Tasks

TCP wrappers

• Configuring TCP wrappers (tcpd) using /etc/hosts.allow and /etc/hosts.deny can enhance security for daemons controlled by inetd.

• tcpd is often configured to deny access to all systems for all services (a blanket deny), then specific systems are specified for legitimate access to services (limited allow).

• tcpd logs using syslog, commonly to /var/log/secure.

Finding executable SUID files

• find can perform searches for file attributes such as SUID using the -perm option.

Verifying packages

• RPM packages are verified using the Verify mode, enabled using the -V (capital) option.

• The output for each package contains a string of eight characters that are set to dots when the attribute has not changed. The columns represent each of eight different attributes: MD5 checksum, file size, symlink attributes, the file's mtime, device file change, user/owner change, group change, and mode change.

SGID workgroups

• The SGID bit can be applied to directories to enforce a policy whereby new files created within the directory are assigned the same group ownership as the directory itself.

The Secure Shell

• The Secure Shell, or SSH, can be used as an alternative to Telnet for secure communications.

• SSH can also protect FTP and other data streams, including X sessions.

• The Secure Shell daemon is sshd.

Objective 2: Set Up Host Security

Shadow passwords

• Enabling the use of shadow passwords can enhance local security by making encrypted ...