Notes

Outline

Chapter 3 Unix Overview

Figure 3.1 Unix file system

Table 3.1 Important Directories in the Unix file system

Figure 3.2 Unix Architecture

Figure 3.3 Relationship between init, inetd, and various network services

Sample /etc/inetd.conf  file containing services spawned by inetd

Common Unix Administration Tasks Vulnerability of using  “.” in  your search path $PATH Showing all running processes ps –aux ps –aef Killing/restarting processes kill –HUP pid killall –HUP inetd /etc/passwd file Unix permissions rwxrwxrwx chmod command

Common Unix Administration Tasks (cont.) SetUID programs Executes with permissions of its owner, not of its user /etc/passwd setUID root r-s--x--x Creating setUID files #chmod 4741 foo Finding setUID files

Unix Trust Authenticating users on behalf of another machine R-commands rlogin rsh rcp Weakness of r-commands Actions based on IP address of trusted machine Undermining r-commands via IP address spoofing

Logs and Auditing Syslog daemon Syslogd /etc/syslog.conf /var/log /var/log/messages /var/log/http Accounting files Utmp Records who is currently logged into a system used by who command Wtmp records all logins and logouts used by last command lastlog Records time and location of each user’s last login to system

Network File System (NFS) mountd Nfsd Share only folders that require sharing Export files only to hosts requiring access Carefully assign permissions to shared files Avoid NFS sharing across the Internet Alternatives Secure ftp IPSec-based VPN