1. Using Networks

2. Assignment Issues find syntax Permissions HW4 3c /proc vs /tmp vs /var

3. Network Utilities ifconfig – shows active network configuration –eth0 is usually primary interface –lo0 is loopback ssh – Secure SHell, allows access to servers ping – is a server alive? traceroute – how do I get there?

4. Network Utilities ftp – File Transfer Protocol, transfer files –Password is passed in plain text (meaning anybody can read it) –sftp is a passable replacement wget – command line web browser (sort of)

5. Regular Expression for IP Question 3 says to search for IP addresses in /etc A regexp of: –[0-255].[0-255].[0-255].[0-255] will not work! –One that does: "(([0-9]|[1-9][0-9]|1[0- 9]{2}|2[0-4][0-9]|25[0- 5])\.){3}"

6. Network Configuration

7. More utilities arp – Address Resolution Protocol ifconfig (again) –ifconfig down/up route – shows routing information – netstat –r is equivalent

8. Genmask/Netmask Used to get the network and computer from an IP address –Network: 10.11.12.13 + 255.255.255.0 == 10.11.12.0 –Computer: 10.11.12.13 + 0.0.0.255 == 0.0.0.13

9. Initialization/Booting

10. Boot Process From http://www.ibm.com/developerworks/library/l- linuxboot/index.html

11. Run Levels /etc/inittab tells Linux how/what to start # Default runlevel. The runlevels used by RHS are: # 0 - halt (Do NOT set initdefault to this)‏ # 1 - Single user mode # 2 - Multiuser, without NFS (The same as 3, if you do not have networking)‏ # 3 - Full multiuser mode # 4 - unused # 5 - X11 # 6 - reboot (Do NOT set initdefault to this)‏ # id:3:initdefault:

12. rc.sysinit /etc/rc.d/rc.sysinit – just a script –985 lines on Red Hat 5

13. /etc/rc.d/rc Does the work of the run level Be sure to read the man page on runlevel (hint! hint!) – man 8 runlevel

14. Services/Daemons Depend on run level from inittab –/etc/rc#.d – SysV –/etc/rc.d/rc#.d – Linux (/etc/rc#.d are sym links)‏

15. /etc/rc.d/rc#.d Runlevel directories Tell what to start or stop on this level S = start K = kill Linux – S/K go from low to high SysV (Commerical Unix) – S goes from low to high – K goes from high to low