Networking C Shell Programming

1. Networking C Shell Programming

2. Network Services • Having your systems available over a network is required for most businesses today • Providing those services is the task of the System Administrator

3. Network Services • How do your users connect to your systems • tera term • telnet • rlogin • rcp • ftp

4. Type of Networks • broadcast • each system examines the address of every message and picks up its own i.e. Ethernet can be CSMA/CD or CSMA/CA • token ring • only one system transmits at a time i.e. FDDI • point-to-point • only two endpoints • most connections to WANs are point-to-point

5. Internetworking • Gateways • devices that switch packets between different physical networks • deciding which gateway to use is called routing • Routers • a device that filters traffic based on IP address • Bridges • a device that filters traffic based on ethernet address

6. Network Protocols • TCP/IP • Transmission Control Protocol/Internet Protocol • Not based on OSI model, has a 4 layer model • UDP - User Datagram Protocol • Alternate layer above IP, less robust than TCP • NFS is based on UDP • XNS (Xerox Network Software) • DECnet (DEC Network) • Can coexist on the same network or even the same computer...

7. Unix Network Services • Seven layer model - OSI Reference Model • Application • Presentation • Session • Transport • Network • Data Link • Physical

8. Communicating on the Network • use the hostname command to find the identity of your local system #hostname -s aries • uname -a will show hostname, domain name and version of operating system #uname -a SunOS poincare 5.6 Generic_105181-11 sun4u sparc SUNW,Ultra-1

9. Communicating on the Network • finger • used to learn about remote users • finger @aries • shows info about all users logged onto host aries • finger dbittrol@aires • shows info about the user dbittrol on host aries • only works if the site is running the appropriate software (the finger daemon)

10. Communicating on the Network • mail and mailx • most commonly available email software • create, send and receive email • front end to sendmail daemon • you need to know address • considered by some to be difficult to use • ...actually these programs are just very basic • ...and command line oriented

11. Host Addresses • most common is IP addresses • four octets separated by periods • 192.192.192.2 • Will talk about more in Sys Admin classes • Network Information Center (NIC) • hands out blocks of addresses to organizations • each organization assigns individual addresses

12. Host Addresses • Typically.... 131.251.252.253 • 131.251 represents campus/company • 252 represents subnetwork • 253 represents individual equipment • Example is a Class B Address • range for each octet is 0 to 255 • symbolic names can be associated with each IP address

13. Host Addresses • 127.0.0.1 is reserved for localhost name • hook for network software when no network is actually available. • more efficient name services include... • DNS (Domain Name Service) • NIS (Network Information Service) • NIS+

14. Host Addresses • oldest (and simplest) name service is • /etc/hosts file 127.0.0.1 localhost 192.168.3.8 aries loghost 192.168.3.12 linux01 192.168.3.251 matthew

15. Network Utilities • rlogin and telnet • provide ability to connect to a remote host over the network and start a login session there. • you must have an account on the remote system to gain access • rlogin assumes your user name at login • if your rhost allows, no password needed • telnet asks for user name at login • telnet also works with non-UNIX systems • and has more configuration options

16. Network Utilities • Tera Term (Pro) is a free software terminal emulator (communication program) for MS-Windows. It supports VT100 emulation, telnet connection, serial port connection, and so on. • Reflection connectivity software establishes and maintains communications between your computer and a host computer .  This software allows your computer to operate like a Digital VT terminal.

17. Trusted Hosts • Some commands only work if the remote system trusts your local computer • like rcp and rsh • trusted systems are listed in /etc/hosts.equiv • Often not allowed due to security • can also use .rhosts in your home directory • beware - using .rhosts allows another user to log in as you on a remote system, without knowing your password!!!

18. Transferring Files • rcp (remote copy) • works like cp (but only for Trusted Hosts) • copy between systems without logging in • examples • rcp memo.921 bravo:memo.921 • copies from home directory on current system to home directory on bravo • rcp memo.921 watson@bravo:memos • if memos exists as directory then memo.921 is copied into it - if not memo.921 is copied to file memos

19. Transferring Files • ftp (file transfer protocol) • an interactive program • use commands like: • binary, ascii, prompt • put, get, mput, mget • cd, ls • help, quit

20. Commands • rsh (remote shell) • run a command on a remote system without logging in (see Trusted Hosts) • will prompt for your password if the local host is not trusted • local host gets standard out from remote host • special characters on command line are interpreted by the local host • rsh bravo ls -Fla - list home dir on remote host • rsh bravo - start shell on remote host • traceroute - you provide IP or full name and the route from your machine to the system named is shown

21. Testing Network Connection • ping - sends a test packet to a remote system which then sends back a reply # /usr/sbin/ping matthew matthew is alive # /usr/sbin/ping -s matthew PING matthew: 56 data bytes 64 bytes from matthew (192.168.3.251): icmp_seq=0. time=1. ms 64 bytes from matthew (192.168.3.251): icmp_seq=1. time=0. ms 64 bytes from matthew (192.168.3.251): icmp_seq=2. time=0. ms 64 bytes from matthew (192.168.3.251): icmp_seq=3. time=0. ms ----matthew PING Statistics---- 4 packets transmitted, 4 packets received, 0% packet loss round-trip (ms) min/avg/max = 0/0/1- end with <ctrl>-c

22. Domain Name Service (DNS) • a distributed service • name servers around the world cooperate to keep the database up to date • no one system has a complete copy • organized hierarchically • local name server knows local hosts • and how to contact other name servers

23. DNS • Seven original top level domains • countries outside U.S. use ISO country code • au for Australia, ja for Japan • inside U.S. the other six are: • .com commercial enterprises • .edu educational institutions • .gov nonmilitary government agencies • .mil military government agencies • .net networking organizations • .org other (often nonprofit) organizations

24. DNS • New TLDs started coming online late 2001 • .biz • .info • .name • .museum • .coop • .aero • .pro

25. DNS • some examples • the same host name can be used by two completely different systems! • okeefe.berkeley.edu • host okeefe at University of California • okeefe.mma.org • host okeefe at Museum of Modern Art • NOTE: DNS is not case-sensitive

26. DNS • most common interface is BIND software • Berkeley Internet Name Domain • translates host name <=> ip address • follows client/server model • client looks to name server to resolve host ip addresses • nslookup - interface to any DNS server • DNS Server resolving, name and ip

27. Network Information Service (NIS) • developed by Sun Microsystems to help simplify network administration • formerly called Yellow Pages (yp) • hence, commands like.... • ypcat - display NIS database table • ypmatch - search NIS database table • etc... etc... • used in addition to /etc system config files • which now only contain minimum info

28. Network File System (NFS) • work locally with files that are stored on a remote system’s disks • remote file system appears to be local • remote system acts as server • local system acts as client • users mount dirs from other systems on their systems to use. Can “automount” • df command (display filesystems)

29. example output of df aries% df / (/dev/dsk/c0d0s0 ): 106980 blocks 85665 files /usr (/dev/dsk/c0d0s6 ): 17590 blocks 30931 files /proc (/proc ): 0 blocks 958 files /dev/fd (fd ): 0 blocks 0 files /export (/dev/dsk/c0d0s3 ): 1415974 blocks 498944 files /usr/openwin (/dev/dsk/c0d0s4 ): 59752 blocks 68067 files /tmp (swap ): 114808 blocks 11689 files /cdrom/devpro_v5n1_intel(/vol/dev/dsk/c1d0/devpro_v5n1_intel): -1 blocks -1 files aries% df -k Filesystem kbytes used avail capacity Mounted on /dev/dsk/c0d0s0 159919 106429 37500 74% / /dev/dsk/c0d0s6 91039 82244 0 100% /usr /proc 0 0 0 0% /proc fd 0 0 0 0% /dev/fd /dev/dsk/c0d0s3 1013807 305820 606607 34% /export /dev/dsk/c0d0s4 137631 107755 16116 87% /usr/openwin swap 57416 12 57404 1% /tmp /vol/dev/dsk/c1d0/devpro_v5n1_intel 234370 -1 0 100% /cdrom/devpro_v5n1_intel From Aries (Solaris)

30. AFS File System • created at Carnegie Mellon University - hence name “Andrew File System” • commercially available from Transarc • provides ability for few sys admins to administer hundreds of systems • provides virtual file system, transparent to users, looks like one big tree

31. AFS File System (cont) • provides enhanced security on top of Unix • rwlidka • read, write, lookup, insert, delete, lock, admin • On every directory (not file level) • Permissions granted to users or groups of users • Overlays Unix owner permissions • Unix group and other permissions are ignored • User obtains a data structure called a “token” to authenticate themselves

32. DFS File System • Distributed File System - follow on to AFS • Added more layers of permissions • Mask for files created in a dir • Another mask for dirs created in a dir • Very hard to manage permissions • New versions of AFS are now being made available

33. C Shell • The Bourne shell and the C shell are not compatible syntactically • Both interactive commands and shell scripts differ • The aim was to allow users to easily substitute custom programs for existing UNIX commands • Made the syntax for shell scripts similar to that of the C programming language

34. C Shell • When you are using the C shell your prompt should either be $ or % • $ standard shell • % C shell • C shell has special files you can use to customize your working environment • .login #For things that you want active during current login • .cshrc #Defines special characteristics local to a shell • .logout #What happens when you log off the system

35. Built-in Commands • history • set history = 20 • history will list out last # of commands (but not history command) • !! repeats last command • !4 repeats 4th command

36. Built-in Commands • alias is an abbreviation for a frequently used command • alias h history would set up h • alias dir ls –l if you liked your old DOS commands like dir

37. Built-in Commands Some that are built into the C-shell are: bg cd set echo exec stop exit fg suspend glob jobs umask kill notify unalias

38. C-Shell • Filename completion (must be turned on) • set filec (this turns it on, you must be in csh) • cat myrpt [press ESC key not Enter] • Will look for a match for myrpt, it will display the remainder of the file name (if it’s unique) so you can press enter to run the command. If the match isn’t found then it will do nothing. Sometimes you need to type in more of the file name to get a unique match

39. C-Shell • ~ represents your home directory • du ~ > disk_info& • Pattern matching (BSD only) • =~ match • !~ does not match

40. .login • stty - set terminal command will show your current terminal settings • to change your settings type in: stty erase ^h stty kill ^x stty intr DEL

41. .login • env is established from here • Use setenv to declare • setenv TERM vt100 • .login should include anything you want executed once

42. .cshrc • Is invoked each time you start up a new C shell • Used to establish variables and parameters that are local to a specific shell • It is not required that there is a .cshrc file

43. .logout • Runs when you end your session • You can use it to clean up directories, track your sessions etc. • This is a file you can create (not required by the system)

44. C Shell • To do the equivalent of a read command you would do the following: • set variablename =$< • To display a string of data to the screen use the echo command such as: • echo “Hello World!”

45. C Shell - If Constructs • You’ll find that script syntax differs from what you used in the bash, bourne or ksh environments • If statements do not end in fi, etc.

46. C Shell - If Constructs 1. if (expression) command 2. if (expression) then command(s) endif 3. if (expression) then command(s) else command(s) endif

47. C Shell - If Constructs 4. if (expression) then command(s) else if (expression) then command(s) else command(s) endif

48. C Shell - goto • Has the form goto word word: for example goto err err: exit 1

49. C Shell -Foreach • Allows script to process a set number of items placed in a list foreach person ( ann bruce tim sam deb) echo “Dear $person.\ You are cordially invited to a Welcome luncheon for our new employee, Jane Doe” | mail $person end

50. C Shell – While Loop • While loop handles situations where the number of iterations is not know in advance. This loop terminates when the controlling expression becomes false. while (expression) command(s) end