Review

1. Review • Please hand in your homework and practicals • Advanced Redirection • >> • 2> • &> • More VI • Scripting

2. Today • Folders • /dev • More vi • Cheatsheets! • Processes

3. Folders - /dev • /dev – holds the raw devices used by the system • Hard drives (HDDs) referenced by connection type • IDE - /dev/hda • SAS/SATA - /dev/sda • CDROM - /dev/cdrom • DVD - /dev/dvd (sometimes /dev/cdrom) • Printer - /dev/lp • RAM - /dev/ram • TTY’s - /dev/tty • Random - /dev/random

4. Using /dev • Most things will be automatically used by the system • RAM/TTY/RAID • HP’s RAID is /dev/cciss – this is probably different between each RAID card vendor (LSI, Dell, HP, etc…) • They will have documentation telling you where to go • Sometimes you’ll need to manually “mount” a new HDD or a CDROM • mount <device> <target> • You can’t access /dev directly, you have to “mount” it on the system to access it

5. Using /dev - /mnt • /mnt – location where extra devices are to be “mounted” or set for access on the system • Changing to /media, either works, our VM’s will use /media for auto-discovered CD’s • mkdir /mnt/usb • mount <device> <target> • mount /dev/sdc /mnt/usb • So if we were going to “mount” a floppy drive – fd1 – what would the command be?

6. /dev • We’ll get to adding hdd’s – that’s it’s own process • When you want to attach a “hot plug” device • To update, recover, move files, etc… • If the system is up, it will print out the new hdd is found • If it doesn’t print out, there is a special log called the dmesg that will show you

7. dmesg • dmesg – the kernel message buffer (also a command) • Typing in dmesg will show you the kernel info since boot • Usually used to capture boot information or errors (dmesg | grep) • Earliest at the beginning, most recent at the end • Typing in dmesg (and looking for a new hard drive) will usually be right at the bottom unless there’s a lot of activity on the system

8. Quick Review - Vi • vi <filename> • Opens file for editing • Inside vi you always start in command mode • i, a, A to get into insert mode, escape key to get back out • While there, you can do things like copying, pasting, and jumping around • New: • yy copies • p pastes

9. Vi Review, part 2 • Move around through the line number • When you open a file, vi prints the filename, lines, and characters in the bottom left • “/home/student/script.sh” 19L, 383C • So to jump to the end • Assuming you’re already in vi in command mode • :19 <enter> • To jump to line ten, :10 <enter>

10. More vi Fun • Can open to a specific line number, or jump to a specific line when inside a file • For instance, vi’s configuration file /etc/vimrc • We want to do ‘syntax highlighting’ in vi to make it easier to read • [student@it136centos65vm ~]# grep -in ‘syntax’ /etc/vimrc • 47:”Switch syntax highlighting on, when the terminal has colors • 50: syntax off • Quick glance shows line 47 as a descriptor, and line 50 as the setting

11. vi Jump to Line • We can open vi to a specific line: • Notice ‘etc’ in the current directory below - we’re in /etcso we can use the “relative path” of vimrc • [student@it136rhel65vm conf]$ vi +50 vimrc • Or inside vi we can jump to a specific line • (in command mode) • :50

12. Searching vim • Inside vi we use the / to denote a search string • /syntax • It is case-sensitive: /Syntax would not show us anything • Takes us to line 47 • Switch to next instance by using the n key • Go back with the ? key

13. Other Useful Options • y is the ‘yank’ character, actually copies • yy will copy the line • p will ‘put’ it into wherever the cursor is • dd deletes the line • u is undo • set <option> allows configuration of vi - this is not saved, these should go into /etc/virc or /etc/vimrc files • r replaces a single character (puts you into insert mode for that single character) • R replaces until you leave ‘insert’ mode (esc key)

14. Scripts • So we have seen commands for management • useradd, usermod, sudocat • But what happens when you have a task you need to do several hundred times over? • We use a script • A script is simply a collection of commands

15. Every Script • We went over ! (called bang) • Well, # is called ‘she’ (many refer to it as hash) • The first line of EVERY script must have a ‘shebang’ • The shebang is the script telling the shell which shell to use to execute the script • We use • #!/bin/bash • #!/bin/zsh • #!/bin/csh…

16. Now we get interesting • All we need to do is add commands • There are a few constructs to help us, though • We can make comments • Comments must have # in front of them • They only go from where # starts to the end of the line • We can use variables • ‘Best practice’ is to use all caps • FLAGS = “-alh” • ls $FLAGS • So once we set it, we reference it with $

17. Finally • We can take arguments • $1 is the variable inside a script for whatever was passed as the first argument • You run a script (or a command not set in /bin or /sbin) by running ./script • Sometimes you need to ‘build from source’ and you’ll use ./configure • So if we pass an argument • ./script argument • $1 = argument

18. Extrapolation • We used $FLAGS as a variable, if we’re debugging a script, how do we do a quick ‘sanity check’ (or log check) to print out to STDIN what value is in $FLAGS? • What might $2 stand for?

19. Putting it all together • #!/bin/bash • # script to review the basic parts of a script • # takes path as arg, flags are set as a variable • # lists the path • FLAGS=“-$1” • echo $1 # show what was passed as argument • ls $FLAGS $2 • #done • [student@it136centos58vm ~]$ ./ls_script.sh /tmp

20. Questions on Scripting? • Any command in Linux is available in a script • You can use ‘loops’ or ‘control structures’ • You can create functions • You can include libraries • You can do lots of fun stuff • Even more useful after we hit regular expressions

21. Questions on Scripting? • What is the one thing that is needed in a Linux script? What’s it called and where is it located? • Once we have that one thing, what else do we put inside the script?

22. Communication Between Systems • From the command line, we can open up communications to other systems • The SSH command allows us to open a remote shell • ssh 192.168.1.100 • Replace 192.168.1.100 with any IP you want • You are unable to do this, you don’t have another VM set up at the above IP address

23. Not So Quick Aside Computers talk to each other over 'interfaces' NIC = Network Interface Card - adds a connection to a system Onboard/embedded – means it's built into the motherboard Speeds usually 1G (negotiated with switch) Linux has lo, ppp, wlan0, wlan1, etc..., eth0, eth1, etc...

24. “Corporate” Networks • Several overarching types • Not topologies – that’s for another class • Now mostly traditional and “services oriented” • Traditional is broken down into 3 ‘subnets’: • Development (Dev), Test, and Production (Prod) • Development is random, little security, considered unstable, not a priority • Test is a ‘mirror’ (or as close to as possible) of Production and is used to ensure a patch or update will not crash a network

25. “Corporate” Networks, 2 • Production is your corporate network • Hp.com is public-facing web server • If that went down, customers couldn’t contact us online – very bad! • Also, internal “mission critical” applications • Payroll, networks, firewalls, etc… • In HP’s case we have tools to help us build systems, track quotes, etc… • At BlueCross, the system that processes insurance claims are ‘production’ systems (term covers hardware and software)

26. New Networks • Google, Amazon, Facebook, etc… a new type • Services Oriented Architecture (SOA) • Each module is a ‘service’ • You connect to Amazon.com server • Amazon.com server “aggregates” search, recommendations, current product list index, current deal of the day, current ads on one display page • Then displays them • Facebook staggers updates • Will test on a subset of users • Then either push to all or rollback

27. And IPs • I used 192.168.1.100 as an example • This is a “Class C” range of IP’s = 192.x.x.x • Used heavily on home wifi devices • These ranges will depend on who implemented your network • Most businesses with an IT staff of over 50 people have a “class A” IP address range (10.x.x.x) • Small offices will use class C’s

28. Back to SSH/SCP • ssh 192.168.1.100 will connect me with the system that has that IP address, I have to know a system is there • Prompts for username and password, all of the sudden: • [ndillon@testvm ~]# • A shell! We can use that! • We can specify a user too • ssh student@192.168.1.100 will login a student user

29. Drawn Out • ssh 192.168.1.100 # from 192.168.1.50

30. SCP • What if we want to transfer files between computers? • We use scp(cp command over SSH) • scp <path1> <path2> • Simple right? Not so fast • Our file is on our system, we want to put it on the other system • scp /tmp/file.backup 192.168.1.100:/tmp

31. SCP • scp <path1> <path2> • Our file is on the other system • scp 192.168.1.100:/tmp/install.rpm /tmp • So IPAddress:/file/path is a common structure on Linux (you’ll see it elsewhere too) • I want to copy the /etc/profile file from my ‘dev’ system at 10.12.12.100 to my system – command?

32. Questions on SSH/SCP? • ? • Useful programs: Putty, WinSCP, Cygwin • These allow SSH and SCP connections from Windows • Widely used in IT • WinSCP allows FTP, SFTP, and SCP so it’s very useful • Also SecureCRT (licensed product)

33. Quick Demo • Scripting • SSH • SCP • Practical

34. Own Study • VI – Sobell p161 • Scripting – Sobell p284 • Device Communication – Sobell p687 • SSH • SCP