Introduction to Linux

Key Takeaways

hello and welcome to the sands intro to Linux video now this particular video is put together for any and all sans classes they use Linux as one of the operating systems for the various labs but we're going through the internal in exception that we provide for sans 504 hacker techniques exploits and incident handling to that end my name is John strand I am a co-author of sans 504 hacker techniques and incident handling and today I'm gonna walk you through some basic things that you'll need to get started on Linux for using the operating system for sans classes or whatever you decide to do when working with Linux now first things first don't panic ok I know a lot of you that are new to Linux are completely freaking out because you've been on like message boards online people have said well you know Linux is really really hard oh don't don't worry Linux isn't not that hard in fact it's a lot easier than a lot of other operating systems like like Windows for example a lot of people to believe that Windows is easy and Linux is hard once they start learning how Linux is structured and how its set up these learn to stop fearing the operating system also whenever you're progressing in your career you shouldn't look at operating systems kind of a religious avocation an operating system is merely a collection of tools that you use to be successful in what you do in your day to day activities and to be honest to be completely successful in computer security you have to learn how to use Linux that's why a lot of our classes like our forensics classes are network intrusion detection classes and of course our pen testing hacking and security classes use Linux so incredibly heavily now the goal of this particular section is not to make you an expert but it's just kind of get you introduced to Linux in a nice gentle way without having a bunch of people telling you to RTFM which by the way stands for read the fine manual first and foremost some ease of use shell tips okay whenever you're using Linux sometimes you'll see a linux guru just go flying through how they use their linux operating system just like my gosh how are they doing that so fast well one of the things excuse me is linux has a command history let me show you what that looks like so for our Linux demonstrations I'm going to be using the active defense harbinger distribution this is freely available you guys can download it online and it's available audit SourceForge if you just google active defense harbinger distribution feel free to play along now if I hit the up arrow you see that I have a bunch of commands in my history that's because Linux is smart enough or more accurately using bash as your command prompt but Linux is smart enough for you to basically create a history file of all the commands that you've run on that system so if you see someone that's just flying through rerunning commands it's because they're using the up arrow it's not a lot of magic it's just you know they're using the up arrow to run different commands so that's pretty neat the next thing that's available is we can also use tab autocomplete now this is absolutely essential whenever you're using Linux and it's absolutely essential if you're planning on going through some labs in various sans classes because some of these commands get really really long and you see people type them and abuse limits for a long time and it looks like they're just typing at lightning speed well that's because it's have autocomplete so if I go to my command prompt and I type cd' /i hit o P and I hit tab it autocompletes for me if I type W EB I hit tab nothing happens but watch what happens when I hit a second time shows me that there's two separate directories that have web in the front of them so if I hit L it autocompletes for me get into the habit of using tab autocomplete for everything you do when using Linux it'll help greatly reduce the amount of typos on problems that you ultimately run into you also have a history search so if I use ctrl R and then I start typing something it's gonna basically search through my history and it's gonna bring any of those commands back so let's take a look at that so if I do CD to web labyrinth and I do control R and I do CD you can see it has the history there so now all's I have to do is just hit enter and it automatically reruns the exact same command that's hitting ctrl + R at the same time and then it'll go through and show my history all right so it's very very very helpful when working with the Linux and UNIX command prompt as well now let's say I've got a whole bunch of things running on my on my screen and it's starting to get cluttered and this is gonna happen in your sans class you're gonna let a whole bunch of commands and your screens gonna have all kinds of stuff set up on it and your screens just gonna look like this and the only thing you want is just to make it a little bit cleaner if you do ctrl L bang it completely cleans it off and you now have a nice command prompt to work from now all of your files and all of the things that you type they're still present it's still there it just puts it over the top of the screen making it a lot easier sometimes it helps to clear the head clear the screen and move forward ctrl C is what will kill a current command so if I go to a file let's say I have let's do the reading if I do less read me all right I can go through the file and if I hit control C or Q it allows me to quit out of that if I run a program that's going to take a while in the computer system I can hit control C to end that particular program so if you're in less you want to get out try Q or if you're in a program that's running hit control C and it'll kill that particular program very very very helpful all right now account stuff whenever you log in but whenever you log in you're gonna have something called a prompt let me talk to you about what I prompt is promise little indication as far as who you are on the computer now by and large on most Linux computer systems when your prompt is a pound prompt that thing that looks like a tic-tac-toe game that means your root that means your Super User root is all-powerful if you have a dollar sign it means you're not rude so if I go back over to my Linux computer system and i zoom in you can see that my command prompt is a dollar sign so if I do ID it says that I am ADHD if I do Who am I it says that I am ADHD that's a dollar sign that means I am NOT fruit at the point that means I'm just a standard user nothing too terribly special about the user it's just I'm a standard user now throughout the sans classes we have a very consistent kind of iconic icon free I guess oh if you look at the notes if you need to be rude it's going to be a pound prompt if you need to be a user or you can be a user you need to do just the standard command now whenever you see commands and they start with a pound prompt or a dollar sign you do not have to type the pound prompt or the dollar sign you just type the command after it right and then also whenever you log in is not route you're going to be in a home directory of a user so it whenever I first log in as ADHD if I've type PWD for print working directory it says I'm in home ADHD that is where you go that is your home so that's what kind of happens whenever you do a Wizard of Oz moment you're going to be at home there's no place like home we'll talk more about that all right now one of the first things you're going to want to do on your Linux or UNIX computer system is change your password you're gonna need to type PA sswd now this particular command right here gives us a little bit of an indication of the mindset of people that came up with Linux and UNIX they hated typing because typing password was just far too difficult for them to type you've got a type PA sswd to change your password and this is just good practice to change your password to the VMS and the reason why is a lot of other students in the class are gonna have the exact same VM with the exact same user ID and password so change it to something that you can remember you don't have to go overboard and create a super-secret awesome password just make it long and something that you can remember we recommend passphrases at the SANS Institute now I would talked a little while ago about how I'm currently logged in to my ADHD VM as a user called ADHD now if I wish to become root I can use the su command I can use the su command if I want to know who I am I just type who am i and if I want account details I can use the ID command so let's jump over to the VM and let's run through these so the first thing is if in life you ever get lost and you don't know who you are no worries Linux has a solution to that problem you just type Who am I type Who am I I hit enter it says I'm ADHD if I want to know what types of groups and permissions and roles I have on the computer system I type ID and I'll tell me all the groups all the permissions that I am currently LA able to use but I'm not rude you see I'm gonna want to become root because a lot of labs in Santa that sans will require you to become root for those labs to do that we use s you now that stands for switch user now you can switch user to any user you want as long as you know the account name and the password you can become that account if you do not specify account it's going to assume that you want to become rude so if I do su space - - is really really really critical because in Linux and even on Windows as a matter of fact you have something called your search path and you have environmental variables whenever you use that - it tells you to bring the environmental variables of the account you wish to become that's really critical you gotta do su space - if you wish to become rude now if I do su space - it's gonna ask me for the password another way I can do this is su do su space - ask me for the password and I can type in the password for the account and now I'm Groot now some systems unsanded space - it's gonna ask you for the root password and other ones you'll be using sudo su space - where you use your own password to become ro now sudo means switch users and do something so that's is where you can use your user account to do kind of quick administrative level functions now if I do Who am I it says that I'm root if I do ID it says that I am root on the computer system so I just became root now root as I mentioned earlier is the most powerful account on your Linux and UNIX computer system let's talk about the file system structure now whenever I first logged in as student if you guys remember I was in the home I was in the home directory but now I'm logged in as Ruth what's roots home well roots home is root ok roots home is the root directory and you can see these various directories by running PWD and you can see that I'm now in the root directory that's roots home if I wish to go back a directory I can use CD or change directory dot dot that means go to the parent directory and I can type LS and it'll list out the directories there's a whole bunch of different directories here but you see that we have root we have boot we have been we have cd-rom we have mount as well so there's a number of directories that you see one of them is bin if I CD into bin and I type ls' these are all binaries or as we like to call them programs so these are the programs that you can access we have net cat we have copy we have F user which doesn't stand for what you think it does we have IP we have ifconfig all kinds of different commands available to you to use now let's talk about etc etc is really cool a one of the neat things about Linux and Unix is Linux in UNIX allow you to kind of separate your executables from the configurations of those executables so if I CD into the etc directory you're going to see a whole bunch of comp files and a whole bunch of program directories the blue ones that you see here are directories that I can access and then these other files are just standard configuration files by separating out the executables from the configuration files it actually is a very powerful concept because it makes it easier to distinguish where these things are now this is very different from Windows where you have executables you'll have configuration files and then you'll have some configuration and the registry as well it can get a bit confusing but just understand that on Linux and UNIX systems you'll have binaries executables many times those are in bin and s-pen and then you will also have configuration files and those are generally in etc as well it's pretty cool then we have Lib let's go to the Lib directory let's take a look around so now if I jump in to the Lib directory I type ls' we have a whole bunch of s or served object library files now on Linux in UNIX you have libraries and this is pretty much the same concept as Windows if you guys know dynamic link libraries or DLL files those are libraries of function functionality for your operating system and for the applications that run on Linux and UNIX same thing you have a whole bunch of libraries of functionality that can be invoked so those are your core libraries as well we also have the mount directory by CD to the mounted record I shouldn't have anything in there right now but whenever you plug in like a USB Drive or you plug in a cd-rom drive on your computer system it's going to put it into the mount directory it's going to install it in the mount directory by and large it's going to install it in the mount directory under most situations um and other situations is going to put it into other directories like my version of an boon to here on the ad/hd instance has something called cd-rom if I put it in a cd-rom it's gonna show up there USB many times will show up in media as well they'll show up in different places and that's different from different flavors of Linux and UNIX one of the things that I don't like about a lot of newer versions of Linux and UNIX everything should be in mount but they're trying to put it into other files and directories to make it easier for users we also have the proc directory a proc is kind of interesting because proc actually doesn't really exist on the hard drive if I type LS and proc you see all of these numbers all of these numbers are the process IDs for the various processes that are executing on my computer system so if I CD 214 i type LS you can see we've got the executable we've got root we got the page mount IO latency the prog file system exists whenever the computer is running now you don't really have to worry about a lot of this for most of your sans classes it's just good to know temp is for temporary temporary files and of course you'll have user binaries man pages which we're going to talk about here in a bit and service binaries and then of course var for variable files and that's where the vast majority of your logs exist on Linux and UNIX right so navigating the file system you've seen me running these commands it's the CD command change directory command is what you'll use to navigate around the file system very very similar to what we do on Windows as well now if I go CD - let's say forward slash that takes me to the top of the directory structure on the file system and then I can work down from there so I can just CD that if I do CD by itself it takes me home so if I do PWD print working directory you can see that I'm in the root directory so very very easy to use and I can do CD space dot dot to go up one directory and lo and behold I'm back at the top of the directory structure makes it very very easy for you to navigate around and you can also instead of doing CD space or CD enter you can do CD space tilde which will take you back to your home directory as well now you've seen me looking at the contents of directories I can list out the contents of directories with the LS command so let's go ahead and let's play around with that just a little bit if I just type LS by itself it's going to list out all the contents of the directory however if I do LS space minus a it's gonna show me all the files and notice how there's really no difference files that we see with the LS command are the same that I saw with the LS - a command but watch what happens when I go to routes home directory if I do LS space minus a you see all these dot files these are called hidden files now that doesn't mean that they're evil it just means that they're files that you generally don't use very often their configuration data the cache logs for individual commands that you use so it just kind of suppresses that information from you so if i type LS epsilon if i type LS it shows me the files that would be of interest to me if I do LS space minus a it shows me all of the quote unquote hidden files and directories as well and once again please don't look at hidden as though they are absolutely evil also on my version of Linux you can see that we have different directory colors you can see that on my system the directories are blue and the individual files are black and you can see that I have red files for like dead packages that I can install your colors are going to change based on the tie of the Linux operating system that you are in fact using we also have absolute and relative referencing of files I just want to show you guys this one really quick so if I go back to the command prompt and I go CD space /opt I'm starting at the top-level directory and then if I do web Labyrinth that takes me into the web labyrinth directory I'm doing the full explicit path of that directory alright now I can goo CD space /opt and now I'm in the OP directory and then I could do CD web labyrinth web labyrinth notice I didn't have to do the forward slash at the beginning because I'm already in the optic referee you'll only start with the forward slash if you're starting at the very top of the directory structure ejecting the CD or ejecting USB you really want to get into the habit of ejecting various devices that you insert Linux is not at Linux and UNIX and Mac's just aren't nearly as forgiving about just yanking a USB Drive out or just you know ejecting a CD without you know typing the eject command first so you want to be nice and tell it to eject it making directories is the same way that you do it in Windows if I go CD home which brought me back to the root directory I can do make der make der and then I can do hello but you make der hello I have just created a Hello directory I can change directories into that hello directory they're very easy to create directories as you need alright copying files is very very very similar to Windows you simply copy from source to the destination except it's not typing out copy once again remember the people that came up with Linux and UNIX they flat-out hated typing so instead of typing copy we just do CP so you can see that I'm in the hello directory let's say I want to download or pull this ql proxy file into the hello directory I can do let's go copy root and then I can do ql proxy caf deb and then dot that that dot means we're gonna copy that ql proxy deb file and the dot directory is the current directory so i do it LS and sure enough it copied that file to the current directory so it's CP source and destination CP source and destination now on linux and unix there's this really cool feature where it goes through and it indexes the entire it indexes all the files on the hard drive and you can search for those fraud files so if i do locate and I do LS it's going let's do something else let's do a spider locate spider it's going through and it's finding every single file with the word spider in it it's a really quick index search of all these files on the system now you might get an error on some of your Linux distributions for classes now if you do if you do get something like since the database is currently 23 days out of date or a year out of date just run the update DB command and it reinvents is all of the files on your hard drive and then you can find things pretty well now sometimes you want to have a more exhaustive search so I can do fine start at the top level directory and then name this is allowing me to restrict my search to just the thought just the file name so if you notice if I ran spider with locate it brought back any file with spider in the name now if I do the - name with the find command it's just gonna pop by into the file with that specific name so if we do that we do find and we do forward slash start at the top level directory name and we'll do spider let's just do Who am I stick with the book now it's going to exhaustively search the entire file system looking for any file with the entire name is who am i it's a very very very cool powerful command to find where things are located now on linux and unix you have to choose which type of editor you want to use you can use G edit of course but there's a whole number of other editors that exist VI Emacs Pico Nano tons of them out there for people that are just getting started with Len unikz we recommend that you use G at it and most of the classes will have G at it and G edit is nice because it has like full word pad type capabilities you can use your mouse and navigate around easily but at some point you're going to have to learn another editor and I recommend VI VI is a very very powerful editor so let's go ahead and let's play around with VI really quick so I'm gonna CD back to my home directory for rude and we're gonna clear our screen with ctrl L and I'm going to create a file and a touch of file called high alright so I touch hi highest creative I don't think I do have G edit if I do G at it high the G edit editor is going to open up and as you can see it's really not that bad I can type stuff in I can move the cursor around it's just like you would normally and I can save it so go file save not too bad but as I said you really need to learn VI VI is just one of the kind of the stalwarts of the Linux and UNIX world I can do VI is another editor and I can edit the high file so I do VI and I can do was it hello yeah hi do VI hi and there's my file now I can edit this in a number of different ways the first thing you got to understand is when you're working in VI we recommend hitting the a key to allow you to type in additional things into the file and you can delete and you can add things your your mouse isn't gonna work for moving you around visual editor is merely a text-based editor and we can do all of the editing that we need to do now if you're done editing a file with VI you have to hit the Escape key and then you have to hold shift and then the the colon or semicolon key it's right to the right of the L on your computer and it's gonna bring this little prompt up at the lower left hand corner and then you can hit Q to quit or you can do WQ to write and quit so we've changed that file and I do shift : WQ enter and I am now there's a lot of there's a lot more that you can do with VI just to be completely clear there's a lot more that you can do with VI however um it's more than we can go into in this but I'd recommend just doing a google search for a VI cheat sheet and there's of EIT cheats out there to get you started if we ever want to view the contents of the file I can use cat to look at that file so I can do cat and I can run hi cat hi and there's the contents of the file cat stands for concatenate not cow get not like cat like we have two completely different things cat means concatenate out the contents of that file and I could also use less to we'll talk about less more a little bit later but there's a number of ways to do the exact same thing in Linux and UNIX now the less command as I said we'd talk about that a little bit more years ago when they had the more command the more command wouldn't allow you to do things like searches would allow you to move back and forth in the buffer so by and large if you want to edit a file very easily you can use the less command to do so unless if we talked about it on the one of the very first slides is you can use queue to get out of less so if I go through and I can chain commands together let me show you how that works if I run a command that's going to take just a tremendous amount of data and kick it out I can do LS dev and bam we've got a whole bunch of different things in dev well that could be kind of a bit crazy so I can take that output and I can pipe it so I can do LS dev space and the pipe key is the little key that's right above the enter key on your keyboard and then I can pipe that through less and it allow me to go up and down and it presents that data in a way that goes by slower so I can go through it once again queue allows me to exit out of the less command all right so let's talk about running programs in your path now let's play around a little bit with the path and what it is so if I do echo dollar sign path it's going to show me the search path and it helps to actually type echo correctly these are all the directories that well the operating system will automatically search through to try and find the program I'm trying to run so if i type LS LS is an in my current directory however if I do which LS you see that LS is in the bin directory and sure enough you can see the bin directory is in my search path so this makes it so you don't have to type the exact command every single time you run it you can just type LS and it'll automatically run bin LS for you so very very powerful very very easy to try to run programs on your computer system now if you want to run programs that are not in your path the current directory is not in your path on most Linux and UNIX computer systems let me show you what that means so if I go to a program let's go CD opt and let's do spider trap if I do spider trap you can see I have a no that would be a bad one let's go to which one is a set executable how about keepo oh no that's Python 2 let's do set all right so if I go to the set directory for the social engineering toolkit my type LS you can see that we have an executable here called set and I just type set it just dumps that to the screen that's not very cool at all so if I do dot /set it actually executes that program so you want to you want to be able to execute the program in the current directory rather than the overall set command that would execute so if I do which set it's not gonna bring back anything it's not gonna find anything now if I do dot /set it executes sit so this allows us to execute files in the current directory this is one of the more frustrating things for people that just get started using Linux and UNIX because they want to run a program like they do on Windows you just go to the directory and you execute it know on Linux in UNIX you have to do the dot forward slash first and the reason why is really this is ultimately a security issue years ago people would create backdoor Trojans and little evil programs and if you ran like the LS command it would execute the LS command of the current directory and they would take over the computer like wasn't good dogs and cats were living together so they got rid of the current directory as an executable path and now you have to be explicit dot towards the left dot forward slash in the program now if you wish to edit your path and we strongly recommend you do this until you've gotten some miles underneath you using Linux and UNIX you can do path equals dollar sign path which is your current path : and then you can add an additional directory so it can search through that directory if you want to see what's running on your computer this is kind of cool on on Linux and UNIX systems I can run the the PS command let me show you what that looks like I do PS these are the processes that I can see that I'm currently executing you see I got sudo su bash and PS however if a new PS space AAA UX it's going to show me all processes sorted by user including the ones associated with the teletype terminal or sudo teletype terminal so now we got a whole bunch of a whole bunch of additional programs that are running which is pretty darn knee the next thing you can do is you can do tough and what top does is it's very similar to task manager on Windows and whenever top is running it updates like every few seconds and it shows you all the programs that are running now this is very very useful when you're looking for malware it's very very useful if you have a process that's hit or hung and to get out of it just hit the Q key and it breaks you out and you're back to life being normal very very cool to see the processes that are running all right so let's talk about some networking stuff the most important command on your one of your taking sans classes is ifconfig now ifconfig will show you your current network adapter interface IP address so you can see that mine is eat 0 yours might be different but it's 10 12 1 186 pretty neat I can also change this to whatever I want it to be I can do ifconfig and I can do eth0 the Ethernet adapter that you see here and I can give it a new IP address let's just give it an IP address of 10 10 10 not 10 ok I hit enter and now I've officially changed my IP address to be 10 10 10 10 now some of your classes are going to use DHCP to do that just do de-age client and then your Ethernet adapter and it'll get you a new IP address you can see I have 10 done 10 10 again and I may not have a DHCP server running inside this VM but d.h client works great for getting you an IP address now if I want to change my IP address back I can just go back and I can grab that IP address that 1012 1 186 I'd simply highlight it right click copy don't use control-c because that'll actually like kill your current command and I'll do I have config and then I'll do eth0 then I can put back in that IP address that was up above there we go my IP address has changed back to 1012 1 1 186 pretty cool next we can ping remote systems now I have this kind of troubleshooting series of steps that I go through in sans classes called ping port parse first if you're having trouble connecting to a server or making something work ping the remote system to make sure that it's accessible then make sure the port is open and nmap is a great tool and you'll learn about nmap in your classes and then parse any error messages that you receive so if i want to find out if Google's DNS servers are up and running all's I need to do is do ping 8888 hit enter sure enough it is responsive so you can see ping 888 I'm getting a response you can also ping by like names like a new WWE yahoo.com you see yahoo comm is responding but if I die yahoo DG it's gonna say unknown host so it's a good way to find out if a system is alive or if a system is dead or not accessible to you if we don't want to look at network usage there's a couple of commands you can run you can run net stat net stat - like na will show me all of the open network connections and net stat is kind of nice but I personally prefer El SOF space - space - capital P I'll show me all the ports what services are associated with them and of course whether I'm listing or I'm talking to a remote computer system l SOF is a very very powerful command that you can use now let's talk about building tools now on different Linux and UNIX based systems you have something called tarballs whenever you're trying to install different programs or move large file sets over this was created years ago to make life much much much easier for administrators because they used to have to copy files over one at a time or write a program to do it it was just a pain so what at our archive does is it takes all of these different files and it can like binds them together into one file we call it a tarball now on some of your classes you're going to have to extract tar archives if you want to extract the tar archive you just do tar xvf to go ahead and it distract that tar archive now some of your tire archives are going to be compressed if they're compressed they'll have like a GZ or a tgz at the end for that you just need to do tar xvf z and it'll automatically decompress and extract the archive for you sometimes you'll be in a situation where you have to install some tools and configure make make install allows you to configure the particular tools code so it matches your specific architecture your specific CPU your specific architecture of Linux and then make and make install allow you to install that program to the appropriate directories on your system some tools all you have to do is just straight up make some of them merge is very straightforward but trust me and whatever sans class you're taking they'll be very explicit about how you're supposed to install your programs talk about other odds and ends so the grep command allows you to search for a specific string and you can also use regular expressions and all kinds of additional things so if I wanted to find all the files in the current directory that contain the word root I could do grep root that's the string I'm looking for star and star means all the files in the current directory very very powerful command to find different things so if I wanted to find all of the listening ports on port 7777 I could do net stat space - n AP I can pipe that through grep and then I can pull out anything that has 777 in it or I can find any bash programs that are running now one of the coolest things about Linux and UNIX is there's something called the man pages installed on Linux and UNIX it was really neat about the man pages is there a little manual for all of the programs that exists so let's pop on over to my system let's say you see that in the class we're using a tool called nmap Wow what's n mapless have to do we can do man n map and it'll open up the reference guide for n map and you can see oh well nmap is a network exploration tool security and port scanner and talks about a description of what n map does common example usage options that are available now many times when you go online and you have a question you go to like a form and you'll type in you know how do I use this particular command they'll tell you to RTFM now whenever they're telling you to RTFM they're telling you to read the find manual and that in fact is the find manual for n map I've got a man page for the LS command I've got man pages for the man page as well so there's all kinds of different manual pages and this is one of those things that just makes Linux so awesome and easy to use because it has user manuals built into it which is just great now if you just want a quick hint what does something do you can use what is a command and we'll give you just a quick update on what that particular program does instead of giving you the entire man page now the other thing that you can do is you can try to find every single command that is associated with a particular topic like networking so you can use apropos network and we'll bring back any of the programs that has networking in the description of that or you can use man - ok finally shutting down if we want to shut down our computer system and just kind of close it out at the end end of the day we can just use shut down and then we can do - H and it will halt the system so you do shut down - H now and it's going to go through the process of making my computer system go night-night and that's putting the active defence harbinger' distribution to sleep so it just shut the computer system down so Linux is a very very powerful operating system I hope that you don't just use it for whatever class you're teaching but I hope that excuse me whatever class you're taking I hope that you get the opportunity to get to know and love this operating system and a couple of tips first I recommend that you download a distribution like umbuntu or linux mint or something that's really user accessible a you make that your distribution that you use on your computer I kind of get yourself away from using Windows for everything um you can either install it on your computer directly or you could just run it inside of a virtual machine for getting started I recommend you download VMware Player and just get started using it inside of a virtual machine that would be best for now but really try to do things like surf the internet watch youtube videos try to gain access to your email try to make your wireless USB cards work really just sit down and try to do things with the operating system because the best way to learn how to use Linux is just to use it and that as you use it you continue to use it more you get more and more adept at it and you're going to start having a very good time it's a great operating system and you're gonna get a lot of mileage out of it in whatever sans class it is that you're tanking thank you so much for your time today my name is John strand I am a co-author of sans 504 hacker techniques exploits an incident handling and I hope to see you at a sans conference in the very near future thanks again