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System Monitoring.

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Now we are getting deep into the system administration type

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of commands or roles that you will be working

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on. If you really want to get a job in

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system administration or systems engineering or Linux related field, you

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do need to know all those system monitoring commands.

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Some of them are top, df, dmesg, iostat,

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netstat, free, and cpuinfo, and meminfo.

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All these commands will list all the system resources and

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will tell you how the system is doing, how is

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it behaving, whether it's running high or low.

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So let's look at them one by one by logging

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into our Linux machine, log into our VM console.

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All right, the top command you

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can run without being root.

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So if you notice in the top command

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once again, it has cpu information, memory information,

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it tells you which process it's on, which

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user is running, and what command it's running.

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This is again one very powerful command and you should really

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spend some time to look into every field, and I would

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highly recommend you to go look for the documentation or Google

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it and find out more information about it. If you want

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to get out of it, hit q.

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The next one we have df.

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df gives you your disk partition information.

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You could run df minus man space df,

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it tells you report file system disk usage.

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We'll run df again and it tells you

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the file system is mapped right here.

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It has this block, this is available,

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what percent is used.

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Now, the most common options that is used

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with df is -h. h is easier, it's

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human readable, it's easy to understand.

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So now it tells you we have a disk size

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at the root level, which is eight gig and 3.4

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gig is used and 4.6 is available and uses 43%,

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it also gives you a percentage, and so on

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is the memory, which is about two gig.

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And then we have a boot file system

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which when the system boots everything is located,

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and what to boot, which files to boot.

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It has one gig, and so one gig here, eight

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gig here, so nine gig, and this free memory, which is

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the swap, or virtual memory is about one gig.

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That makes it ten gigs.

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And if you remember we created our

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virtual machine with ten gig and that's

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what it's telling you, the partition information.

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If your system is dead or crashed, one of

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the things you should look into it is df

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-h output, once again df -h.

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And if the usage right here says 100%, or any of

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the usage says 100%, then definitely you are in trouble, and

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you need to free up your disk space, and you need

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to find out how to free up your disk space.

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You need another command that is you sorry, du.

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You could do man on du and learn more about it.

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It tells you the estimated file space usage,

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which file is taking up all the space.

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Next command we have dmesg.

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dmesg gives you the output of the

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system related warnings, error messages, failures or

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anything like that. When you run it,

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of course it throws bunch of error messages,

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a bunch of information at you.

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And if you want to view that one

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page at a time, what do you do?

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You pipe it to more. When you pipe it to more,

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you will see, it gives you the BIOS information,

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when the system initialized, how it went to what

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CPU, if there is any issues with the memory,

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it will report you right here.

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If there's a memory leak, if there's an

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issue with CPU that's crashed, motherboard issue.

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Anything related to your system

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hardware will be listed here.

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And this is again one of the good things that

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you should look at, if you are in system administration,

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If you are going for an interview, the interviewer

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is going to ask you give me the commands

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that you use to monitor your system.

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These are the commands, you

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should list them right away.

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And I'm telling you, he or she will

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be impressed right away that you know your

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commands, you know your system administration skills.

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The next command we will learn is iostat.

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IO stands for input and output statistics. What's

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coming in, what's going out, how we are communicating

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with our system peripheral devices or system internal devices,

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even if it's a disk or network. When you run

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it, it's going to give you the information right away

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that the disk is being used with the read per

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second, write per second, and a lot of different information.

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You could also run iostat with space

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one, which is telling it to refresh.

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Keep running it, but refresh it every 1 second.

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So it will refresh it, it will refresh it, it will keep

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telling you, keep updating you to read and write.

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If it is doing any read and write,

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it will update it as it goes.

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You could quit out of it by simply typing,

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I think you have to do control C to quit out of it.

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The next one we have netstat. netstat -rnv

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is the option that I mostly use

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if I want to find out my gateway information,

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If I wanted to find out my subnet mask, and what interface

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it is going through, this is the command I will use.

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There are other options that you could use with netstat.

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Just netstat, and if you pipe it, and you do

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more, you're going to see a lot of information.

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What is connected to your system, what has been

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disconnected, what's the process ID, which processes is it running,

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and, and the name of the owner of the process.

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So it does give you all the information.

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Once again, I apologize,

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I cannot cover every single detail.

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If I cover it, it's going to take me hours and

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hours, and days and days, to cover every single command.

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So my recommendation to you is just to simply

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man netstat, and you look into the description of

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this command, and the option of this command.

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Now please do remember, I've been doing the Linux for

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a very long time, and trust me, I myself don't

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know every single option that a command has to offer.

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If I wanted to find out or if I wanted

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to look for a specific output, then yes, then I

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will look into the options that is available.

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But it's completely understandable that not every

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person needs to remember every command or

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every option associated with every command.

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The next command we have free. free gives you your

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physical memory, and your swap space, which is a

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virtual memory, utilization, usage, and free.

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The next one we have is cat. cat is to read the

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file of cpuinfo. Every time your computer is started,

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it keeps all its system resources information into

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files and those files are located in proc.

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This proc is the directory where

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it keeps us all system information.

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So you could just do simply cat /proc/cpuinfo, you

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will find your cpu information right here.

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If you want to know your memory

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information you could do /proc/meminfo.

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Of course it's throwing all the messages, all the

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screen multiple at one shot so you could just

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do simply pipe it, and more it, and you

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will view it one page at a time.

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So these are system monitoring commands.

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You do need to remember these specific

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commands on top of your head,

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if you are going for an interview, if you're

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going for a technical interview, or even if you

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are new to Linux environment and you want to

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learn more commands by monitoring the system resources, you

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should look into these commands.

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