Kill Command (Demo)
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Video Transcription
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>> Hey Cybrarians and welcome back to
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the Linux+ Course here at Cybrary.
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I'm your instructor Rob Goelz and in
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today's lesson we're going to be covering
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the kill command.
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Upon completion of this lesson,
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you are going to be able to understand
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why the kill command is important.
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We're going to talk about the common types of
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kill commands and process signals and
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then we'll use some kill commands to
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terminate processes during demo time.
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The kill command is a sysadmins best friend?
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Yes, it is.
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The kill commands and processing signals are
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tremendously important in dealing with processes.
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At some point in your professional career,
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you will have to deal with a bad process.
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It could be that your colleague
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ran off and left something
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nohup running in the
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>> background now it's causing issues.
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>> You've got a user job that crashed and it
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stranded a bunch of child processes behind
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creating zombies or maybe you have
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a process that's just leaking
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>> memory all over the system.
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>> Knowing the appropriate kill command
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or signal to use is important.
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It's going to save you a lot of problems down the road.
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Now, we cover processes a lot more in Module 22,
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but for now, recall we
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covered the top command in module 11.
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Top is going to show the process ID
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or PID for each running process.
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We can then pass that PID for
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the process to the kill command
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>> in order to terminate it.
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>> We can just run kill and then the PID, the process ID.
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But if we don't know the PID,
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but we do know the process name,
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we can run another kill command
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which is called pkill or process kill.
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The pkill command will kill
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all processes related to a process name.
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For example, if we wanted to
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kill all of the CUPS related processes,
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all the printer related processes, remember CUPS,
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common unix printing system,
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we could run P kill CUPS and that will kill all of
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the printer related processes on the system.
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Now we saw this in the last lesson.
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There are few process signals.
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We talked about single hang up,
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which hangs up and cleans up
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a terminal after log out to make sure that there's
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no user processes running after they exit this session.
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The signal interrupt or
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SIGINT quits a running process on the terminal.
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We use Control Z to run a SIGNIT.
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SIGSTP, which is process ID 19, stops a process.
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Puts that process memory,
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essentially pauses it, We do that with Control Z.
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But the kill command can also
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accept processed signals and
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it has two specific process signals of its own.
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If you run the kill command with
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just the kill command and the process ID,
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it runs a SIGTERM,
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or single ID 15 by default.
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SIGTERM tells a process to terminate gracefully.
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SIGKILL 9 is the brute force kill.
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It's called the kill-9 and then the PID.
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SIGKILL kills a process
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without waiting for it to exit gracefully.
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It can leave files and and handles open
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and causes issues sometimes,
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but unfortunately sometimes that's your only option,
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is just to kill with fire.
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Let's take a look at doing this with some demo time.
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Here we are in our CentOS environment and let's
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go ahead and start some processes
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running them in the background.
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I'm going to start up Firefox,
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and I'm going to put it in
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the background by running ampersand.
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Remember that's how we background
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processes and we'll see that startup and then I'm
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going to go back over here to
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my screen and we're
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also going to run in the background Nautilus,
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which is the file manager.
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Run nautilus &,
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and that will start that running in the background.
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When this starts up, it actually tells us the job ID as
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well as the PID but if we didn't have the process ID,
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we could get that by running the PS or top command.
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I'm going to jump ahead a little bit and use
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the PS command because I like that a lot.
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We're just going to run ps aux
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and then we could do a grep for, let's say firefox.
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Let's find out what the PIDs are for Firefox. Oh wow.
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We can see that it actually started
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quite a bit of process ID is right.
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I thought for 5078,
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it's spawned a bunch of child processes as well.
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If we do the same thing,
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we do at ps aux and grep for nautilus.
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We can see the process ID there as well, the 5346.
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You'll also sometimes see a line for grep
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because basically our grep is using the word Nautilus.
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You just disregard that.
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A lot of times when I run this,
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I'll actually do a grep minus V
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on grep just to make sure that I don't get
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an extra line here that isn't
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the process ID because sometimes they can screw you up.
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But anyway, we can see that
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the Firefox process spawned a bunch of child processes.
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In this case, it would be easiest to use
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the pkill command and just
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>> get them all at the same time.
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>> What we can do to do that,
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let's clear our screen and then we'll run
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pkill and then firefox.
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Now we can see that firefox is
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gone. Died in the background.
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We can also use ps aux
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grep firefox and now all we see is my grep command.
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Again, I can get rid of that.
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I Just want to do a grep minus V. For the word grep,
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we see nothing has returned.
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There's no Firefox running here.
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We found the process ID for Nautilus here.
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We'll just do this again.
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We see that that's 5346.
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Now we could kill it normally.
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We just do kill 5346,
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but let's have a little bit of fun
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and kill it with kill-9.
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Kill-9, 5346 and that kills it immediately.
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We see that it's killed and we get our screen back.
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We saw that some of that Nautilus process
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in the background, that window close.
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If we run ps aux grep nautilus again,
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we'll see that nothing is running.
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But with that, we've reached into this lesson.
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In this lesson we covered the importance
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of the kill command in Linux.
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We talked about the different types
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of kill commands and the process,
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signals for kill and then we talked about how to
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find and kill a process during our demo time.
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Thanks so much for being here and I look
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forward to seeing you in the next lesson.
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