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Hey guys and welcome back. So in the previous nuggets we had talked about how we could modify

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our run levels. We could use the command init as well as tell init which would be the preferred

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method and as opposed to being able to change our particular run level we could also modify what

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particular services were starting or stopped during a particular run level. Now the way we

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actually saw this was by renaming simlinks. So we would ultimately move a particular simlink to

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rename it and if it started with an s we could change it to begin with a k and ultimately modify

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the behavior. Now this is not the most practical way to do such a thing and we do have different

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commands that we can use to ultimately modify and determine when services are started or stopped.

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Now we have two commands the first one is called check config or chk config. This command is going

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to be based on red hat based systems so on your Ubuntu machine this command is not going to be

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present instead if you're using a debian based machines such as ubuntu or ubuntu the command

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we're going to use instead will be update in fact let me just write that a little bit clearer hyphen

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rc.d now this actually looks like a directory but no indeed this is actually the command you would

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use on a debian based system so right now I want to demonstrate the check config command and as we

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know this is not available on a debian based system so what I've actually done in the meantime is

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I've actually booted up a rocky linux distribution which I have on my computer now rocky linux happens

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to come from red hat so because it is red hat based we're going to have the check config command so

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if I go into the man page for check config we can see this utility updates in queries run level

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information for system services now we have all of these different options we can go through

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but one thing I will say is that when we try to use this command such as check config dash

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dash list in fact I would help if I could type this correctly so check config notice we have

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some crucial information it says here the sysv configuration data might be overridden by the

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native system d pretty much what I'm saying is that whilst this command is actually available here

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we have a man page for it because we are now using modern system d we're actually not really getting

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the outputs from the check config dash dash list option which is a little bit unfortunate like I say

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this is a bit of a problem when we're dealing with such old legacy based systems but for the purposes

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of the examination you just want to be able to understand the basic syntax now ordinarily if we

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were on a much older machine this command would actually output the particular service such as

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maybe network manager and it would also tell you for every single run level if this service is on

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or off so you might see zero for run level zero and then the word off of course run level zero

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as a shutdown state so that would make sense but we would also have one for run level one that could

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also be off and then two and three and four all the way up to six you kind of get the drift maybe

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you'll see on number three that the network manager is on perhaps and the output of this command would

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show you this information for all of the services on the system so you would be able to determine

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from that output oh that service is switched on at run level five for example but switched off at

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run level three and with this command what you can also do is modify this setting so let's maybe say

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you were on a particular system and the bluetooth service was switched off so pretty much you did

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your check config list and you saw for all the run levels bluetooth was off what you then could do

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is you could take the command check config bluetooth on and then hit enter now as it transpires this

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is not going to work on my modern based system but nevertheless for the purposes of the examination

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this would be the syntax you would use and if you wanted to switch it off we could just say

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off now if you wanted to control a particular service and for run level three we could switch

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that service on now if you wanted to change a particular service turn it on or turn it off

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but at a specific run level the check config command would also allow you to do that you could

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say something like say check config network manager to take the network manager service

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you can say dash dash level three for example and turn it on for level three then if you happen to

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confirm this by using your dash dash list command suddenly for the network manager service you would

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see for run level three this was on or if you wanted to turn it off you could do a very similar

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thing you could just say you know check config for network manager at run level three i want to turn

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it off so check config makes this really quite easy to be able to manage these types of services

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as opposed to you manually having to go in and rename all of these sim links which is really

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quite messy now like i say this would be the solution you would use on a red hat based system

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let me just turn off this machine here okay and let me open up my zubuntu machine okay so we go

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back to our zubuntu machine if i go into the man page for update hyphen rc.d we can see this is used

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to remove and install system v style init script links so if we go down to the example you can see

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some of the example syntax we can use and what we can also do is we can actually use the update rc

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command to specify which levels to start or stop a particular script so what i could say here for

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example i could say updates hyphen rc.d which is the command and then give the name of the service

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that may be be something let's say an Apache 2 server and i could start that and then i'll give a

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priority value let's just maybe see 10 and then i can specify the run levels where i would want the

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Apache 2 service to actually start so i could say at run level 2 3 4 and 5 we would want it to start

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and then i can do a dot to separate this out and then say we would want this service to stop at

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run level 0 which is shut down also at run level 1 and run level 6 of course because that is the

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reboot state and then another dot and suddenly with a lot of granular control we can specify

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whether a particular service starts at all these different run levels and when it should be stopped

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so again if i decided that you know what i only wanted to run at run level 5 i could start it at

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run level 5 and make sure it's stopping at 2 3 4 as well as obviously 0 and 6 now like i say the

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big disadvantage here is that these tools are pretty much antiquated and this is the frustrating

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part at least in my opinion with its heavy presence in the lpik 2 examination but nevertheless even

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though we are almost always using system d based systems in modern linux system administration

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we do have to be aware of these legacy tools and these legacy systems so we have the update rc.d

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command on debian based systems again this is going to allow you to control what particular

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services are starting and stopping at particular run levels and with red hat based systems we can

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do a similar thing with the check config command now these two commands ultimately do very very

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similar things but as we can see here the syntax is a little bit different so i really would encourage

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you to read demand pages in their entirety to help you understand the differences with respect to

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the syntax and the options that each command provides okay dox i hope this has been informative

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for you and i'd like to thank you for viewing