76 lines
4.3 KiB
Plaintext
76 lines
4.3 KiB
Plaintext
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Episode: 287
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Title: HPR0287: sysctl
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Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr0287/hpr0287.mp3
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Transcribed: 2025-10-07 15:35:22
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---
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uh
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oh
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oh
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Hello and welcome to another exciting episode of Hacker Public Radio.
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My name is Collette too and I wanted to talk a little bit about a program that I know
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a little bit about called CISCTL.
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That is S-Y-S-C-T-L.
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And if you, the easiest way to, it's a complex command but it's also kind of simple.
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I mean in that the man page is just about a screen full and that's about it.
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What CISCTL does is it allows you to configure kernel parameters at runtime.
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So anything that is being controlled by some kernel parameter or controlled by the kernel
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or has been set by the kernel, you can then modify it via CISCTL.
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So the easiest way to get an idea of the capabilities of this application is to simply type in CISCTL-A into a terminal.
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And that will list a lot of different parameters that are set within your kernel.
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Now this will include things like the reading and writing speed of your CD-ROM drive for instance.
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This would be the kernel scheduling. This would be Internet IP version 4 and IP version 6 settings.
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Just all kinds of things. It will be a very, very long list.
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And most of it is, well most of it is way beyond my understanding,
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but there are things like debugging, whether debugging for something is on or off, things like that.
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The one thing that I really use is for is CISCTL is replying to ping.
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So if you want to not reply to a ping, for instance if you're on a public network,
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if you're a bit nervous about people snooping around, sniffing out things,
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you could be a lot more invisible if you just don't reply to any ping.
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CISCTL-A, well let's find the attribute first.
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So CISCTL-A will obviously list them all, but then if you pipe it through GREP
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and just do a GREP on anything with containing the letters ICMP and hit return.
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You get about eight returns on that.
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And most of them are the net.ipv4.ICMP group.
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And one of them is net.ipv4.ICMP underscore, echo underscore, ignore underscore all, and it's equaling zero.
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So that means that this is set right now to not ignore pings.
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So if someone's pinging your IP address, you're going to respond to it like a good little computer.
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Now to turn that to switch, to flip that switch to where it will ignore them,
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you would want to simply put CISCTL-W.
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And the W is the flag to say yes and when to change an attribute here.
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And then you do net.ipv4.ICMP underscore, echo underscore, ignore underscore all,
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equals, there's no spaces here, equals one.
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And I got permission denied.
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But if I do that as root, now it is set to ignore all the pings.
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So if I go to another computer and start pinging this IP address, I will find that this IP address does not seem to exist.
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And we could try that out right now in my key.
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Hold on.
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And yes, it is expected.
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My Nokia is attempting to ping.
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And there's just no response.
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So it's kind of a nice little barrier to have between people pinging you and not responding to them.
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Now if not responding to them at all, it's something that maybe you don't need.
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You can also slow down your pinging response rate.
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I don't really do that, but I understand that it is good for servers because I guess servers could get...
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I mean, there's no reason necessarily for a server to respond right away to ping.
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And the way to do that is, again, ctl.
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And then you're going to need to set a new attribute.
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And the attribute you'll want to set is going to be net.ipv4.ICMP underscore echo reply.
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That's all one word, echo reply.
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underscore rate equals whatever, 30.
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So rather than just your computer automatically right away responding to a ping,
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it'll be a slower rate of response, which if there's not really much of a reason for people to be pinging you,
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that could probably help you out, just not tying up your server quite as much.
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So those are the two tricks I know with ctl.
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And if you know more about this command, you can certainly do an hacker public radio episode on the subject.
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Which would be very interesting.
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I just remember that ctl.a lists everything that is set right now.
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ctl.w will allow you to change or create a new key in value pair.
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And you plug that in and see what happens.
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Until next time, thanks for listening.
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Thank you for listening to hackers public radio.
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hpr is sponsored by caro.net.
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So head on over to caro.nc for all of our community.
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You
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