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I'm not a power user; I don't get too much time to learn about command lines. I'm using Ubuntu to browse the web, play the Steam for Linux beta, and do some image editing.

I recently installed avast!, but in order for it to function properly, I was told that I needed to edit /etc/sysctl.conf and add kernel.shmmax = 128000000. So I'm wondering: How do I know if a command is safe? Sure it fixes my problem, but what else does it do? If a user with more than 5k rep uses it, does it mean that any command he gives you is trustworthy? I'm not gonna enter every command I see. I'd just like to know if a simple command (as the one said before) could open a window to an invasion or any other vulnerability. I didn't find anything on Google about that command, so is it safe?

I'm too nervous about getting hacked. On Windows I had Kaspersky Internet Security, now I'm alone with avast and clamtk (both only scan by demand) and bitdefender (bootable CD). My games and software are all genuine, but I torrent legal content. I just want some additional reassuring.


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closed as not a real question by Tom Brossman, RobotHumans, Alvar, Ringtail, stephenmyall Dec 30 '12 at 0:48

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

Generally google is your friend.… was the second google result and explains what kernel.shmmax is and does. – RobotHumans Dec 29 '12 at 22:49
Thank you Abraham. I was looking for the command itself, not what the kernel.shmmax does. My mistake. – Amanda Dec 29 '12 at 22:51
As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or specific expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, see the FAQ for guidance. – Ringtail Dec 29 '12 at 22:51
@Amanda - I'm fairly confident this question is about to get hammered with closevotes...and for valid reason. The best comments/answers you could have gotten have already been provided. I'ld accept that answer that is here. – RobotHumans Dec 29 '12 at 22:58
@Abraham - Yeah, even Ubuntu community can be that harsh sometimes. Got it. – Amanda Dec 29 '12 at 23:04
up vote 4 down vote accepted

Generally editing a system file means that you're sacrificing security for functionality, the only way to know for sure if something is safe is to either have knowledge of Linux yourself or to trust someone with a good reputation.

But on the subject of security, Linux is by far the most secure OS you could choose. Add on to that the fact that because of it's low userbase, desktop linux distros are hardly ever targeted by a virus and the inherent differences between different distros makes developing viruses more complicated and less worth it in the eyes of hackers. Your more at risk from Browser exploits. Generally if you just install and setup a Firewall (like ufw) and keep your Browser and Plug-Ins updated your fine. Also make sure to download updates to Ubuntu as often as you can. It's all Free and very low profile. You don't even need Avast as what I suggested above is fine. Virus Scanners aren't very useful on Linux in my experience and I've never run into a virus in my 3+ years of using Linux as my primary OS.

Just Relax and stop being paranoid. The best defence against attacks is to be wise of what you click on the Internet.

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Thank you. I'm using avast to scan my PC for Windows viruses, as I connect my mobile on it and on other PC's, so even if Linux is invulnerable to Windows viruses I don't want to infect other machines. PS: Is the firewall you said easy-to-use and configurable? Because I installed some firewall a couple of months back and the only options were: block/allown income - block/allow outcome. – Amanda Dec 29 '12 at 22:50
@Amanda That's what a Firewall is supposed to do. You limit the connections and keep all the ports closed until you need one open. On Windows all the Virus Suites have a lot of bloated features and don't actually help in the end(and even slow down your PC). On Linux you'll be prompted whenever a program wishes to have Root(aka:System) access so that covers those "Program Intercept" features that fancy Firewall programs provide. Basically Linux was designed from the ground up to be inherently secure – japzone Dec 29 '12 at 22:59

This four letter word is pretty much the one you gotta watch out for:


This is when you really need to understand what you are doing or trust what you are doing. For most other tasks, you are ok if you stick to running software from the repos.

As a beginning user, where fundamental changes to the system are up for consideration, where these changes are not well documented or untrusted, I suggest you use remastersys to first create a live bootable dvd backup of the present state of your system.

Instead of testing on your installed system, boot your back up. Now you can play around with a mirror of your existing system without really hurting anything because it only affects things in a live environment.

If you do commit to changes on your installed version, but later on you notice some bugs, you can fall back to your remastersys dvd. It will allow you to reinstall your back up to your hard drive and regain the stability that was compromised.

sudo apt-get install remastersys

I wish I had it when I was a newbie. Can't go without it now.

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Thanks. Funny because you told me to care about sudo, and gave me a sudo command. I guess I'll do some research on that command, and if all point to a safe moethod, I'll sure use the live to test. Thank you. – Amanda Dec 30 '12 at 6:12

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