If you've ever been in charge of a network you've definitely had the need for a secure remote connection. Maybe you just need to keep an eye on employees or kids. Doing so can be a hassle to some while crossing networks and subnets. On top of that, many businesses may have Internet but no DHCP to more protected machines. Many do this to network machines while keeping employees from surfing the Web. Whatever the case, Linux has many great tools to enable remote encrypted GUI administration. Even better, we will get everything we need for free for accessing a Linux or Windows client.
You should have root privileges on the machine you wish to monitor from as well as on the clients. You are not required to have administrator rights on a Windows client if you can at least enable remote desktop. To follow this tutorial you can use virtual machines if you do not have physical clients to test on. As long as you have the rights above and an IP address you should be fine.
While I've already mentioned legitimate purposes for this tutorial, it can be abused. The purpose of this writing is to help people network their own machines. Please use this information for legal monitoring of clients only!
Setting up our host
The first thing you should do is download the necessary packages with apt-get, if you're on Debian or derivatives:
# apt-get install xrdp openssh-server
After that we need to do some configuration to make sure our ssh server runs correctly. In a terminal type "ssh-keygen" to create the rsa keys for encryption. You will see some ascii art go by and then it's done. Most likely your rsa keys will be stored in /home//username/.ssh/ if you ever need to find them.
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For most of us WEP encryption has become a joke. WPA is quickly going the same way thanks to many tools such as Aircrack-ng. On top of this, wired networks are no strangers to unwanted guests as well. Anyone serious about security should have a good Intrusion Detection system in their toolbox.
There are already some very good IDS's (Intrusion Detection Systems) available. Why would anyone want to re-invent the wheel in Bash??? There are a couple of reasons for this. Obviously Bash scripts can be very light weight. Especially compared to some of the GUI programs that are out there. While programs like Etherape suck us in with pretty colors, they require constant monitoring to know when the network has changed. If you are like most of us, you only use the computer for two things, work and play. By using the system bell to alert for new clients online you can leave this script running and not have to have a constant watch. If you do decide you want to inspect what a suspicious client is doing more closely, you can always open up etherape, wireshark, or your tool of choice. But until you have a problem you can play or work on other things.
Another bonus to this program is that it will only show ip addresses on the networks connected to your computer. If you were hosting a busy server or perhaps downloading the latest Linux distro though a torrent client, an IDS may be flooded with connections. Looking for a new malicious client can be like looking for a needle in a hay stack. While this script may seem simple compared to other IDS's, simplicity can have its perks too.
What you will need
Nmap is required for this script to work. We will not be doing any port scanning. However, to make this script fast we needed something better than a regular ping. Nmap's -sP parameter will only use a ping scan to check if a clients up. There were some variations in how Nmap outputs information between versions. So far this script has only been tested using Nmap 5.00 (Debian Squeeze) and 5.21 (Debian Sid). You may have luck with other distros and versions of Nmap. However, with all the possibilities I could only support a couple at this time.
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When navigating the Linux file system you are sure to encounter different file types. The most used and obvious file types are regular files and directories. However, the Linux operating system has more to offer in terms of file types as it also includes another 5 file types. This short article will help you to recognize all the 7 different file types within the Linux operating system.
Identifying Linux File types
There is only 1 command you need to know, which will help you to identify and categorize all the seven different file types found on the Linux system.
$ ls -ld <file name>
Here is an example output of the above command.
$ ls -ld /etc/services
-rw-r--r-- 1 root root 19281 Feb 14 2012 /etc/services
ls command will show the file type as an encoded symbol found as the first character of the file permission part. In this case it is "-", which means "regular file". It is important to point out that Linux file types are not to be mistaken with file extensions. Let us have a look at a short summary of all the seven different types of Linux file types and ls command identifiers:
- - : regular file
- d : directory
- c : character device file
- b : block device file
- s : local socket file
- p : named pipe
- l : symbolic link
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If you ask around about Gentoo, chances are you will get mixed reviews : some will say it's a waste of time, others will say it's only for ubergeeks, yet others will tell you it's the only way, but no one can deny the power that Gentoo offers in terms of choices and speed. Gentoo is a rolling release distribution, which means it has no release numbers and it's updated continuously.Gentoo is also a source-based distribution, which means that everything you install you must compile first. What Gentoo is not : it certainly isn't for everyone. If you prefer the comfort of binary package managers that install desired software on-the-fly, if you like to install your distro in an hour or so, then you might not like Gentoo. That being said, if you're curious, aren't afraid of the command line and some compilation, if you want to have your system just the way you want it or you just want to be more 1337, this article is just what you need. You will learn how to install, what to install, how to get the most out of your system and of course have some fun in the process. We must warn you before we start : Gentoo has some of the best written documentation of all the Linux distributions and this article cannot and does not want to take its place, by no means. Although you will have a working Gentoo system after going through our tutorial, you are advised to read the handbook and all other sections of general interest, like Portage (the software management tool), for example. That said, let's get ready and start installing Gentoo.
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System monitoring is an important aspect of any more-or-less advanced Linux user, because there comes a time when you want to know what is taking precious resources or simply how much it does take. And despite what some people think, this is not applicable only to server systems. Desktop applications go haywire too, and you find your system slowed down to a crawl because some "rogue" app decided to eat up all your memory. For enterprise users there are lots of potent free or commercial solutions for monitoring, but for the old-school Linux user and/or someone that prefers to keep it simple, there is always top(1). If you're somewhat familiar with the command line, you will probably benefit more from this article, but that doesn't mean GUI-centric users won't.
Frequently used options
Command line options
- -d delay
This option specifies delay in seconds between top's updates
- -p pid
Monitoring a specific PID ( process ID )
- -b <number>
This is a batch mode usually used to log top's output.
- -n iter
Specifies a number of updates required. For example to log top's single output this option can be combined with -b top -n 1 -b > top.log
top's internal commands
- H or ?
Displays top's keystrokes help
Kill process. Top command will ask for a PID of a process to kill.
Change process priority same by functionality as renice command
Change update rate. This is in number of seconds: 1, 0.5 and etc.
This command sorts all displayed processes by CPU usage
Same as above but sorts by Memory usage
Quit from top
You might've noticed we said nothing about installing top. That's because it's usually already installed in your distribution, and it's even to be found in a Gentoo minimal install. If you remember, top is not strange to us, as we mentioned it before, except now it's gonna receive more attention and you will get more examples and real-life use cases. As before in our Linux commands series, our main inspiration source are the manual pages, and we recommend you take a look at'em too, as these series aren't a substitute.
Actually, top can do more than just display a table of running processes. We will first concentrate on the CLI options, then what keys and options you can use in conjunction with the existing fields top displays, then we'll go on with the other possible uses of top and, of course, examples.
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