System Notes Org

How to Buy, Accept, or Mine Bitcoin and Other Cryptocurrencies - Quick Intro Buy Bitcoin on an Exchange One easy way to get started with owning bitcoin is to buy some on an exchange, such as Coinbase. I offer this link because I think it is helpful, not just because I could get $10.  Sometimes you can't tell why people recommend things.  I figure, if you plan to sign up anyway, why not save a little money? With this referral link, we each get $10 in bitcoin after the new account is opened, and a trade of $100 or more is completed: https://www.coinbase.com/join/592f371c2ae3540ae4a4eb70 Note that it is not necessary to buy a full coin, but there are commissions for buying and selling, and  mining fees for transfers.   To minimize commissions, try entering different amounts to see how much makes sense, before completing the transaction.  For example, buying $100 of bitcoin may cost as much in commissions as buying $200 worth, or around $3.00.  In 2...

Introduction to Online Security, Internet Privacy, Anonymous browsing.   As an honest hard-working citizen, you may think you have nothing to hide, but at the same time you may be annoyed with intrusive advertizing, or you may be concerned with the ability of hackers to see your bank accounts, or for governments, foreign or domestic to watch what you do online. Advertising Some people are surprised to see ads shortly after visiting a website.  For example, suppose you want to check the price of flights to Seattle, just out of curiosity to compare prices to different cities, but with no intention of ever going there.  Then, you notice over the next few days, that there all kinds of advertisements in your browser for flights, or hotels in Seattle.  Then you wonder how did those advertisers get the crazy idea that I might be interested in going to Seattle?  Or why do I keep seeing ads for something in which I have no interest?  That is tracking te...

I explained how to get a list of hosts using nmap -- using-nmap-to-generate-host-lists.html , but here is another look at the subject. The question is, how do I ping multiple hosts to find out which ones are down? Sure this could be considered a topic of system monitoring, but maybe you just want to reboot a bunch of machines, and make sure they all come back online. This quick check will tell you whether there is a problem or not. Here are three methods for pinging a list of hosts: 1.) for host in `cat all.txt `;do ping -c 1 $host; done 2.) nmap -sP -R -iL all.txt 3.) sudo fping -u < xyz/all.txt First, we assume that you have a text file named all.txt that contains a list of hostnames, one per line. Obviously, the examples here contain fake hostnames, domain names and IPs, as described in another article about vi: vim-tips-search-and-replace.html . --- all.txt --- xyz-1 xyz-2 xyz-3 xyz-4 xyz-5 xyz-6 xyz-7 xyz-8 --- end all.txt --- 1.) Use a for loop in ...

IP Forwarding Effectively makes a Linux box act as a router Is usually used with two network interfaces (one internal, and one external) Can be used with firewall services and is often used for NAT Steps to Turn on IP Forwarding  1) Modify /etc/sysctl.conf      vi /etc/sysctl.conf      add this line:      inet.ipv4.ip_forward=1  2) Make the Change Active      sysctl -p  3) To View Current Settings:      sysctl -a | grep ipv4 More info can be found on the redhat site: https://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/security-guide/s1-firewall-ipt-fwd.html We'll leave firewall rules for another topic... rhce linux

This procedure assumes you have console access, and are authorized to make changes to accounts on the machine, including root. If you own the machine, you can boot into single user mode, and change the password, or create an account. If using grub (you should see a blue bootup screen), press "a", "space", "1", "enter" a 1 That will boot to single user mode. Then you can change the root password passwd Then reboot Ctrl-Alt-Del You should create user accounts other than root. Use the useradd command. useradd someone passwd someone rhce linux

An easy way to get a list of hosts from a single domain that you are a part of, is to query DNS host -l mydomain.com But that is not always practical. Sometimes you have machines that are in different domains, but they all are part of a network you manage. Rather than trying write a script that pings hosts and reports the output, just use nmap for a very fast scan. To scan all hosts in a list of subnets 1) Create a subnets.dat file with one subnet on each line: $ cat subnets.dat 192.168.0.* 192.168.1.* 2) Run nmap with the subnets.dat file as input $ nmap -sP -R -iL subnets.dat Reading target specifications from FILE: subnets.dat Starting nmap V. 3.00 ( www.insecure.org/nmap/ ) Host (192.168.0.0) appears to be down. Host box1.mydomain.com (192.168.0.1) appears to be up. Host box2.mydomain.com (192.168.0.2) appears to be down. Host box3.mydomain.com (192.168.0.3) appears to be up. Host (192.168.0.4) appears to be up. ... Notice how names are resolved ...