How to ask a question and be secure

Being secure is not an easy task. When you're online, you don't know who's on the other side. You don't know who's reading your posts and answering them, either. That's why my first rule is

Do not fully trust the answers you get

What if you got a command that deletes all your files? Check the commands. It's easy. Just run

man command

to see what does the command do. You can also scroll down and check all options given.

If the solution is to change a configuration file, make a backup copy.

Example:

You don't know how to set up a default gateway. You have asked a question and got an answer. Inside there's a command

route add default eth0

You've never heard about that command, so you check if that's what you want. Run

man route

to see route's manual. You'll get something like

route - show / manipulate the IP routing table

It's good. The routing table modification is what you need.

I started with answers, but more things should be said about questions and follow-ups.

You don't know who's reading your posts. In fact, they're accessible by search engines (LQ's engine, but also Google etc.). That's why

Don't post your passwords. Never.

Your password is not needed to solve your problem. I may write this, as I have never seen a situation it would be. If a command should be run that requires password, you can do it yourself. Again, remember about rule no. 1.

Don't post personal information (credit card number, serial number etc.)

It has been said many times. It's still worth repeating.

Don't allow remote access to your machine someone you've just met online

When asking a questions, someone may ask you to give him/her remote access to your machine so they can solve your problem faster than you. Don't do it if you don't know that person really well. Most of the people would just do this: help you. But you don't know for sure.

There are more things that should be kept secure, especially when you're asking a network-related question.

Don't post your real, global IP address or hostname

If you're asking a question, in most cases you have a problem. It may mean your machine is not as secure as it should be and you may be an easy target. Don't give your address to an attacker. When you're posting results of route or ifconfig, remove all that may lead to you. Replace global address with a private one.

What's a private address? An address that's local to your network and it's not accessible from outside. There are 3 main ranges of such addresses:
10.0.0.0 to 10.255.255.255
172.16.0.0 to 172.31.255.255
192.168.0.0 to 192.168.255.255
You don't have to replace addresses from that ranges.

Change your domain to be something like 'example.com' (reserved domain name for documentation and similar things).

Example:

You were asked to post results of route and ifconfig. An example how it should look below:

ifconfig eth0
eth0      Link encap:Ethernet  HWaddr XX:XX:XX:XX:XX:XX
          inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:3754 errors:0 dropped:0 overruns:0 frame:0
          TX packets:3855 errors:0 dropped:0 overruns:0 carrier:0
          collisions:1 txqueuelen:100
          RX bytes:2687451 (2.5 Mb)  TX bytes:502075 (490.3 Kb)
          Interrupt:11 Base address:0x3800

Replaces elements are shown in color. HWaddr is a unique number of your NIC. You don't need to show it to public. Second bolded field shows IP address of eth0 interface. 192.168.1.1 is in the third local range.

route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
localnet        *               255.255.255.0   U     0      0        0 eth0
default         mygateway 0.0.0.0         UG    0      0        0 ppp0

In this case default gateway IP (or hostname) was changed.

You should also apply the rule above when you're posting your firewall (iptables) script and in many other situations.

Update your system

When you post something like I have a problem using Programname version some-version... when some-version is known to have security holes, it's not good. Especially when you also provide your IP.

To sum up: you don't know who reads your posts. That's why don't post your passwords, sensitive information, real IPs and domain names. Before running a command check it.