Fixee's questions

I was showing my kids some basic things about directory permissions on an EC2 ubuntu instance, and did this

$ sudo chmod 700 /home

Then demonstrated that I could no longer cd to my home directory because permission was denied.

Then I inadvertantly disconnected from the EC2 instance. Now I cannot log back in because the sshd on the ubuntu side cannot access my /home/ubuntu/.ssh/authorized_keys file. I've tried to think about workarounds, but I'm out of ideas.

I am prepared to delete and recreate the entire instance, but would much rather salvage this one if possible. Any ideas?!

I want to forward port 2222 on an Ubuntu 12.04 server to remote host 1.2.3.4 port 22, using iptables.

After reading many web pages on port-forwarding, I issue

$ sysctl net.ipv4.conf.eth0.forwarding
net.ipv4.conf.eth0.forwarding = 1
$ sudo iptables -t nat -A PREROUTING -p tcp -i eth0 --dport 2222 -j DNAT --to-destination 1.2.3.4:22

Which forwards traffic as I desired. But ssh does not work. Turns out I needed to also supply

$ sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

And now it's good. I understand the above commands; what I don't understand is the plethora of sites giving the first command and none giving the second. Under what conditions would the first command suffice?

Note: Example site giving only the DNAT commmand.

The last guy quit (I think a lot of adventures begin this way?) and I've been given the job to build a new machine room. I am coordinating with 2 engineers, campus ITS, campus Facilities Management, a project manager, a construction company and 2 subcontractors (electrical and mechanical). Yay.

Most of these folks have done this before, but I have not. The construction is underway, and everything is fine, but honestly I'm at a total loss about things like where the racks should go, where the floor cutouts should be made, etc. I need to understand things like power consumption, PDUs, CRAC units, BTU generation, cabling, etc. After the construction is finished, I will be in charge of who gets to use the room and what the rules are.

I know there are people who are experts at this stuff, but none of the people involved so far know much (including me). Where do I learn this stuff? Google hasn't turned up much for me.

To summarize, I'm looking for a tutorial reference that answers questions like:

• Understanding cooling requirements and cooling capacities in a server room
• Understanding power supply and consumption
• How to set policy for users in a server room (including things to think about like safety, fire prevention, data security, good custodianship)

I'm a competent software guy, but have very little experience with machines beyond building my own small computers.

What software is typically used to redirect users on a public WAP to a TOU page?

For example, at McDonald's if you jump on their free wireless, you cannot SSH until first attempting to use a browser, which is redirected to a corporate TOU page that you must agree to before you get a fully-capable connection.

I've noticed a lot of open wireless access points will associate but won't forward your traffic until you attempt a web connection. This attempt is redirected to a TOU page. If I want to do something similar, what's the "best" way to set this up? I assume low-end WAPs (like the ubiquitous Linksys WRT54G) can't support this directly, so I'd set the WAP as a router (rather than gateway) and then use some kind of software on a Linux box to handle this?

I have two windows open on the same machine (Ubuntu 9, ia32, server). I'll call these windows W1 and W2.

W1:

$ cd ~/test  
$ ls  
sample  
$  

In W2 I run "make" from a parent directory that recreates file test/sample:

$ make project
.
.
$ cd test
$ ls 
sample
$

Now, returning to W1:

$ ls
$ cd ../test
$ ls 
sample
$

In other words, after I build from another window and the file test/sample is replaced, ls shows the file as missing in the 2nd window until I cd ../test back into the directory whereupon it reappears.

I can give more details if required, but just wondering if this is a well-known behavior.