No Open Blockers

Repost: This happened back in Feburary 2009 and was posted as “Disaster Averted” mainly to annoy my students with the fact that class was *almost* cancelled that night. I’m reposting it with a more accurate title for searching purposes (read: I needed to find this again but couldn’t because of my annoying title).

When I got to campus today and turned on my laptop, I was greeted with an all black screen and just the word “GRUB”.

Shit.

Some quick background for my students… GRUB is one of the bootloaders available for Fedora. In short, a bootloader is what takes control from the BIOS at boot time and passes it to the operating system. No bootloader = no operating system. So here I found myself, on campus needing my laptop for class tonight, without anything to help me.

That last part needs some elaboration. Fedora added a really cool feature where the Fedora installation can be installed to a USB drive. While I was at Red Hat Summit last year, I got Fedora 9 installed to the USB drive they gave out as swag. That doesn’t really help much since I kept forgetting to swap out the USB drive on my keys with my newly pimped out Fedora install stick.

My forgetfulness came back to bite me, since when I needed it most, what should have been an extremely conveniently located live Fedora install is sitting in my office at home, a few feet away from half a dozen Live CDs of various Linux distros that also would have been helpful to have around.

That aside, this was actually sort of cool in a way. While studying for my RHCE, I found new and creative ways to destroy a Red Hat installation to practice for the exam. I had managed to run into this exact issue and knew how to fix it, I just needed some form of rescue CD to do it.

The first half of that was easy, I logged into a machine in the lab and downloaded the Fedora 10 ISO from fedoraproject.org (insert generic “Try that with Windows” comment here). Thankfully, the lab machines have CD burners. However, I needed to find a CD first. Having no luck digging around the lab, I went downstairs to the university IT department’s tech helpdesk.

“Are you a student?”

Ok, so it was a fair question to ask me. It’s the last class before Spring Break and I’m not feeling well, so I’m here in a Villanova sweatshirt, jeans, and sneakers.

“No, I’m a professor. I need the CD for class tonight.”
“Really?”
“I assure you, I’m not a student.”

Thankfully, one of my students last semester had introduced me to one of the IT guys in the room who recognized me and vouched for my employment. I can’t really fault them for asking; I’d get annoyed too if a student bust in the helpdesk asking for free stuff.

One burnt CD later and I was into the Live CD. A few commands after that, I rebooted sans CD and was up and running.

Which brings me to the meat of this post, how to reinstall GRUB from a Live CD. It’s actually pretty simple. After booting into rescue mode, run:

grub

That’ll bring you into the interactive GRUB shell (notice the prompt changes to “grub>”).

grub> find /grub/grub.conf
(hd0,0)
grub> root (hd0,0)
grub> setup (hd0)

The find command was just to verify the hard drive where the boot files are located. The setup command completed almost instantly, which actually had me a bit worried that it did nothing. But the output looked pretty convincing:

Checking if "/boot/grub/stage1" exists... no
Checking if "/grub/stage1" exists... yes
Checking if "/grub/stage2" exists... yes
Checking if "/grub/e2fs_stage1_5" exists... yes
Running "embed /grub/e2fs_stage1_5 (hd0)"... 16 sectors are embedded... succeeded
Running "install /grub/stage1 (hd0) (hd0)1+16 p (hd0,0)/grub/stage2 /grub/grub.conf"... succeeded
Done.

After that, it was as simple as rebooting without the CD. I’ll still need to look around to make sure nothing else is messed up, and even more disconcerting is what caused this in the first place. But for now, at least I’m not stranded on campus with a dead laptop.

In the meantime, hopefully now I’ll remember to put the damn bootable USB stick on my keys… (Update: I put it on my keys that night when I got home from class)

I can’t help but think of this xkcd comic which feels kinda relevant right now.

I came to the realization that I have too many computers constantly running in my house. It’s not so much a “go green” thing to use less electricity as it is me being cheap and wanting to lower our bill. It’d also be nice to walk in a room and hear silence rather than whirring computer fans or have to clean dead spiders from multiple desktops. After reading an article in Linux Journal about hacking the MyBook (external network drive that runs linux under the covers), it looked like it could serve a lot of uses, starting off with being the house file server and backup system.

So far, I’m off to a good start. To begin with, the Linux Journal article is already somewhat obsolete as there’s no need to hack it anymore. The latest firmware flat out gives you the option to enable SSH on the device; once you’re in you can do pretty much whatever you want. One click in the web UI and one terminal later, I was logged directly into the system.

The MyBook runs BusyBox linux. I’ve never worked on a stripped down linux install like this, but other than missing a few commands I’ve come to love (I continue to type less; my brain just refuses to acknowledge that it’s not there) it’s pretty easy to navigate if you’re comfortable on linux.

Initial Setup

-> nmap -sP 192.168.0.1/24
 
Starting Nmap 4.76 ( http://nmap.org ) at 2009-06-16 17:42 EDT
Host 192.168.0.1 appears to be up.
...
Host 192.168.0.112 appears to be up.
...

I snipped out the rest the results, but you get the idea. I only have a handful of non-static IPs internally so it wasn’t too hard to figure out which one was new. The box runs lighttpd and has a pretty slick (albeit a bit slow) interface to most of its guts, so after digging the included CD out of the trash to look up the default password, I was able to connect to it and start dorking around.

The MyBook comes with a lot of features, with the small caveat that I don’t actually need most of them. So the first thing I did was run around disabling things. It’s very cool that the device supports Samba and AFP, but frankly, I just don’t need them (I’ve had the wife running linux for years now, she rocks). I also killed FTP and the Mionet software. It wasn’t all slash and burn; I enabled SSH and NFS and made a new user for myself. Ultimately I’ll turn off the daemon that controls the slick white light on the front of it, but the novelty is still there and it looks damn cool at night (and really creeps my wife out since the light pulsates).

At that point, I was able to SSH into the box and (potentially) really get myself in trouble.

Enabling Cron

Cron is on the system, but it doesn’t work out of the box. I had to make one small change: creating the directory in which it’s going to store the schedules.

mkdir /var/spool/cron/crontabs

Here’s where I got lazy. I just set the permissions on the cron and crontabs directories to 777 to make my life easier. It’s far from secure, but I’ll work on that later. For now, I just wanted to get my non-root user to be able to schedule things.

The other change that needed to be made was to start the crond daemon. I didn’t find anything in the web UI to support this, but given the rate at which the firmware is exposing functionality I wouldn’t be surprised to find it there in the near future. I hacked up a pretty rudimentary init.d script so it would auto-start on reboot and was on my way.

SSH

The main issue is that the home directory for all created users is simply defaulted to /shares. That directory serves as the root of all of shared files. Not that I’m expecting to create a ton of users, but I didn’t like the idea of a single .ssh directory for all users. I didn’t find any user mod tools on the install, so I just changed the /etc/passwd file to give my user a different (read: private) home directory. After that, it was as simple as running ssh-keygen like any other linux system (I won’t get into those details here, but it’s pretty easy to google around for generating SSH keys).

After installing the public key on my webserver, I was good to go for automatically logging in.

Rsync

Profit

I’ve also copied over the “family” shared files to the MyBook, such as music and pictures. It was done simply through NFS so I won’t go into details here other than to say that there were no unexpected hiccups in the process.

There’s more I want to tinker with on the box. The web UI is in PHP and after a bit of looking around, I was able to find and start editing the web UI site. I’m thinking of adding my own section that will at very least report on the previous night’s backups. I’ll get to that eventually, for now I’m happy to have replaced one of the desktops in my house.

In case you haven’t noticed, there is a pretty common theme among geeks: “Because I can.”

One of the things I was looking forward to in Fedora 11 is better support for dual monitors. I wasn’t disappointed, the UI is very intuitive and it just worked, allowing me to share my laptop screen onto a spare monitor (seriously, I have too much hardware just lying around). So my home office now looks like:

Something else to realize is that with my synergy setup, a single mouse/keyboard is used to control both systems, meaning I can move the mouse from the leftmost side of the laptop to the rightmost side of the right monitor, an act that currently requires me to pick the mouse up to get more space 6 times (yes, I actually counted).

Not sure how long I’ll try this setup out; I’m guessing I’ll have a wicked headache before lunch. But that doesn’t change the fact that my office looks like a NOC right now.

I ordered the replacement video card for my MythTV box–

Actually, that’s not entirely accurate. I could have ordered a cheap replacement card for the Myth box. All it really needs to do is output to DVI, nothing fancy. The alternative is to take my video card from my gaming rig and move that to the Myth box, providing a reason to upgrade my gaming rig. That’s way more expensive, but I was careful to just tell the wife “I ordered a replacement video card.” I never said if I was using a cost optimal solution.

Where was I… oh ya, so I ordered a new video card yesterday at lunch. It arrived today at lunch. For no extra charge. When science perfects instant teleportation of objects, Newegg is going to raise the bar by just guessing at what hardware you need and sending it before you realize you need it.

Last week I was catching up on some shows I recorded on my MythTV box (essentially a computer made into a home made Tivo) when the picture just disappeared. When I rebooted, it didn’t even show the BIOS, so I figured the video card died. I built the box back in 2004 and it’s always on, so it actually had a really good run.

While I’m waiting for the replacement card to arrive from newegg.com, I decided to take the existing card out, make sure the fan still spun, and reseat it back into the motherboard. It was worth a shot.

The inside of the box itself was a disaster. I try to air dust my desktops about once a month, but apparently I’m behind on this one. I tried to take a picture, but it doesn’t do it justice. I’ll simply point out that there is a dead spider inside.

Whenever I’m dealing with a piece of hardware that doesn’t work, I inevitably turn it around in my hands looking for… well, I don’t know what I’m looking for. I’m not an engineer, so short of seeing smoke coming from a part, no amount of physical inspection has ever yielded results.

This time was a bit different. Take a look at the second column of cylinders on the card below. I don’t know what they are or what they do, but I’m pretty sure the tops aren’t supposed to be blown out like that. The one closest to the camera even had what looked like ash coming out of it.

Might be time to plug in some of the fans I disabled to make the box run quieter.

And as a public service announcement, airdust your computer. It will love you for it.

any joy on reproducing?

I sit in a number of non-Spacewalk/Satellite chat rooms at work. This was just seen in a conversation in one of those rooms discussing… well, to be honest, I don’t actually care what bug they were talking about. Taken out of context is way funnier.

...
// Now we filter out an 
List retval = new LinkedList();
...

Shit. Ok, so it’s not too much code after that to see what the filtering is doing, but the comment still left me hanging.