The core dump is a memory image of a processes in-core state that is written to the /cores directory by default and is named core followed by a . and then the pid number. So if a process with pid 87 crashes a file is written by default at /cores/core.87. The feature can be turned off using sysctl, along with the kern.coredump MIB, setting it to 0 (by default it’s 1).
To turn it back on:
Additionally, you can change the path that the files are written into, using sysctl along with the kern.corefile MIB. The corefile is an expression that by defualt writes core.%P where %P is the PID of the process whose memory image is being written. If you wanted to change the path for the corefiles to /cores2, you would run the following:
To change it back to the default:
The sysctl command edits the state but doesn’t persist across reboots, so echo the above lines into /etc/sysctl.conf in order to have them be persistent. To disable core dumps:
echo 'kern.coredump=0' >> /etc/sysctl.conf
Or to change the location:
echo 'kern.corefile=/cores/core2.%P' >> /etc/sysctl.conf
Changing anything with regard to how core dumps would should typically be temporary. If there are no other customizations to sysctl.conf then you can undo these changes by removing the file; otherwise, simply remove the two lines and restart for the kernel to go back to its original state.
krypted August 21st, 2013
Posted In: Mac OS X, Mac Security, Mass Deployment, Ubuntu
core dumps, corefile, echo, kern.corefile, kernel, kernel state, MAC, Mac OS X, sysctl, sysctl.conf
I recently got my hands on one of those Google ChromeBooks (Cr-48). Interesting to have an operating system that is just a web browser. But, as anyone likely reading this article already knows, the graphical interface is the web browser and the operating system is still Linux. But what version? Well, let’s go on a journey together.
First, you need ChromeOS. If you’ve got a ChromeBook this is a pretty easy thing to get. If not, check http://getchrome.eu/download.php
for a USB or optical download that can be run live (or even in a virtual machine). Or, if you know that you’re going to be using a virtual machine, consider a pre-built system from hexxeh at http://chromeos.hexxeh.net/vanilla.php
. I have found the VMware builds to be a bit persnickety about the wireless on a Mac, whereas the VirtualBox builds ran perfectly. I split my time between the two anyway, so I’ve just (for now) been rocking VirtualBox for ChromeOS. When you load it for the first time it asks for a Google account. Provide that, select your network adapter, choose from one of the semi-lame account images ( for the record, I like the mad scientist one) and you’re off to the races.
Next, we need a shell. When you first log in, you see a web page that shows you all of the Chromium apps you have installed. By default, you’ll see File manager and Web Store. If you’ve used the OS X App Store then the Chrome Web Store is going to look pretty darn familiar. My favorite for now is Chrome Sniffer. But all of these kinda’ get away from where we’re trying to go: get a scripting environment for Chrome OS.
Chrome comes with 2 types of shell environments. The first is crosh. To bring up a crosh environment, use Control-Alt-t. This keystroke invokes the crosh shell. Here, type help to see a list of the commands available. Notice that cd, chmod, etc don’t work. Instead, there are a bunch of commands that a basic user environment might need for troubleshooting primarily network connections. “But this is Linux” you ask? Yup.
At the help output you’ll notice shell. Type shell and then hit enter. The prompt will change from crosh> to chronos@localhost. Now you can cd and perform other basic commands to your hearts delight. But you’re probably going to need to elevate privileges for the remainder of this exersize. So let’s type sudo bash and just get there for now. If you’re using a ChromeBook, the root password might be root, or if you’re using a downloaded vm from hexxeh then it might be facepunch (great password, btw).
Provided the password worked, the prompt should turn red. Now, if you’re using a hexxeh build then the file system is going to be read-only. You won’t be able to change the root password nor build scripts. But otherwise, you should be able to use passwd to change the password:
Once you’ve got slightly more secure shell environment (by virtue of not using the default root password), it is time to do a little exploring. Notice that in /bin, you see sh, bash, rbash and the standard fare of Linux commands (chmod, chown, cp, attr, etc. Notice that you don’t see tcsh, csh or ksh. So bash commands from other platforms can come in, but YMMV with tcsh, etc. Running ps will give you some idea of what’s going on process-wise under the hood:
From encrypts to crypto to the wpa supplicant, there’s plenty to get lost in exploring here, but as the title of the article suggests, we’re here to write a script. And where better to start than hello world. So let’s mkdir a /scripts directory:
Then let’s touch a script in there called helloworld.sh:
Then let’s give it the classic echo by opening it in a text editor (use vi as nano and pico aren’t there) and typing:
echo "Hello Cruel World"
Now close, save and then run it:
And you’ve done it. Use the exit command twice to get back to crosh and another time to close the command line screen. You now have a script running on ChromeOS. Next up, it’s time to start looking at deployment. This starts with knowing what you’re looking at. To see the kernel version:
Google has been kind enough to build in similar sandboxing to that in Mac OS X, but the concept that you can’t run local applications is a bit mistaken. Sure, the user interface is a web browser, but under the hood you can still do much of what most deployment engineers will need to do.
If these devices are to be deployed en masse at companies and schools, scripts that setup users, bind to LDAP (GCC isn’t built-in, so it might be a bit of a pain to get there), join networks and the such will need to be forthcoming. These don’t often come from the vendor of an operating system, but from the community that ends up supporting and owning the support. While the LDAP functionality could come from Google Apps accounts that are integrated with LDAP, the ability to have a “One touch deploy” is a necessity for any OS at scale, and until I start digging around for a few specific commands/frameworks and doing some deployment scripts to use them, right now I’m at about a 6 touch deploy… But all in good time!
krypted September 8th, 2011
Posted In: cloud, Mass Deployment, Ubuntu, Unix
bash, cat, chrome OS, chronos, Command line, crosh, echo, Google, Google ChromeOS, Hello World, mkdir, nano, passwd, pico, ps, root password, scripting, Shell, touch, uname, vi