Trivia@Work

Changing ulimit of open files

2013-09-13T23:24:00.000-07:00

I wanted to increase the limit on the number of open files, as needed to install a particular new application.

The output of `ulimit -n` was 1024. I had expected that `ulimit -n 2048` command would set the value. Instead, I got the error `bash: ulimit: open files: cannot modify limit: Operation not permitted`.

I tried increasing the ulimit as root: `sudo su -`, and then `ulimit -n 2048`. While this set the limit for root, it did no change for the non-root user.

I also added the following lines to `/etc/security/limits.conf`:
` soft nofile 2048`
` soft nofile 4096`

I understand that the above is needed to make the change to ulimit persistent.

Finally, what did work to allow ulimit set as root to be set as non-root user, is appending line `session required pam_limits.so` in the file `/etc/pam.d/common-session`.

Find CPU, RAM Size, Cache Size, etc., on Ubuntu Linux

2012-12-29T00:06:00.003-08:00

cat /proc/cpuinfo to get the CPU info.
cat /proc/meminfo to get the RAM info.
lscpu to get the L1, L2 cache size.

Expected Primary Expression Before '>'

2012-08-21T18:41:00.002-07:00

Using gcc 4.x, the above error may be encountered in template code. This discussion is useful for the case.

Starting Testing GAE Python App with Webtest

2012-05-17T22:27:00.001-07:00

Recently I wanted to write automated tests for my GAE WSGI app (the app is written using web2py, but this detail may or may not be relevant to this post). Behavior-driven design, implemented by, e.g., Lettuce, seems to me as an ideal way to write tests---reasons seem to be well-described in this article by Scott Bellware. In python, Webtest is a good way to test WSGI apps. There are a couple of hurdles:

it seems that GAE app.yaml cannot be used to get a WSGI app needed to run Webtest-based tests. One get-around for this hurdle is to use WSGIProxy.
another (easier) problem is that Webtest redirects stdout and stderr streams, so the print function cannot be used for debugging. This problem can be circumvented using logging.

Managing Multiple .bib Files

2012-05-04T05:55:00.000-07:00

I am using latex for multiple papers and to merge the contents into a thesis. I have multiple .bib files, say one for each paper. Unluckily, this does not look like a good situation to be in. There should better be only one .bib file that I should use for all the papers, since then I do not need to worry about duplicates; for example, correction of an entry need not be redone if the entry is duplicated in other bib files.

To extract the subset of the consolidated bib file that a particular paper uses, it is possible to use JabRef.

Here it is also worth to point out that a situation when a cited reference is missing from the bibliography can be detected using the following (assume "make" calls the latex command, namely: latex doc; bibtex doc; latex doc; latex doc):

make | grep -i "warning--" | less

This at best is a hack, but I could not find a better way till now. In particular, there seems to be no easy way to make missing bibentry as an error.

Backing Up My Ubuntu Desktop Settings and Files

2012-05-04T02:35:00.003-07:00

I am using the method at http://askubuntu.com/a/99171. Will shortly need to move my desktop and then I will update how it went.

Easy way to install gcc-4.6 on Ubuntu 10.04

2012-04-20T21:59:00.001-07:00

sudo apt-add-repository ppa:ubuntu-toolchain-r/test/ubuntu
sudo apt-get update
sudo apt-get install gcc-4.6
sudo apt-get install g++-4.6

From here. The alternative is to download gcc sources and install like this.

svn: making trunk identical to a branch

2012-04-19T22:41:00.002-07:00

So, I created a branch, made changes within the branch over a period and periodically kept merging from trunk into the branch.

Now I want to make the trunk identical to the branch. The best approach for this is as described at http://stackoverflow.com/a/1008805/19501, namely use the three-way merge option:

...you want to merge "FROM trunk@HEAD TO branch@HEAD" with the working copy pointing to trunk. In essence:
"Give me all the changes I'd need to make trunk identical to branch".

Copy one sparse matrix into another in Python

2012-04-05T06:39:00.000-07:00

Copying Xf into features. In this case, Xf is a scipy.sparse.csr_matrix and features is a dok_matrix.

nz_indices = Xf.nonzero()
for ix, jx in zip(nz_indices[0], nz_indices[1]):
features[ix, jx] = Xf[ix, jx]

Notes:

1. When I checked, the assignment of a 0 to an element of a dok_matrix resulted in a crash. So 0 assignments have to be avoided.

Installing Graphite-Sim

2012-03-20T05:28:00.001-07:00

I wanted to use a multi-core simulator for scalability testing of our parallelization. Graphite-sim seems to provide the functionality of simulation. However, there were a series of problems during the installation of Graphite-sim:

When I downloaded and tried to install the 32-bit version on my Ubuntu linux host, the compilation failed. It seems that contrary to the documentation, only the 64-bit version currently works, as can be seen on the forums. I tried to fix the compilation for a few times, but soon it became clear that the code was not fixable by me.

Next, I tried to work out if a 64-bit Debian guest VM can be installed so that the guest can contain Graphite-sim. Indeed this is the way that the Graphite-sim documentation seems to be tested. As per
http://ubuntuforums.org/showthread.php?t=1165598 I ran the command provided to ascertain whether my hardware can support a 64-bit vm. I installed virtualbox-ose package from synaptic.
I downloaded Debian-64 from http://www.debian.org/releases/lenny/debian-installer/ . Initially I tried installing ia64 businesscard version, but the VM would not recognize it as a boot iso. Later Ifound out on one of the forums that amd64 businesscard version should be used.

Next, I installed the debian on the virtualbox, but while doing so, I had to enable "Intel Virtualization Technology" in the BIOS settings to overcome an error "VT-x is enabled but is not operational". Besides, amd64 was not installing on the VMWare virtual machine but could install on Virtualbox.

To summarize, the following steps should work using a Ubuntu Linux host:

Install Virtualbox OSE (Open Source Edition).
Enable "Intel Virtualization Technology" in the BIOS settings of the host machine.
Download the amd64 (64-bit) businesscard iso.
Install the iso as a guest on Virtualbox.
Follow up with the instructions at https://github.com/mit-carbon/Graphite/wiki/Getting-Started

and the following would not work (YMMV):

Installing on a 32-bit machine
Installing ia64 guest on VMware/Virtualbox OSE.
Installing amd64 on VMWare player.

I can see that many of the exact specifications of my configuration are incompletely specified, such as the host hardware, VMWare player version, Virtualbox version, etc. Unluckily I do not have the time to find out and list these here right now.

Latex Issues

2012-03-19T23:23:00.001-07:00

I faced an issue while using dvips + ps2pdf to generate pdf from latex. Seems to be this bug (prob in dvips):
http://bugs.ghostscript.com/show_bug.cgi?format=multiple&id=690427

As a getaround, I switched to using dvipdfm.

Setting up Git

2011-05-18T01:12:00.000-07:00

https://help.ubuntu.com/community/Git

There is a local machine and a server which will act as a Git Server.

On the git server:
sudo apt-get install python-setuptools git-core gitosis

On the local machine:
ssh-keygen -t rsa
scp the public key to Git Server at /tmp/pub-key

On the git server:
sudo -H -u gitosis gitosis-init < /tmp/pub-key

To get a Static IP Address from a DHCP Server (On Linux)

2011-03-24T22:57:00.000-07:00

Thanks to Ivan.

Edit /etc/network/interfaces

Change settings to:

# The loopback network interface
auto lo
iface lo inet loopback

# This is a list of hotpluggable network interfaces.
# They will be activated automatically by the hotplug subsystem.
mapping hotplug
script grep
map eth0

# The primary network interface
auto eth0
iface eth0 inet static
address 192.168.1.35
netmask 255.255.255.0
network 192.168.0.0
broadcast 192.168.1.255
gateway 192.168.1.254

Log4J Configuration

2011-03-24T22:29:00.001-07:00

After a lot of headaches and retries, the log4j.properties config file that worked for me is this: http://www.benmccann.com/dev-blog/sample-log4j-properties-file/ . Simply placing this under src/main/resources works. I am using standard maven settings.

Problems in Viewing Docx On Ubuntu?

2011-02-15T20:44:00.000-08:00

After having a lot of trouble in viewing Docx, I installed odf-converter-integrator from http://katana.oooninja.com/w/odf-converter-integrator/download . This helped a lot although the output was not perfect.

Changing Timezone on Ubuntu

2011-01-23T18:41:00.001-08:00

dpkg-reconfigure tzdata

http://webonrails.com/2009/07/15/change-timezone-of-ubuntu-machine-from-command-line/

Disk Check during Shutdown on Ubuntu (and not during startup)

2011-01-22T04:52:00.000-08:00

Just installed autofsck. This goes into the "my base installations" list.

Juniper VPN on Ubuntu

2011-01-14T03:32:00.000-08:00

There are certain issues with Juniper on Ubuntu. The following getaround works well for me though:

http://ubuntuforums.org/showpost.php?p=10346501&postcount=416

Some Windows Commands

2011-01-09T23:44:00.001-08:00

From command prompt, Taskkill /pid to kill a task.

Tasklist /v to get a list of running tasks.

netstat -ano to get the list of used network ports and the pid using the port.

Watching All Files in Mediawiki

2010-12-10T05:28:00.000-08:00

As per the discussion here, the change discussed at the Mediawiki site should be able to provide the functionality of notification on each file change. I verified that this change works.

Logging into Ubuntu from another Ubuntu Machine and View Remote Display

2010-12-07T00:44:00.000-08:00

Lets call the machine on which we want the display to be shown as client machine, and the machine from which the display will be shown as the server machine.

SSH supports X forwarding. To enable X forwarding on the server, first install ssh using

sudo apt-get install ssh

Then, edit /etc/ssh/ssh_config to set

ForwardX11 yes

On the client, you need to start a new X server by running:

sudo xinit -- :2

Then on the client, run

ssh -X server -l user

After logging in onto server via ssh, do "echo $DISPLAY". This variable should have been set by ssh. Then run "gnome-session" on the server. You can now see it displayed onto your client.

Do "Ctrl+Alt+F7" to go back to the X server working with your client, and "Ctrl+Alt+F8/F9" to toggle to the display received from the server.

After logging into the server, you might get errors like:

/usr/bin/xauth: error in locking authority file /home/user/.Xauthority.

The following resolved the issue for me:

xauth -b quit

Eclipse stopping automatic build before launch

2010-11-26T03:08:00.001-08:00

http://dev.eclipse.org/newslists/news.eclipse.tools.cdt/msg14394.html

Preferences > Run/Debug > Launch > untick "Build before launch"

Recursive Find in Windows Command Prompt

2010-11-26T03:07:00.001-08:00

dir . /s /b | find "text"

Freesshd for using SCP to a Windows Machine

2010-11-08T02:30:00.000-08:00

To install Freesshd, run the install using admin privileges, else you will repeatedly get less-privilege-related errors.

In your windows firewall, check that Freesshd service is allowed.

Open Freesshd and check that login is allowed for the user you want to use ssh with.

Hudson on Ubuntu

2010-11-06T04:37:00.000-07:00

http://wiki.hudson-ci.org/display/HUDSON/Installing+Hudson+on+Ubuntu

Worked fine for me, except that Hudson has a dependency on Java. For installing Java I followed:

http://www.cyberciti.biz/faq/howto-ubuntu-linux-install-configure-jdk-jre/