How to Enable Creation of Core Dump Files Due to Crashed Applications in Fedora Linux Distribution

Posted on July 23, 2010 by Lucky

It is needed frequently to analyze the cause of a crashed application. One way to do it is through the creating of core dump files that can be later analyzed to debug the issue. Core dump files are a snapshot of the memory area being used by the application at the time the crash occurred. Creation of core dump files may not be enabled by default, and may require some configuration. The instructions to enable the core dump files, I am going to describe here, are tested on Fedora Linux Distribution.

Enter following line at the command prompt:

$ulimit -c unlimited

Now check the output of the command “ulimit -c”, and it should show “unlimited” as follows.

$ulimit -c
unlimited

The above change, done in the way, will not be permanent. To make them permanent, edit file “/etc/security/limits.conf” (You must either be root user or must have “sudo” permission to edit this file.) and type the following line.

*      soft     core         unlimited

“*” means that this change is applicable for all users. However, to make this change for only a specific user, you should enter as follows:

<user-login-id>      soft     core         unlimited

The core dump files, generated after an application crashes, are stored in the directory from where the application was run. To place the core dump files in another location, the “sysctl” variable, named “kernel.core_pattern”, is used. The value of this variable can be checked as follows:

$sysctl -a|grep core_pattern #(if you are root user.)
kernel.core_pattern = core #(assuming “abrtd” is not running. The explanation about “abrtd” is discussed below.)

or

$sudo sysctl -a|grep core_pattern #(if you are non-root user with sudo permissions.)
kernel.core_pattern = core

The value of kernel.core_pattern is “core” currently. Two ways to change the value of this variable are as follows:

sysctl -w kernel.core_pattern=/tmp/core.%p

Now if you check the value of “kernel.core_pattern”, it will be “/tmp/core.%p”.

$sysctl -a|grep core_pattern
kernel.core_pattern = /tmp/core.%p

This means that the core dump files will be generated in the “/tmp” directory. “%p” extension to core dump files is used to append the process id of the application that crashed. This way, the variable kernel.core_pattern is also used to format the name of core dump files.

ABRT (Automated Bug Reporting Tool) Daemon:

ABRT is an application, included in Fedora Linux Distribution, that is used to report bugs in the software packages whenever crash occurs. Due to this, ABRT also helps in creation of core dump files. Multiple packages may be needed to run various features of ABRT daemon, and their listing is as follows.

abrt
abrt-plugin-bugzilla
abrt-plugin-runapp
abrt-desktop
abrt-addon-ccpp
abrt-addon-kerneloops
abrt-plugin-logger
abrt-libs
abrt-addon-python
abrt-gui

To install these packages in Fedora, one can do:

$yum install <package-name> #(if root user.)

or

$sudo yum install <package-name> #(if non-root user with sudo permissions.)

To check whether ABRT daemon is running on your system, execute:

$service abrtd status or #sudo service abrtd status
abrt is stopped

If it is stopped as shown above, “abrtd” can be started as follows:

$service abrtd start or #sudo service abrtd start
Starting abrt daemon:                                      [  OK  ]

And, now the status should show as follows:
$service abrtd status or #sudo service abrtd status
abrt (pid  5678) is running…

When “abrtd” is running, the value of sysctl variable “kernel.core_pattern” is different from the above as shown below:

$sysctl -a|grep core_pattern
kernel.core_pattern = |/usr/libexec/abrt-hook-ccpp /var/cache/abrt %p %s %u %c

“abrtd” creates a sub-directory (named something like “ccpp-1279914365-14618”) in the directory “/var/cache/abrt” as shown in the value of the variable. This also means that the core files will also be stored in that sub-directory in the “/var/cache/abrt” directory (in addition to the current directory where application was run). ABRT daemon also creates other files in addition to the core dump files in the sub-directory to further help users in debugging the crash issue.

By default, “abrtd” created core dump files only for those executable (or packages) that are managed by “rpm” (red hat package manager) utility. To enable “abrtd” for non-rpm application (something you compiled locally and are not managed through rpm), you need to edit the file cat “/etc/abrt/abrt.conf” , and change the value of the field “ProcessUnpackaged” to “yes” as follows:

ProcessUnpackaged = no   #(before editing the file)

ProcessUnpackaged = yes  #(after editing the file)

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India Makes World’s Cheapest Laptop, Sakshat, based on Open Source Linux Operating System

Posted on July 23, 2010 by Lucky

On 22 July, 2010, India added a new feather to its list of innovations by launching the world’s cheapest laptop, named Sakshat (meaning something real), that will cost around Rs 1500. Kapil Sibal, Human Resource Development Minister of India, unveiled the device, made mainly for student living in rural areas. The device comes with 2GB on-board memory, comprises wireless connectivity, and wired connectivity through Ethernet ports. The device also includes USB ports for interfacing with other external devices. However, due to its low price tag, the laptop does not have a screen, and an external screen has to be connected via USB ports for viewing.  Linux, being open source and available free, is the choice of operating system on the laptop. The choice of Linux also enables the laptop users to use a wide range of other open sources softwares available in the world. This is extremely attracting for students from rural areas with money constraints, and who can not afford to pay for proprietary softwares. In addition, the laptop has solar-powered capability and consumes low power further saving the cost. The laptop can be used for several other interesting applications, such as audio video conference, data editing, and surfing the Internet. The laptop dimensions are 10 inch in length and 5 inch in width. Although, Sakshat does not have as many as features as the previous cheapest laptop by OLPC (One Laptop Per Child) organization,  it seems to be cheapest in terms of money while providing minimal needed features.

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10 Amazing iPhone 4 Features

Posted on July 22, 2010 by Lucky

1. 5-megapixel camera to capture high quality pictures. It also has built-in LED flash that allows to capture pictures where there is dim light or in low illumination areas. The camera has 5X zoom capability. Screen tapping allows to focus on the area you seem more important.

2. Video calling from iPhone 4 to iPhone 4 over Wireless Networks (Wi-Fi). This feature, called FaceTime, allows you and your call receiver to see the faces of each other.

3. Very high resolution phone screen with 4 times pixels as compared to previous iPhones. This feature, called Retina Display, makes text look much sharper and vibrant.

4. The phone screen is stronger and is very scratch resistant.

5. Two cameras: One in the front for video calling, and one in the back that allows to share, what is happening behind the back camera, with your call receiver.

6. IPS technology (in-plane switching) that allows clear and better screens when looking at different angles.

7. Multitasking allows you to use several applications simultaneously. You can switch from one application to another, and vice versa. For example, you can use GPS, listen to your favorite audio, get calls while running some other applications at the same time.

8. You can shoot high-defintion (HD) video wherever you go, and whenever you want. Screen tapping allows to brighten the part you want to focus on. You can also edit your videos the way you want.

9. Application iMovie allows to turn your videos into a movie.

10. Applications to share your photos and videos via MMS, or through emails, or over Internet.

More information can be found at:

http://www.apple.com/iphone/features/camera.html

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Mozilla Firefox Does Not Connect To Internet When Network Connection Is Up

Posted on July 20, 2010 by Lucky

This issue may happen, if you stop managing your network connections through NetworkManager. However, your Mozilla FireFox setting may be dependent upon NetworkManager service. Just to give more insight, first I will describe why this issue was happening on my system. I am using Fedora 12 distribution, and have been using NetworkManager for connection management. However, recently, to setup bridge networking for configuring virtual machines (VM) with KVM and QEMU, I had to setup a bridge interface manually (by editing /etc/sysconfig/network-scripts/ifcfg-br0), as NetworkManager does not support it yet. Due to this, I was starting/stopping network manually too as follows:

service network restart

Or if you are not root user, you must have “sudo” permission, and run:

sudo service network restart

However, with this, although network connections were up, Mozilla Firefox was working in offline mode, and was not able to connect to the Internet.

There are 2 methods by which you can solve this issue:

1. Stop NetworkManager service as follows:

service NetworkManager stop

Or if you are not root user, you must have “sudo” permission, and run:

sudo service NetworkManager stop

Note: you do not need to uninstall NetworkManager for this.

2. In address bar of Mozilla Firefox, type “about:config” (without quotes). It will show several variables associated with it. Then, in the “Filter” bar, type “networkmanager“, it should show “toolkit.networkmanager.disable“. Currently it’s value should be set to “false“. Just double-click on the value and it will switch to “true“, something you need. Specifically, after setting this variable to true, Mozilla FireFox does not depend upon NetworkManager for its connectivity.
The above solution may not work in every scenario, as the above issue is just one of the many issues causing Mozilla FireFox to not connect with Internet. To address other issues, you may go through:

http://support.mozilla.com/en-US/kb/Basic%20Troubleshooting

Or for list of articles, you can have a look at:

http://support.mozilla.com/en-US/kb/Article+list

Or you can also ask a question:

http://support.mozilla.com/en-US/kb/Ask+a+question

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F2 VISA questions asked during interview at USA (United States of America) Embassy or Consulate

Posted on July 8, 2010 by Lucky

These questions have been prepared by collecting information from several friends and also by searching on various sites and forums on Internet. In general, I have heard from my friends that F2 VISA interview process is not difficult and not many questions are asked from F2 visa applicants.  So these questions are just for good preparation and building self-confidence.  If some question is not clear, or you want a suggestion for answers for any questions, please leave a comment, I will try my best to give you “just a suggestion”.

General questions:
Q. What is your name?
Q. What Visa are you applying for?
Q. What is the name of your spouse?
Q. What does your spouse do in USA?
Q. Can I see your spouse’s passport/visa/I-20?
Q. When are you planning to go to USA? Have you made any specific travel arrangements?

Marriage related questions:
Q. When did you get married?
Q. Was it arrange marriage? How did you both meet? Did you know your spouse before marriage?
Q. Do you have your marriage album/photos?
Q. Can I see your marriage certificate?
Q. Have you brought the invitation cards with you?
Q. Why did you not go with your spouse (in case your husband leaves before you)?

Your spouse’s study/work/finance related questions:
Q. What’s your spouse majoring in? What’s his/her research area? What’s the topic of his/her research?
Q. When is your spouse planning to finish his studies? At which stage is he now?
Q. What would your spouse do after finishing his studies?
Q. Where did your spouse work, in India or in USA?
Q. Why did your spouse leave his/her job?
Q. (if you say, your spouse wants to come back to India) Why doesnt your spouse want to work in USA? Would he/she not work there? He/she can continue his research / work there; why does she/he want to come back to India?
Q. What did your spouse study in India? Where (which school/univ) did your spouse do his undergraduation/graduation in India?
Q. How would you fund yourself there? Who would bear your expenses there? Is your husband going to bear your expenses there?
Q. Do you have financial documents? Have you brought your spouse’s bank statements or any other supporting documents?

Your study and work related questions:
Q. What are you studying? Have you finished your studies? Are you done now?
Q. Do you plan on studying in USA? if you answers “NO” then the visa office may ask: Why not?
Q. Do you want to work there? (you can not work on F2 visa)
Q. Did you work in India?
Q. Why not? You have good education and can get good job; why do you not want to work?
Q. How would you spend your time there?

Your parents/in-laws/siblings/relatives related questions:
Q. What do your parents-in-law do in India?
Q: if your parents-in-law are in business, what kind of business?
Q: If your father-in-law is in business, the visa office may ask that who would take care of the business as your husband (if only one son) is in USA?
Q. Does your spouse have any siblings in USA? what do they do? Where do they live/ work in USA?
Q: Do they have Green Card? What kind of Visa do they have? if married, what do their spouses do?
Q: Do they want to come to India?
Q. Do you have any of your relative in US?
Q. Do you have any brothers/sisters? What do they do? Are they planning to go to US?
Q. What do your parents do?

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F2 VISA (F1 Dependent VISA) Requirements and Documents for USA (United States of America) Embassy or Consulate

Posted on June 22, 2010 by Lucky

The most important requirement for obtaining a F2 visa is that the individuals who are planning to visit USA (United States of America) should be a dependant of F1 visa holders. F1 dependants eligible for F2 visa are spouse and children.

In addition to this requirement, another very important thing to not about F2 visa is that F2 visa holders are not allowed to work in any form in USA. F2 visa is not a work permit and the person holding F2 visa can not indulge in any work in which that person gets paid.

F2 visa holders are not eligible to get SSN (social security number). Few years before, I think that F2 visa holders were eligible for getting SSN but were not eligible to work, as F2 visa can not be used as work permit. It seems that some F2 visa holders used their SSN to work illegally. So to prevent this to happen, now all dependants visas (like F2 or H4) where one is not eligible to work, are not granted SSN but just ITIN ((an identification number used in USA for tax purposes)) . These are just  my thoughts and I have not verified any of this.

Anyway, F2 visa holders can get ITIN number. When F1 visa holder files tax return, he/she can show F2 visa holders as dependent using this ITIN number and can get dependant’s benefits such as higher standard deductions on taxes.

Therefore, a person applying for F2 visa should keep above points in mind. Now I will list the documents required at the time of visa interview for F2.

Mandatory documents:
1. Applicant’s passport.
2. DS-160 application confirmation letter with CEAC bar code.
3. Applicant’s visa photos as specified on here.
4. Original HDFC bank visa fee receipt with two bar code stickers.
5. Interview appointment letter.
6. Applicant’s I-20 (original) (your spouse must have got this from his/her university, and sent to you).
7. Photocopy of your spouse’s I-20 document.

Not mandatory, but must-have (highly important) documents:
1. Original marriage registration certificate.
2. Wedding photo album.
3. A few Invitation cards (original).
4. Your spouse’s US bank statements (to show that he/she can finance you).
5. Photocopy of your spouse’s passport.
6. Photocopy of your spouse’s US Visa.
7. Photocopy of your spouse’s I-94 card.
8. Photocopy of your spouse’s Federal Income Tax returns
9. Photocopy of your spouse’s State Income Tax returns
10. Photocopies of your spouse’s paystubs

If your spouse (F1) is working on OPT (optional practical training), then must-have (highly important) documents:
1. Photocopies of your spouse’s (F1’s) current and previous OPT cards (employment authorization cards).
2. Photocopies of your spouse’s (F1’s) paystubs (or salary slips) for almost 1 year (although paystubs of previous few months are also fine)
3. Original and photocopy of employment letter

Supporting documents:
1. Your spouse’s Indian bank statements.
2. Applicant’s mark-sheets and certificates starting from 10th standard.
3. Applicant’s birth certificate.
4. Applicant’s Itinerary details.

Important photocopies to keep with you:
1. Photocopy of applicant’s I-20 form.
2. Photocopies of applicant’s passport’s first page, address page, and last page.

In general, it is good to have at least 2 photocopies of each original document you are carrying with you. One set of photocopies you can carry with you, and another set of photocopies you can leave at home to have backup in case something is lost.

Documents not really needed but you may have:
1. Photocopy of your spouse’s social security card.
2. Photocopy of your spouse’s car title.
3. Photocopy of your spouse’s driving license.

Note: In the above, “Applicant” means person applying for F2 visa, and “your spouse” means applicant’s spouse.

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