lock screen shortcut centos 6

Ctrl + Alt + L

Firefox 31+ crashes in centos 6.4/6+

After updating firefox on Centos 6.4 it started showing the following error and would not start firefox.

$ firefox\n
/usr/lib64/firefox/firefox: symbol lookup error: /usr/lib64/firefox/libxul.so: undefined symbol: gdk_window_get_visual

The issue was resolved after installing

$ sudo yum list gdk-pixbuf2

Still if you get the following error:

/usr/lib64/firefox/firefox: symbol lookup error: /usr/lib64/libgdk-x11-2.0.so.0: undefined symbol: _XGetRequest

Then update gtk and libX11, in my case gtk was already updated to the latest version so, just updated the libX11 and it worked

$ sudo yum update libX11

R snippet to remove quotes from a data frame

as.data.frame(sapply(dataFrameName, function(x) gsub("\"", "", x)))

Eclipse keyboard shortcuts

1. Convert all letters to capitalcase -

 Ctrl + Shift + X 

2. Convert all letters to lowercase -

 Ctrl + Shift + Y 

The method getJspApplicationContext(ServletContext) is undefined for the type JspFactory

Get rid of any servletcontainer-specific libraries such as jsp-api.jar in your /WEB-INF/lib folder. This exception indicates that you've put servletcontainer-specific libraries of a container which supports only Servlet 2.4 / JSP 2.0 or older in there (the getJspApplicationContext() method was introduced in Servlet 2.5 / JSP 2.1). This is a major mistake. Those libraries don't belong in the webapp's classpath.

Perhaps you did this to overcome project compilation errors, which is indeed a pretty common beginner's mistake. This should have been solved differently, you should refer the target runtime in your project, not copy some libraries of an arbitraty servletcontainer make/version into your project. It would make your project incompatible with servletcontainers of a different make and/or version.

Logging not working in spring mvc webapp project

Add the log4j.properties or the log4j.xml to a folder named classes inside web-inf folder

Using Mahout Mapreduce

hadoop jar /home/Jijo/Mahout/mahout-distribution-0.9/mahout-core-0.9-job.jar org.apache.mahout.cf.taste.hadoop.item.RecommenderJob -Dmapred.input.dir=/jijo/mahout/links-simple-sorted.txt -Dmapred.output.dir=/jijo/mahout/output --numRecommendations 5 –b true -s SIMILARITY_TANIMOTOCOEFFICIENT

How to decompile a java class file in linux/centos

Navigate to the class file that has to be decompiled

javap -c classname

No need to include the extension .class

This command outputs the contents on stdout. Use the following to write it to a file

javap -c classname > classname.java

How to remotely lock screen in CentOS

To lock

ssh -X user@node "export DISPLAY=:0; gnome-screensaver; gnome-screensaver-command -l;"

to unlock

ssh -X user@node "export DISPLAY=:0; gnome-screensaver; gnome-screensaver-command -d;"

How to release yum lock

To find out what's locking up yum, try running:

ps aux | grep yum

Note the PID number of the process and run this to kill the process:

kill insert_PID_number

For eg:

$ ps aux | grep yum
root     23861  0.7  0.1 567568 26084 ?        S    10:34   0:01 /usr/bin/python 
/usr/share/PackageKit/helpers/yum/yumBackend.py simulate-install-files 
/tmp/wync_redhat64_v2.0.97.rpm
$ kill 23861

http://fedoraforum.org/forum/showthread.php?t=257689

How to find the count of different values in a column of a dataframe in R

You can use the table command

table(data_frame$column_name)

Rstudio shows error ** package ‘RCurl’ successfully unpacked and MD5 sums checked checking for curl-config... no Cannot find curl-config ERROR: configuration failed for package ‘RCurl’

This is because your system does not have the curl package
To install

sudo yum install curl
sudo yum install libcurl libcurl-devel

Changing ownership in hdfs

To change the owner ie chown you need to run it as hdfs user
It changed the owner to myuser when i copied it from another location but this command saved the day.

sudo -u hdfs hadoop fs -chown -R hbase:hbase /hbase/Table_Name