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