Do You Make These Mistakes?

When i try to compile a jar file using the below command in command prompt, java -jar HelloWorld.jar i got an error like Failed to load Main-Class manifest attribute from HelloWorld.jar This is due to the missing launch configuration.  The Main-Class header needs to be in the manifest for the JAR file - this is metadata about things like other required libraries. See the  Sun documentation  for how to create an appropriate manifest. Simply, i followed the eclipse for exporting the jar file instead of remembering all the commands. and choose as specified below. and choose the following options below. 1. Choose your class that contains MAIN method. 2. Choose the destination of Jar file 3. Once, one and two steps are done, Click Finish. Now run the same command via command prompt,  java -jar HelloWorld.jar This will not throw an

The  -a  in an explicit  AND  operator that allows you to join two primaries. In this case creating a range using  -size . rm -rf `find . -size +300c -a -size -400c`; The above command deletes the files which size are in between 300kb to 400kb. Note the size is a numeric argument that can optionally be appended with  +  and  - .  Numeric arguments can be specified as     +n      for  greater than n,    -n      for  less than n,     n      for  exactly n.

Prerequisites Hadoop requires a working Java 1.5+ (aka Java 5) installation. However, using Java 1.6/1.7 (aka Java 6/7) is recommended for running Hadoop. Please refer to jdk installation instructions here. Dedicated user for Hadoop system A dedicated Hadoop user will help Hadoop installation from other software applications and user accounts running on the same machine. umasarath@ubuntu:~$ sudo addgroup hadoop umasarath@ubuntu:~$ sudo adduser --ingroup hadoop hduser The above two commands will add "hduser" user and "hadoop" group. Hadoop Installation Download Hadoop from the Apache Download Mirrors and extract the contents of the Hadoop package to a location of your choice. The folder I chosen was the hduser home folder. Extract the downloaded file in /home/hduser folder and make sure the file should be extracted in hduser login. hduser@ubuntu:~$ sudo tar xzf hadoop-1.2.1.tar.gz hduser@ubuntu:~$ sudo mv hadoop-1.2.1 hadoop Configuratio

Installing Open JDK from Command Prompt Issue command apt-get install openjdk-7-jdk to install JDK7. Ubuntu will auto download JDK and start the installation, wait a few minutes for the downloading process. umasarath @ ubuntu:~ $ sudo apt-get install openjdk- 7 -jdk Verifying Java after installation Ubuntu installs JDK at /usr/lib/jvm/jdk-folder, for example /usr/lib/jvm/java-7-openjdk-amd64/. In additional, Ubuntu also puts the JDK bin folder in the system path, via symbolic link.  For example, /usr/bin/java. To verify if JDK is installed properly, type java -version in the command prompt. umasarath@ubuntu:~$java-version java version "1.7.0_25" OpenJDK Runtime Environment (IcedTea 2.3.10) (7u25-2.3.10-1ubuntu0.12.04.2) OpenJDK 64-Bit Server VM (build 23.7-b01, mixed mode) umasarath@ubuntu:/usr/lib/jvm/java-7-openjdk-amd64/bin$ Post-Installation Setup To configure JAVA_HOME in system path each time the terminal is started, you can append the expor

The below error was faced and tried for online answers, made my head to heat for couple of days and finally i was able to crack the solution for the below issue. umasarath@ubuntu:~$ tail -50 cron_alc.log Cronjob started for back-up files + rsync -v umasarath@xx.xx.xx.xx:/tmp/compressed_logfiles/*.zip /home/umasarath/archive/ Permission denied, please try again. Permission denied, please try again. Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password). rsync: connection unexpectedly closed (0 bytes received so far) [Receiver] rsync error: unexplained error (code 255) at io.c(601) [Receiver=3.0.7] umasarath@ubuntu:~$ Please follow the below steps inorder to avoid the above error. My script contains the below code. umasarath@ubuntu:~$ cat transfer_files.sh #!/bin/sh set -xv echo "Cronjob started for back-up files" `date` /usr/bin/rsync -vv umasarath@xx.xx.xx.xx:/tmp/compressed_logfiles/*.zip /home/umasarath/archive/ echo "Cronjob ended for back-u

You might come across the below command like  chmod 755 filename and of course you will be wondering what this is.  The thing is, that you can change the entire permission pattern of a file in one go using one number like the one in this example. Every mode has a corresponding code number, and as we shall see there is a very simple way to figure out what number corresponds to any mode.  Every one of the three digits on the mode number corresponds to one of the three permission triplets. (u, g and o) Every permission bit in a triplet corresponds to a value:  4 for r,  2 for w,  1 for x.  If the permission bit you add this value to the number of the permission triplet. If it is cleared, then you add nothing. So if a file has rwxr-xr-x permissions we do the following calculation:  Triplet for u: rwx => 4 + 2 + 1 = 7 Triplet for g: r-x => 4 + 0 + 1 = 5 Triplet for o: r-x => 4 + 0 + 1 = 5   Which makes : 755  Now i guess,

Permissions Every file on the system has associated with it a set of permissions. Permissions tell UNIX what can be done with that file and by whom. There are three things you can (or can't) do with a given file:   read it,   write (modify) it and   execute it. For any given ownership relation, we need three letters to specify access permissions: the first denotes read (r) access, the second denotes write (w) access and the third denotes execute (x) access. We have three ownership relations: 'owner', 'group' and 'all' so we need a triplet for each, resulting in nine letters. Lets try something in our command prompt with ls -l command. umasarath@ubuntu:~$ ls -l total 53780 -rw-r--r-- 1 umasarath group 27455157 2012-11-16 10:28 sample.xml drwxr-xr-x 2 umasarath group      4096 2013-01-23 10:17 files -rw-r--r-- 1 umasarath group      1338 2013-09-14 08:32 keystore drwxr-xr-x 2 umasarath group      4096 2013-09-16 10: