Basic Linux commands

Useful  Linux Commands:

1. How to find and kill a process in Unix:

find a process: ps -ef |grep tomcat

kill process: kill -9 (pid)

2.How will you figure out free available space in Uni

Ans: df command – Shows the amount of disk space used and available on Linux file systems.du command – Display the amount of disk space used by the specified files and for each subdirectory.
df -h

3. Help for any command

man  command name like man df

4.How will you find files recursively that contains specific words in their contents

Search for a given string in all files recursively

$ grep -r "ramesh" * 

  
5.Search for a given string in a file (case in-sensitive search)

$ grep -i "the" demo_file

6. How will you find files recursively that contains specific words in their filename

find . -maxdepth 1 -name "*string*" -print 

It will find all files in the current directory (delete maxdepth 1 if you want

it recursive) containing "string" and will print it on the screen.

7.How to sort a file using unix command
sort -filename
for numeric sort
sort -n filename

reverse sort
sort -r filename      

reverse sort without duplicate

sort -u -i filename

8. How to count number of lines in a file in unix terminal

wc sort.txt

output : 5  5 41 sort.txt 

The three numbers produced in output correspond to number of lines, 

number of words and number of bytes 

9.How will you list nth column of a flat file in Unix ?
awk '{ print $2 $4 }' filename.txt

10.How will you find a process using specific port in Unix and Windows ?

netstat -tulpn

Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 127.0.0.1:3306          0.0.0.0:*               LISTEN      1138/mysqld     
tcp        0      0 0.0.0.0:111             0.0.0.0:*               LISTEN      850/portmap        

  
filter for specfic port:
netstat -tulpn | grep :80 

11.How will you copy a file from one Unix host to another Unix host
In the following example, transfer all files (/var/www/html) from remote server called server1 to another server called server2:
scp -r user@server1:/var/www/html/ user@server2:/var/www/html/

I recommend using rsync command which will only push or download updated files. It can copy locally, to/from another host over any remote shell, or to/from a remote rsync daemon. In this example, copy files from remote server called server1 into /backup directory:
rsync -avz -e ssh user@server1:/var/www/html /backup   

Basic Linux/Unix Commands Part1

Command	Explanation
	Commands are entered at terminal Unix is case sensitive ~ Home directory _ and hyphen allowed in file names, spaces are not allowed hidden files start with . There is no recycle bin in Unix. Files deleted cannot be restored. every user has a home directory denoted by ~
passwd	Change password
ls ls –l <directory>ls -l <directory>ls -t ls -a ls -la	List files and subdirectories All information of files or subdirectories /<fullpath> Sort by creation time all directories including hidden directory . – current .. – parent
cd <directory> cd .. cd / cd ~ pwd	Change directory parent directory root directory home directory of user present working directory
man <command>	documentation for all unix commands if there is : at bottom next page of documentation press <spacebar> to get out of documentation press q
cat <filename> more <filename>	displays contents of file, scrolls if file is large display page wise contents of a file
mkdir <directoryname> mv <filename> <destination_directory> cp <source_file> <new_file> cp -R <source_dir> <destination_dir>	create new directory move a file to another location wildcards can be used to move multiple files copy files copy all files and subdirectories recursively
rm <filename> rmdir <directory> rm -R <directory>	There is no recycle bin in unix and file/directory once deleted cannot be recovered remove a file wildcards can also be used remove the directory Empty directory cannot be removed remove everything in directory including the directory
ln <source_file> <destination_file> ln -s <sourc_dir> <destination_dir> ls <linkeddirectory>	Link file Deleting a linked file does not delete original file Link a directory. create a symbolic link
find <wheretofind> -name <whattofind> -print find <wheretofind> -type d -print find <wheretofind> -type f –print find <wheretofind> -size +10M -print	Find a file. Print results on screen Get all directories Get all files Get all files >10MB

Linux Commands Part2

Command	Explanation
history !<line no>	Get all previous commands Run a command from history list
chmod <permission> <filename>	Change file/directory permissions
wc <file_name> wc -w <file_name> wc -l <file_name> ls | wc -l	count of lines, count of words, count of characters count of words count of lines count of files in a directory
head <file_name> tail <file_name> tail -f <file_name>	first few lines last few lines watch last lines of a file as it grows
clear	Clear screen
grep <word> <filename> grep -c <word> <filename> grep -i <word> <filename> grep -v <word> <filename> grep ^<word> <filename> grep <word>$ <filename> grep a. <filename> grep a* <filename> grep a[bc] <filename>	Searh a word in file count of times a word occurs case insensitive search lines which do not have the word line starting with word line ending with word . means any character. word a followed with any character occurrence of a followed with any number of characters searches for words ab or ac in file
diff <filename1> <filename2>	Compare contents of two files
tar –cvf <tar_file_name> <contents> tar –tvf <tar_file_name> tar –xvf <tar_file_name>	Create a tar file Get list of tar file contents Extract contents of tar file
env | more	get list of all environment variables
echo $SHELL echo $PATH	get name of shell get PATH variable contents
which <command>	Get the location of file for command
ps	Get list of all processes
ps aux | grep <username>	Get list of all process running for all users and then sort the processes for a user
kill <processId> kill -9 <processId>	Kills a process Kills a process and all its child processes
vi editor commands
<ctrl>+o <ctrl>+x vi <filename> i <ESC> x :wq :q	Save Exit Open an existing or new file in vi editor Go to insert mode Get out of insert mode Delete a character Write and quit Quit

 

Java Qestions

1. How do you create an Object instance without using new
   1. Using newInstance method of Class class Eg: Class clas = Class.forName("NewClass"); NewClass obj = (NewClass) clas.newInstance(); - Class.forName() loads the class and to create an object, we need to use newInstance() method of Class class. or using class loader: getClass().getClassLoader().loadClass("NewClass").newInstance();
      
   2. Using Object Deserialization Eg : ObjectInputStream objStream = new ObjectInputStream(inputStream );
      NewClass obj = (NewClass ) inStream.readObject();
      
   3. Using clone() of java.lang.Object Eg: NewClass obj = new NewClass();
      NewClass obj2 = obj.clone(); - Creates copy of an existing object

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4. Equals and HashCode Impl

If you've installed Juno EE it should support .jsp editor. Most probably, your Eclipse is "starting" with java less than v1.6 (for me it was as well, I have 1.3, 1.5, 1.6 javas installed; default was 1.5 and Eclipse was starting with it automatically) I solved same problem with below way: 1) Right click on Juno shortcut and click Properties 2) In the field "Target" You already should have something like below: "D:\PROGRAM INSTALL\eclipse-jee-juno-SR2-win32\eclipse\eclipse.exe" Add to the end of that line one more command as below (show to Eclipse with which java version it should start) -vm "C:\Program Files\Java\jdk1.6.0_20\bin\java.exe" My target looks like below: "D:\PROGRAM INSTALL\eclipse-jee-juno-SR2-win32\eclipse\eclipse.exe" -vm "C:\Program Files\Java\jdk1.6.0_20\bin\java.exe" 3) Start Eclipse with changed target using your shortcut 4) On .jsp file now you will be able to chose "Open with --> JSP Editor 5.http://www.corejavainterviewquestions.com/idiots-guide-big-o/ 6. http://learngitbranching.js.org/ Solr Blog :http://blog.thedigitalgroup.com/dattatrayap/