Tuesday, November 5, 2013

Command used in day to day activity

Command to find the used ports in server

netstat -ln | grep '80 ' | grep 'LISTEN'
netstat -atnp|grep LISTEN 

netstat -ln | grep '99 ' | grep 'LISTEN'
 netstat -ln | grep '16'

telnet <machine_IP> <port>

Command  for copying files to server

 scp -pr RMVServices-0.0.2-SNAPSHOT.war shib@

Command for multiple search 

tail -f /tmp/Liferay-JBoss.out |grep 'PAGENAME\|tabName'

grep 'PAGENAME\|tabName'  for multiple search

Command to set line no in VI Editor

:set nu   for line no

:/ERROR   for ERROR search in VI

grep -r devapp214 ./|grep tst2

Command to shutdown jboss 

./shutdown.sh -s

./shutdown.sh -s

Command to search files

find ./ -name jboss-admin.sh

Command to see difference in  files

sdiff  ./pdf.css  /opt/dadm/liferay-portal-6.0-ee-sp2/jboss-.1.0/server/default/deploy/PPortlet.war/css/pdf.css

 Schedule a Background Cron Job For Every 10 Minutes.

Use the following, if you want to check the disk space every 10 minutes.
*/10 * * * * /home/ramesh/check-disk-space

Monday, January 28, 2013

Hiding a file or directory under Linux

Hiding a file or directory under Linux
To hide a file or directory in Linux, just give it a name preceded by a full stop (.).

For example:
. bash_history
. bash_profile
. ssh 

Hide UNIX file structure
1. Open a terminal and execut "ls -1 / | sudo tee /.hidden"

2. Do "sudo chmod a+r .hidden"

3. If you want all standard files hidden, skip to 5. Otherwise. Open the file with "sudo gedit /.hidden".

4. Remove every directory you don't want to hide from the file. Here's how mine looks like, as an example:


5. Now, let's create some entries that are easier for new users: select "home" and create a link to link to it (for example, by dragging it and holding <ctrl>+<shift>. Your mouse cursor should show two linked circles when dragging while holding them, if they do you're creating a link). Rename that link to "User Data" or something similar. Do the same with media; rename it to "Drives" or "Media" or what you want. (If the files are already hidden. show them with <ctrl>-<h>.)

6. If you want to have a discoverable way to some or all of the now hidden files, create a folder called "System Data". Create links to all the other files and directories there.

7. You're done! :) Update an open Nautilus with <ctrl>-<r>, or restart it with "killall nautilus".

I attached a screenshot of how it looks like.

Now, some anticipated FAQs:

Q: Won't this royally screw my system?
A: I see no reson why it should. Everything is still in it's original place, only no longer visible by default. It definitely works fine here and on several other Ubuntu installations.

Q: Are there any negative side effects?
A: Not that I know of. From the command line, everything stays the same. If you encounter any problem, please tell me!

Q: I want to access one of the hidden folders. How do I do that?
A: View -> Show Hidden Files. Or press <ctrl>-h

Q: I don't like this! How can I undo it?
A: Simple, just remove the .hidden file. Delete the links you created in step 5 and 6 if you want, or leave them there. Just make sure you don't accidentally delete the original folders. :)

Q: Can I have all the files shown automatically if I have a sudo'd nautilus?
A: Certainly. Make sure that the .hidden file is owned by root (should be automatically), then, in the permissions tab, disallow read access for the owner.

Q: Can I do that .hidden stuff in other directories too?
A: Yes. It's a pretty cool feature.

Q: Are there any limitations to this?
A: Yes, the file selector (ie open dialog) will still show all the files. The .hidden file currently only applies to Nautilus.

Wednesday, January 9, 2013

Touch & More


touch [-acm] [-f agefile] [-r agefile] [[-t] time] file ...

touch [-acm] time file ...

The touch command changes certain dates for each file argument. By default, touch sets both the date of last file modification and the date of last file access to the current time. This is useful for maintaining correct release times for software and is particularly useful in conjunction with the MKS Make software development facility.

-a    sets only the access time.
-c    does not create any files that do not already exist. Normally, touch creates such files.
-m    sets only the modification time.
If you do not specify -a or -m, touch behaves as though you specified both.

To tell touch to use a time other than the current, use one of the following options:

-f agefile    is an obsolete version of the POSIX-compliant -r option.
-r agefile    sets the access and modification times (as indicated by the other options) to     those kept for agefile.
-t time     specifies a particular time using this format:


where cc is the optional first 2 digits of the year, yy is the optional last 2 digits of the year, MM is the optional number of the month (01-12), dd is the optional day of the month, hh is the hour in 24 hour format (required), mm is the minutes (required), ss is the optional seconds.


touch newfile

sets the modification time of newfile to the present.

touch -t 8001031305 oldfile

sets the modification time of oldfile to 13:05 on January 3, 1980.

touch -r oldfile newfile

sets the modification time of newfile to that of oldfile.


More is a command used to read text files. For example, we could do this:

% more poems

The effect of this to let you read the file "poems ". It probably will not fit in one screen, so you need to know how to "turn pages". Here are the basic commands:

q --- quit more
spacebar --- read next page
return key --- read next line
b --- go back one page

For still more information, use the command man more.
To display the file named letter.txt on the screen, the user can type either of the following two commands:

more < letter.txt
type letter.txt | more

The command displays the first screen of information from letter.txt, and then the following prompt appears:

-- More --

When the spacebar is pressed, the next screen of information will be displayed. It is also possible to clear the screen and remove all extra blank lines before displaying the file:

more /c /s < letter.txt
type letter.txt | more /c /s

How to concatenate two files line by line 

I have two text files; each of them contains information by line such like that
file1.txt            file2.txt
----------           ---------
linef11              linef21
linef12              linef22
linef13              linef23

I would like to concatenate theses files lines by lines using a bash script in order to obtain:
linef11     linef21
linef12     linef22
linef13     linef23

1.      paste file1.txt file2.txt > fileresults.txt

2.      awk '
  # store the first file, indexed by col2
  NR==FNR {f1[$2] = $0; next}
  # output only if file1 contains file2's col2
  ($2 in f1) {print f1[$2], $0}
' file1 file2

3.      You can do that with a combination of the sort and join commands. The straightforward approach is
join -j2 <(sort -k2 file1) <(sort -k2 file2)
But that displays slightly differently than you're looking for. It just shows the common join field and then the remaining fields from each file

Beginners UNIX Interview Questions Answers

1. Write command to list all the links from a directory?
In this UNIX command interview questions interviewer is generally checking whether user knows basic use of "ls" "grep" and regular expression etc
You can write command like:
ls -lrt | grep "^l"

2. Create a read-only file in your home directory?
This is a simple UNIX command interview questions where you need to create a file and change its parameter to read-only by using chmod command you can also change your umask to create read only file.
touch file
chmod 400 file

3. How will you find which operating system your system is running on in UNIX?
By using command "uname -a" in UNIX

4. How will you run a process in background? How will you bring that into foreground and how will you kill that process?
For running a process in background use "&" in command line. For bringing it back in foreground use command "fg jobid" and for getting job id you use command "jobs", for killing that process find PID and use kill -9 PID command. This is indeed a good Unix Command interview questions because many of programmer not familiar with background process in UNIX.

5. How do you know if a remote host is alive or not?
You can check these by using either ping or telnet command in UNIX. This question is most asked in various Unix command Interview because its most basic networking test anybody wants to do it.

6. How do you see command line history in UNIX?
Very useful indeed, use history command along with grep command in unix to find any relevant command you have already executed. Purpose of this Unix Command Interview Questions is probably to check how familiar candidate is from available tools in UNIX operation system.

7. How do you copy file from one host to other?
Many options but you can say by using "scp" command. You can also use rsync command to answer this UNIX interview question or even sftp would be ok.

8. How do you find which process is taking how much CPU?
By using "top" command in UNIX, there could be multiple follow-up UNIX command interview questions based upon response of this because “TOP” command has various interactive options to sort result based upon various parameter.

9. How do you check how much space left in current drive?
By using "df" command in UNIX. For example "df -h ." will list how full your current drive is. This is part of anyone day to day activity so I think this Unix Interview question will be to check anyone who claims to working in UNIX but not really working on it.

10. What is the difference between Swapping and Paging?
Whole process is moved from the swap device to the main memory for execution. Process size must be less than or equal to the available main memory. It is easier to implementation and overhead to the system. Swapping systems does not handle the memory more flexibly as compared to the paging systems.
Only the required memory pages are moved to main memory from the swap device for execution. Process size does not matter. Gives the concept of the virtual memory. It provides greater flexibility in mapping the virtual address space into the physical memory of the machine. Allows more number of processes to fit in the main memory simultaneously. Allows the greater process size than the available physical memory. Demand paging systems handle the memory more flexibly.

Intermediate UNIX Interview Questions Answers
1. What is difference between ps -ef and ps -auxwww?
This is indeed a good Unix Interview Command Question and I have faced this issue while ago where one culprit process was not visible by execute ps –ef command and we are wondering which process is holding the file.
ps -ef will omit process with very long command line while ps -auxwww will list those process as well.

2. How do you find how many cpu are in your system and there details?
By looking into file /etc/cpuinfo for example you can use below command:
cat /proc/cpuinfo

4. What is Zombie process in UNIX? How do you find Zombie process in UNIX?
When a program forks and the child finishes before the parent, the kernel still keeps some of its information about the child in case the parent might need it - for example, the parent may need to check the child's exit status. To be able to get this information, the parent calls 'wait()'; In the interval between the child terminating and the parent calling 'wait()', the child is said to be a 'zombie' (If you do 'ps', the child will have a 'Z' in its status field to indicate this.)
Zombie : The process is dead but have not been removed from the process table.

5. What is "chmod" command? What do you understand by this line “r-- -w- --x?

6. There is a file some where in your system which contains word "UnixCommandInterviewQuestions” How will find that file in Unix?

7. In a file word UNIX is appearing many times? How will you count number?
grep -c "Unix" filename

8. How do you set environment variable which will be accessible form sub shell?
By using export   for example export count=1 will be available on all sub shell.

9. How do you check if a particular process is listening on a particular port on remote host?
By using telnet command for example “telnet hostname port”, if it able to successfully connect then some process is listening on that port. To read more about telnet read networking command in UNIX

10. How do you find whether your system is 32 bit or 64 bit ?
Either by using "uname -a" command or by using "arch" command.

Advanced UNIX Interview Questions and Answers
1. How do you find which processes are using a particular file?
By using lsof command in UNIX. It wills list down PID of all the process which is using a particular file.

2. How do you find which remote hosts are connecting to your host on a particular port say 10123?
By using netstat command execute netstat -a | grep "port" and it will list the entire host which is connected to this host on port 10123.

3. What is ephemeral port in UNIX?
Ephemeral ports are port used by Operating system for client sockets. There is a specific range on which OS can open any port specified by ephemeral port range.

4. If one process is inserting data into your MySQL database? How will you check how many rows inserted into every second?
Purpose of this Unix Command Interview is asking about "watch" command in UNIX which is repeatedly execute command provided with specified delay.

5. There is a file Unix_Test.txt which contains words Unix, how will you replace all Unix to UNIX?
You can answer this Unix Command Interview question by using SED command in UNIX for example you can execute sed s/Unix/UNIX/g fileName.

6. You have a tab separated file which contains Name, Address and Phone Number, list down all Phone Number without there name and Addresses?
To answer this Unix Command Interview question you can either you AWK or CUT command here. CUT use tab as default separator so you can use
cut -f3 filename.

7. Your application home directory is full? How will you find which directory is taking how much space?
By using disk usage (DU) command in Unix for example du –sh . | grep G  will list down all the directory which has GIGS in Size.

8. How do you find for how many days your Server is up?
By using uptime command in UNIX

9. You have an IP address in your network how will you find hostname and vice versa?
This is a standard UNIX command interview question asked by everybody and I guess everybody knows its answer as well. By using nslookup command in UNIX