Prepare 4 interview - Recent questions and answers in UNIX Interview Questions and Answers

What is Unix?

Thu, 22 Sep 2011 07:21:51 +0000

What is UniX

Answered: options for using df command

Wed, 02 Feb 2011 11:44:18 +0000

u can use df -kh
for showing disk utilization in MB or GB

Can I find several patterns and refer to them in the replacement string?

Fri, 22 Oct 2010 17:34:53 +0000

Answered: How do you inject text with sed?

Fri, 22 Oct 2010 17:34:14 +0000

& in the substitution string defines the pattern found in the search string. As an example, here’s us trying to find a word ‘hello’ and replacing it with ‘hello and how are you’:
echo ‘hello there’ | sed ’s/^hello/& and how are you/’

How do you substitute strings with sed?

Fri, 22 Oct 2010 17:12:13 +0000

Answered: What is sed?

Fri, 22 Oct 2010 17:03:02 +0000

sed is stream editor, a Unix tool for working with streams of text data.

Answered: List some UNIX Commands

Sat, 24 Jul 2010 12:40:44 +0000

ls list files and directories
ls a list all files and directories
mkdir make a directory
cd directory change to named directory
cd change to home directory
cd ~ change to home directory
cd .. change to parent directory
pwd display the path of the current directory

cp file1 file2 copy file1 and call it file2
mv file1 file2 move or rename file1 to file2
rm file remove a file
rmdir directory remove a directory

cat file display a file
more file display a file a page at a time
head file display the first few lines of a file
tail file display the last few lines of a file
grep 'keyword' file search a file for keywords
wc file count number of lines/words/characters in file

command > file redirect standard output to a file
command >> file append standard output to a file
command < file redirect standard input from a file
command1 | command2 pipe the output of command1 to the input of command2
cat file1 file2 > file0 concatenate file1 and file2 to file0
sort sort data
who list users currently logged in
a2ps Pprinter textfile print text file to named printer
lpr Pprinter psfile print postscript file to named printer

* match any number of characters
? match one character
man command read the online manual page for a command
whatis command brief description of a command
apropos keyword match commands with keyword in their man pages

ls lag list access rights for all files
chmod [options] file change access rights for named file
command & run command in background
^C kill the job running in the foreground
^Z suspend the job running in the foreground
bg background the suspended job
jobs list current jobs
fg %1 foreground job number 1
kill %1 kill job number 1
ps list current processes
kill 26152 kill process number 26152

Answered: Explain about Pipes in UNIX?

Sat, 24 Jul 2010 12:38:36 +0000

To see who is on the system with you, type

% who

One method to get a sorted list of names is to type,

% who > names.txt
% sort < names.txt

This is a bit slow and you have to remember to remove the temporary file called names when you have finished. What you really want to do is connect the output of the who command directly to the input of the sort command. This is exactly what pipes do. The symbol for a pipe is the vertical bar |

For example, typing

% who | sort

will give the same result as above, but quicker and cleaner.

To find out how many users are logged on, type

% who | wc -l
Exercise 3b

a2ps -Phockney textfile is the command to print a postscript file to the printer hockney.

Using pipes, print all lines of list1 and list2 containing the letter 'p', sort the result, and print to the printer hockney.

What is the use of Unix command : history

Sat, 24 Jul 2010 12:37:02 +0000

What is the use of Unix command : file?

Sat, 24 Jul 2010 12:36:55 +0000

What is the use of Unix command : gzip?

Sat, 24 Jul 2010 12:36:51 +0000

Answered: What is the use of Unix command : compress?

Sat, 24 Jul 2010 12:36:45 +0000

This reduces the size of a file, thus freeing valuable disk space. For example, type

% ls -l science.txt

and note the size of the file. Then to compress science.txt, type

% compress science.txt

This will compress the file and place it in a file called science.txt.Z

To see the change in size, type ls -l again.

To uncomress the file, use the uncompress command.

% uncompress science.txt.Z

Answered: What is the use of Unix command : du?

Sat, 24 Jul 2010 12:36:19 +0000

The du command outputs the number of kilobyes used by each subdirectory. Useful if you have gone over quota and you want to find out which directory has the most files. In your home-directory, type

% du

What is the use of Unix command : df?

Sat, 24 Jul 2010 12:35:30 +0000

What is the use of Unix command : quota?

Sat, 24 Jul 2010 12:35:19 +0000

Explain about Killing a process in UNIX

Sat, 24 Jul 2010 12:35:13 +0000

Explain about Listing suspended and background processes in UNIX

Sat, 24 Jul 2010 12:35:07 +0000

Explain about Processes and Jobs in UNIX

Sat, 24 Jul 2010 12:34:59 +0000

Explain about Changing access rights in UNIX

Sat, 24 Jul 2010 12:34:49 +0000

Explain about File system security (access rights) in UNIX

Sat, 24 Jul 2010 12:34:38 +0000

Answered: Explain about Getting Help in UNIX

Sat, 24 Jul 2010 12:34:16 +0000

On-line Manuals
---------------
There are on-line manuals which gives information about most commands. The manual pages tell you which options a particular command can take, and how each option modifies the behaviour of the command. Type man command to read the manual page for a particular command.

For example, to find out more about the wc (word count) command, type

% man wc

Alternatively

% whatis wc

gives a one-line description of the command, but omits any information about options etc.
Apropos

When you are not sure of the exact name of a command,

% apropos keyword

will give you the commands with keyword in their manual page header. For example, try typing

% apropos copy

Answered: Explain about Filename conventions in UNIX

Sat, 24 Jul 2010 12:34:10 +0000

We should note here that a directory is merely a special type of file. So the rules and conventions for naming files apply also to directories.

In naming files, characters with special meanings such as / * & % , should be avoided. Also, avoid using spaces within names. The safest way to name a file is to use only alphanumeric characters, that is, letters and numbers, together with _ (underscore) and . (dot).

File names conventionally start with a lower-case letter, and may end with a dot followed by a group of letters indicating the contents of the file. For example, all files consisting of C code may be named with the ending .c, for example, prog1.c . Then in order to list all files containing C code in your home directory, you need only type ls *.c in that directory.

Beware: some applications give the same name to all the output files they generate.

For example, some compilers, unless given the appropriate option, produce compiled files named a.out. Should you forget to use that option, you are advised to rename the compiled file immediately, otherwise the next such file will overwrite it and it will be lost.

Explain about Wildcards in UNIX

Sat, 24 Jul 2010 12:34:00 +0000

Explain about Redirecting the Input in UNIX

Sat, 24 Jul 2010 12:33:19 +0000

Explain about Redirecting the Output in UNIX

Sat, 24 Jul 2010 12:33:13 +0000

Explain about Redirection in UNIX

Sat, 24 Jul 2010 12:33:04 +0000

Explain about Searching the contents of a file in UNIX

Sat, 24 Jul 2010 12:32:56 +0000

Explain about Displaying the contents of a file on the screen in UNIX

Sat, 24 Jul 2010 12:32:48 +0000

Explain about Removing files and directories in UNIX

Sat, 24 Jul 2010 12:32:40 +0000

Explain about Moving files in UNIX

Sat, 24 Jul 2010 12:32:30 +0000

Explain about Copying files in UNIX

Sat, 24 Jul 2010 12:32:15 +0000

Answered: More about Home directories and pathnames

Sat, 24 Jul 2010 12:29:40 +0000

Understanding pathnames
-------------------------------------
First type cd to get back to your home-directory, then type

% ls unixstuff

to list the conents of your unixstuff directory.

Now type

% ls backups

You will get a message like this -

backups: No such file or directory

The reason is, backups is not in your current working directory. To use a command on a file (or directory) not in the current working directory (the directory you are currently in), you must either cd to the correct directory, or specify its full pathname. To list the contents of your backups directory, you must type

% ls unixstuff/backups

~ (your home directory)
-----------------------------------
Home directories can also be referred to by the tilde ~ character. It can be used to specify paths starting at your home directory. So typing

% ls ~/unixstuff

will list the contents of your unixstuff directory, no matter where you currently are in the file system.

What do you think

% ls ~

would list?

What do you think

% ls ~/..

would list?

Answered: Explain about Pathnames in UNIX

Sat, 24 Jul 2010 12:28:02 +0000

pwd (print working directory)

Pathnames enable you to work out where you are in relation to the whole file-system. For example, to find out the absolute pathname of your home-directory, type cd to get back to your home-directory and then type

% pwd

The full pathname will look something like this -

/a/fservb/fservb/fservb22/eebeng99/ee91ab

which means that ee91ab (your home directory) is in the directory eebeng99 (the group directory),which is located on the fservb file-server.

Note:

/a/fservb/fservb/fservb22/eebeng99/ee91ab

can be shortened to

/user/eebeng99/ee91ab

The directories . And .., in UNIX

Sat, 24 Jul 2010 09:43:57 +0000

Explain about the directories . And .., in UNIX

Answered: Changing to a different directory, in UNIX

Sat, 24 Jul 2010 09:35:18 +0000

cd (change directory)
-----------------------------
The command cd directory means change the current working directory to 'directory'. The current working directory may be thought of as the directory you are in, i.e. your current position in the file-system tree.

To change to the directory you have just made, type

% cd unixstuff

Type ls to see the contents (which should be empty)

Answered: Making Directories, in UNIX

Sat, 24 Jul 2010 09:31:33 +0000

mkdir (make directory)

We will now make a subdirectory in your home directory to hold the files you will be creating and using in the course of this tutorial. To make a subdirectory called unixstuff in your current working directory type

% mkdir unixstuff

To see the directory you have just created, type

% ls

Answered: Listing files and directories, in UNIX

Sat, 24 Jul 2010 09:30:06 +0000

ls (list)
---------
When you first login, your current working directory is your home directory. Your home directory has the same name as your user-name, for example, ee91ab, and it is where your personal files and subdirectories are saved.

To find out what is in your home directory, type

% ls (short for list)

The ls command lists the contents of your current working directory.

There may be no files visible in your home directory, in which case, the UNIX prompt will be returned. Alternatively, there may already be some files inserted by the System Administrator when your account was created.

ls does not, in fact, cause all the files in your home directory to be listed, but only those ones whose name does not begin with a dot (.) Files beginning with a dot (.) are known as hidden files and usually contain important program configuration information. They are hidden because you should not change them unless you are very familiar with UNIX!!!

To list all files in your home directory including those whose names begin with a dot, type

% ls -a

ls is an example of a command which can take options: -a is an example of an option. The options change the behaviour of the command. There are online manual pages that tell you which options a particular command can take, and how each option modifies the behaviour of the command.

Answered: Explain iostat, vmstat and netstat.

Tue, 20 Jul 2010 20:13:25 +0000

Iostat reports on terminal, disk and tape I/O activity.
Vmstat reports on virtual memory statistics for processes, disk, tape and CPU activity.
Netstat reports on the contents of network data structures.

Answered: Briefly, how do you install Oracle software on UNIX.

Tue, 20 Jul 2010 10:03:05 +0000

1. Log onto you computer as a member of the administrative group that is authorized to install Oracle software and create and run the database.

2. Insert the distribution CD for the database into your CD drive. The Autorun window will appear automatically.
Select Install/Deinstall Products.

Note: If you are downloading from Oracle’s download site, follow the instructions given on the Web site.

3. The Oracle Universal Installer Welcome window appears. Select Next to begin the installation of your software

4. On UNIX and Linux installations, the Specify Inventory directory and credentials window appears. Enter the full path of the directory in which to install the Oracle
software or accept the default. Enter the name of an operating system group that has write permission to the directory. Click Next. Click OK.

5. A dialog page appears.
Open a new terminal window, log in as root, and run the orainstRoot.sh script as instructed in the dialog page. When the script finishes, return to the Oracle Universal
Installer page and click Continue.

6. The Specify File Locations page appears. Enter the Oracle home name and directory path in which to install the Oracle software or accept the default. Click Next.

7. The Select Installation Type page appears. Select Enterprise Edition or Standard Edition as appropriate for your environment. Click Next.

8. The installer will now verify that your system meets all the minimum requirements for installing and configuring the chosen products. Correct any reported issues before continuing. Click Next.

9. The Select Database Configuration page appears. Select the starter database type of General Purpose, Transaction Processing, or Data Warehouse. Click Next.

10. The Specify Database Configuration Options page appears. Enter the Global Database Name and SID in the Database Naming section. Select the character set in the Database Character Set section. Select Create database with
Sample Schemas to install the Sample schemas. Click Next.

11. The Select Database Management Option page appears. Select Use Database Control for Database Management. Click Next.

12. The Specify Database File Storage Option page appears. Select File System, Automatic Storage Management, or Raw Devices as appropriate to your environment. Click Next.

13. The Specify Backup and Recovery Options page appears. Select Do not enable Automated backups to configure your own backup schedule. Click Next.

14. The Specify Database Schema Passwords page appears. Select Use different passwords for these accounts and enter passwords for the administrative users or select Use the same password for all the accounts and enter the password. Click Next.

15. The Summary page appears containing a list of the products to be installed. Click Install to begin the installation.

16. You will see the progress window.

17. The Configuration Assistants page appears. Allow the assistants to execute. They configure your network, start an Oracle Net Services listener process for connecting to the database, create the database and configure management tools.

18. A page showing a progress bar for database creation appears.

19. When the database creation is finished, a page containing information about your database appears. Review this list. You may click on Password Management at the bottom of the page if you want to unlock or change passwords for database accounts. Otherwise click OK.

20. A dialog page appears.

Open a new terminal window, log in as root, and run the root.sh script. When the script finishes, return to the Oracle Universal Installer page and click OK.

21. The End of Installation page appears with important information about Web application port numbers.

22. Click Yes to exit.

23. You have now completed the installation of Oracle software and database creation.

Answered: What is the difference between a soft link and a hard link in UNIX?

Tue, 20 Jul 2010 09:52:54 +0000

Hard Links :
----------------
1. All Links have same inode number.
2.ls -l command shows all the links with the link column(Second) shows No. of links.
3. Links have actual file contents
4.Removing any link just reduces the link count but doesn't affect other links.

Soft Links(Symbolic Links) :
--------------------------------------
1.Links have different inode numbers.
2. ls -l command shows all links with second column value 1 and the link points to original file.
3. Link has the path for original file and not the contents.
4.Removing soft link doesn't affect anything but removing original file the link becomes dangling link which points to non-existant file.

Answered: Explain the read, write, and execute permissions on a UNIX directory

Tue, 20 Jul 2010 09:48:25 +0000

Read allows you to see and list the directory contents. Write allows you to create, edit and delete files and sub-directories in the directory. Execute gives you the previous read/write permissions plus allows you to change into the directory and execute programs or shells from the directory.

Answered: How do you execute a UNIX command in the background?

Tue, 20 Jul 2010 09:46:57 +0000

In Unix, a background process executes independently of the shell, leaving the terminal free for other work. To run a process in the background, include an & (an ampersand) at the end of the command you use to run the job. Following are some examples:

    * To run the count program, which will display the process identification number of the job, enter: count &
    * To check the status of your job, enter: ps
    * To bring a background process to the foreground, enter: fg
    * If you have more than one job suspended in the background, enter: fg %#

      Replace # with the job number, as shown in the first column of the output of the jobs command.
    * You can kill a background process by entering: kill PID

      Replace PID with the process ID of the job. If that fails, enter the following:
      kill -KILL PID
    * To determine a job's PID, enter: jobs -l
    * If you are using sh, ksh, bash, or zsh, you may prevent background processes from sending error messages to the terminal. Redirect the output to /dev/null using the following syntax: count 2> /dev/null &

Answered: How do you list the files in an UNIX directory while also showing hidden files?

Tue, 20 Jul 2010 09:40:48 +0000

--------------
ls -ltra
--------------

Give two UNIX kernel parameters that effect an Oracle install

Tue, 20 Jul 2010 09:32:32 +0000

How would you change all occurrences of a value using VI, in UNIX?

Tue, 20 Jul 2010 09:32:08 +0000

Give the command to display space usage on the UNIX file system.

Tue, 20 Jul 2010 09:30:23 +0000

What UNIX command will control the default file permissions when files are created?

Tue, 20 Jul 2010 09:29:06 +0000