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Tuesday, September 11, 2012

Interview Questions : Linux/Unix : Part-2

1: What are the 3 standard streams in Linux?
Output stream , represented as 0 , Input stream, represented as 1 and Error stream represented as 2.

2: I want to read all input to the command from file1 direct all output to file2 and error to file 3, how can I achieve this?
command <file1 0>file2 2>file3

3: What will happen to my current process when I execute a command using exec?
“exec” overlays the newly forked process on the current  process ; so when I execute the command using exec  a new process corresponding to the command will be created and the current process will die.
Eg: Executing “exec  com1”  on command prompt will execute com1 and return to login prompt since my logged in shell is superimposed with the new process of the command .

4: How will you emulate wc –l using awk?
awk ‘END {print NR} fileName’

5: Given a file find the count of lines containing word “ABC”.
grep –c  “ABC” file1

6: What is the difference between grep and egrep?
egrep is Extended grep that supports added grep features like “+” (1 or more occurrence of previous character),”?”(0 or 1 occurrence of previous character) and “|” (alternate matching)

7: How will you print the login names of all users on a system?
/etc/shadow file has all the users listed.
awk –F ‘:’ ‘{print $1} /etc/shadow’|uniq -u

8: How to set an array in Linux?
Syntax in ksh:
Set –A arrayname= (element1 element2 ….. element)
In bash
A=(element1 element2 element3 …. elementn)

9: Write down the syntax of “for “ loop
for  iterator in (elements)
execute commands

10:How will you find the total disk space used by a specific user?
du  -s /home/user1             ….where user1 is the user for whom the total disk
space needs to be found.

11: Write the syntax for “if” conditionals in linux?
If  condition is successful
execute commands
execute commands

12:What is the significance of $? ?
$? gives the exit status of the last command that was executed.

13: How do we delete all blank lines in a file?

sed  ‘^ [(backslash)011(backslash)040]*$/d’ file1
where (backslash)011 is octal equivalent of space and
(backslash)040 is octal equivalent of tab

14: How will I insert a line “ABCDEF” at every 100th line of a file?
sed ‘100i\ABCDEF’ file1

15: Write a command sequence to find all the files modified in less than 2 days and print the record count of each.
find . –mtime -2 –exec wc –l {} \;

16: How can I set the default rwx permission to all users on  every file which is created in the current shell?
We can use:

umask 777
This will set default rwx permission for every file which is created to every user.

17: How can we find the process name from its process id?
We can use “ps –p ProcessId”

18: What are the four fundamental components of every file system on linux?
bootblock, super block, inode block and  datablock

19: What is a boot block?
This block contains a small program called “Master Boot record”(MBR) which loads the kernel  during system boot up.

20: What is a super block?
Super block contains all the information about the file system like size of file system, block size used by it,number of free data blocks and list of free inodes and data blocks.

21: What is an inode block?
This block contains the inode for every file of the file system along with all the file attributes except its name.

22: How can I send a mail with a compressed file as an attachment?
  zip file1.zip file1|mailx –s “subject” Recepients email id
 Email content

23: How do we create command aliases in shell?
alias Aliasname=”Command whose alias is to be created”

24: What are “c” and “b” permission fields of a file?
“c “ and “b” permission fields are generally associated with a device file. It specifies whether a file is a character special file or a block special file.

25: What is the use of a shebang line?
Shebang line at top of each script determines the location of the engine which is to be used in order to execute the script.

njoy the simplicity.......
Atul Singh

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