Unix Basics

                                          UNIX BASICS

1) How to find hidden files in current directory?

   $ ls -lrta

2) How to find current running processes in unix server?

  $ ps -ef

and if we want to find specific process we can use 'grep' with pipe
  $ ps -ef | grep -i 'application'

3) How to find process which is taking maximum memory in server?
  $ top
  top command tell us about cpu usage , process id and other details. below is output of top command

4) How to find Exception in log files available in current directory and how to find number of occurrence?
 
   $ grep 'Exception' log1.txt | wc -l

5) find all files in current and subdirectories which contains 'log' name?

   $ find . -name 'log'


6) How do you access command line arguments from within a shell script?

Arguments passed from the command line to a shell script can be accessed within the shell script by using a $ (dollar sign) immediately followed with the argument's numeric position on the command line.

7) How to tails last 200 lines of any log fine?

    $ tail -200f filename.txt

8) How to find remaining disk space in unix\linux server?

    $ df -kl

df -kl

Filesystem   1024-blocks      Used Available Capacity  iused    ifree %iused  Mounted on

/dev/disk0s2   244277768 153679844  90341924    63% 38483959 22585481   63%   /

9) How to make any script file executable?

    $chmod 755 *.sh

10) How to kill process in unix server?
    $ kill -9 #pid
these #pid can be found using ps -ef command.

11) 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"

12. 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

13. How will you find which operating system your system is running on in UNIX?

By using command "uname -a" in UNIX

14. 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.

15. 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.

16. 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.

17. 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

18. 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.

19. How do you find for how many days your Server is up?

By using uptime command in UNIX

BASIC Unix Command List

• ls --- lists your files
  ls -l --- lists your files in 'long format', which contains lots of useful information, e.g. the exact size of the file, who owns the file and who has the right to look at it, and when it was last modified.
  ls -a --- lists all files, including the ones whose filenames begin in a dot, which you do not always want to see.
  There are many more options, for example to list files by size, by date, recursively etc.
• more filename --- shows the first part of a file, just as much as will fit on one screen. Just hit the space bar to see more or q to quit. You can use /pattern to search for a pattern.
• mv filename1 filename2 --- moves a file (i.e. gives it a different name, or moves it into a different directory (see below)
• cp filename1 filename2 --- copies a file
• rm filename --- removes a file. It is wise to use the option rm -i, which will ask you for confirmation before actually deleting anything. You can make this your default by making an alias in your .cshrc file.
• diff filename1 filename2 --- compares files, and shows where they differ
• wc filename --- tells you how many lines, words, and characters there are in a file
• chmod options filename --- lets you change the read, write, and execute permissions on your files. The default is that only you can look at them and change them, but you may sometimes want to change these permissions. For example, chmod o+r filename will make the file readable for everyone, and chmod o-r filename will make it unreadable for others again. Note that for someone to be able to actually look at the file the directories it is in need to be at least executable. 
• File Compression
  • gzip filename --- compresses files, so that they take up much less space. Usually text files compress to about half their original size, but it depends very much on the size of the file and the nature of the contents. There are other tools for this purpose, too (e.g. compress), but gzip usually gives the highest compression rate. Gzip produces files with the ending '.gz' appended to the original filename.
  • gunzip filename --- uncompresses files compressed by gzip.
  • gzcat filename --- lets you look at a gzipped file without actually having to gunzip it (same as gunzip -c). You can even print it directly, using gzcat filename | lpr
• printing
  • lpr filename --- print. Use the -P option to specify the printer name if you want to use a printer other than your default printer. For example, if you want to print double-sided, use 'lpr -Pvalkyr-d', or if you're at CSLI, you may want to use 'lpr -Pcord115-d'. See 'help printers' for more information about printers and their locations.

DIRECTORIES

Directories, like folders on a Macintosh, are used to group files together in a hierarchical structure.

• mkdir dirname --- make a new directory
• cd dirname --- change directory. You basically 'go' to another directory, and you will see the files in that directory when you do 'ls'. You always start out in your 'home directory', and you can get back there by typing 'cd' without arguments. 'cd ..' will get you one level up from your current position. You don't have to walk along step by step - you can make big leaps or avoid walking around by specifying pathnames.
• pwd --- tells you where you currently are.