UNIX Interview questions and answers | Part 1

 

UNIX

UNIX Commands:

 

1.       CAT

2.       CD

3.       CHMOD

4.       df/du

5.       FIND

1.       CAT

cat command allows us to create single or multiple files,

view contain of file,

concatenate files and redirect output in terminal or files

 

-          Cat file.txt à display the content of file

-          Cat> file1 à create the file

-          Cat >> file1 à append the file

-          Cat file1> file2 à copy the file content

-          Cat file1 file2 > file3 à Concatenate Contents of Multiple Files

-          Cat –n file1 à display the line numbers

-          cat -neT program.plà same as below

-          cat -ne program.pl à Display End of Line and TAB characters

2.       CD

-          Cd /à root path

-          Cd /abc/xyz à Change working directory

-          cd ~ à Change working directory to user’s home directory from anywhere in the directory structure

-          Cd - à Sometimes we want to change directory to previous working directory which we changed from. And revert to previous working directory we can use same command. This is very much useful cd command

-          Cd ../.. à Change working directory to parent’s parent directory or two levels up in the directory structure

-          Cd ../../.. à Changing three levels up in the directory

-          cd /var/f* àChange the working directory

Note: This will change the directory to /var/ftp, if /var directory contain only one folder which starts with f letter

-          cd /h<tab>/s<tab>/r<tab>/u<tab> à Change directory to /home/surendra/redhat/ubuntu without typing all the characters using <tab>

Note: Press tab to complete directory name

 

3.       df/du

 

The ‘df‘command stand for “disk file system“, it is used to get full summary of available and used disk space usage of file

-          DF –a  à Display Information of all File System Disk Space Usage

-          Df –h à display disk space usage in human readable format

-          Df –hT/home à display information of home file system

-          Df –I à display file system nodes

-          Df –k à display file space in kb

-          Df –m à display file space in mb

-          Df –mà display file space in gb

-          Df –Tà display file system type

 

Note: Using ‘–help‘switch will display a list of available option that are used with df command

 

Du

-          Du /home/tecmint à to find out the disk usage summary of a /home/tecmint directory tree and each of its sub directories. Enter the command as

-          Du -h /home/tecmint à Using “-h” option with “du” command provides results in “Human Readable Format“. Means you can see sizes in Bytes, Kilobytes, Megabytes, Gigabytes etc

-          Du -sh /home/tecmint à To get the summary of a grand total disk usage size of an directory use the option “-s” as follows

-          Du -a /home/tecmint à Using “-a” flag with “du” command displays the disk usage of all the files and directories

 

4.       FIND

Find command used to search and locate list of files and directories based on conditions you specify for files that match the arguments. Find can be used in variety of conditions like you can find files by permissions, users, groups, file type, date, size and other possible criteria.

1. Find Files Using Name in Current Directory

Find all the files whose name is tecmint.txt in a current working directory.

# find. -name tecmint.txt

./tecmint.txt

 

2. Find Files under Home Directory

Find all the files under /home directory with name tecmint.txt.

# Find /home -name tecmint.txt

/home/tecmint.txt

 

 

3. Find Files Using Name and Ignoring Case

Find all the files whose name is tecmint.txt and contains both capital and small letters in /home directory.

# find /home -iname tecmint.txt

./tecmint.txt

./Tecmint.txt

 

4. Find Directories Using Name

Find all directories whose name is Tecmint in / directory.

# find / -type d -name Tecmint

/Tecmint

 

5. Find PHP Files Using Name

Find all php files whose name is tecmint.php in a current working directory.

# find . -type f -name tecmint.php

./tecmint.php

 

6. Find all PHP Files in Directory

Find all php files in a directory.

# find . -type f -name "*.php"

./tecmint.php

./login.php

./index.php

 

Part II – Find Files Based on their Permissions

 

7. Find Files With 777 Permissions

Find all the files whose permissions are 777.

# find . -type f -perm 0777 -print

 

8. Find Files Without 777 Permissions

Find all the files without permission 777.

# find / -type f ! -perm 777

 

9. Find SGID Files with 644 Permissions

Find all the SGID bit files whose permissions set to 644.

# find / -perm 2644

 

10. Find Sticky Bit Files with 551 Permissions

Find all the Sticky Bit set files whose permission are 551.

# find / -perm 1551

 

11. Find SUID Files

Find all SUID set files.

# find / -perm /u=s

 

12. Find SGID Files

Find all SGID set files.

# find / -perm /g+s

 

13. Find Read Only Files

Find all Read Only files.

# find / -perm /u=r

 

14. Find Executable Files

Find all Executable files.

# find / -perm /a=x

 

15. Find Files with 777 Permissions and Chmod to 644

Find all 777 permission files and use chmod command to set permissions to 644.

# find / -type f -perm 0777 -print -exec chmod 644 {} \;

 

16. Find Directories with 777 Permissions and Chmod to 755

Find all 777 permission directories and use chmod command to set permissions to 755.

# find / -type d -perm 777 -print -exec chmod 755 {} \;

 

17. Find and remove single File

To find a single file called tecmint.txt and remove it.

# find . -type f -name "tecmint.txt" -exec rm -f {} \;

 

18. Find and remove Multiple File

To find and remove multiple files such as .mp3 or .txt, then use.

# find . -type f -name "*.txt" -exec rm -f {} \;

OR

# find . -type f -name "*.mp3" -exec rm -f {} \;

 

19. Find all Empty Files

To file all empty files under certain path.

# find /tmp -type f -empty

 

20. Find all Empty Directories

To file all empty directories under certain path.

# find /tmp -type d -empty

 

21. File all Hidden Files

To find all hidden files, use below command.

# find /tmp -type f -name ".*"

 

Part III – Search Files Based On Owners and Groups

 

22. Find Single File Based on User

To find all or single file called tecmint.txt under / root directory of owner root.

# find / -user root -name tecmint.txt

 

23. Find all Files Based on User

To find all files that belongs to user Tecmint under /home directory.

# find /home -user tecmint

24. Find all Files Based on Group

To find all files that belongs to group Developer under /home directory.

# find /home -group developer

25. Find Particular Files of User

To find all .txt files of user Tecmint under /home directory.

# find /home -user tecmint -iname "*.txt"

 

Part IV – Find Files and Directories Based on Date and Time

 

26. Find Last 50 Days Modified Files

To find all the files which are modified 50 days back.

# find / -mtime 50

 

27. Find Last 50 Days Accessed Files

To find all the files which are accessed 50 days back.

# find / -atime 50

 

28. Find Last 50-100 Days Modified Files

To find all the files which are modified more than 50 days back and less than 100 days.

# find / -mtime +50 –mtime -100

 

29. Find Changed Files in Last 1 Hour

To find all the files which are changed in last 1 hour.

# find / -cmin -60

 

30. Find Modified Files in Last 1 Hour

To find all the files which are modified in last 1 hour.

# find / -mmin -60

 

31. Find Accessed Files in Last 1 Hour

To find all the files which are accessed in last 1 hour.

# find / -amin -60

Part V – Find Files and Directories Based on Size

 

 

32. Find 50MB Files

To find all 50MB files, use.

# find / -size 50M

 

33. Find Size between 50MB – 100MB

To find all the files which are greater than 50MB and less than 100MB.

# find / -size +50M -size -100M

 

34. Find and Delete 100MB Files

To find all 100MB files and delete them using one single command.

# find / -size +100M -exec rm -rf {} \;

 

35. Find Specific Files and Delete

Find all .mp3 files with more than 10MB and delete them using one single command.

# find / -type f -name *.mp3 -size +10M -exec rm {} \;