Basic Linux commands to know system

• date - display date and time of the system

• pwd - display present working directory

• whoami - display user

• cal - display current month calander

• man - display help of the commad specified. man -ls

• sudo -  sudo command stands for Super User Do. x`

• sudo -su gives root permission

• sudo -V gives version of linux

• sudo -h display help

• history display history of the all the commands executed during the session

• uptime Display How long the server is on

Directory Commands

• ls - list files

  • ls -a list hidden files

  • ls -l   list the files and directories in long list format with extra information 

  • ls -lh ls -lh /boot  list the files and directories in human readable numbers format with extra information 

  • ls *.sh  list files ends with .sh

  • ls -d */  list all the directory

  • ls ../  list all the files from root directory

  • ls -R list the subdirectory

• mkdir - create a directory

  • mkdir -p create nested directory mkdir ~/testdir

  • mkdir /home/usr/ 

• rmdir

  • rmdir -r remove nested directory

  • rm -rf remove all files and directories

• cd Used to move around in the directory/file structure. 

  • • cd .. go to the previous directory.

    • cd ~ go to the home directory

    • cd / go to the root directory.

    • cd ../..  go up by 2 directories.

Practice

1. Display your current directory.  

2. Change to the /etc directory. 

3. . Go to the root directory.

4. List the contents of the root directory. 

5. List the files in /boot in a human-readable format. 

6. Create a directory testdir in your home directory. 

7. Create in one command the directories ~/dir1/dir2/dir3 (dir3 is a subdirectory from dir2, and dir2 is a subdirectory from dir1 ). 

8. Remove the directory testdir. 

9. Remove dir1

Answers by Tawheed

[root@localhost /]# history

    1  pwd

    2  cd /etc

    3  cd ..

    4  ls -l

    5  ls -lh /boot

    6  mkdir tesdir

    7  mkdir -p dir1/dir2/dir3/dir4

    8  rm testdir

    9  rm -rf testdir

   10  rm -rf dir1

   11  history 

Linux is case sensitive so file.txt is different from File.txt

File commands

1. touch <filename> <filename> <filename> create zero size file

2. cat <filename> display file content

   1. cat -b: This adds line numbers to non-blank lines

   2. cat -n: This adds line numbers to all lines

   3. cat -s: This squeezes blank lines into one line

   4. cat –E: This shows $ at the end of the line

   5. cat <file name> <filename>

   6. cat > filename.txt create file press ctrl+d to end the file

   7. cat  filename 1  > filename2  copy file1 to file 2

3. file <filename> display type of file irrespective of the filename

4. rm <filename>/<directoryname> remove file or directory

   1. rm -rf  rm -rf (the f means force and the r means recursive) 

   2. rm -r remove recursive

   3. rm -i provides for interactive option  before delete

5. cp <source file/directory name>  <destination filename/directory name> copy files and directory from source to destination 

   1. cp -r <source file/directory name>  <destination filename/directory name> recursive copy

   2. cp <filename> <filename> <filename>  <destination directoryname>  for multiple copy of files the destination must be directory

   3. cp -i ask when file already exists to overwrite or not. 

6. mv <source file/directory name>  <destination filename/directory name> move or rename files

   1. mv <source directory name> <destination directory name>

   2. mv -i will ask permission to overwrite an existing file. 

7. rename <oldname> <newname> *.txt  example : rename .txt .newtxt *.txt 

8. file <filename> display the file type 

9. Tr: Tr stands for translation. This command is for translating or deleting characters.  

10. cut - used to cut the characters from output

Practice

1. Display the content of file /etc/passwd

2. Create file file1.txt file2.txt file3.txt using touch

3. Create a directory test

4. Display all the created files

5. Remove file1.txt

6. Copy file2.txt  and file3.txt to test/ using a single command

7. Copy file2.txt to newfile2.txt

8. Create a Directory backup and copy all the content to the backup directory 

9. Copy all the text files to backup directory 

10. Copy backup directory to newbackup directory

11. Move file2.txt to file22.txt and then move to backup directory

12. Rename all .txt files to .html

13. delete backup directory 

/etc/hosts contains hostnames with their ip address 

/etc/resolv.conf should contain the ip address of a DNS name server 

/etc/passwd contains user password

environment variables in Linux

1. printenv print all environment variables. 

2. USER - The current logged in user.

3. HOME - The home directory of the current user.

4. EDITOR - The default file editor to be used. This is the editor that will be used when you type edit in your terminal.

5. SHELL - The path of the current user’s shell, such as bash or zsh.

6. LOGNAME - The name of the current user.

7. PATH - A list of directories to be searched when executing commands. When you run a command the system will search those directories in this order and use the first found executable.

8. LANG - The current locales settings.