Introduction<\/h2>\n
Linux is a Unix like operating system. It is open source and free. We might sometimes use the word “Unix” instead of Linux.<\/span><\/p>\n A user can interact with Linux either using a ‘graphical interface’ or using the ‘command line interface’.<\/span><\/p>\n Learning to use the command line interface has a bigger learning curve than the graphical interface but the former can be used to automate very easily. Also, most of the server side work is generally done using the command line interface.<\/span><\/p>\n The operating system is made of three parts:<\/span><\/p>\n A user executes programs. AngryBird is a program that gets executed by the kernel, for example. When a program is launched, it creates processes. Program or process will be used interchangeably.<\/span><\/p>\n The Kernel handles the main work of an operating system:<\/span><\/p>\n A user interacts with the Kernel via the Shell. The console as opened in the previous slide is the shell. A user writes instructions in the shell to execute commands. Shell is also a program that keeps asking you to type the name of other programs to run.<\/span><\/p>\n <\/p>\n Everything in Unix is either a file or a process.<\/span><\/p>\n When you run a program, a process is created. Every process is identified by a number called process ID. To check the processes you are running, execute “ps” command on the shell. You can think of the process ID to be a sequence number given by the operating system. It may be different at a different execution of the same program.<\/span><\/p>\n A file is a sequence of data. A file could be created by users using word processors or text editors or by the program to keep the information. A program is kept in the form of a file and when it is run by the kernel, it loads as a process.<\/span><\/p>\n A file is generally written on the disk so that it exists even after the computer restarts. It is saved in a disk – either hard disk drive (HDD – cheaper and slower) or solid state drive (SSD – faster but costlier).<\/span><\/p>\n A file is identified by a name called file path. In Unix, everything is represented as file:<\/span><\/p>\n Attend the quiz on Process<\/a><\/p>\n A file is kept inside a directory. A directory can have a file or another directory inside it. It is like an inverted tree.<\/span><\/p>\n The top-level directory is “\/” called root. “\/” directory does not have a parent. \/A\/B means B is inside A which is inside top-level directory “root”.<\/span><\/p>\n To see the list of files use the command:<\/span><\/p>\n There are two ways to represent a file\/directory path:<\/span><\/p>\n This way of representing a file\/directory is independent of current directory of the user. Such paths start with “\/”. Examples: \/etc\/passwd.<\/span><\/p>\n Relative to the current working directory. Examples: ..\/..\/etc\/passwd<\/span><\/p>\n You can change directory using “cd” command. Every user is given a separate home directory.<\/span><\/p>\n Inside the console, you are always in the directory. On login, by default, you land in your home directory.<\/span><\/p>\n To see the present working directory use: <\/span>pwd<\/strong><\/p>\n To change the directory to your home directory use only “<\/span>cd<\/strong>“<\/span> command without any arguments.<\/span><\/p>\n Attend the quiz on directory<\/a><\/p>\n You can create a\u00a0directory using mkdir<\/strong> command in the following way:<\/p>\n To delete a file you can use ‘rm<\/strong>‘ command. To delete the directory you have to have “-r<\/strong>” switch with rm command.<\/p>\n A file is a sequence of bytes and represents data. It is found in a directory. A file could contain any kind of data: an executable program, data representing movies, music, pictures or plain text.<\/p>\n You can create an empty file using the touch<\/strong> command. Please note that the extension of the file doesn’t matter much in Unix.<\/p>\n You can use a text editor to edit or create a text file. There are many editors in Linux such as nano, pico, vi, emacs. Let’s try to use nano for creating a file<\/p>\n 1. Launch nano to edit:<\/p>\n 2. Type the following text into it:<\/p>\n 3. Press “Control+x” to save and then confirm by typing y<\/p>\n To copy files and directories we use the cp<\/strong> command. Following is the way to make a copy of a file.<\/p>\n mv<\/strong> command is used to move or rename files and directories.<\/p>\n rename myfirstfile.txt to firstfile.txt<\/p>\n To see what is inside a text file, you can use either cat, tail, or head<\/strong>.<\/span><\/p>\n Using cat<\/strong> you can see the whole content of the file:<\/span><\/p>\n Do not use this command to look inside a huge file. For the huge file, you can use the “more” command which would display the content of a file in a paginated way:<\/span><\/p>\n tail<\/strong> shows you the last few lines of a file<\/span><\/p>\n By default tail shows you only last 10 lines, you can change it using command line option. For example, to see last 20 lines, you can use<\/span><\/p>\n If you want to chase a file – continuously print newlines appended to the file – use the following command:<\/span><\/p>\n If you are interested in the first few lines, you can use head.\u00a0 By default head<\/strong> shows you only first 10 lines, you can change it using command line option. For example, to see first 20 lines, you can use<\/span><\/p>\n Attend the quiz on commands<\/a><\/p>\n Sometimes you might want to search for a particular file based on various attributes of a file such as size or name etc. The find command comes in very handy for such use cases.<\/span><\/p>\n For example, to find all the text files in current directory, you can use this command<\/span><\/p>\n If you want to locate a word in files, you can use the grep<\/strong> command. Grep lists all the lines from files in which a particular word exists. Examples of grep<\/span><\/p>\n If you want to search in files recursively – inside every subdirectory of a directory, use the following command<\/span><\/p>\n If you want to search case insensitive, use “-i” switch<\/span><\/p>\n grep is a very powerful tool. It can somewhat behave like where clause in sql queries.<\/span><\/p>\n Few Examples are:<\/span><\/p>\n To find the number of characters, words, and lines, use the wc<\/strong> command.<\/span><\/p>\n If you are only looking for the number of lines you could use:<\/span><\/p>\n Attend the quiz on wc command<\/a><\/p>\n Permissions in unix are integral part of the operating system.<\/span><\/p>\n You can see the details of a file using ls -la command:<\/span><\/p>\n And you can see the details of all files in the current directory by using:<\/span><\/p>\n Every file has an owner (also referred as a user), a group and permissions. A user can be part of many groups. A group can have many users.<\/span><\/p>\n The permission attributes of a file signify who can do what.<\/span><\/p>\n <\/p>\n You can change the permissions of a file using chmod command: chmod permission_cmd myfile<\/span><\/p>\n You can allow or disallow the user (u), group (g) or other(o) the following actions: read (r), write (w) and execute (x).<\/span><\/p>\n So, if you want to allow the user (the person who owns it) to execute the file:<\/span><\/p>\n And to disallow the user (the person who owns it) to execute the file:<\/span><\/p>\n Say you want to give the rw permissions to owner and group of a file, you will have to use the following command:<\/span><\/p>\n or<\/span> To give members of a group ability to modify a file, use:<\/span><\/p>\n Create a new file called myemptyfile. You can use:<\/span><\/p>\n Check its permissions using:<\/span><\/p>\n Using chmod<\/strong>, give it permissions such that owner of a file should be able to modify. Everyone else should be able to only read.<\/span><\/p>\n Hint: You can use the following command to remove the write permissions from group and others:<\/span><\/p>\n Create a new file called myemptyfile. You can use:<\/span><\/p>\n Check its permissions using:<\/span><\/p>\n Using chmod<\/strong>, give it permissions such that the owner of a file should be able to modify. Everyone should be able to execute but no one can modify the file.<\/span><\/p>\n Create a new file called myemptyfile. You can use:<\/span><\/p>\n Check its permissions using:<\/span><\/p>\n Using chmod<\/strong>, give it permissions such that nobody other than the owner of a file can read the file.<\/span><\/p>\n Create a new file called myemptyfile. You can use:<\/span><\/p>\n Check its permissions using:<\/span><\/p>\n Using chmod<\/strong>, give it permissions such that owner of a file should be able to read and modify, members of groups can only read, others can’t read or modify.<\/span><\/p>\n You can also use numbers to represent the permissions.<\/span><\/p>\n So, for a file with permissions rwxr-xr-x, the owner has rwx permission which 4+2+1=7 and group and others have r-x which means 4+0+1 = 5. Thus the command you would use to set such permission would be: chmod 755 myfile.<\/span><\/p>\n Attend the quiz on permission – numeric<\/a><\/p>\n There is a special user called root on Unix systems which has all the privileges which can give permission to any user on any file.<\/span><\/p>\n Some users who are allowed to act on behalf of the root are called sudoers. This list of sudoers can be edited using the sudoedit<\/strong> command. Such users are allowed to run commands as if they are root using: sudo .<\/span><\/p>\n You can change the owner of a file using chown<\/strong> and change the group of a file using the chgrp<\/strong> command. Please note that changing the owner of the file is possible only with the administrative account.<\/span><\/p>\nLinux Operating System<\/h2>\n
1. The Programs<\/h3>\n
2. The Kernel<\/h3>\n
\n
3. The Shell<\/h3>\n
Linux Files & Processes<\/h2>\n
Process<\/h3>\n
File<\/h3>\n
\n
The Directory Structure<\/h2>\n
![\"\"](\"http:\/\/blog.cloudxlab.com\/wp-content\/uploads\/2017\/12\/filesystem.png\")
<\/p>\nList Files and Directory<\/h3>\n
ls<\/pre>\n
Relative & Absolute Paths – Change the Directory<\/h3>\n
1. Absolute<\/b><\/h5>\n
2. Relative<\/b><\/h5>\n
Home Directory & Current Directory<\/h3>\n
Create Directory<\/h3>\n
mkdir directoryname<\/pre>\n
Delete a file<\/h3>\n
rm -r directoryname<\/pre>\n
Create File<\/h3>\n
touch myemptyfile.txt<\/pre>\n
Create Text File Using Nano<\/h3>\n
nano myfirstfile.txt<\/pre>\n
He walked into his exile<\/pre>\n
Copy File<\/h3>\n
cp myfirstfile.txt myfirstfile_copy.txt<\/pre>\n
Move Files & Directories<\/h3>\n
mv myfirstfile.txt firstfile.txt<\/pre>\n
Seeing inside\u00a0the File – cat, tail, head<\/h3>\n
cat myfirstfile_copy.txt<\/pre>\n
more myfirstfile_copy.txt<\/pre>\n
tail myfirstfile_copy.txt<\/pre>\n
tail -20 myfirstfile_copy.txt<\/pre>\n
tail -f myfirstfile_copy.txt<\/pre>\n
head -20 myfirstfile_copy.txt<\/pre>\n
Use find command<\/h3>\n
find . -name '*.txt'<\/pre>\n
Use grep command<\/h3>\n
grep myword file1 file2<\/pre>\n
grep -r myword directory<\/pre>\n
grep -i myword file1 file2\r\n<\/pre>\n
Practical Use Cases<\/strong><\/h5>\n
\n
Use wc command<\/h3>\n
wc -l<\/pre>\n
Permissions – Overview<\/h2>\n
ls -la myfile<\/pre>\n
ls -la<\/pre>\n
Using chmod To Change<\/h3>\n
chmod u+x myfile<\/pre>\n
chmod u-x myfile<\/pre>\n
chmod u+r,u+w,g+r,g+w myfile<\/pre>\n
\n<\/span><\/p>\nchmod u+rw,g+rw myfile<\/pre>\n
chmod g+w myfile\r\n\r\n<\/pre>\n
Assignment – Owner can change, others can only read<\/h3>\n
touch myemptyfile<\/pre>\n
ls -l myemptyfile<\/pre>\n
chmod o-w,g-w myemptyfile<\/pre>\n
Assignment – Everyone can execute<\/h3>\n
touch myemptyfile<\/pre>\n
ls -l myemptyfile<\/pre>\n
Assignment – Nobody other than owner can read the file<\/h3>\n
touch myemptyfile<\/pre>\n
ls myemptyfile<\/pre>\n
Assignment – Only Group Members can read<\/h3>\n
touch myemptyfile<\/pre>\n
ls myemptyfile<\/pre>\n
Permissions – Numeric<\/h3>\n
![\"\"](\"http:\/\/blog.cloudxlab.com\/wp-content\/uploads\/2017\/12\/permissions.png\")
<\/p>\nPermissions – Advanced<\/h3>\n