Hi, everyone. As a Linux user, we often use basic commands like sudo, cd, ls, etc. But there are so many commands that we don’t use that much, like the chmod command in Linux and other commands, but in this post we have to see what the chmod command is and how to use the chmod command in Linux.
The chmod command is used for giving permissions to the file, like write, read, execute, etc. So, yes, chmod acts as a permissions giver to our file, but this explanation is not enough to understand chmod, so let’s dive into our full guide for the chmod command in Linux.
What Is Chmod Command in Linux
chmod is a command in Linux and Unix-based operating systems used for changing modes or permissions of files and directories. It allows us to set permissions like who can read the file, who can write it, or who can execute our file. If you want to check the uptime of your Linux machine then check this post on the uptime command in Linux
How to use the chmod command in Linux
Using the chmod command is very simple; we just need to learn some basics and we are ready to go with this below example command
Chmod [options] mode fileDon’t worry, we will cover everything in detail, so please stay focused and read the full post without skipping anything. Giving commands in Linux is not a copy-paste task; we have to understand it, so without further ado, let’s get started with some basics.
File permissions in Linux
When we create a file in Linux or any other operating system, the file contains its permissions. So in Linux, every file and directory has permissions associated with it that determine who can read, write, or execute it. File permissions are divided into 4 categories.
Permission categories
| User (u) | File Owner |
| group (g) | Other Users Present In Same Group as the file owner |
| Others (o) | Everyone else |
| a (for All) | all (owner, group, and others) |
Permission Types
| Read (r) | Read permission only allows the user to read the content or list the content of a directory. |
| Write (w) | Right permissions allow us to modify the content of a file or make changes like deleting or creating our files. |
| Execute (e) | execute permission gives us a right to execute our files and to run a program or access a directory. |
If you want to know file permissions in detail, then you can read this post, Linux file permissions explained.
The syntax for the chmod command
The syntax for running the chmod command is very simple; we just need to type this in our terminal
chmod [options] mode fileSo in this command, we first have to type Chmod then options then mode, and then our file name Let’s see what options and mode are.
- options: Optional flex to modify the behavior of our chmod command.
- Mode: mode is used for defining the permissions to set mode and can be in numeric or symbolic form. We will discuss this further in this post in detail.
Notations For chmod command in Linux
So we saw the syntax and how to use it now we have to know a little bit about notations basically There are two main types of notation used with the chmod command in Linux to change and represent the file permissions.
Symbolic Notations
Symbolic notations use symbols and letters to represent file permissions. The symbols are used for giving or removing permissions for our users, groups, & other users, as seen before in the permissions categories.
Permission symbols
| r | read |
| w | write |
| x | execute |
Operator Symbolic Notations
| + | adds the specified permission |
| – | removes the specified permission |
| = | sets the exact permission |
Let’s take some examples to understand symbolic notions in the chmod command.
Example for Symbolic notations
Add execute permission to the owner:
chmod u+x filenameRemove write permission for others:
chmod o-w filenameGive read, write, and execute permissions to everyone:
chmod a+rwx filenameSet read and write permissions for the owner, and read-only for the group and others:
chmod u=rw,g=r,o=r filenameNumeric ( Octal ) Notations
In numeric notations, numbers are used and permission is given in the three-digit numbers, This three-digit number is a sum of 3 values of 3 permissions. Each permission category has its own number value, as we can see in the below table
| Read (r) | 4 |
| Write (w) | 2 |
| Execute (x) | 1 |
To use numerical notations, we have to add this value set for each category And the sum will determine the permission set for each category. It feels confusing but after taking some examples, you will think it’s a child’s play.
Example for Numerical Notations
| Read, write, execute ( rwx ) | 4+2+1 = 7 |
| Read, write ( rw- ) | 4+2 =6 |
| Read only ( r- -) | 4 |
Let’s See an Example command where we want to give permission of: rwx for owner, rx for group, and rx for others (755):
chmod 755 filenameSet permissions to rw for owner, and r for group and others (644):
chmod 644 filenameGive everyone read and execute permission, but only the owner can write (555):
chmod 555 filenameChmod Additional options
-r : This Option repeats the task of applying permissions to all files & subdirectories
Example: Change the permissions of a directory and all its contents:
chmod -R 755 /path/to/directory–reference : This option Takes a reference from other files and applies the same permissions to our file.
Example: Apply the same permissions as referencefile to targetfile:
chmod --reference=referencefile targetfileHow to view file permissions in Linux
Checking file permission is the easiest part of our conversation. So for checking the permissions of our file, first we have to navigate to the directory where our file is located, then we have to run this command.
ls -l filenameBut there is a catch when we run this command we will see some output like this:
-rwxr-xr--This string can be broken down as:
| – d | – for a file (or d for a directory). |
| rwx | for the owner (read, write, execute). |
| r-x | for the group (read, no write, execute). |
| r– | for others (read, no write, no execute) |
Conclusion
So finally, We Have Seen A detailed Explanation of the Chmod command in Linux. We Saw What the chmod command is and how to use it the detailed process of using it and a beautiful explanation of every syntax and small thing. If you found this blog post helpful, then don’t forget to share and rate. And at last, thanks for reading.
FAQs
What is chmod command in Linux?
chmod is a command in Linux it allows us to set permissions like who can read the file who can write it or who can execute our file
What is the meaning of chmod 777?
This is an example command of numerical notation uses in chmod command we already see a complete guide above you can check it out here.
What are the 4 numbers in chmod?
In chmod command we use Numerical notation in which we have values given to each permissions categories like read (r) = 4 , write (w) = 2 , execute (x) = 1 , etc.
What is permission chmod 400?
The chmod 400 commands have 3 values 4,0,0 the first value is related to owner and it’s giving only read permissions to owner while 2nd value is for group related to same owner and the value means nothing and last one is related to everyone else. Which Mean this command giving permission of read to owner and restricting others.
What is chmod 444?
By running chmod 444 command means giving all users like owner, group, other read only permissions.
