# Day - 06

## File Permissions in Linux:

In Linux, the `ls` command is used to list the files and directories in a directory.

If the `ls` command is supplemented with `-l` option, it displays the long format listing of files and directories. The information displayed in the long format includes the following attributes and permissions:

Here's an example output of `ls -l`:

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1690756667734/e072a2d7-4ef2-413c-a75a-2c263a9bab9e.png align="center")

The `-t` and `-r` options used with `ls -l` (as in `ls -ltr`) sort the files in reverse order by modification time, displaying the most recently modified files at the end.

1. **File Type and Permissions**: The first column represents the file type and permissions. For each file or directory, there are ten characters in this column. The first character indicates the file type:
    
    * `-`: Indicates a regular file (a standard file that contains data).
        
    * `d`: Indicates a directory (a folder that can contain other files and directories).
        
    
    The next nine characters represent the permissions, which are divided into three sets of three characters each:
    
    * The first set (`rw-`) represents the permissions for the owner (user) of the file. In this example, the owner can read and write (`rw-`) the file but cannot execute it (`-`).
        
    * The second set (`r--`) represents the permissions for the group to which the file belongs. In this case, the group can only read (`r--`) the file but cannot write or execute it (`-`).
        
    * The third set (`r--`) represents the permissions for others (everyone else). In this example, others can also only read (`r--`) the file but cannot write or execute it (`-`).
        
2. **Number of Links**: The second column represents the number of hard links to the file or directory. **Ex**: file1.txt (1), test1 (2).
    
3. **Owner and Group**: The third and fourth columns display the owner (`ec2-user`) and the group (`ec2-user`) to which the file or directory belongs.
    
4. **Modification Time**: The next two columns (columns five and six) show the date and time when the file or directory was last modified.
    
5. **Filename**: The last column displays the name of the file or directory.
    

## Changing the File Permissions in Linux Using Commands:

In Linux, we can change the permissions of a file or directory using the following commands:

**chmod**: It helps modify the read (r), write (w), and execute (x) permissions for the owner, group, and others.

Here are some common examples of how to use the `chmod` command to change permissions:

1. **Changing Permissions Using Numeric Mode**:
    
    The numeric mode is a convenient way to specify permissions using a three-digit octal number. Each digit represents the permissions for the owner, group, and others, respectively. The values are calculated as follows:
    
    * 4 (Read): Add 4 to the sum if the read permission is desired.
        
    * 2 (Write): Add 2 to the sum if the write permission is desired.
        
    * 1 (Execute): Add 1 to the sum if the execute permission is desired.
        
    
    For example, to set read and write permissions for the owner, read-only permissions for the group, and no permissions for others, you can use the octal number 744:
    
    ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1690839314556/60900b87-264b-4dc6-b921-7d39c60bcb14.png align="center")
    
    In this case, the owner gets read, write execute permissions (4 + 2 +1 = 6), and the group and others get read-only permissions (4) permissions.
    
2. **Changing Permissions Using Symbolic Mode**:
    
    The symbolic mode allows you to modify permissions using symbols like `+`, `-`, and `=` along with letters `r`, `w`, and `x`.
    
    * `+`: Adds the specified permission(s).
        
    * `-`: Removes the specified permission(s).
        
    * `=`: Sets the exact permission(s) specified, while removing all others.
        
    
    For example, to remove execute permission for the owner of a file:
    
    **chmod u-x <filename/directoryname>**
    
    ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1690769230946/5d63951e-382d-46c8-bdea-5e86236b1b4b.png align="center")
    
3. **Combining Multiple Permissions**:
    
    You can combine multiple permissions in a single `chmod` command. For example, to remove read permissions for both the owner and the group following command will be used:
    
    **chmod ug-r <filename/directoryname>**
    
    ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1690772678163/387aa988-0e9a-497b-967d-74f99879e1c9.png align="center")
    
4. **Recursively Changing Permissions for Directories**:
    
    To change permissions for directories and their contents recursively, you can use the `-R` option:
    
    ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1690841070550/33e2745a-6e20-4b01-8b11-8c00b402a781.png align="center")
    
    Be cautious when using the recursive option, as it will change permissions for all files and subdirectories within the specified directory.