File Permissions in Linux

In Linux, each file and directory has a set of permissions that determine who can access the file and what actions they can perform on it. These permissions are represented by a series of letters and numbers that are displayed when you run the ls -l command in the terminal.

The permissions for each file are divided into three categories: user, group, and others. The user category refers to the owner of the file, the group category refers to users who belong to the same group as the owner, and the others category refers to everyone else.

There are three types of permissions that can be set for each category: read, write, and execute.

• Read permission (represented by r) allows the user to view the contents of a file or list the contents of a directory.

• Write permission (represented by w) allows the user to modify the contents of a file or create, delete, or rename files in a directory.

• Execute permission (represented by x) allows the user to run executable files or access directories.

These permissions are represented in a 10-character string, where the first character represents the file type (- for a regular file, d for a directory, l for a symbolic link, and so on), and the next three characters represent the user permissions, the following three characters represent the group permissions, and the last three characters represent the others permissions.

For example, consider the following output of the ls -l command:

-rw-r--r-- 1 user group 0 Mar 24 10:15 myfile.txt

In this example, myfile.txt is a regular file (-rw-r--r--). The first character (-) indicates that it is a regular file. The next three characters (rw-) indicate that the owner (user) has read and write permissions, but not execute permissions. The following three characters (r--) indicate that the group (group) has only read permissions. The last three characters (r--) indicate that everyone else also has only read permissions.

To modify the permissions of a file, you can use the chmod command followed by the desired permissions in the format rwx. For example, to give the owner of a file read, write, and execute permissions, but only give everyone else read permissions, you can run the following command:

chmod 744 myfile.txt

This will set the permissions to -rwxr--r--, which means the owner has read, write, and execute permissions, the group and others have read permissions only.

I hope this explanation helps you understand file permissions in Linux.In Linux, every file and directory has a set of permissions assigned to it. These permissions determine who can access the file or directory and what actions they can perform. The ls -ltr command can be used to view the details of the file, including the permissions assigned to it.

For example, let's create a file and view its permissions using the ls -ltr command:

touch myfile.txt
ls -ltr myfile.txt

This will display the permissions for myfile.txt, which will look something like this:

-rw-r--r-- 1 user user 0 Mar 24 2023 myfile.txt

The first ten characters '-rw-r--r--' indicate the permissions for the file. The first character '-' indicates that it is a regular file. The next three characters 'rw-' represent the owner's permissions, which are read and write, but not execute. The following three characters 'r--' represent the group permissions, which are read-only. The last three characters 'r--' represent the permissions for others, which are also read-only.

To change the permissions of a file, you can use the chmod command. For example, to give read, write, and execute permissions to the owner of the file, you can use the command:

chmod u+rwx myfile.txt

Here, the 'u' indicates the owner, and '+rwx' indicates that we are adding read, write, and execute permissions. Similarly, we can change the permissions for the group using 'g' instead of 'u' and for others using 'o' instead of 'u.'

To change the ownership of a file, we can use the chown command. For example, to change the ownership of the file to a different user, we can use:

chown newuser myfile.txt

Similarly, to change the group ownership of a file, we can use the chgrp command.

Advanced File Permissions: ACL

ACL (Access Control Lists) provides a more flexible way of setting file permissions. It allows us to set permissions for specific users or groups that are not part of the owner or group categories. In addition, it allows us to set more fine-grained permissions, such as read or write only for specific users.

To view the ACL permissions for a file, we can use the getfacl command. For example:

getfacl myfile.txt

This will display the ACL permissions for myfile.txt.

To set the ACL permissions for a file, we can use the setfacl command. For example, to give read-only permission to a specific user, we can use:

setfacl -m u:newuser:r myfile.txt

Here, the '-m' option indicates that we are modifying the ACL permissions. 'u:newuser' indicates the user we want to give permission to, and 'r' indicates the read permission.

Conclusion

File Permissions are an essential aspect of Linux operating systems. It allows us to control the access of files or directories by different users or groups. The permissions can be modified using the chmod, chown, and chgrp commands. ACL provides a more flexible way of setting file permissions, allowing us to set permissions for specific users or groups that are not part of the owner or group categories. The getfacl and setfacl commands are used to view and modify ACL permissions.

Happy Learning 😄

Bhaktiben Kadiya