Linux is a clone of UNIX, the multi-user operating system which can be accessed by many users simultaneously. Linux can also be used in mainframes and servers without any modifications. But this raises security concerns as an unsolicited or malign user can corrupt, change or remove crucial data. For effective security, Linux divides authorization into 2 levels. Show In this Linux file commands tutorial, you will learn- The concept of Linux File permission and ownership is crucial in Linux. Here, we will explain Linux permissions and ownership and will discuss both of them. Let us start with the Ownership.
Click here if the video is not accessible Linux File OwnershipEvery file and directory on your Unix/Linux system is assigned 3 types of owner, given below. UserA user is the owner of the file. By default, the person who created a file becomes its owner. Hence, a user is also sometimes called an owner. GroupA user- group can contain multiple users. All users belonging to a group will have the same Linux group permissions access to the file. Suppose you have a project where a number of people require access to a file. Instead of manually assigning permissions to each user, you could add all users to a group, and assign group permission to file such that only this group members and no one else can read or modify the files. OtherAny other user who has access to a file. This person has neither created the file, nor he belongs to a usergroup who could own the file. Practically, it means everybody else. Hence, when you set the permission for others, it is also referred as set permissions for the world. Now, the big question arises how does Linux distinguish between these three user types so that a user ‘A’ cannot affect a file which contains some other user ‘B’s’ vital information/data. It is like you do not want your colleague, who works on your Linux computer, to view your images. This is where Permissions set in, and they define user behavior. Let us understand the Permission system on Linux. Linux File PermissionsEvery file and directory in your UNIX/Linux system has following 3 permissions defined for all the 3 owners discussed above.
Let’s see file permissions in Linux with examples: ls – l on terminal gives
Here, we have highlighted ‘-rw-rw-r–‘and this weird looking code is the one that tells us about the Unix permissions given to the owner, user group and the world. Here, the first ‘–‘ implies that we have selected a file.p>
Else, if it were a directory, d would have been shown.
The characters are pretty easy to remember. r = read permission Let us look at it this way. The first part of the code is ‘rw-‘. This suggests that the owner ‘Home’ can:
By design, many Linux distributions like Fedora, CentOS, Ubuntu, etc. will add users to a group of the same group name as the user name. Thus, a user ‘tom’ is added to a group named ‘tom’. The second part is ‘rw-‘. It for the user group ‘Home’ and group-members can:
The third part is for the world which means any user. It says ‘r–‘. This means the user can only:
Changing file/directory permissions in Linux Using ‘chmod’ commandSay you do not want your colleague to see your personal images. This can be achieved by changing file permissions. We can use the ‘chmod’ command which stands for ‘change mode’. Using the command, we can set permissions (read, write, execute) on a file/directory for the owner, group and the world. Syntax: chmod permissions filenameThere are 2 ways to use the command –
Absolute(Numeric) Mode in LinuxIn this mode, file permissions are not represented as characters but a three-digit octal number. The table below gives numbers for all for permissions types.
Let’s see the chmod permissions command in action.
In the above-given terminal window, we have changed the permissions of the file ‘sample to ‘764’.
‘764’ absolute code says the following:
This is shown as ‘-rwxrw-r– This is how you can change user permissions in Linux on file by assigning an absolute number. Symbolic Mode in LinuxIn the Absolute mode, you change permissions for all 3 owners. In the symbolic mode, you can modify permissions of a specific owner. It makes use of mathematical symbols to modify the Unix file permissions.
The various owners are represented as –
We will not be using permissions in numbers like 755 but characters like rwx. Let’s look into an example
Changing Ownership and Group in LinuxFor changing the ownership of a file/directory, you can use the following command: chown user filenameIn case you want to change the user as well as group for a file or directory use the command chown user:group filenameLet’s see this in action
In case you want to change group-owner only, use the command chgrp group_name filename‘chgrp’ stands for change group.
Tip
Summary:
|