Which Command Is Used To Change Permissions On Files And Directories?

Linux is a clone of UNIX, the multi-user operating system which can be accessed by many users simultaneously. Linux tin can also be used in mainframes and servers without any modifications. Simply this raises security concerns as an unsolicited or malign user can corrupt, change or remove crucial information. For constructive security, Linux divides authorisation into 2 levels.

1. Ownership
2. Permission

In this Linux file commands tutorial, you will learn-

• Linux File Ownership
• Linux File Permissions
• Changing file/directory permissions in Linux Using 'chmod' command
• Absolute(Numeric) Way in Linux
• Symbolic Fashion in Linux
• Changing Ownership and Group in Linux

The concept of Linux File permission and buying is crucial in Linux. Hither, we will explain Linux permissions and buying and will discuss both of them. Allow us beginning with the Ownership.

Click here if the video is not attainable

Linux File Ownership

Every file and directory on your Unix/Linux organisation is assigned 3 types of owner, given below.

User

A user is the possessor of the file. By default, the person who created a file becomes its owner. Hence, a user is as well sometimes called an possessor.

Group

A user- group can contain multiple users. All users belonging to a group volition accept the same Linux grouping permissions access to the file. Suppose you have a projection 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 grouping permission to file such that only this group members and no i else tin read or modify the files.

Other

Any other user who has access to a file. This person has neither created the file, nor he belongs to a usergroup who could ain the file. Practically, it ways everybody else. Hence, when you set the permission for others, it is too referred as gear up permissions for the world.

Now, the large question arises how does Linux distinguish betwixt 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 similar you practise not want your colleague, who works on your Linux computer, to view your images. This is where Permissions gear up in, and they ascertain user behavior.

Let the states understand the Permission arrangement on Linux.

Linux File Permissions

Every file and directory in your UNIX/Linux arrangement has following iii permissions defined for all the 3 owners discussed above.

• Read: This permission give yous the authority to open and read a file. Read permission on a directory gives you the power to lists its content.
• Write: The write permission gives yous the say-so to modify the contents of a file. The write permission on a directory gives you lot the authority to add together, remove and rename files stored in the directory. Consider a scenario where you take to write permission on file but practise non have write permission on the directory where the file is stored. Yous will be able to modify the file contents. Only you lot will not be able to rename, move or remove the file from the directory.
• Execute: In Windows, an executable program ordinarily has an extension ".exe" and which you lot can easily run. In Unix/Linux, you cannot run a program unless the execute permission is set. If the execute permission is not gear up, you lot might even so be able to see/change the program code(provided read & write permissions are set), just not run information technology.

File Permissions in Linux/Unix

Let's see file permissions in Linux with examples:

ls – l on terminal gives

ls - 50

Hither, nosotros 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 beginning '–' implies that nosotros have selected a file.p>

Else, if it were a directory, d would have been shown.

The characters are pretty easy to recollect.

r = read permission
w = write permission
x = execute permission
– = no permission

Let us look at it this way.

The first part of the code is 'rw-'. This suggests that the owner 'Dwelling house' can:

• Read the file
• Write or edit the file
• He cannot execute the file since the execute flake is set to '-'.

By design, many Linux distributions like Fedora, CentOS, Ubuntu, etc. will add users to a group of the same group proper noun every bit the user proper noun. Thus, a user 'tom' is added to a group named 'tom'.

The 2d part is 'rw-'. It for the user grouping 'Home' and group-members tin can:

• Read the file
• Write or edit the file

The third part is for the world which means any user. Information technology says 'r–'. This means the user can just:

• Read the file

Changing file/directory permissions in Linux Using 'chmod' command

Say you do non desire your colleague to see your personal images. This tin exist achieved past irresolute file permissions.

We can use the 'chmod' command which stands for 'change manner'. Using the command, we tin can set up permissions (read, write, execute) on a file/directory for the possessor, group and the world.

Syntax:

chmod permissions filename

At that place are 2 ways to employ the control –

1. Accented manner
2. Symbolic manner

Absolute(Numeric) Manner in Linux

In this mode, file permissions are not represented as characters merely a 3-digit octal number.

The table beneath gives numbers for all for permissions types.

Number	Permission Type	Symbol
0	No Permission	—
1	Execute	–10
2	Write	-w-
3	Execute + Write	-wx
4	Read	r–
five	Read + Execute	r-x
six	Read +Write	rw-
vii	Read + Write +Execute	rwx

Let'south see the chmod permissions control in activity.

In the above-given concluding window, we have inverse the permissions of the file 'sample to '764'.

'764' absolute code says the following:

• Owner can read, write and execute
• Usergroup can read and write
• Globe can simply read

This is shown equally '-rwxrw-r–

This is how you can change user permissions in Linux on file by assigning an absolute number.

Symbolic Fashion in Linux

In the Absolute mode, yous change permissions for all 3 owners. In the symbolic mode, you can modify permissions of a specific owner. It makes utilize of mathematical symbols to alter the Unix file permissions.

Operator	Clarification
+	Adds a permission to a file or directory
–	Removes the permission
=	Sets the permission and overrides the permissions set earlier.

The various owners are represented every bit –

User Denotations
u	user/possessor
g	group
o	other
a	all

We will non be using permissions in numbers like 755 simply characters like rwx. Allow'south await into an example

Changing Ownership and Group in Linux

For changing the buying of a file/directory, y'all can use the following command:

chown user filename

In example you want to alter the user every bit well as grouping for a file or directory use the command

chown user:grouping filename

Let's encounter this in activeness

In case you lot want to change grouping-possessor just, use the command

chgrp group_name filename

'chgrp' stands for change group.

Tip

• The file /etc/group contains all the groups defined in the organization
• You can use the control "groups" to discover all the groups you are a fellow member of



• Y'all can use the command newgrp to piece of work equally a member a group other than your default group



• You cannot have ii groups owning the aforementioned file.
• You do not have nested groups in Linux. One group cannot exist sub-group of other
• x- eXecuting a directory ways Being immune to "enter" a dir and gain possible access to sub-dirs
• There are other permissions that yous can assault Files and Directories which will be covered in a later advanced tutorial

Summary:

• Linux being a multi-user organization uses permissions and ownership for security.
• There are three user types on a Linux organization viz. User, Group and Other
• Linux divides the file permissions into read, write and execute denoted by r,westward, and ten
• The permissions on a file tin be changed by 'chmod' command which can be further divided into Absolute and Symbolic mode
• The 'chown' command tin change the buying of a file/directory. Apply the following commands: chown user file or chown user:group file
• The 'chgrp' control can modify the group buying chrgrp group filename
• What does x – eXecuting a directory mean? A: Existence allowed to "enter" a dir and gain possible admission to sub-dirs.

Source: https://www.guru99.com/file-permissions.html

Posted by: shuttleworthofore1954.blogspot.com

Share this post