Chmod File Only Read and Written to by Root Access

Linux is a clone of UNIX, the multi-user operating system which tin exist accessed by many users simultaneously. Linux tin also be used in mainframes and servers without any modifications. But this raises security concerns as an unsolicited or malign user can decadent, alter or remove crucial data. For constructive security, Linux divides authorization 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
• Accented(Numeric) Way in Linux
• Symbolic Mode in Linux
• Changing Buying and Group in Linux

The concept of Linux File permission and ownership is crucial in Linux. Here, we will explicate Linux permissions and ownership and will discuss both of them. Permit usa showtime with the Ownership.

Click hither if the video is non accessible

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 possessor. Hence, a user is likewise sometimes called an owner.

Group

A user- group tin contain multiple users. All users belonging to a group will have the same Linux group permissions access to the file. Suppose you accept a project where a number of people require access to a file. Instead of manually assigning permissions to each user, yous could add together all users to a group, and assign group permission to file such that only this group members and no one else can read or alter 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 own the file. Practically, information technology means everybody else. Hence, when you lot ready the permission for others, it is also referred as set permissions for the world.

Now, the big question arises how does Linux distinguish betwixt these 3 user types then that a user 'A' cannot affect a file which contains another user 'B'southward' vital information/information. It is like you do not want your colleague, who works on your Linux computer, to view your images. This is where Permissions prepare in, and they define user behavior.

Let us sympathise the Permission system on Linux.

Linux File Permissions

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

• Read: This permission give you the authority to open and read a file. Read permission on a directory gives you the ability to lists its content.
• Write: The write permission gives you the authority to modify the contents of a file. The write permission on a directory gives you lot the authorization to add, remove and rename files stored in the directory. Consider a scenario where you have to write permission on file but do not have write permission on the directory where the file is stored. Y'all will be able to modify the file contents. Just y'all will not be able to rename, movement or remove the file from the directory.
• Execute: In Windows, an executable program unremarkably has an extension ".exe" and which y'all can easily run. In Unix/Linux, you cannot run a program unless the execute permission is set. If the execute permission is not set up, you might yet exist able to encounter/change the programme code(provided read & write permissions are set), only not run it.

File Permissions in Linux/Unix

Let's see file permissions in Linux with examples:

ls – l on terminal gives

ls - l

Hither, we have highlighted '-rw-rw-r–'and this weird looking code is the one that tells united states of america about the Unix permissions given to the owner, user grouping and the world.

Hither, the first '–' implies that we have selected a file.p>

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

The characters are pretty like shooting fish in a barrel to call back.

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

Allow united states look at information technology this way.

The outset part of the lawmaking is 'rw-'. This suggests that the possessor 'Home' can:

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

By pattern, many Linux distributions like Fedora, CentOS, Ubuntu, etc. volition add users to a grouping of the same group name as the user proper name. Thus, a user 'tom' is added to a group named 'tom'.

The second part is 'rw-'. It for the user grouping 'Dwelling' and grouping-members can:

• Read the file
• Write or edit the file

The tertiary part is for the earth which ways whatever user. Information technology says 'r–'. This means the user can only:

• Read the file

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

Say you do not want your colleague to run across your personal images. This tin be achieved by changing file permissions.

We can utilize the 'chmod' command which stands for 'alter fashion'. Using the command, we tin gear up permissions (read, write, execute) on a file/directory for the owner, group and the world.

Syntax:

chmod permissions filename

There are two means to utilise the control –

1. Absolute way
2. Symbolic style

Absolute(Numeric) Mode in Linux

In this way, file permissions are not represented equally characters but a three-digit octal number.

The table below gives numbers for all for permissions types.

Number	Permission Blazon	Symbol
0	No Permission	—
i	Execute	–ten
ii	Write	-westward-
3	Execute + Write	-wx
4	Read	r–
v	Read + Execute	r-x
half dozen	Read +Write	rw-
7	Read + Write +Execute	rwx

Permit's see the chmod permissions command in action.

In the in a higher place-given terminal window, nosotros have changed the permissions of the file 'sample to '764'.

'764' accented code says the post-obit:

• Possessor can read, write and execute
• Usergroup can read and write
• World can simply read

This is shown every bit '-rwxrw-r–

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

Symbolic Fashion in Linux

In the Absolute mode, you change permissions for all three owners. In the symbolic mode, y'all can modify permissions of a specific possessor. Information technology makes utilise of mathematical symbols to modify the Unix file permissions.

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

The various owners are represented as –

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

Nosotros will non be using permissions in numbers like 755 but characters similar rwx. Let'south look into an case

Changing Ownership and Group in Linux

For changing the buying of a file/directory, you tin apply the following control:

chown user filename

In example you lot desire to change the user also as group for a file or directory use the control

chown user:group filename

Let's see this in action

In case yous want to change group-owner simply, use the control

chgrp group_name filename

'chgrp' stands for change group.

Tip

• The file /etc/group contains all the groups defined in the system
• You can employ the control "groups" to notice all the groups you lot are a member of



• Yous tin can use the command newgrp to work as a member a group other than your default group



• You cannot have 2 groups owning the aforementioned file.
• You do not have nested groups in Linux. I grouping cannot be sub-group of other
• x- eXecuting a directory ways Being allowed to "enter" a dir and gain possible admission to sub-dirs
• There are other permissions that yous can set on Files and Directories which will be covered in a afterward advanced tutorial

Summary:

• Linux being a multi-user system uses permissions and buying for security.
• There are 3 user types on a Linux system viz. User, Group and Other
• Linux divides the file permissions into read, write and execute denoted by r,w, and 10
• The permissions on a file tin can exist changed past 'chmod' command which can be further divided into Accented and Symbolic mode
• The 'chown' control tin alter the ownership of a file/directory. Use the post-obit commands: chown user file or chown user:group file
• The 'chgrp' command can modify the group ownership chrgrp group filename
• What does 10 – eXecuting a directory hateful? A: Existence allowed to "enter" a dir and gain possible access to sub-dirs.

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

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