How To Manage Permissions | how to change file permissions | read write execute permissions In Linux
Linux File Permissions
Every file and directory in your UNIX/Linux system has following 3 permissions defined 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 the authority 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. You will be able to modify the file contents. But you will not be able to rename, move or remove the file from the directory.
Execute: In Windows, an executable program usually has an extension “.exe” and which you can easily run. In Unix/Linux, you cannot run a program unless the execute permission is set. If the execute permission is not set, you might still be able to see/modify the program code(provided read & write permissions are set), but not run it.
The characters are pretty easy to remember.
r = read permission
w = write permission
x = execute permission
– = no permission
Symbolic Mode in Linux
In 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.
Operator Description
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 as –
User Denotations
u user/owner
g group
o other
a all
Linux being a multi-user system uses permissions and ownership for security.
There are three 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 x
The permissions on a file can be changed by ‘chmod’ command which can be further divided into Absolute and Symbolic mode
The ‘chown’ command can change the ownership of a file/directory. Use the following commands: chown user file or chown user:group file
The ‘chgrp’ command can change the group ownership chrgrp group filename
What does x – eXecuting a directory mean? A: Being allowed to “enter” a dir and gain possible access to sub-dirs.
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