In Unix-like operating systems, including Linux, file permissions and access modes are fundamental concepts for controlling access to files and directories. Each file and directory has an associated set of permissions that define who can read, write, or execute the file. These permissions are assigned to three different user categories: the owner of the file, the group the file belongs to, and all other users on the system. The permissions can be represented in both symbolic and octal notation.
In symbolic notation, each permission is represented by a single character, and they are combined to form a 3-character string. The characters used are:
- ‘r’: Read permission
- ‘w’: Write permission
- ‘x’: Execute permission
- ‘-‘: No permission
The order of the three characters represents the permissions for the owner, group, and others (everyone else) respectively.
- For example, if a file has the permission “-rw-r–r–“, it means:
- The owner has read and write permissions (no execute permission).
- The group has read-only permissions (no write or execute permission).
- Others (everyone else) have read-only permissions (no write or execute permission).
In octal notation, each permission is represented by a three-bit number. The three sets of three bits (9 bits in total) represent the permissions for the owner, group, and others, respectively. The binary values for read, write, and execute are 100, 010, and 001, respectively. Adding these values for each permission results in a three-digit octal number.
- For example, if a file has the permission “644” in octal notation, it means:
- The owner has read and write permissions (4 for read + 2 for write = 6).
- The group has read-only permissions (4 for read).
- Others (everyone else) have read-only permissions (4 for read).
File permissions can be changed using the “chmod” command in Unix. To change the permission of a file, you need to specify the desired permissions in symbolic or octal notation, along with the filename.
Changing permissions using symbolic notation:
- chmod u+rwx file.txt # Give read, write, and execute permissions to the owner.
- chmod g-wx file.txt # Remove write and execute permissions from the group.
- chmod o+r file.txt # Give read permission to others (everyone else).
- chmod a+rw file.txt # Give read and write permissions to all (owner, group, and others).
Changing permissions using octal notation:
- chmod 755 file.txt # Sets read, write, and execute permissions for owner and read/execute for group and others.
- chmod 644 file.txt # Sets read and write permissions for owner and read-only for group and others.
EXPLANATION OF THE CHANGING PERMISSION USING OCTAL NOTATION
Changing permissions using octal notation is a way to modify the access rights of a file or directory on a Unix-like operating system, such as Linux. In Unix-based systems, each file or directory has three sets of permissions associated with it: read, write, and execute. These permissions can be granted or denied to three different categories of users: the owner of the file, the group that the file belongs to, and all other users.
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