Linux (Unix) Permissions
Today I will explain Linux permissions and how to modify them. Following pictures explain how its presented in cli
Another good example taken from google
First character represents the type of object in our case its file. In case of folders “d” is written instead of “-”
Next 9 characters allocated to permissions 3 characters for each group.
Thera 3 access types in Linux:
r – read
w – write
x – execute
We can check file permissions by issuing
ls -l
CHMOD command is used for modifying permissions. We can change permissions by two methods
1. Absolute Method
2. Symbolic Method
Following table depicts Absolute Method
From the above example
4+2+1=7
4+2+0=6
4+0+0=4
Therefore when we type:
chmod 764 myfile.txt
File permissions change as rwxrw-r– which results in the following permissions
User(Owner) – full permissions
Group – read, write permissions
Others – read permission
Other method is symbolic method. Following table symbolic method parameters.
In symbolic method we are adding or subtracting permissions by using the parameters in the above table
For example
chmod u+r MyFile.txt
Will add read permission to user(owner)
Set the access type to read and execute for both the user and the group:
chmod ug+rx MyFile.txt
Set the access type to read and remove write access to the group and others:
chmod go+r-w MyFile.txt
Sets all users access type to read only:
chmod a=r MyFile3.txt
The difference between the last example and the others is that this syntax resets any access type bits that were set. In the other examples, the command only affects the access types that are called out in the command. If, in the first example, the write bit for the user was already set, it would remain set.