In linux every file and directory has set of permission.
The structure contains 10 chracter of strings, that broken down into 4 parts.
1st character : Type , - for normal file , d for directory , l for symbolic link
charcter 2 to 4 : Permission for user.
character 5 to 7 : Permission for group.
character 8 to 10 : Permission for others.
basic permission are read , write and execute
kernel sees this as binary bits , binary is too hard for humans to read , thats why we use octal number representing the permissions.
rwx= 111 = 4+2+1 = 7
rw_= 110 = 4+2+0. = 6
r-X = 101 = 4+0+1 = 5
r-- = 100 = 4+0+0 = 4
Example , if file1 has permission 755, then
7(Owner) Read , write , execute
5(Group) Read, execute
5(others) Read, execute
Managing permissions
chmod
umask.
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