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chmod tutorial / cheat sheet / cheatsheet / for dummies

chmod
Forget the chmod octals (the numbers). Set permission the easy way using the keywords

// know the ownerships:
u = User (you)
g = Group
o = Other (aka. 'World')
a = All of the above


// know the permission keywords
  = (blank) no permissions
x = Execute
w = Write
r = Read


// use the operators
+ Add 
- Remove
= Equals
, delimiter


// use:
u=     :  assign User 'blank', results in no permissions
u=r    :  assign user Read (only)
u+wx   :  Add Write and Excute to the User.
u-x    :  Remove Excute from User
a=r    :  assign Read (only) to All Owners


// CLI example:
$ chmod u=rwx foo.txt        // User has full permissions
$ chmod u-wx foo.txt         // User now only has Read permissions
$ chmod u-r,g+w,o= foo.txt   // Remove Read from User, Add Write to Group, Set NO permissions to World




chmod (octals)
but it's good to know the octals

// Octal Permissions; know them, but you don't really have to use them
0 = none
1 = Execute
2 = Write
4 = Read

// the rest are simply combinations of the base Octals
3 is 1 + 2       : Execute and Write
5 is 1 + 4       : Execute and Read.
6 is 2 + 4       : Write and Read
7 is 1 + 2 + 4   : Execute, Write, Read

// eg.
$ chmod 640 foo.txt   // '6' User can Read/Write; '4' Group can Read; '0' World has no permissions
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