Having multiple users and groups with access to the same linux PC/server is great, but not everyone should have access to everything, eh.
+ +For this, we'll use an example file, and switch ownership between root, and our user. So run the following snippet if your're using this as a tutorial, otherwise just read on.
+mkdir ~/permsExample && cd ~/permsExample && sudo touch FILENAMEBasic File Permisssion Breakdown
+For certain things, such as computers with only a few users/groups this works splendid.
+If we run a ls -l FILENAME, we'll see something along the lines of the below.
-rw-r--r-- 1 root root 0 Sep 14 13:02 FILENAME-rw-r--r-- being the permissions for User, Group, and Others which can be rwx for read, write, and executable permissions. Set in groups of 3s for User/Group/Others respectively.
root root refers to the owner user and owner group.
Set User/Group Ownership
+Each file, and directory within UNIX has an owner user, and owner group.
+ By default when you create a file your user will be the owner, and your usergroup will be the owner group.
This can be changed with a simple command (that may need to be run with sudo).
+chown USER FILENAME
+chown :GROUP FILENAME
+chown USER:GROUP FILENAMEThe above snippet has the chown command run three different times with different purposes.
+ The first is to change just the owner user, second to change just the owner group,
+ and third to change both at the same time.
So to change the owner user for FILENAME to our own user, we'd run sudo chown $USER FILENAME, then verify the change by running ls -l FILENAME.
Set Permissions for User/Group/Others
+Now we'll take a look at the file permissions that will affect the owners, and all other users.
+If we look back at the ls -l FILENAME mentioned earlier you'll recall the brief -rw-r--r-- mention.
Intro to the rw-r--r-- meaning
+There are 10 dashes (-) that can be set, ignoring the first for now leaves us with 9, seperated by 3s.
+The first group of three rw- in this example shows that the owner user has read/write permissons, but no executable permissions.
+
The second group r--, shows the owner group only has read permissions, not write/executable permissions.
+
And the third group r--, shows that other users have read permissions, but cannot write/execute the files.
Set permissions
+ +The below commands will set read, write, and execute permissions for the user, and group and give all other users read permissions for filename.file.
+chmod ug+rwx FILENAME
+chmod o+r FILENAMEFirst thing after the chmod command (and a space) can be any combination of ugoa. Referring to user, group, other, and all.
Second, immediately after the letters can be one of +,-,= which are used to add, remove, or set (exact) permissions.
Third, any combination of rwx for read, write, executable permissions.
Follow this up with a space and the file/directory name and poof, permissions are set. If you'd like to set permissions for all files within a directory (and not just new ones created), also add a -R at the end of the command.
Set permissions by number
+Many guides, examples, snippets, and such do not give their demonstration of setting permissions in the same manner as above, instead they'll use numbers, such as the below.
+chmod 755 FILENAMEThis chmod command will give rwx permissions to the owner user, and rx to the owner group, and other.
+ +The numbers are much simpler to understand than you'd think:
+
4 = Read
+
2 = Write
+
1 = Execute/executable
+
These numbers get added up and grant those permissions to the users. So 7 = rwx, 6 = rw, 5 = rx, 3 = wx, 0 = no permissions, etc.
+You'll also spot that there are 3 numbers, 7,5,5. These are for user, group, and other respectively. So each rwx number up to 7 sets the permissions for different users.
+ + +Chmod directories
+The chmod command can also be used on directories. The following example will give all permissions to all users for that directory, and all its child files/directories.
chmod a=rwx directoryName -R