groupmems availability

added groupmems functionality for users.

wiki/source/security.md

@@ -1,10 +1,9 @@
 ---
 title: Editing Basic UNIX Security the Tilde way
-author: michaelcoyote
+author: michaelcoyote. updated by deepend
 category: tutorials
 ---
 
-
 > "Unix is public by default. This means that other people who use the server can see your files. You can change that on a file-by-file basis. You can also change the default behavior for you. It is totally okay to keep your stuff private. Let us show you how." 
 
 Unix was built with a fairly open security policy. It's the kind of system you might expect a bunch of Berkley hippies to design. That said, if it bugs you that someone might be able to look the files in your home directory and you don't want to read any more of this document then run these commands:
@@ -25,7 +24,7 @@ There are several attributes that define a user.
 - user id (or uid)  
     This is your unique numerical id number on the system. This is how the system keeps track of you, your processes, and your files.
 - group id (or gid)  
-    This is a unique numerical id number for your primary user group on the system. User groups are the traditional way that users would colaberate on large projects. 
+    This is a unique numerical id number for your primary user group on the system. User groups are the traditional way that users would collaborate on large projects. 
 
 For now we only need to know about the username.
 
@@ -48,7 +47,6 @@ What does this long file listing of `my_file` show us?
     -rw-rw-r--  1  youruser  youruser   177   Oct 13 04:51    my_file
     ---------- --- -------   --------  -----  ------------ -------------
         |       |     |        |         |         |             |
-        |       |     |        |         |         |         File Name
         |       |     |        |         |         +---  Modification Time
         |       |     |        |         +-------------   Size (in bytes)
         |       |     |        +-----------------------     Group owner
@@ -78,6 +76,7 @@ The first column at first glance looks like a bunch of alphabet soup, however if
 #### Types of permissions
 
 There are three major types of permissions (and a hand full of others)
+
 - Read  
     Read permission is represented as an `r` and will allow a listing of a directory and reading a file.
 - Write  
@@ -116,7 +115,6 @@ Examples
             ls -l test/a_file
             
 
-
 #### Basics about the `finger` and `chfn` commands
 
 How to see others in the system using `finger`
@@ -154,3 +152,46 @@ The `id` command is a tool to show us how the system keeps track of us. From thi
     - use the `grep` command to find your uid in the `/etc/passwd` file
         
 As noted above, we can obtain our group id using the `id` command. Try locating your group in `/etc/group` using the commands that were specified above; your group name will probably be the same as your user (although at times this might not be true depending on the configuration of the system).
+
+#### Using your personal group for collaboration (`groupmems`)
+
+On this tilde server, each user normally has a *personal* group with the same name as their login. For example:
+
+- user: `youruser`  
+- primary group: `youruser`
+
+You can use this personal group to give trusted friends access to files and directories you own, without making them world-readable.
+
+To make this easier, the server provides a helper command you use with `sudo`:
+
+- List who is in your personal group:
+
+    ```sh
+    sudo self-groupmems list
+    ```
+
+- Add another user to your group:
+
+    ```sh
+    sudo self-groupmems add otheruser
+    ```
+
+- Remove a user from your group:
+
+    ```sh
+    sudo self-groupmems del otheruser
+    ```
+
+This only affects membership of **your** personal group. It does **not** change your primary group, and it does not let you modify other system groups.
+
+Once someone is in your group, you can share things with them by making the group the owner and giving it access:
+
+```sh
+# Make a shared directory
+mkdir ~/shared
+
+# Set the group to your personal group (usually already true)
+chgrp "$USER" ~/shared
+
+# Let your group read/write/enter it, but keep others out
+chmod 770 ~/shared