diff --git a/source/Installation/linux_admin.rst b/source/Installation/linux_admin.rst
index 8f17b6a877068293961eafe727d023f8b4850bdf..0a9bfe69bef109cb5db72553f78c98a7b3f52a51 100644
--- a/source/Installation/linux_admin.rst
+++ b/source/Installation/linux_admin.rst
@@ -146,6 +146,46 @@ Create a new user
 
 Only root can perform this command.
 
+Delete a user
+=============
+
+.. code-block:: shell
+
+    userdel [OPTIONS] USERNAME
+
+.. code-block:: shell
+
+    userdel username
+
+The command above remove the user <username> from the system.
+But does not remove it's home directory
+To do this use the `-r` option
+
+.. code-block:: shell
+
+    userdel -r username
+
+.. warning::
+
+    Before to remove a user from the system ensure that he has no job running.
+    Kill all jobs run by user
+
+    .. code-block:: shell
+
+        sudo killall -u username
+
+    Also ensure that he is not logged or force to logout
+
+    .. code-block:: shell
+
+        sudo userdel -f username
+
+    of course you can use `-r` and `-f` on same command.
+
+    .. code-block:: shell
+
+        sudo userdel -rf username
+
 
 create new group
 ================
@@ -158,6 +198,46 @@ Only root can perform this command.
 
 To take into account new user and group you need to logout and login again.
 
+Delete a Group
+==============
+
+.. code-block:: shell
+
+    sudo groupdel groupname
+
+Add an Existing User to a Group
+===============================
+
+.. code-block:: shell
+
+    sudo usermod -a -G <group> <login>
+
+for instance to add the user `zeus` in group `viro`
+
+.. code-block:: shell
+
+    sudo usermod -a -G viro zeus
+
+Always use the `-a` (append) option when adding a user to a new group.
+If you omit the -a option, the user will be removed from any groups not listed after the `-G` option.
+
+On success, the usermod command does not display any output.
+It warns you only if the user or group doesn’t exist.
+
+.. code-block:: shell
+
+    sudo usermod -a -G group1,group2 username
+
+Add username to group1 and group2 in one command
+
+Remove a User From a Group
+==========================
+
+.. code-block:: shell
+
+    sudo gpasswd -d username groupname
+
+
 Check you identity
 ==================