copy over the ACLs guide (#93)

* copy over the ACLs guide
* link to acl docs

Author: bcumming

docs/guides/storage.md

@@ -1,6 +1,118 @@
 [](){#ref-guides-storage}
 # Storage
 
+[](){#ref-guides-storage-sharing}
+## Sharing files and data
+
+Newly created user folders are not accessible by other groups or users on CSCS systems.
+Linux [Access Control Lists](https://www.redhat.com/en/blog/linux-access-control-lists) (ACLs) let you grant access to one or more groups or users.
+
+In traditional POSIX, access permissions are granted to `user/group/other` in mode `read`/`write`/`execute`.
+The permissions can be checked with the `-l`  option of the command `ls`.
+For instance, if `user1` owns the folder `test`, the output would be the following:
+
+```console title="Checking posix permissions with ls"
+$ ls -lahd test/
+drwxr-xr-x 2 user1 csstaff 4.0K Feb 23 13:46 test/
+```
+
+ACLs are an extension of these permissions to give one or more users or groups access to your data.
+The ACLs of the same `test` folder of `user1` can be shown with the command `getfacl`:
+
+```console title="Checking permissions with getfacl"
+$ getfacl test
+# file: test
+# owner: user1
+# group: csstaff
+user::rwx
+group::r-x
+other::r-x
+```
+
+The command `setfacl` is used to change ACLs for a file or directory.
+
+To add users or groups to read/write/execute on a selected file or folder, use the `-M,--modify-file` or `-m,--modify` flags to modify the ACL of a file or directory.
+
+!!! example "give user2 read+write access to test"
+    Where `test` is owned by `user1`.
+    ```console
+    $ setfacl -m user:user2:rw test/
+
+    $ getfacl test/
+    # file: test
+    # owner: user1
+    # group: csstaff
+    user::rwx
+    user:user2:rw
+    group::r-x
+    mask::rwx
+    other::r-x
+    ```
+
+The `-X,--remove-file` and  `-x,--remove` options will remove ACL entries.
+
+!!! example "remove user2 access to test"
+    This reverts the access that was granted in the previous example.
+    ```console
+    $ setfacl -x user:user2 test/
+
+    $ getfacl test/
+    # file: test
+    # owner: user1
+    # group: csstaff
+    user::rwx
+    group::r-x
+    mask::rwx
+    other::r-x
+    ```
+
+Access rights can also be granted recursively to a folder and its children (if they exist) using the option `-R,--recursive`.
+
+!!! note
+    This applies only to existing files - files added after this call won't inherit the permissions.
+
+!!! example "recursively grant user2 access to test and its contents"
+    ```console
+    $ setfacl -Rm user:user2 test
+
+    $ getfacl test/subdir
+    # file: test/subdir
+    # owner: user1
+    # group: csstaff
+    user::rwx
+    user:user2:rwx
+    group::---
+    group:csstaff:r-x
+    mask::rwx
+    other::---
+    ```
+
+To set up a default so all newly created folders and dirs inside or your desired path will inherit the permissions, use the `-d,--default` option.
+
+!!! example "recursively grant user2 access to test and its contents"
+    `user2` will have access to files created inside `test` after this call:
+
+    ```console
+    $ setfacl -dm user:user2:rw test/
+
+    $ getfacl test
+    # file: test
+    # owner: user1
+    # group: csstaff
+    user::rwx
+    group::r-x
+    mask::rwx
+    other::r-x
+    default:user::rwx
+    default:user:user2:rw
+    default:group::r-x
+    default:mask::rwx
+    default:other::r-x
+    ```
+
+!!! info
+    For more information read the setfacl man page: `man setfacl`.
+
 ## Many small files vs. HPC File Systems
 
 Workloads that read or create many small files are not well-suited to parallel file systems, which are designed for parallel and distributed I/O.

docs/software/unsupported.md

@@ -3,10 +3,9 @@
 
 This page documents frequently-requested applications that CSCS won't provide pre-built on Alps as [supported software][ref-support-apps].
 
-!!! warning "License terms"
+!!! danger "License terms"
     Often it is impossible or difficult to provide software for licensing reasons.
-
-    Note that if users are asked to install licensed software because CSCS can't, it is the responsibility of users to ensure that the software is only available to them personally, or to members of their group who are also permitted by the license to access the software.
+    If users are asked to install licensed software because CSCS can't, it is the responsibility of users to ensure that the software is only available to them personally, or to [members of their group][ref-guides-storage-sharing] who are also permitted by the license to access the software.
 
 ## Gaussian
 
@@ -15,6 +14,4 @@ The electronic structure modeling code [Gaussian](https://gaussian.com/) has lic
 ## Matlab
 
 CSCS does not have a license to provide [Matlab](https://www.mathworks.com/products/matlab.html) to users on Alps.
-
 Users or groups with valid licenses can install Matlab themselves as [user software][ref-support-user-apps].
-Please ensure that you install the software in a location where only members of your group who are allowed to use Matlab can access it.