adding PAM Namespace

PAM-Namespace.md

@@ -0,0 +1,87 @@
+## Overview
+
+The `pam_namespace.so` module is typically included by the system PAM packages already, no need to install an extra package.
+
+This example is on Ubuntu 20 LTS, if SElinux is required see the addtional options:
+
+ - https://linux.die.net/man/8/pam\_namespace
+ - https://linux.die.net/man/5/namespace.conf
+
+Mission: create a virtual top-level directory for all users logging in, which is actually a subdirectory in their `$HOME` space.
+
+## Steps
+
+### As root
+
+Make the virtual directory mount point:
+
+```
+# mkdir /vdir
+```
+
+Create a config for mounting the namespace, this will add the username onto the end of the directory; for example `/home/fred/vdirfred` - the idea is that the second field does _not_ have to be `$HOME`, it could be another directory like `/srv/vdirusers` such that each subdir gets a unique name dynamically like `/srv/vdirusers/vdirfrank` - see the man pages.
+
+```
+# vi /etc/security/namespace.conf
+
+/vdir  $HOME/vdir  user:iscript=userperms.sh
+```
+
+Create the above mentioned script to have the user own the new directory created the first time they log in (by default it's `root:root` so users cannot write to it):
+
+```
+# vi /etc/security/namespace.d/userperms.sh
+
+== cut here ==
+#!/bin/sh
+# polydir path as $1, the instance path as $2,
+# instance dir was newly created (0 - no, 1 - yes) in $3
+# user name in $4
+if [ "$3" = 1 ]; then
+  user="$4"
+  inst="$2"
+  passwd=$(getent passwd "$user")
+  gid=$(echo "$passwd" | cut -f4 -d":")
+  chown -R "$user":"$gid" "$inst"
+fi
+exit 0
+== cut here ==
+
+# chmod +x /etc/security/namespace.d/userperms.sh
+```
+
+Activate the new configuration - note that this edits PAM, the rule of thumb is to never log out as root until you've verified it's working by logging in with other terminals as other users.
+
+**IF YOU BREAK PAM, YOU LOCK EVERYONE OUT - INCLUDING `root`**
+
+```
+# vi /etc/pam.d/common-session
+
+session  required  pam_namespace.so  ignore_instance_parent_mode
+```
+
+### As user
+
+Log in as the user and test:
+
+```
+$ ssh fred@server
+
+server$ touch vdirfred/foo
+server$ ls /vdir
+foo
+
+server$ touch /vdir/bar
+server$ ls vdirfred/
+bar  foo
+```
+
+### As root
+
+As root, `/vdir` should remain empty (no user created files) as it's a virtual mount point:
+
+```
+# ls /vdir
+#
+```
+

_Sidebar.md

@@ -40,6 +40,7 @@
 - [[MySQL Connections]]
 - [[NFS 10G Tuning]]
 - [[Netcat Replacements]]
+- [[PAM Namespace]]
 - [[Proxmox Doodads]]
 - [[RPM Info]]
 - [[Radeon Temperature]]