diff --git a/sys/user_cull.py b/sys/user_cull.py
new file mode 100755
index 0000000..70c23f6
--- /dev/null
+++ b/sys/user_cull.py
@@ -0,0 +1,122 @@
+#!/usr/bin/env python3
+
+# Because:
+#   - SSH timeout doesn't work with byobu/screen/tmux
+#   - SSH timeout can be overridden client-side
+#   - $TMOUT can be overridden user-side
+# we need to actually kill the sshd process attached to the SSH session.
+
+import datetime
+import os
+import psutil
+import subprocess
+
+# in seconds. 5 minutes = 300 seconds.
+# if "auto", we'll try checking $TMOUT in the system bashrc and sshd_config, in that order.
+timeout = 'auto'
+# only apply to ssh connections instead of ssh + local.
+# THIS WILL KILL SCREEN/TMUX CONNECTIONS. USE WITH CAUTION.
+only_ssh = True
+# send a closing message.
+goodbye = True
+# the message to send to the user if goodbye == True.
+# can use the following for substitution:
+#   pid          - The PID if the user's login process.
+#   terminal     - The terminal they're logged in on.
+#   loginlength  - How long they've been logged in (in minutes).
+#   logintime    - When they logged in.
+#   timeout      - The allowed length of time for inactivity until a timeout.
+goodbye_mesg = ('You have been logged in for {loginlength} seconds (since {logintime}) on '
+                '{terminal} ({pid}).\n'
+                'However, as per security policy, you have exceeded the allowed idle timeout ({timeout}).\n'
+                'As such, your session will now be terminated. Please feel free to reconnect.')
+# exclude these usernames
+exclude_users = []
+
+
+# Get the SSHD PIDs.
+ssh_pids = [p for p in psutil.process_iter() if p.name() == 'sshd']
+# If the timeout is set to auto, try to find it.
+if timeout == 'auto':
+    import re
+    #tmout_re = re.compile('^\s*#*(export\s*)?TMOUT=([0-9]+).*$')
+    tmout_re = re.compile('^\s*(export\s*)?TMOUT=([0-9]+).*$')
+    # We don't bother with factoring in ClientAliveCountMax.
+    # sshd_re = re.compile('^\s*#*ClientAliveCountMax\s+([0-9+]).*$')
+    sshd_re = re.compile('^\s*ClientAliveInterval\s+([0-9+]).*$')
+    for f in ('/etc/bashrc', '/etc/bash.bashrc'):
+        if not os.path.isfile(f):
+            continue
+        with open(f, 'r') as fh:
+            conf = f.read()
+        for line in conf.splitlines():
+            if tmout_re.search(line):
+                try:
+                    timeout = int(tmout_re.sub('\g<2>', line))
+                    break
+                except ValueError:
+                    continue
+    if not isinstance(timeout, int):  # keep going; check sshd_config
+        with open('/etc/ssh/sshd_config', 'r') as f:
+            conf = f.read()
+        for line in conf.splitlines():
+            if sshd_re.search(line):
+                try:
+                    timeout = int(tmout_re.sub('\g<1>', line))
+                    break
+                except ValueError:
+                    continue
+    # Finally, set a default. 5 minutes is sensible.
+    timeout = 300
+
+
+def kill_user(user):
+    pass
+
+def get_idle(user):
+    idle_time = None
+    pty = user.terminal
+    for sssn in subprocess.run(['who', '-u'], stdout = subprocess.PIPE).stdout.decode('utf-8').splitlines():
+        session = sssn.split()
+        # This is probably overkill, but.
+        if not all((
+                (session[0] != user.name),
+                (session[1] != user.terminal),
+                (session[5] != user.pid))):
+            continue
+        # https://unix.stackexchange.com/a/332704/284004
+        last_used = datetime.datetime.fromtimestamp(os.stat('/dev/{0}'.format(user.terminal)).st_atime)
+        idle_time = datetime.datetime.utcnow() - last_used
+        break
+    return(idle_time)
+
+
+for user in psutil.users():
+    if user.name in exclude_users:
+        continue
+    login_pid = user.pid
+    login_length = (datetime.datetime.utcnow() - datetime.datetime.fromtimestamp(user.started))
+    if login_length.total_seconds() < timeout:
+        continue  # they haven't even been logged in for long enough yet.
+    idle_time = get_idle(user)
+    if idle_time.total_seconds() >= timeout:
+        fmtd_goodbye = goodbye_mesg.format({'pid': user.pid,
+                                            'terminal': user.terminal,
+                                            'loginlength': login_length,
+                                            'logintime': datetime.datetime.fromtimestamp(user.started),
+                                            'timeout': timeout})
+        if only_ssh:
+            if user.pid in ssh_pids:
+                if goodbye:
+                    subprocess.run(['write',
+                                    user.name,
+                                    user.terminal],
+                                   input = fmtd_goodbye.encode('utf-8'))
+                psutil.Process(user.pid).terminate()
+        else:
+            if goodbye:
+                subprocess.run(['write',
+                                user.name,
+                                user.terminal],
+                               input = fmtd_goodbye.encode('utf-8'))
+            psutil.Process(user.pid).terminate()