Send a message to all users on a system. Depends on the `libnotify-bin` package.

gistfile1.txt

spam.py

#!/usr/bin/python
# -*- coding: utf-8 -*-
# Licensed under MIT license: http://www.opensource.org/licenses/mit-license.php
import os, subprocess, sys

# thanks: Martin-Éric Racine, Roger Pate
# http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=433960
# http://chat.askubuntu.com/rooms/3/conversation/spam-py

message = " ".join(sys.argv[1:])
command = "notify-send -u critical -i dialog-warning Warning!".split() + [message]
   
if not message:
  sys.exit("Usage: spam Your message to all users goes here.")
if not os.geteuid() == 0:
  sys.exit("Sorry, you need to be root to spam all users on this system.")
command = "notify-send -u critical -i dialog-warning Warning!".split() + [message]

def readfile(fname):
  with open(fname, "r") as fobj:
    return fobj.read()

def get_enviro_for(pid, interesting_fields = None):
  environment = {}
  for line in readfile("/proc/%s/environ" % pid).split("\x00")[:-1]:
    param, _, value = line.partition("=")
    if (interesting_fields) and (param in interesting_fields):
      environment[param] = value
  return environment

#warning: reading world-readable files such as /etc/passwd
# will make people go apeshit -- especially if you're skype.
def __get_uname_for(uid):
  users = (line.split(":") for line in open("/etc/passwd"))
  for line in users:
    if line[2] == uid:
      return line[0]

_usernames = {}
def get_uname_for(uid):
  try:
    return _usernames[uid]
  except KeyError:
    uname = _usernames[uid] = __get_uname_for(uid)
    return uname

def get_basic_info_about(pid):
  status = readfile("/proc/%s/status" % pid).split("\n")
  for line in status:
    if line.startswith("Name"):
      _, _, proc_name = line.partition(":\t")
    if line.startswith("Uid"):
      _, _, uids = line.partition(":\t")
      uid = uids.split()[0]
      break
  return proc_name, get_uname_for(uid)

for pid in os.listdir("/proc"):
  if not pid.isdigit():
    continue

  proc_name, user_name = get_basic_info_about(pid)
  if "gnome-session" != proc_name:
    continue

  # get display and auth
  enviro = get_enviro_for(pid, ["DISPLAY","XAUTHORITY"])

  print "Notifying %s..." % user_name,
  sys.stdout.flush()
  error_code = subprocess.check_call(command, env=enviro)
  if error_code == 0:
    print "success."
  else:
    print "failed (error %d)." %  error_code