Advanced Network and System Administration

Transcription

1 Advanced Network and System Administration Remote Desktops HaiVDC 1

2 Topics 1. X Windows 1. Client/server windowing 2. Window managers and desktops 3. Security 2. VNC 1. Why VNC? 2. Configuring 3. Security 3. NX Copyright@2009, HaiVDC 2

3 X-Windows Network-based windowing system. Server Client Handles user input and graphical display. Runs on the machine with display unit. Graphical applications are clients. Can run on a different machine than server. Set DISPLAY environment variable. Or use display command line option. Copyright@2009, HaiVDC 3

4 Window Manager X client that provides features like: Move, resize, iconify, and kill windows. Window title bars. Popup menus. Example window managers twm: Tab, primitive early window manager mwm: Motif, found on commercial UNIXes fvwm: Free, fast, very customizable. WindowMaker: NeXT-like, see also AfterStep. Copyright@2009, HaiVDC 4

5 TWM Screenshot HaiVDC 5

6 FVWM Screenshot HaiVDC 6

7 WindowMaker HaiVDC 7

8 Desktops CDE Common desktop env for commercial UNIXes. Gnome Standard Linux desktop based on GTK+. KDE Windows-like free desktop based on QT. Xfce Lightweight desktop, also based on GTK+. HaiVDC 8

9 X-Windows Security Why do we need security? An evil client can capture/create any X events. Even if you re not using any network clients! Host authentication Limit who can start clients by IP address. Set by xhost + or xhost - commands. Token authentication Only clients with token can access server. Set by the xauth command. Copyright@2009, HaiVDC 9

10 X-Windows Security Tunneling + host authentication. All clients appear to be from localhost. Therefore disable remote clients with xhost Use ssh client to tunnel X: ssh X host Server must have X11Forwarding set to yes. Use echo DISPLAY to test if X forwarding is on. Note that local users can still attack X session. Copyright@2009, HaiVDC 10

11 VNC: Virtual Network Computing HaiVDC 11

12 Why VNC? 1. Remote desktop access. 2. Helpdesk: control a remote desktop. 3. Persistent desktop. 4. Use same desktop from multiple clients. 5. Need Linux access from Windows. 6. Need Windows access from Linux. Copyright@2009, HaiVDC 12

13 What is VNC? Open remote desktop protocol. Many implementations RealVNC: VNC from original researchers. TightVNC: VNC with high compression. VNCj: Java VNC, can run within web browser. PalmVNC: VNC for Palm Pilots. UltraVNC: enhanced VNC, only for Windows. HaiVDC 13

14 Using VNC 1. Start VNC server UNIX: vncserver Win: Start menu>programs>realvnc>vncserver 1. Write down server name and display number. It will look something like unix3:1 1. Start VNC client UNIX: vncviewer Win: Start menu>programs>realvnc>vncviewer 1. Enter server and display to connect to (from step 2). 2. A VNC remote desktop should appear. Copyright@2009, HaiVDC 14

15 Configuring and Troubleshooting On UNIX, VNC stores files under ~/.vnc Configuration: xstartup Indicates which X clients to start with server. Typically includes vncconfig application. Configuration: passwd Contains VNC server session password. Log files: host:display#.log Any errors should appear in these logs. Copyright@2009, HaiVDC 15

16 Securing VNC VNC does not provide encryption. Use ssh tunneling to encrypt login + data: ssh L 5901:remotehost:5901 remotehost vncviewer localhost:1 Copyright@2009, HaiVDC 16

17 NX Advantages over VNC: Speed: fast enough to use over dialup. Built-in ssh encryption. Disadvantages Immature code; hard to install + set up. GPL client/server for Linux only. Free Windows client; commercial server. Copyright@2009, HaiVDC 17

18 References 1. Daniel J. Barrett, Robert G. Byrnes, Richard E. Silverman, SSH, The Secure Shell, 2 nd edition, O Reilly, John Fisher, Secure X Windows, CIAC 2316, No Machine NX, 4. RedHat, Red Hat Enterprise Linux 4 System Administration Guide, Real VNC, 6. runeb, Crash Course in X Windows Security, 7. Carla Schroeder, Linux Cookbook, O Reilly, Carla Schroeder, FreeNX ups the Remote Linux Desktop Ante, Enterprise Networking Planet, http :// Webmin, Window Managers for X, Copyright@2009, HaiVDC 18