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Aspects of System Administration CS765A

X Window Systems

Neha Dhawale [email protected] X Window Systems: Introduction

X window System or X is a terminal for environment with a X Window Systems: History

• Originally created in 1984 at MIT •1984 – X10 •1987 – X11 •1996 – X11R6.3 by X Consortium •1998 – X11R6.4 by Open Group •1999 – X11R6.5.1 by X.org •Latest Version – X11R6.7 •XFree86 – Flavor of X used by BSD X Window Systems: Architecture

• Client Server Model • Network Transparent • Model for Thin Clients X Window Systems: Client Server Model Components of X: • X Server – “Serves up” the screen information • X Client – actually runs the user requested applications Other Elements of X: • – Special Client allowed to control placement and decoration of windows eg , , wmaker, , (resembling Windows95) •Desk top Manager(optional) – Suite of integrated softwares designed to provide a range of softwares eg KDE, GNOME X Window Systems: N/W Transparency

• Protocol for Client/Server communication - X Protocol •X protocol - device dependent and independent Thus hides hardware and OS peculiarities making it N/W Transparent •X – can invoke remote applications integrated with HTTP making it platform independent and universally accessible X Window Systems: Thin Client • X can run applications on remote hosts thus forming a model for Thin Clients

Configuration Hints • Except for minimal config. of BSD, X is preinstalled •Create /etc/XFree86Config file •Manually •Using programs like XF86Config, XF86Setup, XF86Cfg X Window Systems: File Structure

• startx – initializes an xsession using files: •.startxrc •/usr/lib/X11/sys.startxrc. • xinit – initializer •$HOME/.xinitrc X Window Systems: XDM

XDM(default ) •Responsible for providing the user with a login prompt and initial X session •Manages sessions local as well as remote hosts •Communication between XDM and Xserver through XDMCP – X Display Manager Control Protocol •X Server sends login queries to the host running XDM •New projects have their XDMS eg KDM, GDM X Window Systems: • First client being activated • Xterm is an instance of a • Applications can be run and commands be executed • Customizing xterm: - fg Window foreground - bg Window background color - display Client host specification - geometry size and location of the window - title Name of the new window X Window Systems: DISPLAY X allows user to: • Run client on a remote host and get display on the local host • Access permission to remote host using xhost • Set DISPLAY variable • Run client on local host and redirect display • $netscape –display : X Window Systems: Approaches to Security

Vulnerability Access to display of another host Attacks Flooding, Keyboard Snooping Solution Host Authentication connection accepted based on origin(IP) – xhost(1) Token Authentication connection based on a magic cookie – xauth(1) Secure Keyboard provides keyboard snooping X Window Systems: Approaches to Security

Vulnerability Unreliable channel during data transfer over the network Attacks Packet Capturing, Spoofing Solution X Forwarding Encrypts X Window sessions between the X Client and Server and forwards it through a secure channel $ssh –X smuttynose X Window Systems: X Utilities • Extracting Window Information: •xwininfo(1) – provides information about a window •xlsclients – lists clients running on a display • System Load: •xload – histogram of system load average • Screen Capturing: •xwd – dump an image of an X Window •xwud – image undumping utility X Window Systems: References

• UNIX Concepts and Applications – Sumitabha Das • Running – O’reilly Online Catalog • Unix man pages • Securing X Window - http://ciac.llnl.gov/ciac/documents/ciac2316.html