note to self....

OVERVIEW:

    This paper outlines - in a very general way - the steps needed to
    set up VNC servic on a host machine such that VNC will provide
    remotely accessible, multi-user graphical loging functionality on a
    Unixish server.

    Additionally, these steps include information about how to custom-
    tailor the Xvnc configuration such that connection to various
    defined ports can provides specified client screen resolution.

    Using well-crafted VNC startup initialization scripts in concert
    with the named port mapping technique shown here, these methods
    could could produce highly customized. specialized services on VNC
    service ports in the specified range.

    Ports may be named appropirately, and portions of the configuration
    scripts may be dynamic.



PRECONDITIONS:

    The the following conditions should pertain for the host which is to
    provide the VNC service:

    * is running the display manager XDM (X-windows Display Manager)

    * is running the Internet meta-deamon INETD

    * has Xvnc installed

    Additionally, the user performing the configuration must have system
    administrative privileges for the host.



STEPS:

    1. Add VNC User account

        the VNC server application runs as this user.  This should be
        generic system user ID, a bit like the user 'nobody' which
        Apache runs as.


    2. Add VNC Port names to /etc/services

        VNC uses TCP/IP ports 5900 to 5999.  These ports map to display
        numbers in VNC client connect strings, and by inetd (or xinetd)
        to start the VNC service.


    3. Add VNC service definitions to /etc/inetd.conf

        For each VNC port name defined in step 2, above, a line is
        placed in the /etc/inetd.comf file.  These are standard inetd
        configuration / invocation syntax definitions that are used to
        configure services that are requested via inetd.


    4. Modify Display Manager startup scripts

        a) /etc/X11/xdm/Xaccess

          The file /etc/X11/xdm/Xaccess contains rules which control
          access to the XDM display manager.  These rules must remote
          access to XDM in order that remote users be able to use XDM
          for login.

          The simplest way to accomplish that is to simply place a
          single asterick character (*) on a line by itself in this
          file.

          For example. an /etc/X11/xdm/Xaccess rule allowing access to
          Xdm from any network host is:

          *  # any  host can get a login window

        b) /etc/X11/xdm/xdm-config

          Comment out the DisplayManager.requestPort line.


    5. Restart System Services XDM and INETD

        % /etc/init.d/xdm restart
        % /etc/init.d/inetd restart



NOTES:

    For additional information about XDM initialization and
    configuration, see the XDM manual pages.

    For additional information about VNC session startup initialization,
    see the VNC documentation.

    For additional information about INETD and the /etc/services file,
    see the manual pages for those.



EXAMPLE FOR /etc/services FILE:

    ## ===========================================================
    ##  /etc/services Modifications
    ##  VNC services using ports 5900 thru 5999
    ##  ---------------------------------------------------------
    # name          port/proto      resolution      screen number
    # ------------  --------------  --------------- -------------
    vnc             5900/tcp        # site default  :0
    vnc-tiny        5901/tcp        # 320x240       :1
    vnc-small       5902/tcp        # 640x480       :2
    vnc-med         5903/tcp        # 800x600       :3
    vnc-large       5904/tcp        # 1024x764      :4
    vnc-xlrg        5905/tcp        # 1280x1024     :5
    vnc-huge        5906/tcp        # 1600x1200     :6
    vnc-cust        5907/tcp        # 1160x960      :7
    ## ===========================================================



EXAMPLE FOR /etc/inetd.conf FILE:

    # ============================================================
    # Add to /etc/inetd.conf
    # ===========================================================
    # Start VNC services based on TCP port name.
    #
    # In this example, ports are named for their resolutions.
    #
    # All servers in this example uses a default pixel color depth of
    # 24bpp.
    #
    # All servers currently run under username "netcusr".
    #
    # Port numbers are defined in /etc/services
    #
    #       name            resolution      VNC screen
    #       -------------   -------------   ----------
    #       vnc             1160x960        :0
    #       vnc-tiny        320x240         :1
    #       vnc-small       640x480         :2
    #       vnc-med         800x600         :3
    #       vnc-large       1024x768        :4
    #       vnc-xlrg        1280x1024       :5
    #       vnc-huge        1600x1200       :6
    #       vnc-cust        1160x960        :7
    #
    # ===========================================================
    vnc     stream tcp nowait netcusr /usr/X11R6/bin/Xvnc Xvnc\
            -geometry 1160x960 -depth 24 -desktop NetC\
            -inetd -once -query localhost
    vnc-tiny stream tcp nowait netcusr /usr/X11R6/bin/Xvnc Xvnc\ 
           -geometry 320x240 -depth 24 -desktop NetC\
           -inetd -once -query localhost
    vnc-small stream tcp nowait netcusr /usr/X11R6/bin/Xvnc Xvnc\
           -geometry 640x480 -depth 24 -desktop NetC\
           -inetd -once -query localhost
    vnc-med stream tcp nowait netcusr /usr/X11R6/bin/Xvnc Xvnc\
           -geometry 800x600 -depth 24 -desktop NetC\
           -inetd -once -query localhost
    vnc-large stream tcp nowait netcusr /usr/X11R6/bin/Xvnc Xvnc\
           -geometry 1024x768 -depth 24 -desktop NetC\
           -inetd -once -query localhost
    vnc-xlrg stream tcp nowait netcusr /usr/X11R6/bin/Xvnc Xvnc\
           -geometry 1280x1024 -depth 24 -desktop NetC\
           -inetd -once -query localhost
    vnc-huge stream tcp nowait netcusr /usr/X11R6/bin/Xvnc Xvnc\
           -geometry 1600x1200 -depth 24 -desktop NetC\
           -inetd -once -query localhost
    vnc-cust stream tcp nowait netcusr /usr/X11R6/bin/Xvnc Xvnc\
           -geometry 1160x960 -depth 24 -desktop NetC\
           -inetd -once -query localhost
    # ===========================================================



ADDITIONAL CONFIGURATION AND EXTENSION INFORMATION:

    From the XDM manual page:

      "For X terminals that do not offer a menu of hosts to get display
       management  from,  xdm  can collect  willing  hosts and run the
       chooser program to offer the user a menu.  For X displays
       attached to a host, this step is typically not used, as the local
       host does the display  management."

    ...this chooser behaviour may be automated server side such that it
    could select a login host form a cluster of hosts based on e.g. load
    balancing parameters.


    Also from the manual page:

      "After  resetting  the X server, xdm runs the Xsetup script to
       assist in setting up the screen the user sees along with the
       xlogin widget."

   ...the Xsetup script exists as /etc/X11/xdm/Xsetup - this is the
   script to customize to control what the user sees on the login
   screen.


   Manual page, again:

     "The xlogin widget, which xdm presents, offers the familiar login
      and password prompts."

   ...the xlogin widget resources may be specified using standard X
   resource specifications.  This gives fine-grained control over the
   appearance and behaviour of the login widget (which displays the
   'Username:' and 'Password:' prompts)...

   The manual page specifies the order in which the other session setup
   scripts run:

     "After the user logs in, xdm runs the Xstartup script as root.

     "Then xdm runs the Xsession script as the user.  This system
      session file may  do  some  additional  startup  and  typically
      runs the .xsession script in the user's home directory.  When the
      Xsession script exits, the session is over."

   ...note that the ~/.vnc session initialization scripts are not be
   being used, here, since the VNC service is running at a system level,
   allowing the user to log in using standard X login methods. This
   means that, assuming the user logins in only using VNC (i.e. never
   logs in locally), the standard startup scripts may be used to
   initialize the session, even though some session initialization may
   be VNC-specific.


     "At the end of the session, the Xreset script is run to clean up,
     the X server is  reset,  and the cycle starts over."

   ...so any session tear-down should be done in Xreset.  There should
   also be a user-specific version of this file.  If there is not, one
   should be added.


   To summarize:  VNC can be used to set up the connection and do
   authentication, following which the XDM and standard X session
   configurations can be used to control the what gets displayed on the
   "desktop" that the user sees following the login authenitcation
   sequence.

posted by 0x0000  # 13:43