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When connecting remotelyto a Unix system from a PC, Mac, or
other Unix
system, you may wish to display X Windows applications on your local computer.
To do this, you need to have an X Windows display manager with an access
control program on the local computer, as well as a proper setup for the
X Windows forwarding from the remote system to the local system. To do
this, the
local system needs to be running an X Windows server (display manager);
the remote Unix host has the X Windows client application.
The Univeristy of Maryland's (UM) Unix systems (Sun and Linux hosts)
and newer Mac
systems (including the TerpConnect Macs) have an X Windows server
installed as part
of the operating system. Some Macs and all Windows PCs do not have an X
Windows manager as part of the operating system; it will have to be installed
prior to running remote X Windows applications successfully. On Mac OS X,
the X Windows component is a part of the extended operating system; it may
need to be explicitly installed from the Xcode2 (or Xcode, for older versions
of OS X) developer tools. There are several X Windows display managers
available for Microsoft Windows, both free and for a cost. The one the Office of Information Technology (OIT)
Help Desk currently recommends for the Windows platform is the free
XLiveCD distribution (from Indiana
University, based on the Cygwin
environment), that can either be installed on the hard drive or run
directly
from the CD. Mac OS X users can use the Apple-provided X server.
When you wish to connect from a local PC/Mac/Unix host to a remote Unix
system, you must do two things before applications running on the remote
host
can be displayed on the local host:1) you must allow the remote host to
display windows on the local host (access control), and 2) you must tell
the remote host where to display those windows (display name).
Access Control
The simplest way to provide access control to the remote host is to use
the xhost program, which maintains a list of remote hosts
that
are allowed to make connections to the local X server. To add a host to the
access list, use the syntax:
xhost +remote_host
where remote_host is the hostname of the remote Unix system. You
can allow multiple remote hosts display access to your local system. To
remove a host from the access list, use the syntax:
xhost -remote_host
To list which remote hosts are in the access list, simply type
xhost, this will tell you if access control is currently
enabled, and if so, which hosts are allowed access to the local display.
Note: On the OIT Computer Lab Macs, you may need to specify the
complete path to the xhost command:
/usr/X11R6/bin/xhost +remote_host
Local display
On the remote system, you must define it where to display the X Windows
application prior to running it. This is done by setting the DISPLAY
environment variable. The syntax to do this varies depending upon which
login shell you're using on the remote host:
csh/tcsh: setenv DISPLAY local_host:0
sh/bash/ksh: DISPLAY=local_host:0; export DISPLAY
(Note that "DISPLAY" is all caps.) Once you've added the
remote host to the access control list and correctly specified the local
display, you should be able to run X applications on the remote host and have
them display on the local host.
Note: You can skip the DISPLAY step above if you are using the
ssh program with the "-X" option to connect to the
remote host. This will automatically enable X forwarding to the local
display:
ssh -X remote_host
For further information, refer to the Unix online documentation:
man xhost
man ssh
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