gnuserv, gnuclient - Server and Clients for Emacs and XEmacs
gnuclient [-display display] [-q] [-v] [-l library] [-batch] [-f
function] [-eval form] [-h hostname] [-p port] [-r remote-pathname]
[[+line] file] ...
gnudoit [-q] form
gnuattach Removed as of gnuserv 3.x
gnuclient allows the user to request a running Emacs or XEmacs process
to edit the named files or directories and/or evaluate lisp forms.
Depending on your environment, it can be an X frame or a TTY frame.
One typical use for this is with a dialup connection to a machine on
which an Emacs or XEmacs process is currently running.
gnudoit is a shell script frontend to ``gnuclient -batch -eval form''.
Its use is deprecated. Try to get used to calling gnuclient directly.
gnuserv is the server program that is set running by Emacs or XEmacs to
handle all incoming and outgoing requests. It is not usually invoked
directly, but is started from Emacs or XEmacs by loading the gnuserv
package and evaluating the Lisp form (gnuserv-start).
gnuattach no longer exists.
gnuclient supports as much of the command line options of Emacs as
makes sense in this context. In addition it adds a few of its own.
Options with long names can also be specified using a double hyphen
instead of a single one.
-display display, --display display
If this option is given or the `DISPLAY' environment variable
is set then gnuclient will tell Emacs to edit files in a frame
on the specified X device.
-q This option informs gnuclient to exit once connection has been
made with the XEmacs process. Normally gnuclient waits until
all of the files on the command line have been finished with
(their buffers killed) by the XEmacs process, and all the forms
have been evaluated.
-v When this option is specified gnuclient will request for the
specified files to be viewed instead of edited.
Tell Emacs to load the specified library.
-batch Tell Emacs not to open any frames. Just load libraries and
evaluate lisp code. If no files to execute, functions to call
or forms to eval are given using the -l, -f, or -eval options,
then forms to eval are read from STDIN.
Make Emacs execute the lisp function.
Make Emacs execute the lisp form.
Used only with Internet-domain sockets, this option specifies
the host machine which should be running gnuserv. If this
option is not specified then the value of the environment
variable GNU_HOST is used if set. If no hostname is specified,
and the GNU_HOST variable is not set, an internet connection
will not be attempted. N.B.: gnuserv does NOT allow internet
connections unless XAUTH authentication is used or the
GNU_SECURE variable has been specified and points at a file
listing all trusted hosts. (See SECURITY below.)
Note that an internet address may be specified instead of a
hostname which can speed up connections to the server by quite
a bit, especially if the client machine is running YP.
Note also that a hostname of unix can be used to specify that
the connection to the server should use a Unix-domain socket
(if supported) rather than an Internet-domain socket.
-p port Used only with Internet-domain sockets, this option specifies
the service port used to communicate between server and
clients. If this option is not specified, then the value of
the environment variable GNU_PORT is used, if set, otherwise a
service called ``gnuserv'' is looked up in the services
database. Finally, if no other value can be found for the
port, then a default port is used which is usually 21490 + uid.
Note that since gnuserv doesn't allow command-line options, the
port for it will have to be specified via one of the
Used only with Internet-domain sockets, the pathname argument
may be needed to inform Emacs how to reach the root directory
of a remote machine. gnuclient prepends this string to each
path argument given. For example, if you were trying to edit a
file on a client machine called otter, whose root directory was
accessible from the server machine via the path /net/otter,
then this argument should be set to '/net/otter'. If this
option is omitted, then the value is taken from the environment
variable GNU_NODE, if set, or the empty string otherwise.
This is the path of the file to be edited. If the file is a
directory, then the directory browsers dired or monkey are
usually invoked instead. The cursor is put at line number 'n'
gnuserv is packaged standardly with recent versions of XEmacs.
Therefore, you should be able to start the server simply by evaluating
the XEmacs Lisp form (gnuserv-start), or equivalently by typing `M-x
The behavior of this suite of program is mostly controlled on the lisp
side in Emacs and its behavior can be customized to a large extent.
Type `M-x customize-group RET gnuserv RET' for easy access. More
documentation can be found in the file `gnuserv.el'
gnuclient -q -f mh-smail
gnuclient -h cuckoo -r /ange@otter: /tmp/*
More examples and sample wrapper scripts are provided in the
etc/gnuserv directory of the Emacs installation.
SysV IPC is used to communicate between gnuclient and gnuserv if the
symbol SYSV_IPC is defined at the top of gnuserv.h. This is
incompatible with both Unix-domain and Internet-domain socket
communication as described below. A file called /tmp/gsrv??? is created
as a key for the message queue, and if removed will cause the
communication between server and client to fail until the server is
A Unix-domain socket is used to communicate between gnuclient and
gnuserv if the symbol UNIX_DOMAIN_SOCKETS is defined at the top of
gnuserv.h. A file called /tmp/gsrvdir????/gsrv is created for
communication. If the symbol USE_TMPDIR is set at the top of
gnuserv.h, $TMPDIR, when set, is used instead of /tmp. If that file is
deleted, or TMPDIR has different values for the server and the client,
communication between server and client will fail. Only the user
running gnuserv will be able to connect to the socket.
Internet-domain sockets are used to communicate between gnuclient and
gnuserv if the symbol INTERNET_DOMAIN_SOCKETS is defined at the top of
gnuserv.h. Both Internet-domain and Unix-domain sockets can be used at
the same time. If a hostname is specified via -h or via the GNU_HOST
environment variable, gnuclient establish connections using an internet
domain socket. If not, a local connection is attempted via either a
unix-domain socket or SYSV IPC.
Using Internet-domain sockets, a more robust form of security is needed
that wasn't necessary with either Unix-domain sockets or SysV IPC.
Currently, two authentication protocols are supported to provide this:
MIT-MAGIC-COOKIE-1 (based on the X11 xauth(1) program) and a simple
host-based access control mechanism, hereafter called GNUSERV-1. The
GNUSERV-1 protocol is always available, whereas support for MIT-MAGIC-
COOKIE-1 may or may not have been enabled (via a #define at the top of
gnuserv.h) at compile-time.
gnuserv, using GNUSERV-1, performs a limited form of access control at
the machine level. By default no internet-domain socket is opened. If
the variable GNU_SECURE can be found in gnuserv's environment, and it
names a readable filename, then this file is opened and assumed to be a
list of hosts, one per line, from which the server will allow requests.
Connections from any other host will be rejected. Even the machine on
which gnuserv is running is not permitted to make connections via the
internet socket unless its hostname is explicitly specified in this
file. Note that a host may be either a numeric IP address or a
hostname, and that any user on an approved host may connect to your
gnuserv and execute arbitrary elisp (e.g., delete all your files). If
this file contains a lot of hostnames then the server may take quite a
time to start up.
When the MIT-MAGIC-COOKIE-1 protocol is enabled, an internet socket is
opened by default. gnuserv will accept a connection from any host, and
will wait for a "magic cookie" (essentially, a password) to be
presented by the client. If the client doesn't present the cookie, or
if the cookie is wrong, the authentication of the client is considered
to have failed. At this point. gnuserv falls back to the GNUSERV-1
protocol; If the client is calling from a host listed in the GNU_SECURE
file, the connection will be accepted, otherwise it will be rejected.
Using MIT-MAGIC-COOKIE-1 authentication
When the gnuserv server is started, it looks for a cookie defined
for display 999 on the machine where it is running. If the cookie
is found, it will be stored for use as the authentication cookie.
These cookies are defined in an authorization file (usually
~/.Xauthority) that is manipulated by the X11 xauth(1) program. For
example, a machine "kali" which runs an emacs that invokes gnuserv
should respond as follows (at the shell prompt) when set up
kali% xauth list
GS65.SP.CS.CMU.EDU:0 MIT-MAGIC-COOKIE-1 11223344
KALI.FTM.CS.CMU.EDU:999 MIT-MAGIC-COOKIE-1 1234
In the above case, the authorization file defines two cookies. The
second one, defined for screen 999 on the server machine, is used
for gnuserv authentication.
On the client machine's side, the authorization file must contain
an identical line, specifying the server's cookie. In other words,
on a machine "foobar" which wishes to connect to "kali," the
`xauth list' output should contain the line:
KALI.FTM.CS.CMU.EDU:999 MIT-MAGIC-COOKIE-1 1234
To create the cookie, you can use a command like
xauth add `hostname`:999 MIT-MAGIC-COOKIE-1 `head -c512
For more information on authorization files, take a look at the
xauth(1X11) man page, or invoke xauth interactively (without any
arguments) and type "help" at the prompt. Remember that case in the
name of the authorization protocol (i.e.`MIT-MAGIC-COOKIE-1') is
DISPLAY Default X device to put edit frame.
(unix domain sockets only)
Emacs customization file, see emacs(1) and xemacs(1).
dtemacs(1), xauth(1X11), Xsecurity(1X11), gnuserv.el
NULs occurring in result strings don't get passed back to gnudoit
Andy Norman (email@example.com), based heavily upon
etc/emacsclient.c, etc/server.c and lisp/server.el from the GNU Emacs
18.52 distribution. Various modifications from Bob Weiner
(firstname.lastname@example.org), Darrell Kindred (email@example.com), Arup Mukherjee
(firstname.lastname@example.org), Ben Wing (email@example.com) and Hrvoje Niksic