| GNUSERV(1) | General Commands Manual | GNUSERV(1) |
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
gnuserv
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.
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.
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 gnuserv-start'.
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'
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 restarted.
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.
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:
To create the cookie, you can use a command like
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 significant!
NULs occurring in result strings don't get passed back to gnudoit properly.
Andy Norman (ange@hplb.hpl.hp.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 (weiner@mot.com), Darrell Kindred (dkindred@cmu.edu), Arup Mukherjee (arup@cmu.edu), Ben Wing (ben@xemacs.org) and Hrvoje Niksic (hniksic@xemacs.org).
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