gnuserv - Online in the Cloud

PROGRAM:

NAME

gnuserv, gnuclient - Server and Clients for Emacs and XEmacs

SYNOPSIS

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

DESCRIPTION

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.

OPTIONS

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.

-l library
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.

-f function,
Make Emacs execute the lisp function.

-eval form
Make Emacs execute the lisp form.

-h hostname
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 alternative methods.

-r pathname
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.

[+n] file
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' if specified.

SETUP

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'.

CONFIGURATION

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'

EXAMPLE

gnuclient -q -f mh-smail
gnuclient -h cuckoo -r /ange@otter: /tmp/*
gnuclient ../src/listproc.c

More examples and sample wrapper scripts are provided in the etc/gnuserv directory of the
Emacs installation.

SYSV IPC

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.

UNIX-DOMAIN SOCKETS

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

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.

SECURITY

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 correctly.

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 /dev/urandom|md5sum`

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!

ENVIRONMENT

DISPLAY Default X device to put edit frame.

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