GNUSERV

Section: User Commands (1)
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NAME

gnuserv, gnuclient, gnudoit - Server and Clients for GNU Emacs

SYNOPSIS

gnuclient [-q] [[-h hostname] [-p port] [-r pathname]] [[+line] path] ...
gnudoit [-q] [[-h hostname] [-p port]] [sexpr] ...
gnuserv

DESCRIPTION

gnuclient allows the user to request a running GNU Emacs process to edit the named files or directories.

gnudoit allows the user to request a running GNU Emacs process to evaluate the given arguments inside a progn LISP form.

gnuserv is the server program that is set running by GNU Emacs to handle all incoming and outgoing requests. It is not usually invoked directly, but is started from GNU Emacs by loading the gnuserv package and evaluating the LISP form (gnuserv-start).

OPTIONS

-q

This option informs both gnuclient and gnudoit to exit once connection has been made with the GNU Emacs process. Normally gnuclient waits until all of the files on the command line have been finished with (their buffers killed) by the GNU Emacs process, and gnudoit normally waits around for evaluation of its arguments by the GNU Emacs process, and prints the results or error conditions.

-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 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 GNU 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.

path

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.

sexpr

This is part of a GNU Emacs LISP expression to evaluate. All the sexprs are concatenated together and wrapped in a progn form before sending to GNU Emacs. If no sexpr is supplied on the gnudoit commandline, gnudoit will read the sexpr to be evaluated from standard input.

SETUP

If gnuserv was packaged along with your emacs distribution, you should be able to start the server simply by evaluating the GNU Emacs lisp form (gnuserv-start). If that doesn't work, or if you obtained gnuserv separately from your emacs distribution, copy the file gnuserv.el into a directory on your GNU Emacs load-path. Load it into GNU Emacs by evaluating the GNU Emacs lisp form (load "gnuserv"). You should now be able to start the server by evaluating the lisp form (gnuserv-start).

EXAMPLE

: gnudoit -q '(mh-smail)'
gnuclient -h cuckoo -r /ange@otter: /tmp/*

SYSV IPC

SysV IPC is used to communicate between gnuclient, gnudoit 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, gnudoit 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 and if deleted will cause communication between server and client to 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, gnudoit 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, gnudoit and 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

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!

FILES

/tmp/gsrv???: (SYSV_IPC only)
/tmp/gsrvdir???/gsrv: (unix domain sockets only)
~/.emacs: GNU Emacs customization file, see gnu-emacs(1).

BUGS

Ctrl-D's occurring in gnudoit input strings won't be handled correctly.

NULs occurring in result strings don't get passed back to gnudoit properly.

When using SYSV IPC, the maximum allowable sizes of a gnudoit request and response are governed by the size of the message buffer (defined at compile time). Responses that exceed the maximum allowed size are truncated.

Long response strings that result from a gnudoit invocation may sometimes cause the gnuserv process to exit if used with a gnu-emacs version 19 release that predates release 23. This is due to a bug in gnu-emacs, so an upgrade to a more recent version will cure the problem. A similar problem may also occur in lucid emacs 19.9, but should not in later versions.

AUTHOR.

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.

This document was created by man2html, using the manual pages.
Time: 00:26:03 GMT, February 16, 2023