GNUSERV(1)

📦 version 21.4.24, in debian bookworm, ubuntu jammy, ubuntu noble, ubuntu resolute, ubuntu stonking

✨ NAME ✨

okay so bestie, GNUSERV(1) is serving from the General Commands Manual, and it's literally about gnuserv and gnuclient — the server and clients for XEmacs. periodt. 💅

💅 SYNOPSIS 💅

the receipts, exactly as they are:

gnuclient [-nw] [-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 is the way you ask a running 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 is with a dialup connection to a machine on which an 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, bestie. 😭

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

gnuattach no longer exists. Its functionality has been replaced by gnuclient -nw. 🫶

🎀 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.

  • -nw — This option makes gnuclient act as a frontend such that XEmacs can attach to the current TTY. XEmacs will then open a new TTY frame. The effect is similar to having started a new XEmacs on this TTY with the -nw option. It currently only works if XEmacs is running on the same machine as gnuclient. This is the default if the DISPLAY environment variable is not set.
  • -display display, --display display — If this option is given or the DISPLAY environment variable is set then gnuclient will tell XEmacs 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 XEmacs 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. slay. ✨

💖 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 -nw ../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 🔐

Okay bestie, this is the part where things get real. When you're using Internet-domain sockets, you need a much beefier form of security than what was needed for Unix-domain sockets or SysV IPC. Like, those were the cozy locked-door vibes; this is the whole internet knocking.

Right now there are two authentication protocols to do this:

  • MIT-MAGIC-COOKIE-1 — based on the X11 xauth(1) program
  • GNUSERV-1 — a simple host-based access control mechanism

GNUSERV-1 is always available (no cap, it's just there). But support for MIT-MAGIC-COOKIE-1 may or may not have been enabled at compile-time (it depends on a #define at the top of gnuserv.h). So yeah, it's giving ✨build-config dependent✨.

🛡️ GNUSERV-1, the always-there one

gnuserv, using GNUSERV-1, does a limited form of access control at the machine level. By default, no internet-domain socket is opened. None. Zero. The door stays shut.

But here's the tea: if the variable GNU_SECURE can be found in gnuserv's environment, and it names a readable filename, then that file gets opened and is assumed to be a list of hosts — one per line — from which the server will allow requests. Any connection from any other host? Rejected. 💀

And listen, even the machine gnuserv is running on isn't permitted to make connections via the internet socket unless its hostname is explicitly specified in that file. Yes, even localhost has to show its ID at the door.

Heads up, bestie: a host can be either a numeric IP address or a hostname. And here's the scary part — any user on an approved host may connect to your gnuserv and execute arbitrary elisp. Like, delete all your files arbitrary. So choose that host list wisely. 😭

Also, if that file contains a lot of hostnames, the server may take quite a time to start up. It's reading the whole guest list at the door, every single time.

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. So if the client is calling from a host listed in the GNU_SECURE file, the connection will be accepted — otherwise it will be rejected. 💅

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. So 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 the one 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! It is literally not playing about that capitalization, bestie. 🙈

🌍 ENVIRONMENT 🌍

  • DISPLAY — Default X device to put edit frame. 🖥️✨

📁 FILES 📁

  • /tmp/gsrv??? — (SYSV_IPC only)
  • /tmp/gsrvdir???/gsrv — (unix domain sockets only)
  • ~/.emacs — XEmacs customization file, see xemacs(1).

👀 SEE ALSO 👀

xauth(1X11), Xsecurity(1X11), gnuserv.el

💀 BUGS 💀

NULs occurring in result strings don't get passed back to gnudoit properly. So like, yeah, that's a known thing. Not us being dramatic, it's literally in the docs. 🫠

🌸 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.

Various modifications from:

  • Bob Weiner (weiner@mot.com)
  • Darrell Kindred (dkindred@cmu.edu)
  • Arup Mukherjee (arup@cmu.edu)
  • Ben Wing (ben@xemacs.org)
  • Hrvoje Niksic (hniksic@xemacs.org)

And that's the whole page, bestie!! 🎀 This iconic little manual page comes from the 4th Berkeley Distribution, dated the 4th Berkeley Distribution release of GNUSERV(1) — go forth and connect securely, mwah 💅✨🦋

📦 where this page comes from