1nxagent(1) NX Agent (Xserver) nxagent(1)
2
6 nxagent - nested Xserver optimized for remote computing
7
9 nxagent [options]
10
12 nxagent is an X server for remote application/desktop access similar to
13 Xnest or Xephyr.
14 nxagent implements a very efficient compression of the X11 protocol,
16 called the NX protocol.
17 The NX protocol increases performance when using X applications over
19 high latency and low bandwidth networks, while providing a local (LAN-
20 like) usage experience even if connecting from off-site locations (via
21 cable modem or GSM).
22 nxagent can be used standalone as a nested X server (with NX protocol
24 disabled), but its real benefits are gained when using it over remote
25 connections via the nxcomp compression library. The counterpart appli‐
26 cation on the other end (i.e. the client) is called nxproxy.
27 When used in proxy <-> agent mode, nxagent adds the feature of being
29 suspendible. Sessions can be started from one client, suspended and
30 then resumed from another (or the same) client.
31 nxagent and nxproxy are utilized by various remote application/desktop
33 frameworks for providing server-side GUI application access from remote
34 client systems.
35 Currently, nxagent is co-maintained by three of these projects: The
37 Arctica Project, TheQVD and X2Go.
38
40 nxagent should be run in user space. Other than the system's local
41 X.org server, nxagent does not require to be run as root. When bundled
42 with a remote application framework, you normally don't have to launch
43 nxagent manually. nxagent startup is usually managed by the underlying
44 framework (e.g. Arctica Session Manager, X2Go Server, etc.).
45 When nxagent starts up (e.g. by typing 'nxagent -ac :1' in a terminal
47 window), it typically launches in "windowed desktop" mode. On your
48 local X server a new window appears being an X server itself.
49 However, nxagent also supports rootless (or seamless) application mode
51 and a shadow session mode (similar to what VNC does).
52 Example: You can launch a complete desktop session inside this nested X
54 server now:
55 The Debian way...
57 $ export DISPLAY=:1
59 $ STARTUP=mate-session /etc/X11/Xsession
60 The Fedora / Gentoo / openSUSE way...
62 ### FIXME / TODO ###
64 However, nxagent also supports rootless (or seamless) application mode
66 and a shadow session mode (similar to what VNC does).
67
70 nxagent accepts a range of default X server options as described below.
71 Those default options have to be provided via the command line.
72 Furthermore, nxagent accepts some nx-X11 specific options, described
74 further below.
75 Last but not least, nxagent accepts several more options, the so-called
77 nx/nx options, provided via the $DISPLAY environment variable or the
78 -options command line option. See below for further details.
79
82 :displaynumber
83 The X server runs as the given displaynumber, which by default
84 is 0. If multiple X servers are to run simultaneously on a
85 host, each must have a unique display number. See the DISPLAY
86 NAMES section of the X(__miscmansuffix__) manual page to learn
87 how to specify which display number clients should try to use.
88 -a number
90 sets pointer acceleration (i.e. the ratio of how much is
91 reported to how much the user actually moved the pointer).
92 -ac disables host-based access control mechanisms. Enables access
94 by any host, and permits any host to modify the access control
95 list. Use with extreme caution. This option exists primarily
96 for running test suites remotely.
97 -audit level
99 sets the audit trail level. The default level is 1, meaning
100 only connection rejections are reported. Level 2 additionally
101 reports all successful connections and disconnects. Level 4
102 enables messages from the SECURITY extension, if present,
103 including generation and revocation of authorizations and vio‐
104 lations of the security policy. Level 0 turns off the audit
105 trail. Audit lines are sent as standard error output.
106 -auth authorization-file
108 specifies a file which contains a collection of authorization
109 records used to authenticate access. See also the xdm(1) and
110 Xsecurity(__miscmansuffix__) manual pages.
111 -bs disables backing store support on all screens.
113 -br sets the default root window to solid black instead of the
115 standard root weave pattern.
116 -c turns off key-click.
118 c volume
120 sets key-click volume (allowable range: 0-100).
121 -cc class
123 sets the visual class for the root window of color screens.
124 The class numbers are as specified in the X protocol. Not
125 obeyed by all servers.
126 -co filename
128 This used to be the option for specifying the path to the RGB
129 color database file. As the RGB color database is now embedded
130 into the binary this option has no effect but is kept for com‐
131 patibility. Deprecated.
132 -core causes the server to generate a core dump on fatal errors.
134 -displayfd fd
136 specifies a file descriptor in the launching process. Rather
137 than specifying a display number, the X server will attempt to
138 listen on successively higher display numbers, and upon finding
139 a free one, will write the port number back on this file
140 descriptor as a newline-terminated string. The -pn option is
141 ignored when using -displayfd.
142 nxagent specific:
144 (1) Other than in X.org's Xserver, you can use -displayfd in
146 conjunction with an explicit display number. If the explicit
147 display number is not available (i.e., already in use), nxagent
148 tries to figure out the next available display number,
149 e.g.:
151 nxagent -displayfd 2 :50
153 (2) If -displayfd <X> is given with <X> equaling 2 (STDERR),
155 then the display number string written to STDERR is beautified
156 with some human-readable (machine-parseable) text.
157 -deferglyphs whichfonts
159 specifies the types of fonts for which the server should
160 attempt to use deferred glyph loading. whichfonts can be all
161 (all fonts), none (no fonts), or 16 (16 bit fonts only).
162 -dpi resolution
164 sets the resolution for all screens, in dots per inch. To be
165 used when the server cannot determine the screen size(s) from
166 the hardware.
167 dpms enables DPMS (display power management services), where sup‐
169 ported. The default state is platform and configuration spe‐
170 cific.
171 -dpms disables DPMS (display power management services). The default
173 state is platform and configuration specific.
174 -f volume
176 sets feep (bell) volume (allowable range: 0-100).
177 -fc cursorFont
179 sets default cursor font.
180 -fn font
182 sets the default font.
183 -fp fontPath
185 sets the search path for fonts. This path is a comma separated
186 list of directories which the X server searches for font data‐
187 bases. See the FONTS section of this manual page for more
188 information and the default list.
189 -help prints a usage message.
191 -I causes all remaining command line arguments to be ignored.
193 -maxbigreqsize size
195 sets the maximum big request to size MB.
196 -nolisten trans-type
198 disables a transport type. For example, TCP/IP connections can
199 be disabled with -nolisten tcp. This option may be issued mul‐
200 tiple times to disable listening to different transport types.
201 -noreset
203 prevents a server reset when the last client connection is
204 closed. This overrides a previous -terminate command line
205 option.
206 -p minutes
208 sets screen-saver pattern cycle time in minutes.
209 -pn permits the server to continue running if it fails to establish
211 all of its well-known sockets (connection points for clients),
212 but establishes at least one. This option is set by default.
213 -nopn causes the server to exit if it fails to establish all of its
215 well-known sockets (connection points for clients).
216 -r turns off auto-repeat.
218 r turns on auto-repeat.
220 -s minutes
222 sets screen-saver timeout time in minutes.
223 -su disables save under support on all screens.
225 -t number
227 sets pointer acceleration threshold in pixels (i.e. after how
228 many pixels pointer acceleration should take effect).
229 -terminate
231 causes the server to terminate at server reset, instead of con‐
232 tinuing to run. This overrides a previous -noreset command
233 line option.
234 -to seconds
236 sets default connection timeout in seconds.
237 -tst disables all testing extensions.
239 v sets video-off screen-saver preference.
241 -v sets video-on screen-saver preference.
243 -wm forces the default backing-store of all windows to be When‐
245 Mapped. This is a backdoor way of getting backing-store to
246 apply to all windows. Although all mapped windows will have
247 backing store, the backing store attribute value reported by
248 the server for a window will be the last value established by a
249 client. If it has never been set by a client, the server will
250 report the default value, NotUseful. This behavior is required
251 by the X protocol, which allows the server to exceed the
252 client's backing store expectations but does not provide a way
253 to tell the client that it is doing so.
254 [+-]xinerama
256 enables(+) or disables(-) XINERAMA provided via the PanoramiX
257 extension. This is set to off by default.
258 [+-]rrxinerama
260 enables(+) or disables(-) XINERAMA provided via the RandR
261 extension. By default, this feature is enabled. To disable XIN‐
262 ERAMA completely, make sure to use both options (-xinerama and
263 -rrxinerama) on the command line.
264
267 nxagent additionally accepts the following non-standard options:
268 -logo turns on the X Window System logo display in the screen-saver.
270 There is currently no way to change this from a client.
271 nologo turns off the X Window System logo display in the screen-saver.
273 There is currently no way to change this from a client.
274 -render
276 default|mono|gray|color
278 sets the color allocation policy that will be used by the ren‐
280 der extension.
281 default selects the default policy defined for the display
283 depth of the X server.
284 mono don't use any color cell.
286 gray use a gray map of 13 color cells for the X render
288 extension.
289 color use a color cube of at most 4*4*4 colors (that is 64
291 color cells).
292 -dumbSched
294 disables smart scheduling on platforms that support the smart
295 scheduler.
296 -schedInterval interval
298 sets the smart scheduler's scheduling interval to interval mil‐
299 liseconds.
300
302 The nx-X11 system adds the following command line arguments:
303 -forcenx
305 force use of NX protocol messages assuming communication
306 through nxproxy
307 -nxrealwindowprop
309 set property NX_REAL_WINDOW for each X11 client inside nxagent,
310 providing the window XID of the corresponding window object on
311 the X server that nxagent runs on
312 -reportwids
314 explicitly tell nxagent to report its externally exposed X11
315 window IDs to the session log (in machine readable form), so
316 that external parsers can obtain that information from there
317 -reportprivatewids
319 explicitly tell nxagent to report X11 window IDs of internally
320 created window objects to the session log (in machine readable
321 form), so that external parsers can obtain that information
322 from there; this creates a lot of output and may affect perfor‐
323 mance
324 -timeout int
326 auto-disconnect timeout in seconds (minimum allowed: 60)
327 -norootlessexit
329 don't exit if there are no clients in rootless mode
330 -autodpi
332 detect real server's DPI and set it in the agent session; the
333 -dpi <dpi> cmdline option overrides -autodpi
334 -nomagicpixel
336 disable magic pixel support at session startup, can be re-
337 enabled via nx/nx option on session resumption
338 -norender
340 disable the use of the render extension
341 -nocomposite
343 disable the use of the composite extension
344 -nopersistent
346 disable disconnection/reconnection to the X display on SIGHUP
347 -noshmem
349 disable use of shared memory extension
350 -shmem enable use of shared memory extension
352 -noshpix
354 disable use of shared pixmaps
355 -shpix enable use of shared pixmaps
357 -noignore
359 don't ignore pointer and keyboard configuration changes man‐
360 dated by clients. As a result, configuration commands like dis‐
361 abling the keyboard bell (xset -b) will also affect the real X
362 server.
363 -nokbreset
365 don't reset keyboard device if the session is resumed
366 -noxkblock
368 this is only relevant if you also specify -keyboard=query. In
369 that case nxagent will lock the keyboard settings and clients
370 will get an error when trying to change keyboard settings via
371 XKEYBOARD. With -noxkblock the lock is not applied and clients
372 can change the keyboard settings through XKEYBOARD.
373 -tile WxH
375 size of image tiles (minimum allowed: 32x32)
376 -D enable desktop mode (default)
378 -R enable rootless mode
380 -S enable shadow mode
382 -B enable proxy binding mode
384 -version
386 show version information and exit
387 -options filename
389 path to an options file containing nx/nx options (see below).
390 Other than the command line options, nxagent can be configured at ses‐
392 sion startup and at runtime (i.e. when resuming a suspended session) by
393 so-called nx/nx options.
394 As nx/nx options all options supported by nxcomp (see nxproxy man page)
396 and all nxagent nx/nx options (see below) can be used. When launching
397 an nxcomp based nxagent session (i.e. proxy <-> agent), you will nor‐
398 mally set the $DISPLAY variable like this:
399 $ export DISPLAY=nx/nx,listen=<proxy-port>,options=<options.file>:<nx-display-port>
401 $ nxagent <command-line-options> :<nx-display-port>
402 The value for <nx-display-port> is some value of a not-yet-used X11
404 display (e.g. :50).
405 Using an options file is recommended, but you can also put available
407 nx/nx options (see below) into the DISPLAY variable directly. Note,
408 that the $DISPLAY variable field is of limited length.
409 As <proxy-port> you can pick an arbitrary (unused) TCP port or Unix
411 socket file path. This is the port / socket that you have to connect to
412 with the nxproxy application.
413 The right hand side of an option (the part following the "=" character)
415 can include URL encoded characters. It is required to URL encode at
416 least "," (as %2D) and "=" (as %3D) to avoid wrong parsing of the
417 options string.
418 Available nxagent options (as an addition to nx/nx options supported by
420 nxcomp already):
421 options=<string>
423 read options from file, this text file can contain a single
424 loooong line with comma-separated nx/nx options
425 rootless=<bool>
427 start nxagent in rootless mode, matches -R given on the command
428 line, no-op when resuming (default: false)
429 geometry=<string>
431 desktop geometry when starting or resuming a session, no-op in
432 rootless mode (default 66% of the underlying X server geometry)
433 resize=<bool>
435 set resizing support (default: true)
436 fullscreen=<bool>
438 start or resume a session in fullscreen mode (default: off)
439 keyboard=<string> or kbtype=<string>
441 query|<model>/<layout>
443 query use the default XKB keyboard layout (see below) and
446 only allow clients to query the settings but prevent
447 any changes. query is especially helpful for setups
448 where you need to set/modify the actual keyboard layout
449 using core X protocol functions (e.g. via xmodmap). It
450 is used for MacOS X clients to handle some keyboard
451 problems that are special for this platform. Note that
452 in this case XKEYBOARD will always report the default
453 layout which will most likely not match the experienced
454 settings.
455 <model>/<layout>
457 use the given model and layout. You can not modify key‐
458 board rules, variant or options. Instead preset values
459 are used. These are xfree86 for rules and empty strings
460 for variant and options.
461 If keyboard is omitted the internal defaults of nxagent will be
465 used (rules: xfree86, layout: us, model: pc102, empty variant
466 and options).
467 keyconv=<string>
470 set keycode conversion mode
471 auto|on|off
473 by default (auto) nxagent will activate keycode conversion if
475 it detects an evdev XKEYBOARD setup on the client side (the
476 standard on linux systems nowadays). Keycode conversion means
477 that certain keycodes are mapped to make the keyboard appear as
478 an pc105 model. Using off this conversion can be suppressed and
479 with on it will be forced.
480 clipboard=<string>
483 both|client|server|none
485 enable / disable (set to: none) clipboard support, uni-direc‐
487 tional (server or client) or bi-directional (both, default set‐
488 ting) support
489 streaming=<int>
491 streaming support for images, not fully implemented yet and
492 thus non-functional
493 backingstore=<int>
495 disable or enforce backing store support (default: Backing‐
496 StoreUndefined)
497 composite=<int>
499 enable or disable Composite support in nxagent (default:
500 enabled)
501 xinerama=<int>
503 enable or disable XINERAMA support in nxagent (default:
504 enabled)
505 shmem=<bool>
507 enable using shared memory
508 shpix=<bool>
510 enable shared pixmaps support
511 client=<string>
513 type of connecting operating system (supported: linux, windows,
514 solaris and macosx)
515 shadow=<int>
517 start nxagent in shadow mode, matches -S given on the command
518 line, no-op when resuming (default: false)
519 shadowuid=<int>
521 unique identifier for the shadow session
522 shadowmode=<string>
524 full access (set to 1) or viewing-only (set to 0, default)
525 defer=<int>
527 defer image updates (enabled for all connection types except
528 LAN), accepts values 0, 1 and 2
529 The default value can be set via the command line (-defer). The
531 value provided as nx/nx option is set when resuming a session,
532 thus it overrides the command line default.
533 tile=<string>
535 set the tile size in pixels (<W>x<H>) for bitmap data sent over
536 the wire
537 The default value can be set via the command line (-tile). The
539 value provided as nx/nx option is set when resuming a session,
540 thus it overrides the command line default.
541 menu=<int>
543 support pulldown menu in nxagent session (only available on
544 proxy <-> agent remote sessions)
545 magicpixel=<bool>
547 enable/disable magic pixel support in fullscreen mode (default:
548 1, enabled)
549 autodpi=<bool>
551 enable/disable deriving session DPI automatically from real
552 server (default: 0, disabled); only takes effect on session
553 startups, gets ignored when reconnecting to a suspended session
554 sleep=<int>
556 delay X server operations when suspended (provided in msec),
557 set to 0 to keep nxagent session fully functional when sus‐
558 pended (e.g. useful when mirroring an nxagent session via VNC)
559 tolerancechecks=<string>
561 strict|safe|risky|bypass
563 strict means that the number of internal and external pixmap
565 formats must match exactly and every internal pixmap
566 format must be available in the external pixmap format
567 array. This is the default.
568 safe means that the number of pixmap formats might diverge,
570 but all internal pixmap formats must also be included
571 in the external pixmap formats array. This is recom‐
572 mended, because it allows clients with more pixmap for‐
573 mats to still connect, but not lose functionality.
574 risky means that the internal pixmap formats array is allowed
576 to be smaller than the external pixmap formats array,
577 but at least one pixmap format must be included in
578 both. This is potentially unsafe.
579 bypass means that all of these checks are essentially deacti‐
581 vated. This is a very bad idea.
582 If you want to use nxagent as a replacement for Xnest or Xephyr you can
584 pass options like this:
585 $ echo nx/nx,fullscreen=1$DISPLAY >/tmp/opt
587 $ nxagent <command-line-options> -options /tmp/opt :<nx-display-port>
588
591 X servers that support XDMCP have the following options. See the X
592 Display Manager Control Protocol specification for more information.
593 -query hostname
595 enables XDMCP and sends Query packets to the specified host‐
596 name.
597 -broadcast
599 enable XDMCP and broadcasts BroadcastQuery packets to the net‐
600 work. The first responding display manager will be chosen for
601 the session.
602 -multicast [address [hop count]]
604 Enable XDMCP and multicast BroadcastQuery packets to the net‐
605 work. The first responding display manager is chosen for the
606 session. If an address is specified, the multicast is sent to
607 that address. If no address is specified, the multicast is
608 sent to the default XDMCP IPv6 multicast group. If a hop count
609 is specified, it is used as the maximum hop count for the mul‐
610 ticast. If no hop count is specified, the multicast is set to
611 a maximum of 1 hop, to prevent the multicast from being routed
612 beyond the local network.
613 -indirect hostname
615 enables XDMCP and send IndirectQuery packets to the specified
616 hostname.
617 -port port-number
619 uses the specified port-number for XDMCP packets, instead of
620 the default. This option must be specified before any -query,
621 -broadcast, -multicast, or -indirect options.
622 -from local-address
624 specifies the local address to connect from (useful if the con‐
625 necting host has multiple network interfaces). The local-
626 address may be expressed in any form acceptable to the host
627 platform's gethostbyname(3) implementation.
628 -once causes the server to terminate (rather than reset) when the
630 XDMCP session ends.
631 -class display-class
633 XDMCP has an additional display qualifier used in resource
634 lookup for display-specific options. This option sets that
635 value, by default it is "MIT-Unspecified" (not a very useful
636 value).
637 -cookie xdm-auth-bits
639 When testing XDM-AUTHENTICATION-1, a private key is shared
640 between the server and the manager. This option sets the value
641 of that private data (not that it is very private, being on the
642 command line!).
643 -displayID display-id
645 Yet another XDMCP specific value, this one allows the display
646 manager to identify each display so that it can locate the
647 shared key.
648
651 X servers that support the XKEYBOARD (a.k.a. "XKB") extension accept
652 the following options. All layout files specified on the command line
653 must be located in the XKB base directory or a subdirectory, and speci‐
654 fied as the relative path from the XKB base directory. The default XKB
655 base directory is /usr/share/X11/xkb.
656 [+-]kb enables(+) or disables(-) the XKEYBOARD extension.
658 [+-]accessx [ timeout [ timeout_mask [ feedback [ options_mask ] ] ] ]
660 enables(+) or disables(-) AccessX key sequences.
661 -xkbdir directory
663 base directory for keyboard layout files. This option is not
664 available for setuid X servers (i.e., when the X server's real
665 and effective uids are different).
666 -ardelay milliseconds
668 sets the autorepeat delay (length of time in milliseconds that
669 a key must be depressed before autorepeat starts).
670 -arinterval milliseconds
672 sets the autorepeat interval (length of time in milliseconds
673 that should elapse between autorepeat-generated keystrokes).
674 -xkbmap filename
676 loads keyboard description in filename on server startup.
677
680 X servers that support the SECURITY extension accept the following
681 option:
682 -sp filename
684 causes the server to attempt to read and interpret filename as
685 a security policy file with the format described below. The
686 file is read at server startup and reread at each server reset.
687 The syntax of the security policy file is as follows. Notation: "*"
689 means zero or more occurrences of the preceding element, and "+" means
690 one or more occurrences. To interpret <foo/bar>, ignore the text after
691 the /; it is used to distinguish between instances of <foo> in the next
692 section.
693 <policy file> ::= <version line> <other line>*
695 <version line> ::= <string/v> '\n'
697 <other line > ::= <comment> | <access rule> | <site policy> | <blank line>
699 <comment> ::= # <not newline>* '\n'
701 <blank line> ::= <space> '\n'
703 <site policy> ::= sitepolicy <string/sp> '\n'
705 <access rule> ::= property <property/ar> <window> <perms> '\n'
707 <property> ::= <string>
709 <window> ::= any | root | <required property>
711 <required property> ::= <property/rp> | <property with value>
713 <property with value> ::= <property/rpv> = <string/rv>
715 <perms> ::= [ <operation> | <action> | <space> ]*
717 <operation> ::= r | w | d
719 <action> ::= a | i | e
721 <string> ::= <dbl quoted string> | <single quoted string> | <unquoted string>
723 <dbl quoted string> ::= <space> " <not dqoute>* " <space>
725 <single quoted string> ::= <space> ' <not squote>* ' <space>
727 <unquoted string> ::= <space> <not space>+ <space>
729 <space> ::= [ ' ' | '\t' ]*
731 Character sets:
733 <not newline> ::= any character except '\n'
735 <not dqoute> ::= any character except "
736 <not squote> ::= any character except '
737 <not space> ::= any character except those in <space>
738 The semantics associated with the above syntax are as follows.
740 <version line>, the first line in the file, specifies the file format
742 version. If the server does not recognize the version <string/v>, it
743 ignores the rest of the file. The version string for the file format
744 described here is "version-1" .
745 Once past the <version line>, lines that do not match the above syntax
747 are ignored.
748 <comment> lines are ignored.
750 <sitepolicy> lines are currently ignored. They are intended to specify
752 the site policies used by the XC-QUERY-SECURITY-1 authorization method.
753 <access rule> lines specify how the server should react to untrusted
755 client requests that affect the X Window property named <property/ar>.
756 The rest of this section describes the interpretation of an <access
757 rule>.
758 For an <access rule> to apply to a given instance of <property/ar>,
760 <property/ar> must be on a window that is in the set of windows speci‐
761 fied by <window>. If <window> is any, the rule applies to <prop‐
762 erty/ar> on any window. If <window> is root, the rule applies to
763 <property/ar> only on root windows.
764 If <window> is <required property>, the following apply. If <required
766 property> is a <property/rp>, the rule applies when the window also has
767 that <property/rp>, regardless of its value. If <required property> is
768 a <property with value>, <property/rpv> must also have the value speci‐
769 fied by <string/rv>. In this case, the property must have type STRING
770 and format 8, and should contain one or more null-terminated strings.
771 If any of the strings match <string/rv>, the rule applies.
772 The definition of string matching is simple case-sensitive string com‐
774 parison with one elaboration: the occurrence of the character '*' in
775 <string/rv> is a wildcard meaning "any string." A <string/rv> can con‐
776 tain multiple wildcards anywhere in the string. For example, "x*"
777 matches strings that begin with x, "*x" matches strings that end with
778 x, "*x*" matches strings containing x, and "x*y*" matches strings that
779 start with x and subsequently contain y.
780 There may be multiple <access rule> lines for a given <property/ar>.
782 The rules are tested in the order that they appear in the file. The
783 first rule that applies is used.
784 <perms> specify operations that untrusted clients may attempt, and the
786 actions that the server should take in response to those operations.
787 <operation> can be r (read), w (write), or d (delete). The following
789 table shows how X Protocol property requests map to these operations in
790 The Open Group server implementation.
791 GetProperty r, or r and d if delete = True
793 ChangeProperty w
794 RotateProperties r and w
795 DeleteProperty d
796 ListProperties none, untrusted clients can always list all properties
797 <action> can be a (allow), i (ignore), or e (error). Allow means exe‐
799 cute the request as if it had been issued by a trusted client. Ignore
800 means treat the request as a no-op. In the case of GetProperty, ignore
801 means return an empty property value if the property exists, regardless
802 of its actual value. Error means do not execute the request and return
803 a BadAtom error with the atom set to the property name. Error is the
804 default action for all properties, including those not listed in the
805 security policy file.
806 An <action> applies to all <operation>s that follow it, until the next
808 <action> is encountered. Thus, irwad means ignore read and write,
809 allow delete.
810 GetProperty and RotateProperties may do multiple operations (r and d,
812 or r and w). If different actions apply to the operations, the most
813 severe action is applied to the whole request; there is no partial
814 request execution. The severity ordering is: allow < ignore < error.
815 Thus, if the <perms> for a property are ired (ignore read, error
816 delete), and an untrusted client attempts GetProperty on that property
817 with delete = True, an error is returned, but the property value is
818 not. Similarly, if any of the properties in a RotateProperties do not
819 allow both read and write, an error is returned without changing any
820 property values.
821 Here is an example security policy file.
823 version-1
825 # Allow reading of application resources, but not writing.
827 property RESOURCE_MANAGER root ar iw
828 property SCREEN_RESOURCES root ar iw
829 # Ignore attempts to use cut buffers. Giving errors causes apps to crash,
831 # and allowing access may give away too much information.
832 property CUT_BUFFER0 root irw
833 property CUT_BUFFER1 root irw
834 property CUT_BUFFER2 root irw
835 property CUT_BUFFER3 root irw
836 property CUT_BUFFER4 root irw
837 property CUT_BUFFER5 root irw
838 property CUT_BUFFER6 root irw
839 property CUT_BUFFER7 root irw
840 # If you are using Motif, you probably want these.
842 property _MOTIF_DEFAULT_BINDINGS rootar iw
843 property _MOTIF_DRAG_WINDOW root ar iw
844 property _MOTIF_DRAG_TARGETS any ar iw
845 property _MOTIF_DRAG_ATOMS any ar iw
846 property _MOTIF_DRAG_ATOM_PAIRS anyar iw
847 # The next two rules let xwininfo -tree work when untrusted.
849 property WM_NAME any ar
850 # Allow read of WM_CLASS, but only for windows with WM_NAME.
852 # This might be more restrictive than necessary, but demonstrates
853 # the <required property> facility, and is also an attempt to
854 # say "top level windows only."
855 property WM_CLASS WM_NAME ar
856 # These next three let xlsclients work untrusted. Think carefully
858 # before including these; giving away the client machine name and command
859 # may be exposing too much.
860 property WM_STATE WM_NAME ar
861 property WM_CLIENT_MACHINE WM_NAME ar
862 property WM_COMMAND WM_NAME ar
863 # To let untrusted clients use the standard colormaps created by
865 # xstdcmap, include these lines.
866 property RGB_DEFAULT_MAP root ar
867 property RGB_BEST_MAP root ar
868 property RGB_RED_MAP root ar
869 property RGB_GREEN_MAP root ar
870 property RGB_BLUE_MAP root ar
871 property RGB_GRAY_MAP root ar
872 # To let untrusted clients use the color management database created
874 # by xcmsdb, include these lines.
875 property XDCCC_LINEAR_RGB_CORRECTION rootar
876 property XDCCC_LINEAR_RGB_MATRICES rootar
877 property XDCCC_GRAY_SCREENWHITEPOINT rootar
878 property XDCCC_GRAY_CORRECTION rootar
879 # To let untrusted clients use the overlay visuals that many vendors
881 # support, include this line.
882 property SERVER_OVERLAY_VISUALS rootar
883 # Dumb examples to show other capabilities.
885 # oddball property names and explicit specification of error conditions
887 property "property with spaces" 'property with "'aw er ed
888 # Allow deletion of Woo-Hoo if window also has property OhBoy with value
890 # ending in "son". Reads and writes will cause an error.
891 property Woo-Hoo OhBoy = "*son"ad
892
895 The X server supports client connections via a platform-dependent sub‐
896 set of the following transport types: TCPIP, Unix Domain sockets and
897 several varieties of SVR4 local connections. See the DISPLAY NAMES
898 section of the X(__miscmansuffix__) manual page to learn how to specify
899 which transport type clients should try to use.
900
903 The X server implements a platform-dependent subset of the following
904 authorization protocols: MIT-MAGIC-COOKIE-1, XDM-AUTHORIZATION-1, XDM-
905 AUTHORIZATION-2, SUN-DES-1, and MIT-KERBEROS-5. See the Xsecu‐
906 rity(__miscmansuffix__) manual page for information on the operation of
907 these protocols.
908 Authorization data required by the above protocols is passed to the
910 server in a private file named with the -auth command line option.
911 Each time the server is about to accept the first connection after a
912 reset (or when the server is starting), it reads this file. If this
913 file contains any authorization records, the local host is not automat‐
914 ically allowed access to the server, and only clients which send one of
915 the authorization records contained in the file in the connection setup
916 information will be allowed access. See the Xau manual page for a
917 description of the binary format of this file. See xauth(1) for main‐
918 tenance of this file, and distribution of its contents to remote hosts.
919 The X server also uses a host-based access control list for deciding
921 whether or not to accept connections from clients on a particular
922 machine. If no other authorization mechanism is being used, this list
923 initially consists of the host on which the server is running as well
924 as any machines listed in the file /etc/Xn.hosts, where n is the dis‐
925 play number of the server. Each line of the file should contain either
926 an Internet hostname (e.g. expo.lcs.mit.edu) or a complete name in the
927 format family:name as described in the xhost(1) manual page. There
928 should be no leading or trailing spaces on any lines. For example:
929 joesworkstation
931 corporate.company.com
932 star::
933 inet:bigcpu
934 local:
935 Users can add or remove hosts from this list and enable or disable
937 access control using the xhost command from the same machine as the
938 server.
939 If the X FireWall Proxy (xfwp) is being used without a sitepolicy,
941 host-based authorization must be turned on for clients to be able to
942 connect to the X server via the xfwp. If xfwp is run without a config‐
943 uration file and thus no sitepolicy is defined, if xfwp is using an X
944 server where xhost + has been run to turn off host-based authorization
945 checks, when a client tries to connect to this X server via xfwp, the X
946 server will deny the connection. See xfwp(1) for more information
947 about this proxy.
948 The X protocol intrinsically does not have any notion of window opera‐
950 tion permissions or place any restrictions on what a client can do; if
951 a program can connect to a display, it has full run of the screen. X
952 servers that support the SECURITY extension fare better because clients
953 can be designated untrusted via the authorization they use to connect;
954 see the xauth(1) manual page for details. Restrictions are imposed on
955 untrusted clients that curtail the mischief they can do. See the SECU‐
956 RITY extension specification for a complete list of these restrictions.
957 Sites that have better authentication and authorization systems might
959 wish to make use of the hooks in the libraries and the server to pro‐
960 vide additional security models.
961
963 The X server attaches special meaning to the following signals:
964 SIGHUP This signal causes the server to close all existing connec‐
966 tions, free all resources, and restore all defaults. It is
967 sent by the display manager whenever the main user's main
968 application (usually an xterm or window manager) exits to force
969 the server to clean up and prepare for the next user.
970 SIGTERM This signal causes the server to exit cleanly.
972 SIGUSR1 This signal is used quite differently from either of the above.
974 When the server starts, it checks to see if it has inherited
975 SIGUSR1 as SIG_IGN instead of the usual SIG_DFL. In this case,
976 the server sends a SIGUSR1 to its parent process after it has
977 set up the various connection schemes. Xdm uses this feature
978 to recognize when connecting to the server is possible.
979
981 The X server can obtain fonts from directories and/or from font
982 servers. The list of directories and font servers the X server uses
983 when trying to open a font is controlled by the font path.
984 The default font path is __default_font_path__ .
986 The font path can be set with the -fp option or by xset(1) after the
988 server has started.
989
991 /etc/Xn.hosts Initial access control list for display
992 number n
993 /usr/share/fonts/X11/misc,
995 /usr/share/fonts/X11/75dpi,
996 /usr/share/fonts/X11/100dpi Bitmap
997 font directories
998 /usr/share/fonts/X11/Type1 Outline font directories
1000 /usr/share/nx/rgb Color database
1002 /tmp/.X11-unix/Xn Unix domain socket for display number n
1004 /tmp/rcXn Kerberos 5 replay cache for display num‐
1006 ber n
1007
1009 Protocols: X Window System Protocol, NX Compression Protocol, The X
1010 Font Service Protocol, X Display Manager Control Protocol
1011 Fonts: bdftopcf(1), mkfontdir(1), mkfontscale(1), xfs(1), xlsfonts(1),
1013 xfontsel(1), xfd(1), X Logical Font Description Conventions
1014 Security: Xsecurity(__miscmansuffix__), xauth(1), Xau(1), xdm(1),
1016 xhost(1), xfwp(1), Security Extension Specification
1017 Starting the server: xdm(1), xinit(1)
1019 Controlling the server once started: xset(1), xsetroot(1), xhost(1)
1021 Server-specific man pages: Xdec(1), XmacII(1), Xsun(1), Xnest(1),
1023 Xvfb(1), XFree86(1), XDarwin(1).
1024 Server internal documentation: Definition of the Porting Layer for the
1026 X v11 Sample Server
1027
1029 The first sample X server was originally written by Susan Angebranndt,
1030 Raymond Drewry, Philip Karlton, and Todd Newman, from Digital Equipment
1031 Corporation, with support from a large cast. It has since been exten‐
1032 sively rewritten by Keith Packard and Bob Scheifler, from MIT. Dave
1033 Wiggins took over post-R5 and made substantial improvements.
1034 The first implementation of nx-X11 (version 1.x up to 3.5.x) was writ‐
1036 ten by NoMachine (maintained until 2011).
1037 The current implementation of nx-X11 is maintained by various projects,
1039 amongst others The Arctica Project, TheQVD (Qindel Group) and X2Go.
1040 This manual page was written by Per Hansen <spamhans@yahoo.de>, and
1042 modified by Marcelo Boveto Shima <marceloshima@gmail.com> and Mike
1043 Gabriel <mike.gabriel@das-netzwerkteam.de>. In 2016, the original
1044 Xserver.man page shipped with nx-X11 was merged into the nxagent man
1045 page and received a major update by Mike Gabriel <mike.gabriel@das-net‐
1046 zwerkteam.de>.
1047Version 3.5.99.17 Nov 2018 nxagent(1)