Proofreading changes from Tim Goodwin <tjg@star.le.ac.uk>.
[bpt/emacs.git] / man / trouble.texi
1 @c This is part of the Emacs manual.
2 @c Copyright (C) 1985, 86, 87, 93, 94, 95, 1997 Free Software Foundation, Inc.
3 @c See file emacs.texi for copying conditions.
4 @iftex
5 @chapter Dealing with Common Problems
6
7 If you type an Emacs command you did not intend, the results are often
8 mysterious. This chapter tells what you can do to cancel your mistake or
9 recover from a mysterious situation. Emacs bugs and system crashes are
10 also considered.
11 @end iftex
12
13 @node Quitting, Lossage, Customization, Top
14 @section Quitting and Aborting
15 @cindex quitting
16
17 @table @kbd
18 @item C-g
19 @itemx C-@key{BREAK} @r{(MS-DOS only)}
20 Quit: cancel running or partially typed command.
21 @item C-]
22 Abort innermost recursive editing level and cancel the command which
23 invoked it (@code{abort-recursive-edit}).
24 @item @key{ESC} @key{ESC} @key{ESC}
25 Either quit or abort, whichever makes sense (@code{keyboard-escape-quit}).
26 @item M-x top-level
27 Abort all recursive editing levels that are currently executing.
28 @item C-x u
29 Cancel a previously made change in the buffer contents (@code{undo}).
30 @end table
31
32 There are two ways of canceling commands which are not finished
33 executing: @dfn{quitting} with @kbd{C-g}, and @dfn{aborting} with
34 @kbd{C-]} or @kbd{M-x top-level}. Quitting cancels a partially typed
35 command or one which is already running. Aborting exits a recursive
36 editing level and cancels the command that invoked the recursive edit.
37 (@xref{Recursive Edit}.)
38
39 @cindex quitting
40 @kindex C-g
41 Quitting with @kbd{C-g} is used for getting rid of a partially typed
42 command, or a numeric argument that you don't want. It also stops a
43 running command in the middle in a relatively safe way, so you can use
44 it if you accidentally give a command which takes a long time. In
45 particular, it is safe to quit out of killing; either your text will
46 @emph{all} still be in the buffer, or it will @emph{all} be in the kill
47 ring (or maybe both). Quitting an incremental search does special
48 things documented under searching; in general, it may take two
49 successive @kbd{C-g} characters to get out of a search
50 (@pxref{Incremental Search}).
51
52 On MS-DOS, the character @kbd{C-@key{BREAK}} serves as a quit character
53 like @kbd{C-g}. The reason is that it is not feasible, on MS-DOS, to
54 recognize @kbd{C-g} while a command is running, between interactions
55 with the user. By contrast, it @emph{is} feasible to recognize
56 @kbd{C-@key{BREAK}} at all times. @xref{MS-DOS Input}.
57
58 @findex keyboard-quit
59 @kbd{C-g} works by setting the variable @code{quit-flag} to @code{t}
60 the instant @kbd{C-g} is typed; Emacs Lisp checks this variable
61 frequently and quits if it is non-@code{nil}. @kbd{C-g} is only
62 actually executed as a command if you type it while Emacs is waiting for
63 input. In that case, the command it runs is @code{keyboard-quit}.
64
65 If you quit with @kbd{C-g} a second time before the first @kbd{C-g} is
66 recognized, you activate the ``emergency escape'' feature and return to
67 the shell. @xref{Emergency Escape}.
68
69 @cindex NFS and quitting
70 There may be times when you cannot quit. When Emacs is waiting for
71 the operating system to do something, quitting is impossible unless
72 special pains are taken for the particular system call within Emacs
73 where the waiting occurs. We have done this for the system calls that
74 users are likely to want to quit from, but it's possible you will find
75 another. In one very common case---waiting for file input or output
76 using NFS---Emacs itself knows how to quit, but many NFS implementations
77 simply do not allow user programs to stop waiting for NFS when the NFS
78 server is hung.
79
80 @cindex aborting recursive edit
81 @findex abort-recursive-edit
82 @kindex C-]
83 Aborting with @kbd{C-]} (@code{abort-recursive-edit}) is used to get
84 out of a recursive editing level and cancel the command which invoked
85 it. Quitting with @kbd{C-g} does not do this, and could not do this,
86 because it is used to cancel a partially typed command @emph{within} the
87 recursive editing level. Both operations are useful. For example, if
88 you are in a recursive edit and type @kbd{C-u 8} to enter a numeric
89 argument, you can cancel that argument with @kbd{C-g} and remain in the
90 recursive edit.
91
92 @findex keyboard-escape-quit
93 @kindex ESC ESC ESC
94 The command @kbd{@key{ESC} @key{ESC} @key{ESC}}
95 (@code{keyboard-escape-quit}) can either quit or abort. This key was
96 defined because @key{ESC} is used to ``get out'' in many PC programs.
97 It can cancel a prefix argument, clear a selected region, or get out of
98 a Query Replace, like @kbd{C-g}. It can get out of the minibuffer or a
99 recursive edit, like @kbd{C-]}. It can also get out of splitting the
100 frame into multiple windows, like @kbd{C-x 1}. One thing it cannot do,
101 however, is stop a command that is running. That's because it executes
102 as an ordinary command, and Emacs doesn't notice it until it is ready
103 for a command.
104
105 @findex top-level
106 The command @kbd{M-x top-level} is equivalent to ``enough'' @kbd{C-]}
107 commands to get you out of all the levels of recursive edits that you
108 are in. @kbd{C-]} gets you out one level at a time, but @kbd{M-x
109 top-level} goes out all levels at once. Both @kbd{C-]} and @kbd{M-x
110 top-level} are like all other commands, and unlike @kbd{C-g}, in that
111 they take effect only when Emacs is ready for a command. @kbd{C-]} is
112 an ordinary key and has its meaning only because of its binding in the
113 keymap. @xref{Recursive Edit}.
114
115 @kbd{C-x u} (@code{undo}) is not strictly speaking a way of canceling
116 a command, but you can think of it as canceling a command that already
117 finished executing. @xref{Undo}, for more information
118 about the undo facility.
119
120 @node Lossage, Bugs, Quitting, Top
121 @section Dealing with Emacs Trouble
122
123 This section describes various conditions in which Emacs fails to work
124 normally, and how to recognize them and correct them.
125
126 @menu
127 * DEL Gets Help:: What to do if @key{DEL} doesn't delete.
128 * Stuck Recursive:: `[...]' in mode line around the parentheses.
129 * Screen Garbled:: Garbage on the screen.
130 * Text Garbled:: Garbage in the text.
131 * Unasked-for Search:: Spontaneous entry to incremental search.
132 * Memory Full:: How to cope when you run out of memory.
133 * After a Crash:: Recovering editing in an Emacs session that crashed.
134 * Emergency Escape:: Emergency escape---
135 What to do if Emacs stops responding.
136 * Total Frustration:: When you are at your wits' end.
137 @end menu
138
139 @node DEL Gets Help
140 @subsection If @key{DEL} Fails to Delete
141 @cindex @key{DEL} vs @key{BACKSPACE}
142 @cindex @key{BACKSPACE} vs @key{DEL}
143 @cindex usual erasure key
144
145 Every keyboard has a large key, a little ways above the @key{RET} or
146 @key{ENTER} key, which you normally use outside Emacs to erase the
147 last character that you typed. We call this key @dfn{the usual
148 erasure key}. In Emacs, it is supposed to be equivalent to @key{DEL},
149 and when Emacs is properly configured for your terminal, it translates
150 that key into the character @key{DEL}.
151
152 When Emacs starts up using a window system, it determines
153 automatically which key should be @key{DEL}. In some unusual cases
154 Emacs gets the wrong information from the system. If the usual
155 erasure key deletes forwards instead of backwards, that is probably
156 what happened---Emacs ought to be treating the @key{DELETE} key as
157 @key{DEL}, but it isn't.
158
159 With a window system, if the usual erasure key is labeled
160 @key{BACKSPACE} and there is a @key{DELETE} key elsewhere, but the
161 @key{DELETE} key deletes backward instead of forward, that too
162 suggests Emacs got the wrong information---but in the opposite sense.
163 It ought to be treating the @key{BACKSPACE} key as @key{DEL}, and
164 treating @key{DELETE} differently, but it isn't.
165
166 On a text-only terminal, if you find the usual erasure key prompts
167 for a Help command, like @kbd{Control-h}, instead of deleting a
168 character, it means that key is actually sending the @key{BS}
169 character. Emacs ought to be treating @key{BS} as @key{DEL}, but it
170 isn't.
171
172 In all of those cases, the immediate remedy is the same: use the
173 command @kbd{M-x normal-erase-is-backspace-mode}. This toggles
174 between the two modes that Emacs supports for handling @key{DEL}, so
175 if Emacs starts in the wrong mode, it should switch to the right mode.
176 On a text-only terminal, if you want to ask for help when @key{BS} is
177 treated as @key{DEL}, use @key{F1}; @kbd{C-?} may also work, if it
178 sends character code 127.
179
180 @findex normal-erase-is-backspace-mode
181 To fix the problem automatically for every Emacs session, you can
182 put one of the following lines into your @file{.emacs} file
183 (@pxref{Init File}). For the first case above, where @key{DELETE}
184 deletes forwards instead of backwards, use this line to make
185 @key{DELETE} act as @key{DEL} (resulting in behavior compatible
186 with Emacs 20 and previous versions):
187
188 @lisp
189 (normal-erase-is-backspace-mode 0)
190 @end lisp
191
192 @noindent
193 For the other two cases, where @key{BACKSPACE} ought to act as
194 @key{DEL}, use this line:
195
196 @lisp
197 (normal-erase-is-backspace-mode 1)
198 @end lisp
199
200 @vindex normal-erase-is-backspace
201 Another way to fix the problem for every Emacs session is to
202 customize the variable @code{normal-erase-is-backspace}: the value
203 @code{t} specifies the mode where @key{BS} or @key{BACKSPACE} is
204 @key{DEL}, and @code{nil} specifies the other mode. @xref{Easy
205 Customization}.
206
207 With a window system, it can also happen that the usual erasure key
208 is labeled @key{BACKSPACE}, there is a @key{DELETE} key elsewhere, and
209 both keys delete forward. This probably means that someone has
210 redefined your @key{BACKSPACE} key as a @key{DELETE} key. With X,
211 this is typically done with a command to the @code{xmodmap} program
212 when you start the server or log in. The most likely motive for this
213 customization was to support old versions of Emacs, so we recommend
214 you simply remove it now.
215
216 @node Stuck Recursive
217 @subsection Recursive Editing Levels
218
219 Recursive editing levels are important and useful features of Emacs, but
220 they can seem like malfunctions to the user who does not understand them.
221
222 If the mode line has square brackets @samp{[@dots{}]} around the parentheses
223 that contain the names of the major and minor modes, you have entered a
224 recursive editing level. If you did not do this on purpose, or if you
225 don't understand what that means, you should just get out of the recursive
226 editing level. To do so, type @kbd{M-x top-level}. This is called getting
227 back to top level. @xref{Recursive Edit}.
228
229 @node Screen Garbled
230 @subsection Garbage on the Screen
231
232 If the data on the screen looks wrong, the first thing to do is see
233 whether the text is really wrong. Type @kbd{C-l} to redisplay the
234 entire screen. If the screen appears correct after this, the problem
235 was entirely in the previous screen update. (Otherwise, see the following
236 section.)
237
238 Display updating problems often result from an incorrect termcap entry
239 for the terminal you are using. The file @file{etc/TERMS} in the Emacs
240 distribution gives the fixes for known problems of this sort.
241 @file{INSTALL} contains general advice for these problems in one of its
242 sections. Very likely there is simply insufficient padding for certain
243 display operations. To investigate the possibility that you have this sort
244 of problem, try Emacs on another terminal made by a different manufacturer.
245 If problems happen frequently on one kind of terminal but not another kind,
246 it is likely to be a bad termcap entry, though it could also be due to a
247 bug in Emacs that appears for terminals that have or that lack specific
248 features.
249
250 @node Text Garbled
251 @subsection Garbage in the Text
252
253 If @kbd{C-l} shows that the text is wrong, try undoing the changes to it
254 using @kbd{C-x u} until it gets back to a state you consider correct. Also
255 try @kbd{C-h l} to find out what command you typed to produce the observed
256 results.
257
258 If a large portion of text appears to be missing at the beginning or
259 end of the buffer, check for the word @samp{Narrow} in the mode line.
260 If it appears, the text you don't see is probably still present, but
261 temporarily off-limits. To make it accessible again, type @kbd{C-x n
262 w}. @xref{Narrowing}.
263
264 @node Unasked-for Search
265 @subsection Spontaneous Entry to Incremental Search
266
267 If Emacs spontaneously displays @samp{I-search:} at the bottom of the
268 screen, it means that the terminal is sending @kbd{C-s} and @kbd{C-q}
269 according to the poorly designed xon/xoff ``flow control'' protocol.
270
271 If this happens to you, your best recourse is to put the terminal in a
272 mode where it will not use flow control, or give it so much padding that
273 it will never send a @kbd{C-s}. (One way to increase the amount of
274 padding is to set the variable @code{baud-rate} to a larger value. Its
275 value is the terminal output speed, measured in the conventional units
276 of baud.)
277
278 @cindex flow control
279 @cindex xon-xoff
280 @findex enable-flow-control
281 If you don't succeed in turning off flow control, the next best thing
282 is to tell Emacs to cope with it. To do this, call the function
283 @code{enable-flow-control}.
284
285 @findex enable-flow-control-on
286 Typically there are particular terminal types with which you must use
287 flow control. You can conveniently ask for flow control on those
288 terminal types only, using @code{enable-flow-control-on}. For example,
289 if you find you must use flow control on VT-100 and H19 terminals, put
290 the following in your @file{.emacs} file:
291
292 @example
293 (enable-flow-control-on "vt100" "h19")
294 @end example
295
296 When flow control is enabled, you must type @kbd{C-\} to get the
297 effect of a @kbd{C-s}, and type @kbd{C-^} to get the effect of a
298 @kbd{C-q}. (These aliases work by means of keyboard translations; see
299 @ref{Keyboard Translations}.)
300
301 @node Memory Full
302 @subsection Running out of Memory
303 @cindex memory full
304 @cindex out of memory
305
306 If you get the error message @samp{Virtual memory exceeded}, save your
307 modified buffers with @kbd{C-x s}. This method of saving them has the
308 smallest need for additional memory. Emacs keeps a reserve of memory
309 which it makes available when this error happens; that should be enough
310 to enable @kbd{C-x s} to complete its work.
311
312 Once you have saved your modified buffers, you can exit this Emacs job
313 and start another, or you can use @kbd{M-x kill-some-buffers} to free
314 space in the current Emacs job. If you kill buffers containing a
315 substantial amount of text, you can safely go on editing. Emacs refills
316 its memory reserve automatically when it sees sufficient free space
317 available, in case you run out of memory another time.
318
319 Do not use @kbd{M-x buffer-menu} to save or kill buffers when you run
320 out of memory, because the buffer menu needs a fair amount of memory
321 itself, and the reserve supply may not be enough.
322
323 @node After a Crash
324 @subsection Recovery After a Crash
325
326 If Emacs or the computer crashes, you can recover the files you were
327 editing at the time of the crash from their auto-save files. To do
328 this, start Emacs again and type the command @kbd{M-x recover-session}.
329
330 This command initially displays a buffer which lists interrupted
331 session files, each with its date. You must choose which session to
332 recover from. Typically the one you want is the most recent one. Move
333 point to the one you choose, and type @kbd{C-c C-c}.
334
335 Then @code{recover-session} asks about each of the files that you were
336 editing during that session; it asks whether to recover that file. If
337 you answer @kbd{y} for a file, it shows the dates of that file and its
338 auto-save file, then asks once again whether to recover that file. For
339 the second question, you must confirm with @kbd{yes}. If you do, Emacs
340 visits the file but gets the text from the auto-save file.
341
342 When @code{recover-session} is done, the files you've chosen to
343 recover are present in Emacs buffers. You should then save them. Only
344 this---saving them---updates the files themselves.
345
346 @node Emergency Escape
347 @subsection Emergency Escape
348
349 Because at times there have been bugs causing Emacs to loop without
350 checking @code{quit-flag}, a special feature causes Emacs to be suspended
351 immediately if you type a second @kbd{C-g} while the flag is already set,
352 so you can always get out of GNU Emacs. Normally Emacs recognizes and
353 clears @code{quit-flag} (and quits!) quickly enough to prevent this from
354 happening. (On MS-DOS and compatible systems, type @kbd{C-@key{BREAK}}
355 twice.)
356
357 When you resume Emacs after a suspension caused by multiple @kbd{C-g}, it
358 asks two questions before going back to what it had been doing:
359
360 @example
361 Auto-save? (y or n)
362 Abort (and dump core)? (y or n)
363 @end example
364
365 @noindent
366 Answer each one with @kbd{y} or @kbd{n} followed by @key{RET}.
367
368 Saying @kbd{y} to @samp{Auto-save?} causes immediate auto-saving of all
369 modified buffers in which auto-saving is enabled.
370
371 Saying @kbd{y} to @samp{Abort (and dump core)?} causes an illegal instruction to be
372 executed, dumping core. This is to enable a wizard to figure out why Emacs
373 was failing to quit in the first place. Execution does not continue
374 after a core dump. If you answer @kbd{n}, execution does continue. With
375 luck, GNU Emacs will ultimately check @code{quit-flag} and quit normally.
376 If not, and you type another @kbd{C-g}, it is suspended again.
377
378 If Emacs is not really hung, just slow, you may invoke the double
379 @kbd{C-g} feature without really meaning to. Then just resume and answer
380 @kbd{n} to both questions, and you will arrive at your former state.
381 Presumably the quit you requested will happen soon.
382
383 The double @kbd{C-g} feature is turned off when Emacs is running under
384 the X Window System, since you can use the window manager to kill Emacs
385 or to create another window and run another program.
386
387 On MS-DOS and compatible systems, the emergency escape feature is
388 sometimes unavailable, even if you press @kbd{C-@key{BREAK}} twice, when
389 some system call (MS-DOS or BIOS) hangs, or when Emacs is stuck in a
390 very tight endless loop (in C code, @strong{not} in Lisp code).
391
392 @node Total Frustration
393 @subsection Help for Total Frustration
394 @cindex Eliza
395 @cindex doctor
396
397 If using Emacs (or something else) becomes terribly frustrating and none
398 of the techniques described above solve the problem, Emacs can still help
399 you.
400
401 First, if the Emacs you are using is not responding to commands, type
402 @kbd{C-g C-g} to get out of it and then start a new one.
403
404 @findex doctor
405 Second, type @kbd{M-x doctor @key{RET}}.
406
407 The doctor will help you feel better. Each time you say something to
408 the doctor, you must end it by typing @key{RET} @key{RET}. This lets
409 the doctor know you are finished.
410
411 @node Bugs, Contributing, Lossage, Top
412 @section Reporting Bugs
413
414 @cindex bugs
415 Sometimes you will encounter a bug in Emacs. Although we cannot
416 promise we can or will fix the bug, and we might not even agree that it
417 is a bug, we want to hear about problems you encounter. Often we agree
418 they are bugs and want to fix them.
419
420 To make it possible for us to fix a bug, you must report it. In order
421 to do so effectively, you must know when and how to do it.
422
423 @menu
424 * Criteria: Bug Criteria. Have you really found a bug?
425 * Understanding Bug Reporting:: How to report a bug effectively.
426 * Checklist:: Steps to follow for a good bug report.
427 * Sending Patches:: How to send a patch for GNU Emacs.
428 @end menu
429
430 @node Bug Criteria
431 @subsection When Is There a Bug
432
433 If Emacs executes an illegal instruction, or dies with an operating
434 system error message that indicates a problem in the program (as opposed to
435 something like ``disk full''), then it is certainly a bug.
436
437 If Emacs updates the display in a way that does not correspond to what is
438 in the buffer, then it is certainly a bug. If a command seems to do the
439 wrong thing but the problem corrects itself if you type @kbd{C-l}, it is a
440 case of incorrect display updating.
441
442 Taking forever to complete a command can be a bug, but you must make
443 certain that it was really Emacs's fault. Some commands simply take a
444 long time. Type @kbd{C-g} (@kbd{C-@key{BREAK}} on MS-DOS) and then @kbd{C-h l}
445 to see whether the input Emacs received was what you intended to type;
446 if the input was such that you @emph{know} it should have been processed
447 quickly, report a bug. If you don't know whether the command should
448 take a long time, find out by looking in the manual or by asking for
449 assistance.
450
451 If a command you are familiar with causes an Emacs error message in a
452 case where its usual definition ought to be reasonable, it is probably a
453 bug.
454
455 If a command does the wrong thing, that is a bug. But be sure you know
456 for certain what it ought to have done. If you aren't familiar with the
457 command, or don't know for certain how the command is supposed to work,
458 then it might actually be working right. Rather than jumping to
459 conclusions, show the problem to someone who knows for certain.
460
461 Finally, a command's intended definition may not be the best
462 possible definition for editing with. This is a very important sort
463 of problem, but it is also a matter of judgment. Also, it is easy to
464 come to such a conclusion out of ignorance of some of the existing
465 features. It is probably best not to complain about such a problem
466 until you have checked the documentation in the usual ways, feel
467 confident that you understand it, and know for certain that what you
468 want is not available. If you are not sure what the command is
469 supposed to do after a careful reading of the manual, check the index
470 and glossary for any terms that may be unclear.
471
472 If after careful rereading of the manual you still do not understand
473 what the command should do, that indicates a bug in the manual, which
474 you should report. The manual's job is to make everything clear to
475 people who are not Emacs experts---including you. It is just as
476 important to report documentation bugs as program bugs.
477
478 If the on-line documentation string of a function or variable disagrees
479 with the manual, one of them must be wrong; that is a bug.
480
481 @node Understanding Bug Reporting
482 @subsection Understanding Bug Reporting
483
484 @findex emacs-version
485 When you decide that there is a bug, it is important to report it and to
486 report it in a way which is useful. What is most useful is an exact
487 description of what commands you type, starting with the shell command to
488 run Emacs, until the problem happens.
489
490 The most important principle in reporting a bug is to report
491 @emph{facts}. Hypotheses and verbal descriptions are no substitute for
492 the detailed raw data. Reporting the facts is straightforward, but many
493 people strain to posit explanations and report them instead of the
494 facts. If the explanations are based on guesses about how Emacs is
495 implemented, they will be useless; meanwhile, lacking the facts, we will
496 have no real information about the bug.
497
498 For example, suppose that you type @kbd{C-x C-f /glorp/baz.ugh
499 @key{RET}}, visiting a file which (you know) happens to be rather large,
500 and Emacs displayed @samp{I feel pretty today}. The best way to report
501 the bug is with a sentence like the preceding one, because it gives all
502 the facts.
503
504 A bad way would be to assume that the problem is due to the size of
505 the file and say, ``I visited a large file, and Emacs displayed @samp{I
506 feel pretty today}.'' This is what we mean by ``guessing
507 explanations.'' The problem is just as likely to be due to the fact
508 that there is a @samp{z} in the file name. If this is so, then when we
509 got your report, we would try out the problem with some ``large file,''
510 probably with no @samp{z} in its name, and not see any problem. There
511 is no way in the world that we could guess that we should try visiting a
512 file with a @samp{z} in its name.
513
514 Alternatively, the problem might be due to the fact that the file starts
515 with exactly 25 spaces. For this reason, you should make sure that you
516 inform us of the exact contents of any file that is needed to reproduce the
517 bug. What if the problem only occurs when you have typed the @kbd{C-x C-a}
518 command previously? This is why we ask you to give the exact sequence of
519 characters you typed since starting the Emacs session.
520
521 You should not even say ``visit a file'' instead of @kbd{C-x C-f} unless
522 you @emph{know} that it makes no difference which visiting command is used.
523 Similarly, rather than saying ``if I have three characters on the line,''
524 say ``after I type @kbd{@key{RET} A B C @key{RET} C-p},'' if that is
525 the way you entered the text.@refill
526
527 So please don't guess any explanations when you report a bug. If you
528 want to actually @emph{debug} the problem, and report explanations that
529 are more than guesses, that is useful---but please include the facts as
530 well.
531
532 @node Checklist
533 @subsection Checklist for Bug Reports
534
535 @cindex reporting bugs
536 The best way to send a bug report is to mail it electronically to the
537 Emacs maintainers at @email{bug-gnu-emacs@@gnu.org}, or to
538 @email{emacs-pretest-bug@@gnu.org} if you are pretesting an Emacs beta
539 release. (If you want to suggest a change as an improvement, use the
540 same address.)
541
542 If you'd like to read the bug reports, you can find them on the
543 newsgroup @samp{gnu.emacs.bug}; keep in mind, however, that as a
544 spectator you should not criticize anything about what you see there.
545 The purpose of bug reports is to give information to the Emacs
546 maintainers. Spectators are welcome only as long as they do not
547 interfere with this. In particular, some bug reports contain large
548 amounts of data; spectators should not complain about this.
549
550 Please do not post bug reports using netnews; mail is more reliable
551 than netnews about reporting your correct address, which we may need in
552 order to ask you for more information.
553
554 If you can't send electronic mail, then mail the bug report on paper
555 or machine-readable media to this address:
556
557 @format
558 GNU Emacs Bugs
559 Free Software Foundation
560 59 Temple Place, Suite 330
561 Boston, MA 02111-1307 USA
562 @end format
563
564 We do not promise to fix the bug; but if the bug is serious,
565 or ugly, or easy to fix, chances are we will want to.
566
567 @findex report-emacs-bug
568 A convenient way to send a bug report for Emacs is to use the command
569 @kbd{M-x report-emacs-bug}. This sets up a mail buffer (@pxref{Sending
570 Mail}) and automatically inserts @emph{some} of the essential
571 information. However, it cannot supply all the necessary information;
572 you should still read and follow the guidelines below, so you can enter
573 the other crucial information by hand before you send the message.
574
575 To enable maintainers to investigate a bug, your report
576 should include all these things:
577
578 @itemize @bullet
579 @item
580 The version number of Emacs. Without this, we won't know whether there
581 is any point in looking for the bug in the current version of GNU
582 Emacs.
583
584 You can get the version number by typing @kbd{M-x emacs-version
585 @key{RET}}. If that command does not work, you probably have something
586 other than GNU Emacs, so you will have to report the bug somewhere
587 else.
588
589 @item
590 The type of machine you are using, and the operating system name and
591 version number. @kbd{M-x emacs-version @key{RET}} provides this
592 information too. Copy its output from the @samp{*Messages*} buffer, so
593 that you get it all and get it accurately.
594
595 @item
596 The operands given to the @code{configure} command when Emacs was
597 installed.
598
599 @item
600 A complete list of any modifications you have made to the Emacs source.
601 (We may not have time to investigate the bug unless it happens in an
602 unmodified Emacs. But if you've made modifications and you don't tell
603 us, you are sending us on a wild goose chase.)
604
605 Be precise about these changes. A description in English is not
606 enough---send a context diff for them.
607
608 Adding files of your own, or porting to another machine, is a
609 modification of the source.
610
611 @item
612 Details of any other deviations from the standard procedure for installing
613 GNU Emacs.
614
615 @item
616 The complete text of any files needed to reproduce the bug.
617
618 If you can tell us a way to cause the problem without visiting any files,
619 please do so. This makes it much easier to debug. If you do need files,
620 make sure you arrange for us to see their exact contents. For example, it
621 can often matter whether there are spaces at the ends of lines, or a
622 newline after the last line in the buffer (nothing ought to care whether
623 the last line is terminated, but try telling the bugs that).
624
625 @item
626 The precise commands we need to type to reproduce the bug.
627
628 @findex open-dribble-file
629 @cindex dribble file
630 @cindex logging keystrokes
631 The easy way to record the input to Emacs precisely is to write a
632 dribble file. To start the file, execute the Lisp expression
633
634 @example
635 (open-dribble-file "~/dribble")
636 @end example
637
638 @noindent
639 using @kbd{M-:} or from the @samp{*scratch*} buffer just after
640 starting Emacs. From then on, Emacs copies all your input to the
641 specified dribble file until the Emacs process is killed.
642
643 @item
644 @findex open-termscript
645 @cindex termscript file
646 @cindex @env{TERM} environment variable
647 For possible display bugs, the terminal type (the value of environment
648 variable @env{TERM}), the complete termcap entry for the terminal from
649 @file{/etc/termcap} (since that file is not identical on all machines),
650 and the output that Emacs actually sent to the terminal.
651
652 The way to collect the terminal output is to execute the Lisp expression
653
654 @example
655 (open-termscript "~/termscript")
656 @end example
657
658 @noindent
659 using @kbd{M-:} or from the @samp{*scratch*} buffer just after
660 starting Emacs. From then on, Emacs copies all terminal output to the
661 specified termscript file as well, until the Emacs process is killed.
662 If the problem happens when Emacs starts up, put this expression into
663 your @file{.emacs} file so that the termscript file will be open when
664 Emacs displays the screen for the first time.
665
666 Be warned: it is often difficult, and sometimes impossible, to fix a
667 terminal-dependent bug without access to a terminal of the type that
668 stimulates the bug.@refill
669
670 @item
671 If non-ASCII text or internationalization is relevant, the locale that
672 was current when you started Emacs. On GNU/Linux and Unix systems, or
673 if you use a Unix-style shell such as Bash, you can use this shell
674 command to view the relevant values:
675
676 @smallexample
677 echo LC_ALL=$LC_ALL LC_COLLATE=$LC_COLLATE LC_TYPE=$LC_TYPE \
678 LC_MESSAGES=$LC_MESSAGES LC_TIME=$LC_TIME LANG=$LANG
679 @end smallexample
680
681 Alternatively, use the @command{locale} command, if your system has it,
682 to display your locale settings.
683
684 You can use the @kbd{M-!} command to execute these commands from
685 Emacs, and then copy the output from the @samp{*Messages*} buffer into
686 the bug report. Alternatively, @kbd{M-x getenv @key{RET} LC_ALL
687 @key{RET}} will print the value of @code{LC_ALL} in the echo area, and
688 you can copy its output from the @samp{*Messages*} buffer.
689
690 @item
691 A description of what behavior you observe that you believe is
692 incorrect. For example, ``The Emacs process gets a fatal signal,'' or,
693 ``The resulting text is as follows, which I think is wrong.''
694
695 Of course, if the bug is that Emacs gets a fatal signal, then one can't
696 miss it. But if the bug is incorrect text, the maintainer might fail to
697 notice what is wrong. Why leave it to chance?
698
699 Even if the problem you experience is a fatal signal, you should still
700 say so explicitly. Suppose something strange is going on, such as, your
701 copy of the source is out of sync, or you have encountered a bug in the
702 C library on your system. (This has happened!) Your copy might crash
703 and the copy here might not. If you @emph{said} to expect a crash, then
704 when Emacs here fails to crash, we would know that the bug was not
705 happening. If you don't say to expect a crash, then we would not know
706 whether the bug was happening---we would not be able to draw any
707 conclusion from our observations.
708
709 @item
710 If the bug is that the Emacs Manual or the Emacs Lisp Reference Manual
711 fails to describe the actual behavior of Emacs, or that the text is
712 confusing, copy in the text from the online manual which you think is
713 at fault. If the section is small, just the section name is enough.
714
715 @item
716 If the manifestation of the bug is an Emacs error message, it is
717 important to report the precise text of the error message, and a
718 backtrace showing how the Lisp program in Emacs arrived at the error.
719
720 To get the error message text accurately, copy it from the
721 @samp{*Messages*} buffer into the bug report. Copy all of it, not just
722 part.
723
724 @findex toggle-debug-on-error
725 @pindex Edebug
726 To make a backtrace for the error, use @kbd{M-x toggle-debug-on-error}
727 before the error happens (that is to say, you must give that command
728 and then make the bug happen). This causes the error to run the Lisp
729 debugger, which shows you a backtrace. Copy the text of the
730 debugger's backtrace into the bug report. @xref{Debugger,, The Lisp
731 Debugger, elisp, the Emacs Lisp Reference Manual}, for information on
732 debugging Emacs Lisp programs with the Edebug package.
733
734 This use of the debugger is possible only if you know how to make the
735 bug happen again. If you can't make it happen again, at least copy
736 the whole error message.
737
738 @item
739 Check whether any programs you have loaded into the Lisp world,
740 including your @file{.emacs} file, set any variables that may affect the
741 functioning of Emacs. Also, see whether the problem happens in a
742 freshly started Emacs without loading your @file{.emacs} file (start
743 Emacs with the @code{-q} switch to prevent loading the init file). If
744 the problem does @emph{not} occur then, you must report the precise
745 contents of any programs that you must load into the Lisp world in order
746 to cause the problem to occur.
747
748 @item
749 If the problem does depend on an init file or other Lisp programs that
750 are not part of the standard Emacs system, then you should make sure it
751 is not a bug in those programs by complaining to their maintainers
752 first. After they verify that they are using Emacs in a way that is
753 supposed to work, they should report the bug.
754
755 @item
756 If you wish to mention something in the GNU Emacs source, show the line
757 of code with a few lines of context. Don't just give a line number.
758
759 The line numbers in the development sources don't match those in your
760 sources. It would take extra work for the maintainers to determine what
761 code is in your version at a given line number, and we could not be
762 certain.
763
764 @item
765 Additional information from a C debugger such as GDB might enable
766 someone to find a problem on a machine which he does not have available.
767 If you don't know how to use GDB, please read the GDB manual---it is not
768 very long, and using GDB is easy. You can find the GDB distribution,
769 including the GDB manual in online form, in most of the same places you
770 can find the Emacs distribution. To run Emacs under GDB, you should
771 switch to the @file{src} subdirectory in which Emacs was compiled, then
772 do @samp{gdb emacs}. It is important for the directory @file{src} to be
773 current so that GDB will read the @file{.gdbinit} file in this
774 directory.
775
776 However, you need to think when you collect the additional information
777 if you want it to show what causes the bug.
778
779 @cindex backtrace for bug reports
780 For example, many people send just a backtrace, but that is not very
781 useful by itself. A simple backtrace with arguments often conveys
782 little about what is happening inside GNU Emacs, because most of the
783 arguments listed in the backtrace are pointers to Lisp objects. The
784 numeric values of these pointers have no significance whatever; all that
785 matters is the contents of the objects they point to (and most of the
786 contents are themselves pointers).
787
788 @findex debug_print
789 To provide useful information, you need to show the values of Lisp
790 objects in Lisp notation. Do this for each variable which is a Lisp
791 object, in several stack frames near the bottom of the stack. Look at
792 the source to see which variables are Lisp objects, because the debugger
793 thinks of them as integers.
794
795 To show a variable's value in Lisp syntax, first print its value, then
796 use the user-defined GDB command @code{pr} to print the Lisp object in
797 Lisp syntax. (If you must use another debugger, call the function
798 @code{debug_print} with the object as an argument.) The @code{pr}
799 command is defined by the file @file{.gdbinit}, and it works only if you
800 are debugging a running process (not with a core dump).
801
802 To make Lisp errors stop Emacs and return to GDB, put a breakpoint at
803 @code{Fsignal}.
804
805 For a short listing of Lisp functions running, type the GDB
806 command @code{xbacktrace}.
807
808 The file @file{.gdbinit} defines several other commands that are useful
809 for examining the data types and contents of Lisp objects. Their names
810 begin with @samp{x}. These commands work at a lower level than
811 @code{pr}, and are less convenient, but they may work even when
812 @code{pr} does not, such as when debugging a core dump or when Emacs has
813 had a fatal signal.
814
815 @cindex debugging Emacs, tricks and techniques
816 More detailed advice and other useful techniques for debugging Emacs
817 are available in the file @file{etc/DEBUG} in the Emacs distribution.
818 That file also includes instructions for investigating problems
819 whereby Emacs stops responding (many people assume that Emacs is
820 ``hung,'' whereas in fact it might be in an infinite loop).
821
822 In an installed Emacs, the file @file{etc/DEBUG} is in the same
823 directory where the Emacs on-line documentation file @file{DOC},
824 typically in the @file{/usr/local/share/emacs/@var{version}/etc/}
825 directory. The directory for your installation is stored in the
826 variable @code{data-directory}.
827 @end itemize
828
829 Here are some things that are not necessary in a bug report:
830
831 @itemize @bullet
832 @item
833 A description of the envelope of the bug---this is not necessary for a
834 reproducible bug.
835
836 Often people who encounter a bug spend a lot of time investigating
837 which changes to the input file will make the bug go away and which
838 changes will not affect it.
839
840 This is often time-consuming and not very useful, because the way we
841 will find the bug is by running a single example under the debugger with
842 breakpoints, not by pure deduction from a series of examples. You might
843 as well save time by not searching for additional examples.
844
845 Of course, if you can find a simpler example to report @emph{instead} of
846 the original one, that is a convenience. Errors in the output will be
847 easier to spot, running under the debugger will take less time, etc.
848
849 However, simplification is not vital; if you can't do this or don't have
850 time to try, please report the bug with your original test case.
851
852 @item
853 A system-call trace of Emacs execution.
854
855 System-call traces are very useful for certain special kinds of
856 debugging, but in most cases they give little useful information. It is
857 therefore strange that many people seem to think that @emph{the} way to
858 report information about a crash is to send a system-call trace. Perhaps
859 this is a habit formed from experience debugging programs that don't
860 have source code or debugging symbols.
861
862 In most programs, a backtrace is normally far, far more informative than
863 a system-call trace. Even in Emacs, a simple backtrace is generally
864 more informative, though to give full information you should supplement
865 the backtrace by displaying variable values and printing them as Lisp
866 objects with @code{pr} (see above).
867
868 @item
869 A patch for the bug.
870
871 A patch for the bug is useful if it is a good one. But don't omit the
872 other information that a bug report needs, such as the test case, on the
873 assumption that a patch is sufficient. We might see problems with your
874 patch and decide to fix the problem another way, or we might not
875 understand it at all. And if we can't understand what bug you are
876 trying to fix, or why your patch should be an improvement, we mustn't
877 install it.
878
879 @ifinfo
880 @xref{Sending Patches}, for guidelines on how to make it easy for us to
881 understand and install your patches.
882 @end ifinfo
883
884 @item
885 A guess about what the bug is or what it depends on.
886
887 Such guesses are usually wrong. Even experts can't guess right about
888 such things without first using the debugger to find the facts.
889 @end itemize
890
891 @node Sending Patches
892 @subsection Sending Patches for GNU Emacs
893
894 @cindex sending patches for GNU Emacs
895 @cindex patches, sending
896 If you would like to write bug fixes or improvements for GNU Emacs,
897 that is very helpful. When you send your changes, please follow these
898 guidelines to make it easy for the maintainers to use them. If you
899 don't follow these guidelines, your information might still be useful,
900 but using it will take extra work. Maintaining GNU Emacs is a lot of
901 work in the best of circumstances, and we can't keep up unless you do
902 your best to help.
903
904 @itemize @bullet
905 @item
906 Send an explanation with your changes of what problem they fix or what
907 improvement they bring about. For a bug fix, just include a copy of the
908 bug report, and explain why the change fixes the bug.
909
910 (Referring to a bug report is not as good as including it, because then
911 we will have to look it up, and we have probably already deleted it if
912 we've already fixed the bug.)
913
914 @item
915 Always include a proper bug report for the problem you think you have
916 fixed. We need to convince ourselves that the change is right before
917 installing it. Even if it is correct, we might have trouble
918 understanding it if we don't have a way to reproduce the problem.
919
920 @item
921 Include all the comments that are appropriate to help people reading the
922 source in the future understand why this change was needed.
923
924 @item
925 Don't mix together changes made for different reasons.
926 Send them @emph{individually}.
927
928 If you make two changes for separate reasons, then we might not want to
929 install them both. We might want to install just one. If you send them
930 all jumbled together in a single set of diffs, we have to do extra work
931 to disentangle them---to figure out which parts of the change serve
932 which purpose. If we don't have time for this, we might have to ignore
933 your changes entirely.
934
935 If you send each change as soon as you have written it, with its own
936 explanation, then two changes never get tangled up, and we can consider
937 each one properly without any extra work to disentangle them.
938
939 @item
940 Send each change as soon as that change is finished. Sometimes people
941 think they are helping us by accumulating many changes to send them all
942 together. As explained above, this is absolutely the worst thing you
943 could do.
944
945 Since you should send each change separately, you might as well send it
946 right away. That gives us the option of installing it immediately if it
947 is important.
948
949 @item
950 Use @samp{diff -c} to make your diffs. Diffs without context are hard
951 to install reliably. More than that, they are hard to study; we must
952 always study a patch to decide whether we want to install it. Unidiff
953 format is better than contextless diffs, but not as easy to read as
954 @samp{-c} format.
955
956 If you have GNU diff, use @samp{diff -c -F'^[_a-zA-Z0-9$]+ *('} when
957 making diffs of C code. This shows the name of the function that each
958 change occurs in.
959
960 @item
961 Avoid any ambiguity as to which is the old version and which is the new.
962 Please make the old version the first argument to diff, and the new
963 version the second argument. And please give one version or the other a
964 name that indicates whether it is the old version or your new changed
965 one.
966
967 @item
968 Write the change log entries for your changes. This is both to save us
969 the extra work of writing them, and to help explain your changes so we
970 can understand them.
971
972 The purpose of the change log is to show people where to find what was
973 changed. So you need to be specific about what functions you changed;
974 in large functions, it's often helpful to indicate where within the
975 function the change was.
976
977 On the other hand, once you have shown people where to find the change,
978 you need not explain its purpose in the change log. Thus, if you add a
979 new function, all you need to say about it is that it is new. If you
980 feel that the purpose needs explaining, it probably does---but put the
981 explanation in comments in the code. It will be more useful there.
982
983 Please read the @file{ChangeLog} files in the @file{src} and @file{lisp}
984 directories to see what sorts of information to put in, and to learn the
985 style that we use. If you would like your name to appear in the header
986 line, showing who made the change, send us the header line.
987 @xref{Change Log}.
988
989 @item
990 When you write the fix, keep in mind that we can't install a change that
991 would break other systems. Please think about what effect your change
992 will have if compiled on another type of system.
993
994 Sometimes people send fixes that @emph{might} be an improvement in
995 general---but it is hard to be sure of this. It's hard to install
996 such changes because we have to study them very carefully. Of course,
997 a good explanation of the reasoning by which you concluded the change
998 was correct can help convince us.
999
1000 The safest changes are changes to the configuration files for a
1001 particular machine. These are safe because they can't create new bugs
1002 on other machines.
1003
1004 Please help us keep up with the workload by designing the patch in a
1005 form that is clearly safe to install.
1006 @end itemize
1007
1008 @node Contributing, Service, Bugs, Top
1009 @section Contributing to Emacs Development
1010
1011 If you would like to help pretest Emacs releases to assure they work
1012 well, or if you would like to work on improving Emacs, please contact
1013 the maintainers at @email{bug-gnu-emacs@@gnu.org}. A pretester
1014 should be prepared to investigate bugs as well as report them. If you'd
1015 like to work on improving Emacs, please ask for suggested projects or
1016 suggest your own ideas.
1017
1018 If you have already written an improvement, please tell us about it. If
1019 you have not yet started work, it is useful to contact
1020 @email{bug-gnu-emacs@@gnu.org} before you start; it might be
1021 possible to suggest ways to make your extension fit in better with the
1022 rest of Emacs.
1023
1024 @node Service, Command Arguments, Contributing, Top
1025 @section How To Get Help with GNU Emacs
1026
1027 If you need help installing, using or changing GNU Emacs, there are two
1028 ways to find it:
1029
1030 @itemize @bullet
1031 @item
1032 Send a message to the mailing list
1033 @email{help-gnu-emacs@@gnu.org}, or post your request on
1034 newsgroup @code{gnu.emacs.help}. (This mailing list and newsgroup
1035 interconnect, so it does not matter which one you use.)
1036
1037 @item
1038 Look in the service directory for someone who might help you for a fee.
1039 The service directory is found in the file named @file{etc/SERVICE} in the
1040 Emacs distribution.
1041 @end itemize