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.
5 @chapter Dealing with Common Problems
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
13 @node Quitting, Lossage, Customization, Top
14 @section Quitting and Aborting
19 @itemx C-@key{BREAK} @r{(MS-DOS only)}
20 Quit: cancel running or partially typed command.
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}).
27 Abort all recursive editing levels that are currently executing.
29 Cancel a previously made change in the buffer contents (@code{undo}).
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}.)
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}).
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}.
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}.
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}.
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
80 @cindex aborting recursive edit
81 @findex abort-recursive-edit
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
92 @findex keyboard-escape-quit
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
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}.
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.
120 @node Lossage, Bugs, Quitting, Top
121 @section Dealing with Emacs Trouble
123 This section describes various conditions in which Emacs fails to work
124 normally, and how to recognize them and correct them. For a list of
125 additional problems you might encounter, see @ref{Bugs and problems, ,
126 Bugs and problems, efaq, GNU Emacs FAQ}, and the file @file{etc/PROBLEMS}
127 in the Emacs distribution. Type @kbd{C-h F} to read the FAQ; type
128 @kbd{C-h P} to read the @file{PROBLEMS} file.
131 * DEL Does Not Delete:: What to do if @key{DEL} doesn't delete.
132 * Stuck Recursive:: `[...]' in mode line around the parentheses.
133 * Screen Garbled:: Garbage on the screen.
134 * Text Garbled:: Garbage in the text.
135 * Unasked-for Search:: Spontaneous entry to incremental search.
136 * Memory Full:: How to cope when you run out of memory.
137 * After a Crash:: Recovering editing in an Emacs session that crashed.
138 * Emergency Escape:: Emergency escape---
139 What to do if Emacs stops responding.
140 * Total Frustration:: When you are at your wits' end.
143 @node DEL Does Not Delete
144 @subsection If @key{DEL} Fails to Delete
145 @cindex @key{DEL} vs @key{BACKSPACE}
146 @cindex @key{BACKSPACE} vs @key{DEL}
147 @cindex usual erasure key
149 Every keyboard has a large key, a little ways above the @key{RET} or
150 @key{ENTER} key, which you normally use outside Emacs to erase the
151 last character that you typed. We call this key @dfn{the usual
152 erasure key}. In Emacs, it is supposed to be equivalent to @key{DEL},
153 and when Emacs is properly configured for your terminal, it translates
154 that key into the character @key{DEL}.
156 When Emacs starts up using a window system, it determines
157 automatically which key should be @key{DEL}. In some unusual cases
158 Emacs gets the wrong information from the system. If the usual
159 erasure key deletes forwards instead of backwards, that is probably
160 what happened---Emacs ought to be treating the @key{DELETE} key as
161 @key{DEL}, but it isn't.
163 With a window system, if the usual erasure key is labeled
164 @key{BACKSPACE} and there is a @key{DELETE} key elsewhere, but the
165 @key{DELETE} key deletes backward instead of forward, that too
166 suggests Emacs got the wrong information---but in the opposite sense.
167 It ought to be treating the @key{BACKSPACE} key as @key{DEL}, and
168 treating @key{DELETE} differently, but it isn't.
170 On a text-only terminal, if you find the usual erasure key prompts
171 for a Help command, like @kbd{Control-h}, instead of deleting a
172 character, it means that key is actually sending the @key{BS}
173 character. Emacs ought to be treating @key{BS} as @key{DEL}, but it
176 In all of those cases, the immediate remedy is the same: use the
177 command @kbd{M-x normal-erase-is-backspace-mode}. This toggles
178 between the two modes that Emacs supports for handling @key{DEL}, so
179 if Emacs starts in the wrong mode, it should switch to the right mode.
180 On a text-only terminal, if you want to ask for help when @key{BS} is
181 treated as @key{DEL}, use @key{F1}; @kbd{C-?} may also work, if it
182 sends character code 127.
184 @findex normal-erase-is-backspace-mode
185 To fix the problem automatically for every Emacs session, you can
186 put one of the following lines into your @file{.emacs} file
187 (@pxref{Init File}). For the first case above, where @key{DELETE}
188 deletes forwards instead of backwards, use this line to make
189 @key{DELETE} act as @key{DEL} (resulting in behavior compatible
190 with Emacs 20 and previous versions):
193 (normal-erase-is-backspace-mode 0)
197 For the other two cases, where @key{BACKSPACE} ought to act as
198 @key{DEL}, use this line:
201 (normal-erase-is-backspace-mode 1)
204 @vindex normal-erase-is-backspace
205 Another way to fix the problem for every Emacs session is to
206 customize the variable @code{normal-erase-is-backspace}: the value
207 @code{t} specifies the mode where @key{BS} or @key{BACKSPACE} is
208 @key{DEL}, and @code{nil} specifies the other mode. @xref{Easy
211 With a window system, it can also happen that the usual erasure key
212 is labeled @key{BACKSPACE}, there is a @key{DELETE} key elsewhere, and
213 both keys delete forward. This probably means that someone has
214 redefined your @key{BACKSPACE} key as a @key{DELETE} key. With X,
215 this is typically done with a command to the @code{xmodmap} program
216 when you start the server or log in. The most likely motive for this
217 customization was to support old versions of Emacs, so we recommend
218 you simply remove it now.
220 @node Stuck Recursive
221 @subsection Recursive Editing Levels
223 Recursive editing levels are important and useful features of Emacs, but
224 they can seem like malfunctions to the user who does not understand them.
226 If the mode line has square brackets @samp{[@dots{}]} around the parentheses
227 that contain the names of the major and minor modes, you have entered a
228 recursive editing level. If you did not do this on purpose, or if you
229 don't understand what that means, you should just get out of the recursive
230 editing level. To do so, type @kbd{M-x top-level}. This is called getting
231 back to top level. @xref{Recursive Edit}.
234 @subsection Garbage on the Screen
236 If the data on the screen looks wrong, the first thing to do is see
237 whether the text is really wrong. Type @kbd{C-l} to redisplay the
238 entire screen. If the screen appears correct after this, the problem
239 was entirely in the previous screen update. (Otherwise, see the following
242 Display updating problems often result from an incorrect termcap entry
243 for the terminal you are using. The file @file{etc/TERMS} in the Emacs
244 distribution gives the fixes for known problems of this sort.
245 @file{INSTALL} contains general advice for these problems in one of its
246 sections. Very likely there is simply insufficient padding for certain
247 display operations. To investigate the possibility that you have this sort
248 of problem, try Emacs on another terminal made by a different manufacturer.
249 If problems happen frequently on one kind of terminal but not another kind,
250 it is likely to be a bad termcap entry, though it could also be due to a
251 bug in Emacs that appears for terminals that have or that lack specific
255 @subsection Garbage in the Text
257 If @kbd{C-l} shows that the text is wrong, try undoing the changes to it
258 using @kbd{C-x u} until it gets back to a state you consider correct. Also
259 try @kbd{C-h l} to find out what command you typed to produce the observed
262 If a large portion of text appears to be missing at the beginning or
263 end of the buffer, check for the word @samp{Narrow} in the mode line.
264 If it appears, the text you don't see is probably still present, but
265 temporarily off-limits. To make it accessible again, type @kbd{C-x n
266 w}. @xref{Narrowing}.
268 @node Unasked-for Search
269 @subsection Spontaneous Entry to Incremental Search
271 If Emacs spontaneously displays @samp{I-search:} at the bottom of the
272 screen, it means that the terminal is sending @kbd{C-s} and @kbd{C-q}
273 according to the poorly designed xon/xoff ``flow control'' protocol.
275 If this happens to you, your best recourse is to put the terminal in a
276 mode where it will not use flow control, or give it so much padding that
277 it will never send a @kbd{C-s}. (One way to increase the amount of
278 padding is to set the variable @code{baud-rate} to a larger value. Its
279 value is the terminal output speed, measured in the conventional units
284 @findex enable-flow-control
285 If you don't succeed in turning off flow control, the next best thing
286 is to tell Emacs to cope with it. To do this, call the function
287 @code{enable-flow-control}.
289 @findex enable-flow-control-on
290 Typically there are particular terminal types with which you must use
291 flow control. You can conveniently ask for flow control on those
292 terminal types only, using @code{enable-flow-control-on}. For example,
293 if you find you must use flow control on VT-100 and H19 terminals, put
294 the following in your @file{.emacs} file:
297 (enable-flow-control-on "vt100" "h19")
300 When flow control is enabled, you must type @kbd{C-\} to get the
301 effect of a @kbd{C-s}, and type @kbd{C-^} to get the effect of a
302 @kbd{C-q}. (These aliases work by means of keyboard translations; see
303 @ref{Keyboard Translations}.)
306 @subsection Running out of Memory
308 @cindex out of memory
310 If you get the error message @samp{Virtual memory exceeded}, save your
311 modified buffers with @kbd{C-x s}. This method of saving them has the
312 smallest need for additional memory. Emacs keeps a reserve of memory
313 which it makes available when this error happens; that should be enough
314 to enable @kbd{C-x s} to complete its work.
316 Once you have saved your modified buffers, you can exit this Emacs job
317 and start another, or you can use @kbd{M-x kill-some-buffers} to free
318 space in the current Emacs job. If you kill buffers containing a
319 substantial amount of text, you can safely go on editing. Emacs refills
320 its memory reserve automatically when it sees sufficient free space
321 available, in case you run out of memory another time.
323 Do not use @kbd{M-x buffer-menu} to save or kill buffers when you run
324 out of memory, because the buffer menu needs a fair amount of memory
325 itself, and the reserve supply may not be enough.
328 @subsection Recovery After a Crash
330 If Emacs or the computer crashes, you can recover the files you were
331 editing at the time of the crash from their auto-save files. To do
332 this, start Emacs again and type the command @kbd{M-x recover-session}.
334 This command initially displays a buffer which lists interrupted
335 session files, each with its date. You must choose which session to
336 recover from. Typically the one you want is the most recent one. Move
337 point to the one you choose, and type @kbd{C-c C-c}.
339 Then @code{recover-session} asks about each of the files that you were
340 editing during that session; it asks whether to recover that file. If
341 you answer @kbd{y} for a file, it shows the dates of that file and its
342 auto-save file, then asks once again whether to recover that file. For
343 the second question, you must confirm with @kbd{yes}. If you do, Emacs
344 visits the file but gets the text from the auto-save file.
346 When @code{recover-session} is done, the files you've chosen to
347 recover are present in Emacs buffers. You should then save them. Only
348 this---saving them---updates the files themselves.
350 @node Emergency Escape
351 @subsection Emergency Escape
353 Because at times there have been bugs causing Emacs to loop without
354 checking @code{quit-flag}, a special feature causes Emacs to be suspended
355 immediately if you type a second @kbd{C-g} while the flag is already set,
356 so you can always get out of GNU Emacs. Normally Emacs recognizes and
357 clears @code{quit-flag} (and quits!) quickly enough to prevent this from
358 happening. (On MS-DOS and compatible systems, type @kbd{C-@key{BREAK}}
361 When you resume Emacs after a suspension caused by multiple @kbd{C-g}, it
362 asks two questions before going back to what it had been doing:
366 Abort (and dump core)? (y or n)
370 Answer each one with @kbd{y} or @kbd{n} followed by @key{RET}.
372 Saying @kbd{y} to @samp{Auto-save?} causes immediate auto-saving of all
373 modified buffers in which auto-saving is enabled.
375 Saying @kbd{y} to @samp{Abort (and dump core)?} causes an illegal instruction to be
376 executed, dumping core. This is to enable a wizard to figure out why Emacs
377 was failing to quit in the first place. Execution does not continue
378 after a core dump. If you answer @kbd{n}, execution does continue. With
379 luck, GNU Emacs will ultimately check @code{quit-flag} and quit normally.
380 If not, and you type another @kbd{C-g}, it is suspended again.
382 If Emacs is not really hung, just slow, you may invoke the double
383 @kbd{C-g} feature without really meaning to. Then just resume and answer
384 @kbd{n} to both questions, and you will arrive at your former state.
385 Presumably the quit you requested will happen soon.
387 The double @kbd{C-g} feature is turned off when Emacs is running under
388 the X Window System, since you can use the window manager to kill Emacs
389 or to create another window and run another program.
391 On MS-DOS and compatible systems, the emergency escape feature is
392 sometimes unavailable, even if you press @kbd{C-@key{BREAK}} twice, when
393 some system call (MS-DOS or BIOS) hangs, or when Emacs is stuck in a
394 very tight endless loop (in C code, @strong{not} in Lisp code).
396 @node Total Frustration
397 @subsection Help for Total Frustration
401 If using Emacs (or something else) becomes terribly frustrating and none
402 of the techniques described above solve the problem, Emacs can still help
405 First, if the Emacs you are using is not responding to commands, type
406 @kbd{C-g C-g} to get out of it and then start a new one.
409 Second, type @kbd{M-x doctor @key{RET}}.
411 The doctor will help you feel better. Each time you say something to
412 the doctor, you must end it by typing @key{RET} @key{RET}. This lets
413 the doctor know you are finished.
415 @node Bugs, Contributing, Lossage, Top
416 @section Reporting Bugs
419 Sometimes you will encounter a bug in Emacs. Although we cannot
420 promise we can or will fix the bug, and we might not even agree that it
421 is a bug, we want to hear about problems you encounter. Often we agree
422 they are bugs and want to fix them.
424 To make it possible for us to fix a bug, you must report it. In order
425 to do so effectively, you must know when and how to do it.
427 Before reporting a bug, it is a good idea to see if it is already
428 known. You can find the list of known problems in the file
429 @file{etc/PROBLEMS} in the Emacs distribution; type @kbd{C-h P} to read
430 it. Some additional user-level problems can be found in @ref{Bugs and
431 problems, , Bugs and problems, efaq, GNU Emacs FAQ}. Looking up your
432 problem in these two documents might provide you with a solution or a
433 work-around, or give you additional information about related issues.
436 * Criteria: Bug Criteria. Have you really found a bug?
437 * Understanding Bug Reporting:: How to report a bug effectively.
438 * Checklist:: Steps to follow for a good bug report.
439 * Sending Patches:: How to send a patch for GNU Emacs.
443 @subsection When Is There a Bug
445 If Emacs executes an illegal instruction, or dies with an operating
446 system error message that indicates a problem in the program (as opposed to
447 something like ``disk full''), then it is certainly a bug.
449 If Emacs updates the display in a way that does not correspond to what is
450 in the buffer, then it is certainly a bug. If a command seems to do the
451 wrong thing but the problem corrects itself if you type @kbd{C-l}, it is a
452 case of incorrect display updating.
454 Taking forever to complete a command can be a bug, but you must make
455 certain that it was really Emacs's fault. Some commands simply take a
456 long time. Type @kbd{C-g} (@kbd{C-@key{BREAK}} on MS-DOS) and then @kbd{C-h l}
457 to see whether the input Emacs received was what you intended to type;
458 if the input was such that you @emph{know} it should have been processed
459 quickly, report a bug. If you don't know whether the command should
460 take a long time, find out by looking in the manual or by asking for
463 If a command you are familiar with causes an Emacs error message in a
464 case where its usual definition ought to be reasonable, it is probably a
467 If a command does the wrong thing, that is a bug. But be sure you know
468 for certain what it ought to have done. If you aren't familiar with the
469 command, or don't know for certain how the command is supposed to work,
470 then it might actually be working right. Rather than jumping to
471 conclusions, show the problem to someone who knows for certain.
473 Finally, a command's intended definition may not be the best
474 possible definition for editing with. This is a very important sort
475 of problem, but it is also a matter of judgment. Also, it is easy to
476 come to such a conclusion out of ignorance of some of the existing
477 features. It is probably best not to complain about such a problem
478 until you have checked the documentation in the usual ways, feel
479 confident that you understand it, and know for certain that what you
480 want is not available. If you are not sure what the command is
481 supposed to do after a careful reading of the manual, check the index
482 and glossary for any terms that may be unclear.
484 If after careful rereading of the manual you still do not understand
485 what the command should do, that indicates a bug in the manual, which
486 you should report. The manual's job is to make everything clear to
487 people who are not Emacs experts---including you. It is just as
488 important to report documentation bugs as program bugs.
490 If the on-line documentation string of a function or variable disagrees
491 with the manual, one of them must be wrong; that is a bug.
493 @node Understanding Bug Reporting
494 @subsection Understanding Bug Reporting
496 @findex emacs-version
497 When you decide that there is a bug, it is important to report it and to
498 report it in a way which is useful. What is most useful is an exact
499 description of what commands you type, starting with the shell command to
500 run Emacs, until the problem happens.
502 The most important principle in reporting a bug is to report
503 @emph{facts}. Hypotheses and verbal descriptions are no substitute for
504 the detailed raw data. Reporting the facts is straightforward, but many
505 people strain to posit explanations and report them instead of the
506 facts. If the explanations are based on guesses about how Emacs is
507 implemented, they will be useless; meanwhile, lacking the facts, we will
508 have no real information about the bug.
510 For example, suppose that you type @kbd{C-x C-f /glorp/baz.ugh
511 @key{RET}}, visiting a file which (you know) happens to be rather large,
512 and Emacs displayed @samp{I feel pretty today}. The best way to report
513 the bug is with a sentence like the preceding one, because it gives all
516 A bad way would be to assume that the problem is due to the size of
517 the file and say, ``I visited a large file, and Emacs displayed @samp{I
518 feel pretty today}.'' This is what we mean by ``guessing
519 explanations.'' The problem is just as likely to be due to the fact
520 that there is a @samp{z} in the file name. If this is so, then when we
521 got your report, we would try out the problem with some ``large file,''
522 probably with no @samp{z} in its name, and not see any problem. There
523 is no way in the world that we could guess that we should try visiting a
524 file with a @samp{z} in its name.
526 Alternatively, the problem might be due to the fact that the file starts
527 with exactly 25 spaces. For this reason, you should make sure that you
528 inform us of the exact contents of any file that is needed to reproduce the
529 bug. What if the problem only occurs when you have typed the @kbd{C-x C-a}
530 command previously? This is why we ask you to give the exact sequence of
531 characters you typed since starting the Emacs session.
533 You should not even say ``visit a file'' instead of @kbd{C-x C-f} unless
534 you @emph{know} that it makes no difference which visiting command is used.
535 Similarly, rather than saying ``if I have three characters on the line,''
536 say ``after I type @kbd{@key{RET} A B C @key{RET} C-p},'' if that is
537 the way you entered the text.@refill
539 So please don't guess any explanations when you report a bug. If you
540 want to actually @emph{debug} the problem, and report explanations that
541 are more than guesses, that is useful---but please include the facts as
545 @subsection Checklist for Bug Reports
547 @cindex reporting bugs
548 The best way to send a bug report is to mail it electronically to the
549 Emacs maintainers at @email{bug-gnu-emacs@@gnu.org}, or to
550 @email{emacs-pretest-bug@@gnu.org} if you are pretesting an Emacs beta
551 release. (If you want to suggest a change as an improvement, use the
554 If you'd like to read the bug reports, you can find them on the
555 newsgroup @samp{gnu.emacs.bug}; keep in mind, however, that as a
556 spectator you should not criticize anything about what you see there.
557 The purpose of bug reports is to give information to the Emacs
558 maintainers. Spectators are welcome only as long as they do not
559 interfere with this. In particular, some bug reports contain fairly
560 large amounts of data; spectators should not complain about this.
562 Please do not post bug reports using netnews; mail is more reliable
563 than netnews about reporting your correct address, which we may need
564 in order to ask you for more information. If your data is more than
565 500,000 bytes, please don't include it directly in the bug report;
566 instead, offer to send it on request, or make it available by ftp and
569 If you can't send electronic mail, then mail the bug report on paper
570 or machine-readable media to this address:
574 Free Software Foundation
575 59 Temple Place, Suite 330
576 Boston, MA 02111-1307 USA
579 We do not promise to fix the bug; but if the bug is serious,
580 or ugly, or easy to fix, chances are we will want to.
582 @findex report-emacs-bug
583 A convenient way to send a bug report for Emacs is to use the command
584 @kbd{M-x report-emacs-bug}. This sets up a mail buffer (@pxref{Sending
585 Mail}) and automatically inserts @emph{some} of the essential
586 information. However, it cannot supply all the necessary information;
587 you should still read and follow the guidelines below, so you can enter
588 the other crucial information by hand before you send the message.
590 To enable maintainers to investigate a bug, your report
591 should include all these things:
595 The version number of Emacs. Without this, we won't know whether there
596 is any point in looking for the bug in the current version of GNU
599 You can get the version number by typing @kbd{M-x emacs-version
600 @key{RET}}. If that command does not work, you probably have something
601 other than GNU Emacs, so you will have to report the bug somewhere
605 The type of machine you are using, and the operating system name and
606 version number. @kbd{M-x emacs-version @key{RET}} provides this
607 information too. Copy its output from the @samp{*Messages*} buffer, so
608 that you get it all and get it accurately.
611 The operands given to the @code{configure} command when Emacs was
615 A complete list of any modifications you have made to the Emacs source.
616 (We may not have time to investigate the bug unless it happens in an
617 unmodified Emacs. But if you've made modifications and you don't tell
618 us, you are sending us on a wild goose chase.)
620 Be precise about these changes. A description in English is not
621 enough---send a context diff for them.
623 Adding files of your own, or porting to another machine, is a
624 modification of the source.
627 Details of any other deviations from the standard procedure for installing
631 The complete text of any files needed to reproduce the bug.
633 If you can tell us a way to cause the problem without visiting any files,
634 please do so. This makes it much easier to debug. If you do need files,
635 make sure you arrange for us to see their exact contents. For example, it
636 can often matter whether there are spaces at the ends of lines, or a
637 newline after the last line in the buffer (nothing ought to care whether
638 the last line is terminated, but try telling the bugs that).
641 The precise commands we need to type to reproduce the bug.
643 @findex open-dribble-file
645 @cindex logging keystrokes
646 The easy way to record the input to Emacs precisely is to write a
647 dribble file. To start the file, execute the Lisp expression
650 (open-dribble-file "~/dribble")
654 using @kbd{M-:} or from the @samp{*scratch*} buffer just after
655 starting Emacs. From then on, Emacs copies all your input to the
656 specified dribble file until the Emacs process is killed.
659 @findex open-termscript
660 @cindex termscript file
661 @cindex @env{TERM} environment variable
662 For possible display bugs, the terminal type (the value of environment
663 variable @env{TERM}), the complete termcap entry for the terminal from
664 @file{/etc/termcap} (since that file is not identical on all machines),
665 and the output that Emacs actually sent to the terminal.
667 The way to collect the terminal output is to execute the Lisp expression
670 (open-termscript "~/termscript")
674 using @kbd{M-:} or from the @samp{*scratch*} buffer just after
675 starting Emacs. From then on, Emacs copies all terminal output to the
676 specified termscript file as well, until the Emacs process is killed.
677 If the problem happens when Emacs starts up, put this expression into
678 your @file{.emacs} file so that the termscript file will be open when
679 Emacs displays the screen for the first time.
681 Be warned: it is often difficult, and sometimes impossible, to fix a
682 terminal-dependent bug without access to a terminal of the type that
683 stimulates the bug.@refill
686 If non-ASCII text or internationalization is relevant, the locale that
687 was current when you started Emacs. On GNU/Linux and Unix systems, or
688 if you use a Unix-style shell such as Bash, you can use this shell
689 command to view the relevant values:
692 echo LC_ALL=$LC_ALL LC_COLLATE=$LC_COLLATE LC_TYPE=$LC_TYPE \
693 LC_MESSAGES=$LC_MESSAGES LC_TIME=$LC_TIME LANG=$LANG
696 Alternatively, use the @command{locale} command, if your system has it,
697 to display your locale settings.
699 You can use the @kbd{M-!} command to execute these commands from
700 Emacs, and then copy the output from the @samp{*Messages*} buffer into
701 the bug report. Alternatively, @kbd{M-x getenv @key{RET} LC_ALL
702 @key{RET}} will print the value of @code{LC_ALL} in the echo area, and
703 you can copy its output from the @samp{*Messages*} buffer.
706 A description of what behavior you observe that you believe is
707 incorrect. For example, ``The Emacs process gets a fatal signal,'' or,
708 ``The resulting text is as follows, which I think is wrong.''
710 Of course, if the bug is that Emacs gets a fatal signal, then one can't
711 miss it. But if the bug is incorrect text, the maintainer might fail to
712 notice what is wrong. Why leave it to chance?
714 Even if the problem you experience is a fatal signal, you should still
715 say so explicitly. Suppose something strange is going on, such as, your
716 copy of the source is out of sync, or you have encountered a bug in the
717 C library on your system. (This has happened!) Your copy might crash
718 and the copy here might not. If you @emph{said} to expect a crash, then
719 when Emacs here fails to crash, we would know that the bug was not
720 happening. If you don't say to expect a crash, then we would not know
721 whether the bug was happening---we would not be able to draw any
722 conclusion from our observations.
725 If the bug is that the Emacs Manual or the Emacs Lisp Reference Manual
726 fails to describe the actual behavior of Emacs, or that the text is
727 confusing, copy in the text from the online manual which you think is
728 at fault. If the section is small, just the section name is enough.
731 If the manifestation of the bug is an Emacs error message, it is
732 important to report the precise text of the error message, and a
733 backtrace showing how the Lisp program in Emacs arrived at the error.
735 To get the error message text accurately, copy it from the
736 @samp{*Messages*} buffer into the bug report. Copy all of it, not just
739 @findex toggle-debug-on-error
741 To make a backtrace for the error, use @kbd{M-x toggle-debug-on-error}
742 before the error happens (that is to say, you must give that command
743 and then make the bug happen). This causes the error to run the Lisp
744 debugger, which shows you a backtrace. Copy the text of the
745 debugger's backtrace into the bug report. @xref{Debugger,, The Lisp
746 Debugger, elisp, the Emacs Lisp Reference Manual}, for information on
747 debugging Emacs Lisp programs with the Edebug package.
749 This use of the debugger is possible only if you know how to make the
750 bug happen again. If you can't make it happen again, at least copy
751 the whole error message.
754 Check whether any programs you have loaded into the Lisp world,
755 including your @file{.emacs} file, set any variables that may affect the
756 functioning of Emacs. Also, see whether the problem happens in a
757 freshly started Emacs without loading your @file{.emacs} file (start
758 Emacs with the @code{-q} switch to prevent loading the init file). If
759 the problem does @emph{not} occur then, you must report the precise
760 contents of any programs that you must load into the Lisp world in order
761 to cause the problem to occur.
764 If the problem does depend on an init file or other Lisp programs that
765 are not part of the standard Emacs system, then you should make sure it
766 is not a bug in those programs by complaining to their maintainers
767 first. After they verify that they are using Emacs in a way that is
768 supposed to work, they should report the bug.
771 If you wish to mention something in the GNU Emacs source, show the line
772 of code with a few lines of context. Don't just give a line number.
774 The line numbers in the development sources don't match those in your
775 sources. It would take extra work for the maintainers to determine what
776 code is in your version at a given line number, and we could not be
780 Additional information from a C debugger such as GDB might enable
781 someone to find a problem on a machine which he does not have available.
782 If you don't know how to use GDB, please read the GDB manual---it is not
783 very long, and using GDB is easy. You can find the GDB distribution,
784 including the GDB manual in online form, in most of the same places you
785 can find the Emacs distribution. To run Emacs under GDB, you should
786 switch to the @file{src} subdirectory in which Emacs was compiled, then
787 do @samp{gdb emacs}. It is important for the directory @file{src} to be
788 current so that GDB will read the @file{.gdbinit} file in this
791 However, you need to think when you collect the additional information
792 if you want it to show what causes the bug.
794 @cindex backtrace for bug reports
795 For example, many people send just a backtrace, but that is not very
796 useful by itself. A simple backtrace with arguments often conveys
797 little about what is happening inside GNU Emacs, because most of the
798 arguments listed in the backtrace are pointers to Lisp objects. The
799 numeric values of these pointers have no significance whatever; all that
800 matters is the contents of the objects they point to (and most of the
801 contents are themselves pointers).
804 To provide useful information, you need to show the values of Lisp
805 objects in Lisp notation. Do this for each variable which is a Lisp
806 object, in several stack frames near the bottom of the stack. Look at
807 the source to see which variables are Lisp objects, because the debugger
808 thinks of them as integers.
810 To show a variable's value in Lisp syntax, first print its value, then
811 use the user-defined GDB command @code{pr} to print the Lisp object in
812 Lisp syntax. (If you must use another debugger, call the function
813 @code{debug_print} with the object as an argument.) The @code{pr}
814 command is defined by the file @file{.gdbinit}, and it works only if you
815 are debugging a running process (not with a core dump).
817 To make Lisp errors stop Emacs and return to GDB, put a breakpoint at
820 For a short listing of Lisp functions running, type the GDB
821 command @code{xbacktrace}.
823 The file @file{.gdbinit} defines several other commands that are useful
824 for examining the data types and contents of Lisp objects. Their names
825 begin with @samp{x}. These commands work at a lower level than
826 @code{pr}, and are less convenient, but they may work even when
827 @code{pr} does not, such as when debugging a core dump or when Emacs has
830 @cindex debugging Emacs, tricks and techniques
831 More detailed advice and other useful techniques for debugging Emacs
832 are available in the file @file{etc/DEBUG} in the Emacs distribution.
833 That file also includes instructions for investigating problems
834 whereby Emacs stops responding (many people assume that Emacs is
835 ``hung,'' whereas in fact it might be in an infinite loop).
837 To find the file @file{etc/DEBUG} in your Emacs installation, use the
838 directory name stored in the variable @code{data-directory}.
841 Here are some things that are not necessary in a bug report:
845 A description of the envelope of the bug---this is not necessary for a
848 Often people who encounter a bug spend a lot of time investigating
849 which changes to the input file will make the bug go away and which
850 changes will not affect it.
852 This is often time-consuming and not very useful, because the way we
853 will find the bug is by running a single example under the debugger
854 with breakpoints, not by pure deduction from a series of examples.
855 You might as well save time by not searching for additional examples.
856 It is better to send the bug report right away, go back to editing,
857 and find another bug to report.
859 Of course, if you can find a simpler example to report @emph{instead} of
860 the original one, that is a convenience. Errors in the output will be
861 easier to spot, running under the debugger will take less time, etc.
863 However, simplification is not vital; if you can't do this or don't have
864 time to try, please report the bug with your original test case.
869 Debugging the core dump might be useful, but it can only be done on
870 your machine, with your Emacs executable. Therefore, sending the core
871 dump file to the Emacs maintainers won't be useful. Above all, don't
872 include the core file in an email bug report! Such a large message
873 can be extremely inconvenient.
876 A system-call trace of Emacs execution.
878 System-call traces are very useful for certain special kinds of
879 debugging, but in most cases they give little useful information. It is
880 therefore strange that many people seem to think that @emph{the} way to
881 report information about a crash is to send a system-call trace. Perhaps
882 this is a habit formed from experience debugging programs that don't
883 have source code or debugging symbols.
885 In most programs, a backtrace is normally far, far more informative than
886 a system-call trace. Even in Emacs, a simple backtrace is generally
887 more informative, though to give full information you should supplement
888 the backtrace by displaying variable values and printing them as Lisp
889 objects with @code{pr} (see above).
894 A patch for the bug is useful if it is a good one. But don't omit the
895 other information that a bug report needs, such as the test case, on the
896 assumption that a patch is sufficient. We might see problems with your
897 patch and decide to fix the problem another way, or we might not
898 understand it at all. And if we can't understand what bug you are
899 trying to fix, or why your patch should be an improvement, we mustn't
903 @xref{Sending Patches}, for guidelines on how to make it easy for us to
904 understand and install your patches.
908 A guess about what the bug is or what it depends on.
910 Such guesses are usually wrong. Even experts can't guess right about
911 such things without first using the debugger to find the facts.
914 @node Sending Patches
915 @subsection Sending Patches for GNU Emacs
917 @cindex sending patches for GNU Emacs
918 @cindex patches, sending
919 If you would like to write bug fixes or improvements for GNU Emacs,
920 that is very helpful. When you send your changes, please follow these
921 guidelines to make it easy for the maintainers to use them. If you
922 don't follow these guidelines, your information might still be useful,
923 but using it will take extra work. Maintaining GNU Emacs is a lot of
924 work in the best of circumstances, and we can't keep up unless you do
929 Send an explanation with your changes of what problem they fix or what
930 improvement they bring about. For a bug fix, just include a copy of the
931 bug report, and explain why the change fixes the bug.
933 (Referring to a bug report is not as good as including it, because then
934 we will have to look it up, and we have probably already deleted it if
935 we've already fixed the bug.)
938 Always include a proper bug report for the problem you think you have
939 fixed. We need to convince ourselves that the change is right before
940 installing it. Even if it is correct, we might have trouble
941 understanding it if we don't have a way to reproduce the problem.
944 Include all the comments that are appropriate to help people reading the
945 source in the future understand why this change was needed.
948 Don't mix together changes made for different reasons.
949 Send them @emph{individually}.
951 If you make two changes for separate reasons, then we might not want to
952 install them both. We might want to install just one. If you send them
953 all jumbled together in a single set of diffs, we have to do extra work
954 to disentangle them---to figure out which parts of the change serve
955 which purpose. If we don't have time for this, we might have to ignore
956 your changes entirely.
958 If you send each change as soon as you have written it, with its own
959 explanation, then two changes never get tangled up, and we can consider
960 each one properly without any extra work to disentangle them.
963 Send each change as soon as that change is finished. Sometimes people
964 think they are helping us by accumulating many changes to send them all
965 together. As explained above, this is absolutely the worst thing you
968 Since you should send each change separately, you might as well send it
969 right away. That gives us the option of installing it immediately if it
973 Use @samp{diff -c} to make your diffs. Diffs without context are hard
974 to install reliably. More than that, they are hard to study; we must
975 always study a patch to decide whether we want to install it. Unidiff
976 format is better than contextless diffs, but not as easy to read as
979 If you have GNU diff, use @samp{diff -c -F'^[_a-zA-Z0-9$]+ *('} when
980 making diffs of C code. This shows the name of the function that each
984 Avoid any ambiguity as to which is the old version and which is the new.
985 Please make the old version the first argument to diff, and the new
986 version the second argument. And please give one version or the other a
987 name that indicates whether it is the old version or your new changed
991 Write the change log entries for your changes. This is both to save us
992 the extra work of writing them, and to help explain your changes so we
995 The purpose of the change log is to show people where to find what was
996 changed. So you need to be specific about what functions you changed;
997 in large functions, it's often helpful to indicate where within the
998 function the change was.
1000 On the other hand, once you have shown people where to find the change,
1001 you need not explain its purpose in the change log. Thus, if you add a
1002 new function, all you need to say about it is that it is new. If you
1003 feel that the purpose needs explaining, it probably does---but put the
1004 explanation in comments in the code. It will be more useful there.
1006 Please read the @file{ChangeLog} files in the @file{src} and @file{lisp}
1007 directories to see what sorts of information to put in, and to learn the
1008 style that we use. If you would like your name to appear in the header
1009 line, showing who made the change, send us the header line.
1013 When you write the fix, keep in mind that we can't install a change that
1014 would break other systems. Please think about what effect your change
1015 will have if compiled on another type of system.
1017 Sometimes people send fixes that @emph{might} be an improvement in
1018 general---but it is hard to be sure of this. It's hard to install
1019 such changes because we have to study them very carefully. Of course,
1020 a good explanation of the reasoning by which you concluded the change
1021 was correct can help convince us.
1023 The safest changes are changes to the configuration files for a
1024 particular machine. These are safe because they can't create new bugs
1027 Please help us keep up with the workload by designing the patch in a
1028 form that is clearly safe to install.
1031 @node Contributing, Service, Bugs, Top
1032 @section Contributing to Emacs Development
1034 If you would like to help pretest Emacs releases to assure they work
1035 well, or if you would like to work on improving Emacs, please contact
1036 the maintainers at @email{bug-gnu-emacs@@gnu.org}. A pretester
1037 should be prepared to investigate bugs as well as report them. If you'd
1038 like to work on improving Emacs, please ask for suggested projects or
1039 suggest your own ideas.
1041 If you have already written an improvement, please tell us about it. If
1042 you have not yet started work, it is useful to contact
1043 @email{bug-gnu-emacs@@gnu.org} before you start; it might be
1044 possible to suggest ways to make your extension fit in better with the
1047 @node Service, Command Arguments, Contributing, Top
1048 @section How To Get Help with GNU Emacs
1050 If you need help installing, using or changing GNU Emacs, there are two
1055 Send a message to the mailing list
1056 @email{help-gnu-emacs@@gnu.org}, or post your request on
1057 newsgroup @code{gnu.emacs.help}. (This mailing list and newsgroup
1058 interconnect, so it does not matter which one you use.)
1061 Look in the service directory for someone who might help you for a fee.
1062 The service directory is found in the file named @file{etc/SERVICE} in the