1 @c This is part of the Emacs manual.
2 @c Copyright (C) 1985-1987, 1993-1995, 1997, 2001-2012
3 @c Free Software Foundation, Inc.
4 @c See file emacs.texi for copying conditions.
6 @chapter Dealing with Common Problems
8 If you type an Emacs command you did not intend, the results are often
9 mysterious. This chapter tells what you can do to cancel your mistake or
10 recover from a mysterious situation. Emacs bugs and system crashes are
19 @section Quitting and Aborting
24 @itemx C-@key{BREAK} @r{(MS-DOS only)}
25 Quit: cancel running or partially typed command.
27 Abort innermost recursive editing level and cancel the command which
28 invoked it (@code{abort-recursive-edit}).
29 @item @key{ESC} @key{ESC} @key{ESC}
30 Either quit or abort, whichever makes sense (@code{keyboard-escape-quit}).
32 Abort all recursive editing levels that are currently executing.
36 Cancel a previously made change in the buffer contents (@code{undo}).
39 There are two ways of canceling a command before it has finished:
40 @dfn{quitting} with @kbd{C-g}, and @dfn{aborting} with @kbd{C-]} or
41 @kbd{M-x top-level}. Quitting cancels a partially typed command, or
42 one which is still running. Aborting exits a recursive editing level
43 and cancels the command that invoked the recursive edit
44 (@pxref{Recursive Edit}).
48 Quitting with @kbd{C-g} is the way to get rid of a partially typed
49 command, or a numeric argument that you don't want. Furthermore, if
50 you are in the middle of a command that is running, @kbd{C-g} stops
51 the command in a relatively safe way. For example, if you quit out of
52 a kill command that is taking a long time, either your text will
53 @emph{all} still be in the buffer, or it will @emph{all} be in the
54 kill ring, or maybe both. If the region is active, @kbd{C-g}
55 deactivates the mark, unless Transient Mark mode is off
56 (@pxref{Disabled Transient Mark}). If you are in the middle of an
57 incremental search, @kbd{C-g} behaves specially; it may take two
58 successive @kbd{C-g} characters to get out of a search.
59 @xref{Incremental Search}, for details.
61 On MS-DOS, the character @kbd{C-@key{BREAK}} serves as a quit character
62 like @kbd{C-g}. The reason is that it is not feasible, on MS-DOS, to
63 recognize @kbd{C-g} while a command is running, between interactions
64 with the user. By contrast, it @emph{is} feasible to recognize
65 @kbd{C-@key{BREAK}} at all times.
67 @xref{MS-DOS Keyboard,,,emacs-xtra, Specialized Emacs Features}.
70 @xref{MS-DOS Keyboard}.
74 @kbd{C-g} works by setting the variable @code{quit-flag} to @code{t}
75 the instant @kbd{C-g} is typed; Emacs Lisp checks this variable
76 frequently, and quits if it is non-@code{nil}. @kbd{C-g} is only
77 actually executed as a command if you type it while Emacs is waiting for
78 input. In that case, the command it runs is @code{keyboard-quit}.
80 On a text terminal, if you quit with @kbd{C-g} a second time before
81 the first @kbd{C-g} is recognized, you activate the ``emergency
82 escape'' feature and return to the shell. @xref{Emergency Escape}.
84 @cindex NFS and quitting
85 There are some situations where you cannot quit. When Emacs is
86 waiting for the operating system to do something, quitting is
87 impossible unless special pains are taken for the particular system
88 call within Emacs where the waiting occurs. We have done this for the
89 system calls that users are likely to want to quit from, but it's
90 possible you will encounter a case not handled. In one very common
91 case---waiting for file input or output using NFS---Emacs itself knows
92 how to quit, but many NFS implementations simply do not allow user
93 programs to stop waiting for NFS when the NFS server is hung.
95 @cindex aborting recursive edit
96 @findex abort-recursive-edit
98 Aborting with @kbd{C-]} (@code{abort-recursive-edit}) is used to get
99 out of a recursive editing level and cancel the command which invoked
100 it. Quitting with @kbd{C-g} does not do this, and could not do this,
101 because it is used to cancel a partially typed command @emph{within} the
102 recursive editing level. Both operations are useful. For example, if
103 you are in a recursive edit and type @kbd{C-u 8} to enter a numeric
104 argument, you can cancel that argument with @kbd{C-g} and remain in the
107 @findex keyboard-escape-quit
109 The sequence @kbd{@key{ESC} @key{ESC} @key{ESC}}
110 (@code{keyboard-escape-quit}) can either quit or abort. (We defined
111 it this way because @key{ESC} means ``get out'' in many PC programs.)
112 It can cancel a prefix argument, clear a selected region, or get out
113 of a Query Replace, like @kbd{C-g}. It can get out of the minibuffer
114 or a recursive edit, like @kbd{C-]}. It can also get out of splitting
115 the frame into multiple windows, as with @kbd{C-x 1}. One thing it
116 cannot do, however, is stop a command that is running. That's because
117 it executes as an ordinary command, and Emacs doesn't notice it until
118 it is ready for the next command.
121 The command @kbd{M-x top-level} is equivalent to ``enough''
122 @kbd{C-]} commands to get you out of all the levels of recursive edits
123 that you are in; it also exits the minibuffer if it is active.
124 @kbd{C-]} gets you out one level at a time, but @kbd{M-x top-level}
125 goes out all levels at once. Both @kbd{C-]} and @kbd{M-x top-level}
126 are like all other commands, and unlike @kbd{C-g}, in that they take
127 effect only when Emacs is ready for a command. @kbd{C-]} is an
128 ordinary key and has its meaning only because of its binding in the
129 keymap. @xref{Recursive Edit}.
131 @kbd{C-/} (@code{undo}) is not strictly speaking a way of canceling
132 a command, but you can think of it as canceling a command that already
133 finished executing. @xref{Undo}, for more information about the undo
137 @section Dealing with Emacs Trouble
139 This section describes how to recognize and deal with situations in
140 which Emacs does not work as you expect, such as keyboard code mixups,
141 garbled displays, running out of memory, and crashes and hangs.
143 @xref{Bugs}, for what to do when you think you have found a bug in
147 * DEL Does Not Delete:: What to do if @key{DEL} doesn't delete.
148 * Stuck Recursive:: `[...]' in mode line around the parentheses.
149 * Screen Garbled:: Garbage on the screen.
150 * Text Garbled:: Garbage in the text.
151 * Memory Full:: How to cope when you run out of memory.
152 * Crashing:: What Emacs does when it crashes.
153 * After a Crash:: Recovering editing in an Emacs session that crashed.
154 * Emergency Escape:: What to do if Emacs stops responding.
157 @node DEL Does Not Delete
158 @subsection If @key{DEL} Fails to Delete
159 @cindex @key{DEL} vs @key{BACKSPACE}
160 @cindex @key{BACKSPACE} vs @key{DEL}
162 Every keyboard has a large key, usually labeled @key{Backspace},
163 which is ordinarily used to erase the last character that you typed.
164 In Emacs, this key is supposed to be equivalent to @key{DEL}.
166 When Emacs starts up on a graphical display, it determines
167 automatically which key should be @key{DEL}. In some unusual cases,
168 Emacs gets the wrong information from the system, and @key{Backspace}
169 ends up deleting forwards instead of backwards.
171 Some keyboards also have a @key{Delete} key, which is ordinarily
172 used to delete forwards. If this key deletes backward in Emacs, that
173 too suggests Emacs got the wrong information---but in the opposite
176 On a text terminal, if you find that @key{Backspace} prompts for a
177 Help command, like @kbd{Control-h}, instead of deleting a character,
178 it means that key is actually sending the @key{BS} character. Emacs
179 ought to be treating @key{BS} as @key{DEL}, but it isn't.
181 @findex normal-erase-is-backspace-mode
182 In all of those cases, the immediate remedy is the same: use the
183 command @kbd{M-x normal-erase-is-backspace-mode}. This toggles
184 between the two modes that Emacs supports for handling @key{DEL}, so
185 if Emacs starts in the wrong mode, this should switch to the right
186 mode. On a text terminal, if you want to ask for help when @key{BS}
187 is treated as @key{DEL}, use @key{F1}; @kbd{C-?} may also work, if it
188 sends character code 127.
190 To fix the problem in every Emacs session, put one of the following
191 lines into your initialization file (@pxref{Init File}). For the
192 first case above, where @key{Backspace} deletes forwards instead of
193 backwards, use this line to make @key{Backspace} act as @key{DEL}:
196 (normal-erase-is-backspace-mode 0)
200 For the other two cases, use this line:
203 (normal-erase-is-backspace-mode 1)
206 @vindex normal-erase-is-backspace
207 Another way to fix the problem for every Emacs session is to
208 customize the variable @code{normal-erase-is-backspace}: the value
209 @code{t} specifies the mode where @key{BS} or @key{BACKSPACE} is
210 @key{DEL}, and @code{nil} specifies the other mode. @xref{Easy
213 @node Stuck Recursive
214 @subsection Recursive Editing Levels
216 Recursive editing levels are important and useful features of Emacs, but
217 they can seem like malfunctions if you do not understand them.
219 If the mode line has square brackets @samp{[@dots{}]} around the
220 parentheses that contain the names of the major and minor modes, you
221 have entered a recursive editing level. If you did not do this on
222 purpose, or if you don't understand what that means, you should just
223 get out of the recursive editing level. To do so, type @kbd{M-x
224 top-level}. @xref{Recursive Edit}.
227 @subsection Garbage on the Screen
229 If the text on a text terminal looks wrong, the first thing to do is
230 see whether it is wrong in the buffer. Type @kbd{C-l} to redisplay
231 the entire screen. If the screen appears correct after this, the
232 problem was entirely in the previous screen update. (Otherwise, see
233 the following section.)
235 Display updating problems often result from an incorrect terminfo
236 entry for the terminal you are using. The file @file{etc/TERMS} in
237 the Emacs distribution gives the fixes for known problems of this
238 sort. @file{INSTALL} contains general advice for these problems in
239 one of its sections. If you seem to be using the right terminfo
240 entry, it is possible that there is a bug in the terminfo entry, or a
241 bug in Emacs that appears for certain terminal types.
244 @subsection Garbage in the Text
246 If @kbd{C-l} shows that the text is wrong, first type @kbd{C-h l} to
247 see what commands you typed to produce the observed results. Then try
248 undoing the changes step by step using @kbd{C-x u}, until it gets back
249 to a state you consider correct.
251 If a large portion of text appears to be missing at the beginning or
252 end of the buffer, check for the word @samp{Narrow} in the mode line.
253 If it appears, the text you don't see is probably still present, but
254 temporarily off-limits. To make it accessible again, type @kbd{C-x n
255 w}. @xref{Narrowing}.
258 @subsection Running out of Memory
260 @cindex out of memory
262 If you get the error message @samp{Virtual memory exceeded}, save
263 your modified buffers with @kbd{C-x s}. This method of saving them
264 has the smallest need for additional memory. Emacs keeps a reserve of
265 memory which it makes available when this error happens; that should
266 be enough to enable @kbd{C-x s} to complete its work. When the
267 reserve has been used, @samp{!MEM FULL!} appears at the beginning of
268 the mode line, indicating there is no more reserve.
270 Once you have saved your modified buffers, you can exit this Emacs
271 session and start another, or you can use @kbd{M-x kill-some-buffers}
272 to free space in the current Emacs job. If this frees up sufficient
273 space, Emacs will refill its memory reserve, and @samp{!MEM FULL!}
274 will disappear from the mode line. That means you can safely go on
275 editing in the same Emacs session.
277 Do not use @kbd{M-x buffer-menu} to save or kill buffers when you run
278 out of memory, because the buffer menu needs a fair amount of memory
279 itself, and the reserve supply may not be enough.
282 @subsection When Emacs Crashes
284 Emacs is not supposed to crash, but if it does, before it exits it
285 reports some information about the crash to the standard error stream
286 @code{stderr}. This report may be useful to someone who later debugs
287 the same version of Emacs on the same platform. The format of this
288 report depends on the platform, and some platforms support backtraces.
289 Here is an example, generated on x86-64 GNU/Linux with version 2.15 of
293 Fatal error 11: Segmentation fault
298 /lib64/libpthread.so.0[0x375220efe0]
299 /lib64/libpthread.so.0(read+0xe)[0x375220e08e]
310 The number @samp{11} is the system signal number that corresponds to
311 the problem, a segmentation fault here. The hexadecimal program
312 addresses can be useful in debugging sessions. For example, the GDB
313 command @samp{list *0x509af6} prints the source-code lines
314 corresponding to the @samp{emacs[0x509af6]} entry in the backtrace.
316 The three dots at the end indicate that Emacs suppressed further
317 backtrace entries, in the interest of brevity.
320 @subsection Recovery After a Crash
322 If Emacs or the computer crashes, you can recover the files you were
323 editing at the time of the crash from their auto-save files. To do
324 this, start Emacs again and type the command @kbd{M-x recover-session}.
326 This command initially displays a buffer which lists interrupted
327 session files, each with its date. You must choose which session to
328 recover from. Typically the one you want is the most recent one. Move
329 point to the one you choose, and type @kbd{C-c C-c}.
331 Then @code{recover-session} considers each of the files that you
332 were editing during that session; for each such file, it asks whether
333 to recover that file. If you answer @kbd{y} for a file, it shows the
334 dates of that file and its auto-save file, then asks once again
335 whether to recover that file. For the second question, you must
336 confirm with @kbd{yes}. If you do, Emacs visits the file but gets the
337 text from the auto-save file.
339 When @code{recover-session} is done, the files you've chosen to
340 recover are present in Emacs buffers. You should then save them. Only
341 this---saving them---updates the files themselves.
343 As a last resort, if you had buffers with content which were not
344 associated with any files, or if the autosave was not recent enough to
345 have recorded important changes, you can use the
346 @file{etc/emacs-buffer.gdb} script with GDB (the GNU Debugger) to
347 retrieve them from a core dump--provided that a core dump was saved,
348 and that the Emacs executable was not stripped of its debugging
351 As soon as you get the core dump, rename it to another name such as
352 @file{core.emacs}, so that another crash won't overwrite it.
354 To use this script, run @code{gdb} with the file name of your Emacs
355 executable and the file name of the core dump, e.g. @samp{gdb
356 /usr/bin/emacs core.emacs}. At the @code{(gdb)} prompt, load the
357 recovery script: @samp{source /usr/src/emacs/etc/emacs-buffer.gdb}.
358 Then type the command @code{ybuffer-list} to see which buffers are
359 available. For each buffer, it lists a buffer number. To save a
360 buffer, use @code{ysave-buffer}; you specify the buffer number, and
361 the file name to write that buffer into. You should use a file name
362 which does not already exist; if the file does exist, the script does
363 not make a backup of its old contents.
365 @node Emergency Escape
366 @subsection Emergency Escape
368 On text terminals, the @dfn{emergency escape} feature suspends Emacs
369 immediately if you type @kbd{C-g} a second time before Emacs can
370 actually respond to the first one by quitting. This is so you can
371 always get out of GNU Emacs no matter how badly it might be hung.
372 When things are working properly, Emacs recognizes and handles the
373 first @kbd{C-g} so fast that the second one won't trigger emergency
374 escape. However, if some problem prevents Emacs from handling the
375 first @kbd{C-g} properly, then the second one will get you back to the
378 When you resume Emacs after a suspension caused by emergency escape,
379 it asks two questions before going back to what it had been doing:
383 Abort (and dump core)? (y or n)
387 Answer each one with @kbd{y} or @kbd{n} followed by @key{RET}.
389 Saying @kbd{y} to @samp{Auto-save?} causes immediate auto-saving of
390 all modified buffers in which auto-saving is enabled. Saying @kbd{n}
393 Saying @kbd{y} to @samp{Abort (and dump core)?} causes Emacs to
394 crash, dumping core. This is to enable a wizard to figure out why
395 Emacs was failing to quit in the first place. Execution does not
396 continue after a core dump.
398 If you answer this question @kbd{n}, Emacs execution resumes. With
399 luck, Emacs will ultimately do the requested quit. If not, each
400 subsequent @kbd{C-g} invokes emergency escape again.
402 If Emacs is not really hung, just slow, you may invoke the double
403 @kbd{C-g} feature without really meaning to. Then just resume and
404 answer @kbd{n} to both questions, and you will get back to the former
405 state. The quit you requested will happen by and by.
407 Emergency escape is active only for text terminals. On graphical
408 displays, you can use the mouse to kill Emacs or switch to another
411 On MS-DOS, you must type @kbd{C-@key{BREAK}} (twice) to cause
412 emergency escape---but there are cases where it won't work, when
413 system call hangs or when Emacs is stuck in a tight loop in C code.
416 @section Reporting Bugs
419 If you think you have found a bug in Emacs, please report it. We
420 cannot promise to fix it, or always to agree that it is a bug, but we
421 certainly want to hear about it. The same applies for new features
422 you would like to see added. The following sections will help you to
423 construct an effective bug report.
426 * Known Problems:: How to read about known problems and bugs.
427 * Criteria: Bug Criteria. Have you really found a bug?
428 * Understanding Bug Reporting:: How to report a bug effectively.
429 * Checklist:: Steps to follow for a good bug report.
430 * Sending Patches:: How to send a patch for GNU Emacs.
434 @subsection Reading Existing Bug Reports and Known Problems
436 Before reporting a bug, if at all possible please check to see if it
437 is already known about. Indeed, it may already have been fixed in a
438 later release of Emacs, or in the development version. Here is a list
439 of the main places you can read about known issues:
443 The @file{etc/PROBLEMS} file; type @kbd{C-h C-p} to read it. This
444 file contains a list of particularly well-known issues that have been
445 encountered in compiling, installing and running Emacs. Often, there
446 are suggestions for workarounds and solutions.
449 Some additional user-level problems can be found in @ref{Bugs and
450 problems, , Bugs and problems, efaq, GNU Emacs FAQ}.
454 The GNU Bug Tracker at @url{http://debbugs.gnu.org}. Emacs bugs are
455 filed in the tracker under the @samp{emacs} package. The tracker
456 records information about the status of each bug, the initial bug
457 report, and the follow-up messages by the bug reporter and Emacs
458 developers. You can search for bugs by subject, severity, and other
461 @cindex debbugs package
462 Instead of browsing the bug tracker as a webpage, you can browse it
463 from Emacs using the @code{debbugs} package, which can be downloaded
464 via the Package Menu (@pxref{Packages}). This package provides the
465 command @kbd{M-x debbugs-gnu} to list bugs, and @kbd{M-x
466 debbugs-gnu-search} to search for a specific bug.
469 The @samp{bug-gnu-emacs} mailing list (also available as the newsgroup
470 @samp{gnu.emacs.bug}). You can read the list archives at
471 @url{http://lists.gnu.org/mailman/listinfo/bug-gnu-emacs}. This list
472 works as a ``mirror'' of the Emacs bug reports and follow-up messages
473 which are sent to the bug tracker. It also contains old bug reports
474 from before the bug tracker was introduced (in early 2008).
476 If you like, you can subscribe to the list. Be aware that its purpose
477 is to provide the Emacs maintainers with information about bugs and
478 feature requests, so reports may contain fairly large amounts of data;
479 spectators should not complain about this.
482 The @samp{emacs-pretest-bug} mailing list. This list is no longer
483 used, and is mainly of historical interest. At one time, it was used
484 for bug reports in development (i.e., not yet released) versions of
485 Emacs. You can read the archives for 2003 to mid 2007 at
486 @url{http://lists.gnu.org/archive/html/emacs-pretest-bug/}. Nowadays,
487 it is an alias for @samp{bug-gnu-emacs}.
490 The @samp{emacs-devel} mailing list. Sometimes people report bugs to
491 this mailing list. This is not the main purpose of the list, however,
492 and it is much better to send bug reports to the bug list. You should
493 not feel obliged to read this list before reporting a bug.
499 @subsection When Is There a Bug
501 If Emacs accesses an invalid memory location (``segmentation
502 fault''), or exits with an operating system error message that
503 indicates a problem in the program (as opposed to something like
504 ``disk full''), then it is certainly a bug.
506 If the Emacs display does not correspond properly to the contents of
507 the buffer, then it is a bug. But you should check that features like
508 buffer narrowing (@pxref{Narrowing}), which can hide parts of the
509 buffer or change how it is displayed, are not responsible.
511 Taking forever to complete a command can be a bug, but you must make
512 sure that it is really Emacs's fault. Some commands simply take a
513 long time. Type @kbd{C-g} (@kbd{C-@key{BREAK}} on MS-DOS) and then
514 @kbd{C-h l} to see whether the input Emacs received was what you
515 intended to type; if the input was such that you @emph{know} it should
516 have been processed quickly, report a bug. If you don't know whether
517 the command should take a long time, find out by looking in the manual
518 or by asking for assistance.
520 If a command you are familiar with causes an Emacs error message in a
521 case where its usual definition ought to be reasonable, it is probably a
524 If a command does the wrong thing, that is a bug. But be sure you
525 know for certain what it ought to have done. If you aren't familiar
526 with the command, it might actually be working right. If in doubt,
527 read the command's documentation (@pxref{Name Help}).
529 A command's intended definition may not be the best possible
530 definition for editing with. This is a very important sort of
531 problem, but it is also a matter of judgment. Also, it is easy to
532 come to such a conclusion out of ignorance of some of the existing
533 features. It is probably best not to complain about such a problem
534 until you have checked the documentation in the usual ways, feel
535 confident that you understand it, and know for certain that what you
536 want is not available. Ask other Emacs users, too. If you are not
537 sure what the command is supposed to do after a careful reading of the
538 manual, check the index and glossary for any terms that may be
541 If after careful rereading of the manual you still do not understand
542 what the command should do, that indicates a bug in the manual, which
543 you should report. The manual's job is to make everything clear to
544 people who are not Emacs experts---including you. It is just as
545 important to report documentation bugs as program bugs.
547 If the built-in documentation for a function or variable disagrees
548 with the manual, one of them must be wrong; that is a bug.
550 @node Understanding Bug Reporting
551 @subsection Understanding Bug Reporting
553 @findex emacs-version
554 When you decide that there is a bug, it is important to report it
555 and to report it in a way which is useful. What is most useful is an
556 exact description of what commands you type, starting with the shell
557 command to run Emacs, until the problem happens.
559 The most important principle in reporting a bug is to report
560 @emph{facts}. Hypotheses and verbal descriptions are no substitute
561 for the detailed raw data. Reporting the facts is straightforward,
562 but many people strain to posit explanations and report them instead
563 of the facts. If the explanations are based on guesses about how
564 Emacs is implemented, they will be useless; meanwhile, lacking the
565 facts, we will have no real information about the bug. If you want to
566 actually @emph{debug} the problem, and report explanations that are
567 more than guesses, that is useful---but please include the raw facts
570 For example, suppose that you type @kbd{C-x C-f /glorp/baz.ugh
571 @key{RET}}, visiting a file which (you know) happens to be rather
572 large, and Emacs displays @samp{I feel pretty today}. The bug report
573 would need to provide all that information. You should not assume
574 that the problem is due to the size of the file and say, ``I visited a
575 large file, and Emacs displayed @samp{I feel pretty today}.'' This is
576 what we mean by ``guessing explanations''. The problem might be due
577 to the fact that there is a @samp{z} in the file name. If this is so,
578 then when we got your report, we would try out the problem with some
579 ``large file'', probably with no @samp{z} in its name, and not see any
580 problem. There is no way we could guess that we should try visiting a
581 file with a @samp{z} in its name.
583 You should not even say ``visit a file'' instead of @kbd{C-x C-f}.
584 Similarly, rather than saying ``if I have three characters on the
585 line'', say ``after I type @kbd{@key{RET} A B C @key{RET} C-p}'', if
586 that is the way you entered the text.
588 If possible, try quickly to reproduce the bug by invoking Emacs with
589 @command{emacs -Q} (so that Emacs starts with no initial
590 customizations; @pxref{Initial Options}), and repeating the steps that
591 you took to trigger the bug. If you can reproduce the bug this way,
592 that rules out bugs in your personal customizations. Then your bug
593 report should begin by stating that you started Emacs with
594 @command{emacs -Q}, followed by the exact sequence of steps for
595 reproducing the bug. If possible, inform us of the exact contents of
596 any file that is needed to reproduce the bug.
598 Some bugs are not reproducible from @command{emacs -Q}; some are not
599 easily reproducible at all. In that case, you should report what you
600 have---but, as before, please stick to the raw facts about what you
601 did to trigger the bug the first time.
604 @subsection Checklist for Bug Reports
606 @cindex reporting bugs
608 Before reporting a bug, first try to see if the problem has already
609 been reported (@pxref{Known Problems}).
611 If you are able to, try the latest release of Emacs to see if the
612 problem has already been fixed. Even better is to try the latest
613 development version. We recognize that this is not easy for some
614 people, so do not feel that you absolutely must do this before making
617 @findex report-emacs-bug
618 The best way to write a bug report for Emacs is to use the command
619 @kbd{M-x report-emacs-bug}. This sets up a mail buffer
620 (@pxref{Sending Mail}) and automatically inserts @emph{some} of the
621 essential information. However, it cannot supply all the necessary
622 information; you should still read and follow the guidelines below, so
623 you can enter the other crucial information by hand before you send
624 the message. You may feel that some of the information inserted by
625 @kbd{M-x report-emacs-bug} is not relevant, but unless you are
626 absolutely sure it is best to leave it, so that the developers can
627 decide for themselves.
629 When you have finished writing your report, type @kbd{C-c C-c} and it
630 will be sent to the Emacs maintainers at @email{bug-gnu-emacs@@gnu.org}.
631 (If you want to suggest an improvement or new feature, use the same
632 address.) If you cannot send mail from inside Emacs, you can copy the
633 text of your report to your normal mail client (if your system
634 supports it, you can type @kbd{C-c m} to have Emacs do this for you)
635 and send it to that address. Or you can simply send an email to that
636 address describing the problem.
638 Your report will be sent to the @samp{bug-gnu-emacs} mailing list, and
639 stored in the GNU Bug Tracker at @url{http://debbugs.gnu.org}. Please
640 include a valid reply email address, in case we need to ask you for
641 more information about your report. Submissions are moderated, so
642 there may be a delay before your report appears.
644 You do not need to know how the Gnu Bug Tracker works in order to
645 report a bug, but if you want to, you can read the tracker's online
646 documentation to see the various features you can use.
648 All mail sent to the @samp{bug-gnu-emacs} mailing list is also
649 gatewayed to the @samp{gnu.emacs.bug} newsgroup. The reverse is also
650 true, but we ask you not to post bug reports (or replies) via the
651 newsgroup. It can make it much harder to contact you if we need to ask
652 for more information, and it does not integrate well with the bug
655 If your data is more than 500,000 bytes, please don't include it
656 directly in the bug report; instead, offer to send it on request, or
657 make it available by ftp and say where.
659 To enable maintainers to investigate a bug, your report
660 should include all these things:
664 The version number of Emacs. Without this, we won't know whether there is any
665 point in looking for the bug in the current version of GNU Emacs.
667 @kbd{M-x report-emacs-bug} includes this information automatically,
668 but if you are not using that command for your report you can get the
669 version number by typing @kbd{M-x emacs-version @key{RET}}. If that
670 command does not work, you probably have something other than GNU
671 Emacs, so you will have to report the bug somewhere else.
674 The type of machine you are using, and the operating system name and
675 version number (again, automatically included by @kbd{M-x
676 report-emacs-bug}). @kbd{M-x emacs-version @key{RET}} provides this
677 information too. Copy its output from the @file{*Messages*} buffer,
678 so that you get it all and get it accurately.
681 The operands given to the @code{configure} command when Emacs was
682 installed (automatically included by @kbd{M-x report-emacs-bug}).
685 A complete list of any modifications you have made to the Emacs source.
686 (We may not have time to investigate the bug unless it happens in an
687 unmodified Emacs. But if you've made modifications and you don't tell
688 us, you are sending us on a wild goose chase.)
690 Be precise about these changes. A description in English is not
691 enough---send a context diff for them.
693 Adding files of your own, or porting to another machine, is a
694 modification of the source.
697 Details of any other deviations from the standard procedure for installing
701 The complete text of any files needed to reproduce the bug.
703 If you can tell us a way to cause the problem without visiting any files,
704 please do so. This makes it much easier to debug. If you do need files,
705 make sure you arrange for us to see their exact contents. For example, it
706 can matter whether there are spaces at the ends of lines, or a
707 newline after the last line in the buffer (nothing ought to care whether
708 the last line is terminated, but try telling the bugs that).
711 The precise commands we need to type to reproduce the bug. If at all
712 possible, give a full recipe for an Emacs started with the @samp{-Q}
713 option (@pxref{Initial Options}). This bypasses your personal
716 @findex open-dribble-file
718 @cindex logging keystrokes
719 One way to record the input to Emacs precisely is to write a dribble
720 file. To start the file, use the @kbd{M-x open-dribble-file
721 @key{RET}} command. From then on, Emacs copies all your input to the
722 specified dribble file until the Emacs process is killed.
725 @findex open-termscript
726 @cindex termscript file
727 @cindex @env{TERM} environment variable
728 For possible display bugs, the terminal type (the value of environment
729 variable @env{TERM}), the complete termcap entry for the terminal from
730 @file{/etc/termcap} (since that file is not identical on all machines),
731 and the output that Emacs actually sent to the terminal.
733 The way to collect the terminal output is to execute the Lisp expression
736 (open-termscript "~/termscript")
740 using @kbd{M-:} or from the @file{*scratch*} buffer just after
741 starting Emacs. From then on, Emacs copies all terminal output to the
742 specified termscript file as well, until the Emacs process is killed.
743 If the problem happens when Emacs starts up, put this expression into
744 your Emacs initialization file so that the termscript file will be
745 open when Emacs displays the screen for the first time.
747 Be warned: it is often difficult, and sometimes impossible, to fix a
748 terminal-dependent bug without access to a terminal of the type that
752 If non-@acronym{ASCII} text or internationalization is relevant, the locale that
753 was current when you started Emacs. On GNU/Linux and Unix systems, or
754 if you use a Posix-style shell such as Bash, you can use this shell
755 command to view the relevant values:
758 echo LC_ALL=$LC_ALL LC_COLLATE=$LC_COLLATE LC_CTYPE=$LC_CTYPE \
759 LC_MESSAGES=$LC_MESSAGES LC_TIME=$LC_TIME LANG=$LANG
762 Alternatively, use the @command{locale} command, if your system has it,
763 to display your locale settings.
765 You can use the @kbd{M-!} command to execute these commands from
766 Emacs, and then copy the output from the @file{*Messages*} buffer into
767 the bug report. Alternatively, @kbd{M-x getenv @key{RET} LC_ALL
768 @key{RET}} will display the value of @code{LC_ALL} in the echo area, and
769 you can copy its output from the @file{*Messages*} buffer.
772 A description of what behavior you observe that you believe is
773 incorrect. For example, ``The Emacs process gets a fatal signal'', or,
774 ``The resulting text is as follows, which I think is wrong.''
776 Of course, if the bug is that Emacs gets a fatal signal, then one can't
777 miss it. But if the bug is incorrect text, the maintainer might fail to
778 notice what is wrong. Why leave it to chance?
780 Even if the problem you experience is a fatal signal, you should still
781 say so explicitly. Suppose something strange is going on, such as, your
782 copy of the source is out of sync, or you have encountered a bug in the
783 C library on your system. (This has happened!) Your copy might crash
784 and the copy here might not. If you @emph{said} to expect a crash, then
785 when Emacs here fails to crash, we would know that the bug was not
786 happening. If you don't say to expect a crash, then we would not know
787 whether the bug was happening---we would not be able to draw any
788 conclusion from our observations.
791 If the bug is that the Emacs Manual or the Emacs Lisp Reference Manual
792 fails to describe the actual behavior of Emacs, or that the text is
793 confusing, copy in the text from the online manual which you think is
794 at fault. If the section is small, just the section name is enough.
797 If the manifestation of the bug is an Emacs error message, it is
798 important to report the precise text of the error message, and a
799 backtrace showing how the Lisp program in Emacs arrived at the error.
801 To get the error message text accurately, copy it from the
802 @file{*Messages*} buffer into the bug report. Copy all of it, not just
805 @findex toggle-debug-on-error
807 To make a backtrace for the error, use @kbd{M-x toggle-debug-on-error}
808 before the error happens (that is to say, you must give that command
809 and then make the bug happen). This causes the error to start the Lisp
810 debugger, which shows you a backtrace. Copy the text of the
811 debugger's backtrace into the bug report. @xref{Debugger,, The Lisp
812 Debugger, elisp, the Emacs Lisp Reference Manual}, for information on
813 debugging Emacs Lisp programs with the Edebug package.
815 This use of the debugger is possible only if you know how to make the
816 bug happen again. If you can't make it happen again, at least copy
817 the whole error message.
819 @vindex debug-on-quit
820 If Emacs appears to be stuck in an infinite loop or in a very long
821 operation, typing @kbd{C-g} with the variable @code{debug-on-quit}
822 non-@code{nil} will start the Lisp debugger and show a backtrace.
823 This backtrace is useful for debugging such long loops, so if you can
824 produce it, copy it into the bug report.
826 @vindex debug-on-event
827 If you cannot get Emacs to respond to @kbd{C-g} (e.g., because
828 @code{inhibit-quit} is set), then you can try sending the signal
829 specified by @code{debug-on-event} (default SIGUSR2) from outside
830 Emacs to cause it to enter the debugger.
833 Check whether any programs you have loaded into the Lisp world,
834 including your initialization file, set any variables that may affect
835 the functioning of Emacs. Also, see whether the problem happens in a
836 freshly started Emacs without loading your initialization file (start
837 Emacs with the @code{-Q} switch to prevent loading the init files).
838 If the problem does @emph{not} occur then, you must report the precise
839 contents of any programs that you must load into the Lisp world in
840 order to cause the problem to occur.
843 If the problem does depend on an init file or other Lisp programs that
844 are not part of the standard Emacs system, then you should make sure it
845 is not a bug in those programs by complaining to their maintainers
846 first. After they verify that they are using Emacs in a way that is
847 supposed to work, they should report the bug.
850 If you wish to mention something in the GNU Emacs source, show the line
851 of code with a few lines of context. Don't just give a line number.
853 The line numbers in the development sources don't match those in your
854 sources. It would take extra work for the maintainers to determine what
855 code is in your version at a given line number, and we could not be
859 Additional information from a C debugger such as GDB might enable
860 someone to find a problem on a machine which he does not have available.
861 If you don't know how to use GDB, please read the GDB manual---it is not
862 very long, and using GDB is easy. You can find the GDB distribution,
863 including the GDB manual in online form, in most of the same places you
864 can find the Emacs distribution. To run Emacs under GDB, you should
865 switch to the @file{src} subdirectory in which Emacs was compiled, then
866 do @samp{gdb emacs}. It is important for the directory @file{src} to be
867 current so that GDB will read the @file{.gdbinit} file in this
870 However, you need to think when you collect the additional information
871 if you want it to show what causes the bug.
873 @cindex backtrace for bug reports
874 For example, many people send just a backtrace, but that is not very
875 useful by itself. A simple backtrace with arguments often conveys
876 little about what is happening inside GNU Emacs, because most of the
877 arguments listed in the backtrace are pointers to Lisp objects. The
878 numeric values of these pointers have no significance whatever; all that
879 matters is the contents of the objects they point to (and most of the
880 contents are themselves pointers).
883 To provide useful information, you need to show the values of Lisp
884 objects in Lisp notation. Do this for each variable which is a Lisp
885 object, in several stack frames near the bottom of the stack. Look at
886 the source to see which variables are Lisp objects, because the debugger
887 thinks of them as integers.
889 To show a variable's value in Lisp syntax, first print its value, then
890 use the user-defined GDB command @code{pr} to print the Lisp object in
891 Lisp syntax. (If you must use another debugger, call the function
892 @code{debug_print} with the object as an argument.) The @code{pr}
893 command is defined by the file @file{.gdbinit}, and it works only if you
894 are debugging a running process (not with a core dump).
896 To make Lisp errors stop Emacs and return to GDB, put a breakpoint at
899 For a short listing of Lisp functions running, type the GDB
900 command @code{xbacktrace}.
902 The file @file{.gdbinit} defines several other commands that are useful
903 for examining the data types and contents of Lisp objects. Their names
904 begin with @samp{x}. These commands work at a lower level than
905 @code{pr}, and are less convenient, but they may work even when
906 @code{pr} does not, such as when debugging a core dump or when Emacs has
909 @cindex debugging Emacs, tricks and techniques
910 More detailed advice and other useful techniques for debugging Emacs
911 are available in the file @file{etc/DEBUG} in the Emacs distribution.
912 That file also includes instructions for investigating problems
913 whereby Emacs stops responding (many people assume that Emacs is
914 ``hung'', whereas in fact it might be in an infinite loop).
916 To find the file @file{etc/DEBUG} in your Emacs installation, use the
917 directory name stored in the variable @code{data-directory}.
920 Here are some things that are not necessary in a bug report:
924 A description of the envelope of the bug---this is not necessary for a
927 Often people who encounter a bug spend a lot of time investigating
928 which changes to the input file will make the bug go away and which
929 changes will not affect it.
931 This is often time-consuming and not very useful, because the way we
932 will find the bug is by running a single example under the debugger
933 with breakpoints, not by pure deduction from a series of examples.
934 You might as well save time by not searching for additional examples.
935 It is better to send the bug report right away, go back to editing,
936 and find another bug to report.
938 Of course, if you can find a simpler example to report @emph{instead} of
939 the original one, that is a convenience. Errors in the output will be
940 easier to spot, running under the debugger will take less time, etc.
942 However, simplification is not vital; if you can't do this or don't have
943 time to try, please report the bug with your original test case.
948 Debugging the core dump might be useful, but it can only be done on
949 your machine, with your Emacs executable. Therefore, sending the core
950 dump file to the Emacs maintainers won't be useful. Above all, don't
951 include the core file in an email bug report! Such a large message
952 can be extremely inconvenient.
955 A system-call trace of Emacs execution.
957 System-call traces are very useful for certain special kinds of
958 debugging, but in most cases they give little useful information. It is
959 therefore strange that many people seem to think that @emph{the} way to
960 report information about a crash is to send a system-call trace. Perhaps
961 this is a habit formed from experience debugging programs that don't
962 have source code or debugging symbols.
964 In most programs, a backtrace is normally far, far more informative than
965 a system-call trace. Even in Emacs, a simple backtrace is generally
966 more informative, though to give full information you should supplement
967 the backtrace by displaying variable values and printing them as Lisp
968 objects with @code{pr} (see above).
973 A patch for the bug is useful if it is a good one. But don't omit the
974 other information that a bug report needs, such as the test case, on the
975 assumption that a patch is sufficient. We might see problems with your
976 patch and decide to fix the problem another way, or we might not
977 understand it at all. And if we can't understand what bug you are
978 trying to fix, or why your patch should be an improvement, we mustn't
982 @xref{Sending Patches}, for guidelines on how to make it easy for us to
983 understand and install your patches.
987 A guess about what the bug is or what it depends on.
989 Such guesses are usually wrong. Even experts can't guess right about
990 such things without first using the debugger to find the facts.
993 @node Sending Patches
994 @subsection Sending Patches for GNU Emacs
996 @cindex sending patches for GNU Emacs
997 @cindex patches, sending
998 If you would like to write bug fixes or improvements for GNU Emacs,
999 that is very helpful. When you send your changes, please follow these
1000 guidelines to make it easy for the maintainers to use them. If you
1001 don't follow these guidelines, your information might still be useful,
1002 but using it will take extra work. Maintaining GNU Emacs is a lot of
1003 work in the best of circumstances, and we can't keep up unless you do
1008 Send an explanation with your changes of what problem they fix or what
1009 improvement they bring about. For a fix for an existing bug, it is
1010 best to reply to the relevant discussion on the @samp{bug-gnu-emacs}
1011 list, or the bug entry in the GNU Bug Tracker at
1012 @url{http://debbugs.gnu.org}. Explain why your change fixes the bug.
1015 Always include a proper bug report for the problem you think you have
1016 fixed. We need to convince ourselves that the change is right before
1017 installing it. Even if it is correct, we might have trouble
1018 understanding it if we don't have a way to reproduce the problem.
1021 Include all the comments that are appropriate to help people reading the
1022 source in the future understand why this change was needed.
1025 Don't mix together changes made for different reasons.
1026 Send them @emph{individually}.
1028 If you make two changes for separate reasons, then we might not want to
1029 install them both. We might want to install just one. If you send them
1030 all jumbled together in a single set of diffs, we have to do extra work
1031 to disentangle them---to figure out which parts of the change serve
1032 which purpose. If we don't have time for this, we might have to ignore
1033 your changes entirely.
1035 If you send each change as soon as you have written it, with its own
1036 explanation, then two changes never get tangled up, and we can consider
1037 each one properly without any extra work to disentangle them.
1040 Send each change as soon as that change is finished. Sometimes people
1041 think they are helping us by accumulating many changes to send them all
1042 together. As explained above, this is absolutely the worst thing you
1045 Since you should send each change separately, you might as well send it
1046 right away. That gives us the option of installing it immediately if it
1050 Use @samp{diff -c} to make your diffs. Diffs without context are hard
1051 to install reliably. More than that, they are hard to study; we must
1052 always study a patch to decide whether we want to install it. Unidiff
1053 format is better than contextless diffs, but not as easy to read as
1056 If you have GNU diff, use @samp{diff -c -F'^[_a-zA-Z0-9$]+ *('} when
1057 making diffs of C code. This shows the name of the function that each
1061 Avoid any ambiguity as to which is the old version and which is the new.
1062 Please make the old version the first argument to diff, and the new
1063 version the second argument. And please give one version or the other a
1064 name that indicates whether it is the old version or your new changed
1068 Write the change log entries for your changes. This is both to save us
1069 the extra work of writing them, and to help explain your changes so we
1070 can understand them.
1072 The purpose of the change log is to show people where to find what was
1073 changed. So you need to be specific about what functions you changed;
1074 in large functions, it's often helpful to indicate where within the
1075 function the change was.
1077 On the other hand, once you have shown people where to find the change,
1078 you need not explain its purpose in the change log. Thus, if you add a
1079 new function, all you need to say about it is that it is new. If you
1080 feel that the purpose needs explaining, it probably does---but put the
1081 explanation in comments in the code. It will be more useful there.
1083 Please read the @file{ChangeLog} files in the @file{src} and
1084 @file{lisp} directories to see what sorts of information to put in,
1085 and to learn the style that we use. @xref{Change Log}.
1088 When you write the fix, keep in mind that we can't install a change that
1089 would break other systems. Please think about what effect your change
1090 will have if compiled on another type of system.
1092 Sometimes people send fixes that @emph{might} be an improvement in
1093 general---but it is hard to be sure of this. It's hard to install
1094 such changes because we have to study them very carefully. Of course,
1095 a good explanation of the reasoning by which you concluded the change
1096 was correct can help convince us.
1098 The safest changes are changes to the configuration files for a
1099 particular machine. These are safe because they can't create new bugs
1102 Please help us keep up with the workload by designing the patch in a
1103 form that is clearly safe to install.
1107 @section Contributing to Emacs Development
1108 @cindex contributing to Emacs
1110 If you would like to help pretest Emacs releases to assure they work
1111 well, or if you would like to work on improving Emacs, please contact
1112 the maintainers at @email{emacs-devel@@gnu.org}. A pretester
1113 should be prepared to investigate bugs as well as report them. If you'd
1114 like to work on improving Emacs, please ask for suggested projects or
1115 suggest your own ideas.
1117 If you have already written an improvement, please tell us about it. If
1118 you have not yet started work, it is useful to contact
1119 @email{emacs-devel@@gnu.org} before you start; it might be
1120 possible to suggest ways to make your extension fit in better with the
1123 The development version of Emacs can be downloaded from the
1124 repository where it is actively maintained by a group of developers.
1125 See the Emacs project page
1126 @url{http://savannah.gnu.org/projects/emacs/} for details.
1128 For more information on how to contribute, see the @file{etc/CONTRIBUTE}
1129 file in the Emacs distribution.
1132 @section How To Get Help with GNU Emacs
1134 If you need help installing, using or changing GNU Emacs, there are two
1139 Send a message to the mailing list
1140 @email{help-gnu-emacs@@gnu.org}, or post your request on
1141 newsgroup @code{gnu.emacs.help}. (This mailing list and newsgroup
1142 interconnect, so it does not matter which one you use.)
1145 Look in the service directory for someone who might help you for a fee.
1146 The service directory is found in the file named @file{etc/SERVICE} in the