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6bf7aab6 | 1 | @c This is part of the Emacs manual. |
acaf905b | 2 | @c Copyright (C) 1985-1987, 1993-1995, 1997, 2001-2012 |
893db5bc | 3 | @c Free Software Foundation, Inc. |
6bf7aab6 DL |
4 | @c See file emacs.texi for copying conditions. |
5 | @iftex | |
6 | @chapter Dealing with Common Problems | |
7 | ||
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 | |
11 | also considered. | |
12 | @end iftex | |
13 | ||
0d6e9754 LT |
14 | @ifnottex |
15 | @raisesections | |
16 | @end ifnottex | |
17 | ||
d43f5a42 | 18 | @node Quitting |
6bf7aab6 DL |
19 | @section Quitting and Aborting |
20 | @cindex quitting | |
21 | ||
22 | @table @kbd | |
23 | @item C-g | |
ab26d9a1 RS |
24 | @itemx C-@key{BREAK} @r{(MS-DOS only)} |
25 | Quit: cancel running or partially typed command. | |
6bf7aab6 DL |
26 | @item C-] |
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}). | |
31 | @item M-x top-level | |
32 | Abort all recursive editing levels that are currently executing. | |
b2a42eb7 CY |
33 | @item C-/ |
34 | @itemx C-x u | |
35 | @itemx C-_ | |
6bf7aab6 DL |
36 | Cancel a previously made change in the buffer contents (@code{undo}). |
37 | @end table | |
38 | ||
21c80203 RS |
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 | |
c61ab18c CY |
43 | and cancels the command that invoked the recursive edit |
44 | (@pxref{Recursive Edit}). | |
6bf7aab6 DL |
45 | |
46 | @cindex quitting | |
47 | @kindex C-g | |
21c80203 | 48 | Quitting with @kbd{C-g} is the way to get rid of a partially typed |
3afc838f CY |
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 | |
e1a3f5b1 | 56 | (@pxref{Disabled Transient Mark}). If you are in the middle of an |
c61ab18c | 57 | incremental search, @kbd{C-g} behaves specially; it may take two |
e1a3f5b1 CY |
58 | successive @kbd{C-g} characters to get out of a search. |
59 | @xref{Incremental Search}, for details. | |
6bf7aab6 DL |
60 | |
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 | |
92d05762 EZ |
65 | @kbd{C-@key{BREAK}} at all times. |
66 | @iftex | |
67 | @xref{MS-DOS Keyboard,,,emacs-xtra, Specialized Emacs Features}. | |
68 | @end iftex | |
69 | @ifnottex | |
70 | @xref{MS-DOS Keyboard}. | |
71 | @end ifnottex | |
72 | ||
ab26d9a1 | 73 | @findex keyboard-quit |
6bf7aab6 DL |
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 | |
21c80203 | 76 | frequently, and quits if it is non-@code{nil}. @kbd{C-g} is only |
6bf7aab6 | 77 | actually executed as a command if you type it while Emacs is waiting for |
ab26d9a1 | 78 | input. In that case, the command it runs is @code{keyboard-quit}. |
6bf7aab6 | 79 | |
3b6f40c5 RS |
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}. | |
6bf7aab6 DL |
83 | |
84 | @cindex NFS and quitting | |
21c80203 RS |
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 | |
a80859d4 | 90 | possible you will encounter a case not handled. In one very common |
21c80203 RS |
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. | |
6bf7aab6 DL |
94 | |
95 | @cindex aborting recursive edit | |
96 | @findex abort-recursive-edit | |
97 | @kindex C-] | |
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 | |
105 | recursive edit. | |
106 | ||
107 | @findex keyboard-escape-quit | |
108 | @kindex ESC ESC ESC | |
21c80203 RS |
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. | |
6bf7aab6 DL |
119 | |
120 | @findex top-level | |
2e606829 CY |
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 | |
6bf7aab6 DL |
129 | keymap. @xref{Recursive Edit}. |
130 | ||
b2a42eb7 | 131 | @kbd{C-/} (@code{undo}) is not strictly speaking a way of canceling |
6bf7aab6 | 132 | a command, but you can think of it as canceling a command that already |
b2a42eb7 CY |
133 | finished executing. @xref{Undo}, for more information about the undo |
134 | facility. | |
6bf7aab6 | 135 | |
abb9615e | 136 | @node Lossage |
6bf7aab6 DL |
137 | @section Dealing with Emacs Trouble |
138 | ||
c61ab18c CY |
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. | |
142 | ||
143 | @xref{Bugs}, for what to do when you think you have found a bug in | |
144 | Emacs. | |
6bf7aab6 DL |
145 | |
146 | @menu | |
84c1f5fe | 147 | * DEL Does Not Delete:: What to do if @key{DEL} doesn't delete. |
82f6ab38 EZ |
148 | * Stuck Recursive:: `[...]' in mode line around the parentheses. |
149 | * Screen Garbled:: Garbage on the screen. | |
150 | * Text Garbled:: Garbage in the text. | |
82f6ab38 | 151 | * Memory Full:: How to cope when you run out of memory. |
cf29dd84 | 152 | * Crashing:: What Emacs does when it crashes. |
82f6ab38 | 153 | * After a Crash:: Recovering editing in an Emacs session that crashed. |
c61ab18c | 154 | * Emergency Escape:: What to do if Emacs stops responding. |
6bf7aab6 DL |
155 | @end menu |
156 | ||
82f6ab38 | 157 | @node DEL Does Not Delete |
6bf7aab6 | 158 | @subsection If @key{DEL} Fails to Delete |
7be352a8 RS |
159 | @cindex @key{DEL} vs @key{BACKSPACE} |
160 | @cindex @key{BACKSPACE} vs @key{DEL} | |
161 | ||
09e80d9f | 162 | Every keyboard has a large key, usually labeled @key{Backspace}, |
b2a42eb7 | 163 | which is ordinarily used to erase the last character that you typed. |
c61ab18c | 164 | In Emacs, this key is supposed to be equivalent to @key{DEL}. |
7be352a8 | 165 | |
aa929821 | 166 | When Emacs starts up on a graphical display, it determines |
b2a42eb7 | 167 | automatically which key should be @key{DEL}. In some unusual cases, |
c61ab18c CY |
168 | Emacs gets the wrong information from the system, and @key{Backspace} |
169 | ends up deleting forwards instead of backwards. | |
7be352a8 | 170 | |
b2a42eb7 | 171 | Some keyboards also have a @key{Delete} key, which is ordinarily |
522ddc9f JB |
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 | |
174 | sense. | |
cdf648ca | 175 | |
0be641c0 CY |
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. | |
7be352a8 | 180 | |
c61ab18c | 181 | @findex normal-erase-is-backspace-mode |
7be352a8 | 182 | In all of those cases, the immediate remedy is the same: use the |
405d5e63 RS |
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 | |
21c80203 | 185 | if Emacs starts in the wrong mode, this should switch to the right |
0be641c0 CY |
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. | |
7be352a8 | 189 | |
c61ab18c CY |
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}: | |
7be352a8 RS |
194 | |
195 | @lisp | |
196 | (normal-erase-is-backspace-mode 0) | |
197 | @end lisp | |
198 | ||
199 | @noindent | |
b2a42eb7 | 200 | For the other two cases, use this line: |
7be352a8 RS |
201 | |
202 | @lisp | |
203 | (normal-erase-is-backspace-mode 1) | |
204 | @end lisp | |
205 | ||
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 | |
211 | Customization}. | |
6bf7aab6 DL |
212 | |
213 | @node Stuck Recursive | |
214 | @subsection Recursive Editing Levels | |
215 | ||
216 | Recursive editing levels are important and useful features of Emacs, but | |
aa929821 | 217 | they can seem like malfunctions if you do not understand them. |
6bf7aab6 | 218 | |
c61ab18c CY |
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}. | |
6bf7aab6 DL |
225 | |
226 | @node Screen Garbled | |
227 | @subsection Garbage on the Screen | |
228 | ||
3b6f40c5 RS |
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.) | |
6bf7aab6 | 234 | |
21c80203 RS |
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 | |
c61ab18c CY |
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. | |
6bf7aab6 DL |
242 | |
243 | @node Text Garbled | |
244 | @subsection Garbage in the Text | |
245 | ||
21c80203 RS |
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. | |
6bf7aab6 DL |
250 | |
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}. | |
256 | ||
6bf7aab6 DL |
257 | @node Memory Full |
258 | @subsection Running out of Memory | |
259 | @cindex memory full | |
260 | @cindex out of memory | |
261 | ||
180ff2e5 RS |
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. | |
269 | ||
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. | |
6bf7aab6 DL |
276 | |
277 | Do not use @kbd{M-x buffer-menu} to save or kill buffers when you run | |
cce0aa5a | 278 | out of memory, because the Buffer Menu needs a fair amount of memory |
6bf7aab6 DL |
279 | itself, and the reserve supply may not be enough. |
280 | ||
cf29dd84 PE |
281 | @node Crashing |
282 | @subsection When Emacs Crashes | |
283 | ||
4c1f6a5b | 284 | @cindex crash report |
a33da68b EZ |
285 | @cindex backtrace |
286 | @cindex @file{emacs_backtrace.txt} file, MS-Windows | |
4c1f6a5b CY |
287 | Emacs is not supposed to crash, but if it does, it produces a |
288 | @dfn{crash report} prior to exiting. The crash report is printed to | |
289 | the standard error stream. If Emacs was started from a graphical | |
a33da68b EZ |
290 | desktop on a GNU or Unix system, the standard error stream is commonly |
291 | redirected to a file such as @file{~/.xsession-errors}, so you can | |
292 | look for the crash report there. On MS-Windows, the crash report is | |
293 | written to a file named @file{emacs_backtrace.txt} in the current | |
294 | directory of the Emacs process, in addition to the standard error | |
295 | stream. | |
4c1f6a5b CY |
296 | |
297 | The format of the crash report depends on the platform. On some | |
298 | platforms, such as those using the GNU C Library, the crash report | |
299 | includes a @dfn{backtrace} describing the execution state prior to | |
300 | crashing, which can be used to help debug the crash. Here is an | |
a33da68b | 301 | example for a GNU system: |
cf29dd84 PE |
302 | |
303 | @example | |
304 | Fatal error 11: Segmentation fault | |
305 | Backtrace: | |
306 | emacs[0x5094e4] | |
307 | emacs[0x4ed3e6] | |
308 | emacs[0x4ed504] | |
309 | /lib64/libpthread.so.0[0x375220efe0] | |
310 | /lib64/libpthread.so.0(read+0xe)[0x375220e08e] | |
311 | emacs[0x509af6] | |
312 | emacs[0x5acc26] | |
4c1f6a5b | 313 | @dots{} |
cf29dd84 PE |
314 | @end example |
315 | ||
316 | @noindent | |
4c1f6a5b CY |
317 | The number @samp{11} is the system signal number corresponding to the |
318 | crash---in this case a segmentation fault. The hexadecimal numbers | |
319 | are program addresses, which can be associated with source code lines | |
320 | using a debugging tool. For example, the GDB command | |
321 | @samp{list *0x509af6} prints the source-code lines corresponding to | |
322 | the @samp{emacs[0x509af6]} entry. If your system has the | |
323 | @command{addr2line} utility, the following shell command outputs a | |
324 | backtrace with source-code line numbers: | |
58f3a196 PE |
325 | |
326 | @example | |
327 | sed -n 's/.*\[\(.*\)]$/\1/p' @var{backtrace} | | |
a33da68b | 328 | addr2line -Cfip -e @var{bindir}/@var{emacs-binary} |
58f3a196 PE |
329 | @end example |
330 | ||
331 | @noindent | |
332 | Here, @var{backtrace} is the name of a text file containing a copy of | |
a33da68b EZ |
333 | the backtrace, @var{bindir} is the name of the directory that |
334 | contains the Emacs executable, and @var{emacs-binary} is the name of | |
335 | the Emacs executable file, normally @file{emacs} on GNU and Unix | |
336 | systems and @file{emacs.exe} on MS-Windows and MS-DOS. | |
cf29dd84 | 337 | |
4c1f6a5b | 338 | @cindex core dump |
a33da68b EZ |
339 | Optionally, Emacs can generate a @dfn{core dump} when it crashes, on |
340 | systems that support core files. A core dump is a file containing | |
341 | voluminous data about the state of the program prior to the crash, | |
342 | usually examined by loading it into a debugger such as GDB. On many | |
343 | platforms, core dumps are disabled by default, and you must explicitly | |
344 | enable them by running the shell command @samp{ulimit -c unlimited} | |
345 | (e.g.@: in your shell startup script). | |
4c1f6a5b | 346 | |
6bf7aab6 DL |
347 | @node After a Crash |
348 | @subsection Recovery After a Crash | |
349 | ||
350 | If Emacs or the computer crashes, you can recover the files you were | |
351 | editing at the time of the crash from their auto-save files. To do | |
352 | this, start Emacs again and type the command @kbd{M-x recover-session}. | |
353 | ||
354 | This command initially displays a buffer which lists interrupted | |
355 | session files, each with its date. You must choose which session to | |
356 | recover from. Typically the one you want is the most recent one. Move | |
357 | point to the one you choose, and type @kbd{C-c C-c}. | |
358 | ||
21c80203 RS |
359 | Then @code{recover-session} considers each of the files that you |
360 | were editing during that session; for each such file, it asks whether | |
361 | to recover that file. If you answer @kbd{y} for a file, it shows the | |
362 | dates of that file and its auto-save file, then asks once again | |
363 | whether to recover that file. For the second question, you must | |
364 | confirm with @kbd{yes}. If you do, Emacs visits the file but gets the | |
365 | text from the auto-save file. | |
6bf7aab6 DL |
366 | |
367 | When @code{recover-session} is done, the files you've chosen to | |
368 | recover are present in Emacs buffers. You should then save them. Only | |
369 | this---saving them---updates the files themselves. | |
370 | ||
615cdecf NF |
371 | As a last resort, if you had buffers with content which were not |
372 | associated with any files, or if the autosave was not recent enough to | |
373 | have recorded important changes, you can use the | |
16540869 NF |
374 | @file{etc/emacs-buffer.gdb} script with GDB (the GNU Debugger) to |
375 | retrieve them from a core dump--provided that a core dump was saved, | |
376 | and that the Emacs executable was not stripped of its debugging | |
377 | symbols. | |
378 | ||
21c80203 RS |
379 | As soon as you get the core dump, rename it to another name such as |
380 | @file{core.emacs}, so that another crash won't overwrite it. | |
381 | ||
5cf98ab4 RS |
382 | To use this script, run @code{gdb} with the file name of your Emacs |
383 | executable and the file name of the core dump, e.g. @samp{gdb | |
16540869 NF |
384 | /usr/bin/emacs core.emacs}. At the @code{(gdb)} prompt, load the |
385 | recovery script: @samp{source /usr/src/emacs/etc/emacs-buffer.gdb}. | |
5cf98ab4 RS |
386 | Then type the command @code{ybuffer-list} to see which buffers are |
387 | available. For each buffer, it lists a buffer number. To save a | |
388 | buffer, use @code{ysave-buffer}; you specify the buffer number, and | |
389 | the file name to write that buffer into. You should use a file name | |
390 | which does not already exist; if the file does exist, the script does | |
a5cecf92 | 391 | not make a backup of its old contents. |
615cdecf | 392 | |
6bf7aab6 DL |
393 | @node Emergency Escape |
394 | @subsection Emergency Escape | |
395 | ||
0be641c0 CY |
396 | On text terminals, the @dfn{emergency escape} feature suspends Emacs |
397 | immediately if you type @kbd{C-g} a second time before Emacs can | |
21c80203 RS |
398 | actually respond to the first one by quitting. This is so you can |
399 | always get out of GNU Emacs no matter how badly it might be hung. | |
400 | When things are working properly, Emacs recognizes and handles the | |
401 | first @kbd{C-g} so fast that the second one won't trigger emergency | |
402 | escape. However, if some problem prevents Emacs from handling the | |
403 | first @kbd{C-g} properly, then the second one will get you back to the | |
404 | shell. | |
6bf7aab6 | 405 | |
21c80203 RS |
406 | When you resume Emacs after a suspension caused by emergency escape, |
407 | it asks two questions before going back to what it had been doing: | |
6bf7aab6 DL |
408 | |
409 | @example | |
410 | Auto-save? (y or n) | |
411 | Abort (and dump core)? (y or n) | |
412 | @end example | |
413 | ||
414 | @noindent | |
415 | Answer each one with @kbd{y} or @kbd{n} followed by @key{RET}. | |
416 | ||
21c80203 RS |
417 | Saying @kbd{y} to @samp{Auto-save?} causes immediate auto-saving of |
418 | all modified buffers in which auto-saving is enabled. Saying @kbd{n} | |
419 | skips this. | |
420 | ||
421 | Saying @kbd{y} to @samp{Abort (and dump core)?} causes Emacs to | |
422 | crash, dumping core. This is to enable a wizard to figure out why | |
423 | Emacs was failing to quit in the first place. Execution does not | |
424 | continue after a core dump. | |
6bf7aab6 | 425 | |
21c80203 RS |
426 | If you answer this question @kbd{n}, Emacs execution resumes. With |
427 | luck, Emacs will ultimately do the requested quit. If not, each | |
428 | subsequent @kbd{C-g} invokes emergency escape again. | |
6bf7aab6 DL |
429 | |
430 | If Emacs is not really hung, just slow, you may invoke the double | |
21c80203 RS |
431 | @kbd{C-g} feature without really meaning to. Then just resume and |
432 | answer @kbd{n} to both questions, and you will get back to the former | |
433 | state. The quit you requested will happen by and by. | |
6bf7aab6 | 434 | |
58af1784 RS |
435 | Emergency escape is active only for text terminals. On graphical |
436 | displays, you can use the mouse to kill Emacs or switch to another | |
437 | program. | |
6bf7aab6 | 438 | |
21c80203 RS |
439 | On MS-DOS, you must type @kbd{C-@key{BREAK}} (twice) to cause |
440 | emergency escape---but there are cases where it won't work, when | |
441 | system call hangs or when Emacs is stuck in a tight loop in C code. | |
6bf7aab6 | 442 | |
abb9615e | 443 | @node Bugs |
6bf7aab6 DL |
444 | @section Reporting Bugs |
445 | ||
446 | @cindex bugs | |
63e1eaa1 GM |
447 | If you think you have found a bug in Emacs, please report it. We |
448 | cannot promise to fix it, or always to agree that it is a bug, but we | |
449 | certainly want to hear about it. The same applies for new features | |
450 | you would like to see added. The following sections will help you to | |
451 | construct an effective bug report. | |
9e25ea70 | 452 | |
6bf7aab6 | 453 | @menu |
63e1eaa1 | 454 | * Known Problems:: How to read about known problems and bugs. |
8838673e GM |
455 | * Criteria: Bug Criteria. Have you really found a bug? |
456 | * Understanding Bug Reporting:: How to report a bug effectively. | |
457 | * Checklist:: Steps to follow for a good bug report. | |
458 | * Sending Patches:: How to send a patch for GNU Emacs. | |
6bf7aab6 DL |
459 | @end menu |
460 | ||
63e1eaa1 GM |
461 | @node Known Problems |
462 | @subsection Reading Existing Bug Reports and Known Problems | |
463 | ||
464 | Before reporting a bug, if at all possible please check to see if it | |
465 | is already known about. Indeed, it may already have been fixed in a | |
466 | later release of Emacs, or in the development version. Here is a list | |
467 | of the main places you can read about known issues: | |
468 | ||
469 | @itemize | |
470 | @item | |
c61ab18c CY |
471 | The @file{etc/PROBLEMS} file; type @kbd{C-h C-p} to read it. This |
472 | file contains a list of particularly well-known issues that have been | |
473 | encountered in compiling, installing and running Emacs. Often, there | |
474 | are suggestions for workarounds and solutions. | |
63e1eaa1 GM |
475 | |
476 | @item | |
477 | Some additional user-level problems can be found in @ref{Bugs and | |
478 | problems, , Bugs and problems, efaq, GNU Emacs FAQ}. | |
479 | ||
c61ab18c CY |
480 | @cindex bug tracker |
481 | @item | |
482 | The GNU Bug Tracker at @url{http://debbugs.gnu.org}. Emacs bugs are | |
483 | filed in the tracker under the @samp{emacs} package. The tracker | |
484 | records information about the status of each bug, the initial bug | |
485 | report, and the follow-up messages by the bug reporter and Emacs | |
486 | developers. You can search for bugs by subject, severity, and other | |
487 | criteria. | |
488 | ||
489 | @cindex debbugs package | |
490 | Instead of browsing the bug tracker as a webpage, you can browse it | |
491 | from Emacs using the @code{debbugs} package, which can be downloaded | |
492 | via the Package Menu (@pxref{Packages}). This package provides the | |
493 | command @kbd{M-x debbugs-gnu} to list bugs, and @kbd{M-x | |
87288971 MA |
494 | debbugs-gnu-search} to search for a specific bug. User tags, applied |
495 | by the Emacs maintainers, are shown by @kbd{M-x debbugs-gnu-usertags}. | |
c61ab18c | 496 | |
63e1eaa1 GM |
497 | @item |
498 | The @samp{bug-gnu-emacs} mailing list (also available as the newsgroup | |
ae742cb5 | 499 | @samp{gnu.emacs.bug}). You can read the list archives at |
c61ab18c CY |
500 | @url{http://lists.gnu.org/mailman/listinfo/bug-gnu-emacs}. This list |
501 | works as a ``mirror'' of the Emacs bug reports and follow-up messages | |
502 | which are sent to the bug tracker. It also contains old bug reports | |
503 | from before the bug tracker was introduced (in early 2008). | |
63e1eaa1 | 504 | |
c61ab18c CY |
505 | If you like, you can subscribe to the list. Be aware that its purpose |
506 | is to provide the Emacs maintainers with information about bugs and | |
507 | feature requests, so reports may contain fairly large amounts of data; | |
508 | spectators should not complain about this. | |
63e1eaa1 GM |
509 | |
510 | @item | |
511 | The @samp{emacs-pretest-bug} mailing list. This list is no longer | |
512 | used, and is mainly of historical interest. At one time, it was used | |
513 | for bug reports in development (i.e., not yet released) versions of | |
514 | Emacs. You can read the archives for 2003 to mid 2007 at | |
c61ab18c CY |
515 | @url{http://lists.gnu.org/archive/html/emacs-pretest-bug/}. Nowadays, |
516 | it is an alias for @samp{bug-gnu-emacs}. | |
63e1eaa1 GM |
517 | |
518 | @item | |
519 | The @samp{emacs-devel} mailing list. Sometimes people report bugs to | |
520 | this mailing list. This is not the main purpose of the list, however, | |
521 | and it is much better to send bug reports to the bug list. You should | |
522 | not feel obliged to read this list before reporting a bug. | |
523 | ||
524 | @end itemize | |
525 | ||
526 | ||
6bf7aab6 DL |
527 | @node Bug Criteria |
528 | @subsection When Is There a Bug | |
529 | ||
21c80203 RS |
530 | If Emacs accesses an invalid memory location (``segmentation |
531 | fault''), or exits with an operating system error message that | |
532 | indicates a problem in the program (as opposed to something like | |
533 | ``disk full''), then it is certainly a bug. | |
6bf7aab6 | 534 | |
c61ab18c CY |
535 | If the Emacs display does not correspond properly to the contents of |
536 | the buffer, then it is a bug. But you should check that features like | |
537 | buffer narrowing (@pxref{Narrowing}), which can hide parts of the | |
538 | buffer or change how it is displayed, are not responsible. | |
6bf7aab6 DL |
539 | |
540 | Taking forever to complete a command can be a bug, but you must make | |
c61ab18c CY |
541 | sure that it is really Emacs's fault. Some commands simply take a |
542 | long time. Type @kbd{C-g} (@kbd{C-@key{BREAK}} on MS-DOS) and then | |
543 | @kbd{C-h l} to see whether the input Emacs received was what you | |
544 | intended to type; if the input was such that you @emph{know} it should | |
545 | have been processed quickly, report a bug. If you don't know whether | |
546 | the command should take a long time, find out by looking in the manual | |
547 | or by asking for assistance. | |
6bf7aab6 DL |
548 | |
549 | If a command you are familiar with causes an Emacs error message in a | |
550 | case where its usual definition ought to be reasonable, it is probably a | |
551 | bug. | |
552 | ||
c61ab18c CY |
553 | If a command does the wrong thing, that is a bug. But be sure you |
554 | know for certain what it ought to have done. If you aren't familiar | |
555 | with the command, it might actually be working right. If in doubt, | |
556 | read the command's documentation (@pxref{Name Help}). | |
6bf7aab6 | 557 | |
c61ab18c CY |
558 | A command's intended definition may not be the best possible |
559 | definition for editing with. This is a very important sort of | |
560 | problem, but it is also a matter of judgment. Also, it is easy to | |
ba3ce288 GM |
561 | come to such a conclusion out of ignorance of some of the existing |
562 | features. It is probably best not to complain about such a problem | |
563 | until you have checked the documentation in the usual ways, feel | |
564 | confident that you understand it, and know for certain that what you | |
21c80203 RS |
565 | want is not available. Ask other Emacs users, too. If you are not |
566 | sure what the command is supposed to do after a careful reading of the | |
567 | manual, check the index and glossary for any terms that may be | |
568 | unclear. | |
6bf7aab6 DL |
569 | |
570 | If after careful rereading of the manual you still do not understand | |
571 | what the command should do, that indicates a bug in the manual, which | |
572 | you should report. The manual's job is to make everything clear to | |
573 | people who are not Emacs experts---including you. It is just as | |
574 | important to report documentation bugs as program bugs. | |
575 | ||
c61ab18c | 576 | If the built-in documentation for a function or variable disagrees |
6bf7aab6 DL |
577 | with the manual, one of them must be wrong; that is a bug. |
578 | ||
579 | @node Understanding Bug Reporting | |
580 | @subsection Understanding Bug Reporting | |
581 | ||
582 | @findex emacs-version | |
c61ab18c CY |
583 | When you decide that there is a bug, it is important to report it |
584 | and to report it in a way which is useful. What is most useful is an | |
585 | exact description of what commands you type, starting with the shell | |
586 | command to run Emacs, until the problem happens. | |
6bf7aab6 DL |
587 | |
588 | The most important principle in reporting a bug is to report | |
c61ab18c CY |
589 | @emph{facts}. Hypotheses and verbal descriptions are no substitute |
590 | for the detailed raw data. Reporting the facts is straightforward, | |
591 | but many people strain to posit explanations and report them instead | |
592 | of the facts. If the explanations are based on guesses about how | |
593 | Emacs is implemented, they will be useless; meanwhile, lacking the | |
594 | facts, we will have no real information about the bug. If you want to | |
595 | actually @emph{debug} the problem, and report explanations that are | |
596 | more than guesses, that is useful---but please include the raw facts | |
597 | as well. | |
6bf7aab6 DL |
598 | |
599 | For example, suppose that you type @kbd{C-x C-f /glorp/baz.ugh | |
21c80203 | 600 | @key{RET}}, visiting a file which (you know) happens to be rather |
c61ab18c CY |
601 | large, and Emacs displays @samp{I feel pretty today}. The bug report |
602 | would need to provide all that information. You should not assume | |
603 | that the problem is due to the size of the file and say, ``I visited a | |
604 | large file, and Emacs displayed @samp{I feel pretty today}.'' This is | |
16152b76 | 605 | what we mean by ``guessing explanations''. The problem might be due |
c61ab18c CY |
606 | to the fact that there is a @samp{z} in the file name. If this is so, |
607 | then when we got your report, we would try out the problem with some | |
16152b76 | 608 | ``large file'', probably with no @samp{z} in its name, and not see any |
c61ab18c | 609 | problem. There is no way we could guess that we should try visiting a |
6bf7aab6 DL |
610 | file with a @samp{z} in its name. |
611 | ||
c61ab18c CY |
612 | You should not even say ``visit a file'' instead of @kbd{C-x C-f}. |
613 | Similarly, rather than saying ``if I have three characters on the | |
16152b76 | 614 | line'', say ``after I type @kbd{@key{RET} A B C @key{RET} C-p}'', if |
c61ab18c CY |
615 | that is the way you entered the text. |
616 | ||
617 | If possible, try quickly to reproduce the bug by invoking Emacs with | |
618 | @command{emacs -Q} (so that Emacs starts with no initial | |
619 | customizations; @pxref{Initial Options}), and repeating the steps that | |
620 | you took to trigger the bug. If you can reproduce the bug this way, | |
621 | that rules out bugs in your personal customizations. Then your bug | |
622 | report should begin by stating that you started Emacs with | |
623 | @command{emacs -Q}, followed by the exact sequence of steps for | |
624 | reproducing the bug. If possible, inform us of the exact contents of | |
625 | any file that is needed to reproduce the bug. | |
626 | ||
627 | Some bugs are not reproducible from @command{emacs -Q}; some are not | |
628 | easily reproducible at all. In that case, you should report what you | |
629 | have---but, as before, please stick to the raw facts about what you | |
630 | did to trigger the bug the first time. | |
6bf7aab6 DL |
631 | |
632 | @node Checklist | |
633 | @subsection Checklist for Bug Reports | |
634 | ||
635 | @cindex reporting bugs | |
63e1eaa1 GM |
636 | |
637 | Before reporting a bug, first try to see if the problem has already | |
638 | been reported (@pxref{Known Problems}). | |
639 | ||
640 | If you are able to, try the latest release of Emacs to see if the | |
641 | problem has already been fixed. Even better is to try the latest | |
642 | development version. We recognize that this is not easy for some | |
643 | people, so do not feel that you absolutely must do this before making | |
644 | a report. | |
6bf7aab6 | 645 | |
6bf7aab6 | 646 | @findex report-emacs-bug |
63e1eaa1 GM |
647 | The best way to write a bug report for Emacs is to use the command |
648 | @kbd{M-x report-emacs-bug}. This sets up a mail buffer | |
649 | (@pxref{Sending Mail}) and automatically inserts @emph{some} of the | |
650 | essential information. However, it cannot supply all the necessary | |
651 | information; you should still read and follow the guidelines below, so | |
652 | you can enter the other crucial information by hand before you send | |
653 | the message. You may feel that some of the information inserted by | |
654 | @kbd{M-x report-emacs-bug} is not relevant, but unless you are | |
655 | absolutely sure it is best to leave it, so that the developers can | |
656 | decide for themselves. | |
657 | ||
658 | When you have finished writing your report, type @kbd{C-c C-c} and it | |
659 | will be sent to the Emacs maintainers at @email{bug-gnu-emacs@@gnu.org}. | |
660 | (If you want to suggest an improvement or new feature, use the same | |
661 | address.) If you cannot send mail from inside Emacs, you can copy the | |
91af9d2e GM |
662 | text of your report to your normal mail client (if your system |
663 | supports it, you can type @kbd{C-c m} to have Emacs do this for you) | |
664 | and send it to that address. Or you can simply send an email to that | |
665 | address describing the problem. | |
63e1eaa1 GM |
666 | |
667 | Your report will be sent to the @samp{bug-gnu-emacs} mailing list, and | |
c61ab18c | 668 | stored in the GNU Bug Tracker at @url{http://debbugs.gnu.org}. Please |
63e1eaa1 GM |
669 | include a valid reply email address, in case we need to ask you for |
670 | more information about your report. Submissions are moderated, so | |
671 | there may be a delay before your report appears. | |
672 | ||
c61ab18c CY |
673 | You do not need to know how the Gnu Bug Tracker works in order to |
674 | report a bug, but if you want to, you can read the tracker's online | |
675 | documentation to see the various features you can use. | |
63e1eaa1 GM |
676 | |
677 | All mail sent to the @samp{bug-gnu-emacs} mailing list is also | |
ffda048b | 678 | gatewayed to the @samp{gnu.emacs.bug} newsgroup. The reverse is also |
da3930f3 GM |
679 | true, but we ask you not to post bug reports (or replies) via the |
680 | newsgroup. It can make it much harder to contact you if we need to ask | |
681 | for more information, and it does not integrate well with the bug | |
682 | tracker. | |
63e1eaa1 GM |
683 | |
684 | If your data is more than 500,000 bytes, please don't include it | |
685 | directly in the bug report; instead, offer to send it on request, or | |
686 | make it available by ftp and say where. | |
6bf7aab6 DL |
687 | |
688 | To enable maintainers to investigate a bug, your report | |
689 | should include all these things: | |
690 | ||
691 | @itemize @bullet | |
692 | @item | |
63e1eaa1 GM |
693 | The version number of Emacs. Without this, we won't know whether there is any |
694 | point in looking for the bug in the current version of GNU Emacs. | |
6bf7aab6 | 695 | |
63e1eaa1 GM |
696 | @kbd{M-x report-emacs-bug} includes this information automatically, |
697 | but if you are not using that command for your report you can get the | |
698 | version number by typing @kbd{M-x emacs-version @key{RET}}. If that | |
699 | command does not work, you probably have something other than GNU | |
700 | Emacs, so you will have to report the bug somewhere else. | |
6bf7aab6 DL |
701 | |
702 | @item | |
703 | The type of machine you are using, and the operating system name and | |
63e1eaa1 GM |
704 | version number (again, automatically included by @kbd{M-x |
705 | report-emacs-bug}). @kbd{M-x emacs-version @key{RET}} provides this | |
1c64e6ed | 706 | information too. Copy its output from the @file{*Messages*} buffer, |
63e1eaa1 | 707 | so that you get it all and get it accurately. |
6bf7aab6 DL |
708 | |
709 | @item | |
710 | The operands given to the @code{configure} command when Emacs was | |
63e1eaa1 | 711 | installed (automatically included by @kbd{M-x report-emacs-bug}). |
6bf7aab6 DL |
712 | |
713 | @item | |
714 | A complete list of any modifications you have made to the Emacs source. | |
715 | (We may not have time to investigate the bug unless it happens in an | |
716 | unmodified Emacs. But if you've made modifications and you don't tell | |
717 | us, you are sending us on a wild goose chase.) | |
718 | ||
719 | Be precise about these changes. A description in English is not | |
720 | enough---send a context diff for them. | |
721 | ||
722 | Adding files of your own, or porting to another machine, is a | |
723 | modification of the source. | |
724 | ||
725 | @item | |
726 | Details of any other deviations from the standard procedure for installing | |
727 | GNU Emacs. | |
728 | ||
729 | @item | |
730 | The complete text of any files needed to reproduce the bug. | |
731 | ||
732 | If you can tell us a way to cause the problem without visiting any files, | |
733 | please do so. This makes it much easier to debug. If you do need files, | |
734 | make sure you arrange for us to see their exact contents. For example, it | |
21c80203 | 735 | can matter whether there are spaces at the ends of lines, or a |
6bf7aab6 DL |
736 | newline after the last line in the buffer (nothing ought to care whether |
737 | the last line is terminated, but try telling the bugs that). | |
738 | ||
739 | @item | |
c61ab18c CY |
740 | The precise commands we need to type to reproduce the bug. If at all |
741 | possible, give a full recipe for an Emacs started with the @samp{-Q} | |
742 | option (@pxref{Initial Options}). This bypasses your personal | |
743 | customizations. | |
6bf7aab6 DL |
744 | |
745 | @findex open-dribble-file | |
746 | @cindex dribble file | |
34a41968 | 747 | @cindex logging keystrokes |
63e1eaa1 | 748 | One way to record the input to Emacs precisely is to write a dribble |
fb23ecc2 LMI |
749 | file. To start the file, use the @kbd{M-x open-dribble-file |
750 | @key{RET}} command. From then on, Emacs copies all your input to the | |
6bf7aab6 DL |
751 | specified dribble file until the Emacs process is killed. |
752 | ||
753 | @item | |
754 | @findex open-termscript | |
755 | @cindex termscript file | |
60a96371 | 756 | @cindex @env{TERM} environment variable |
6bf7aab6 | 757 | For possible display bugs, the terminal type (the value of environment |
60a96371 | 758 | variable @env{TERM}), the complete termcap entry for the terminal from |
6bf7aab6 DL |
759 | @file{/etc/termcap} (since that file is not identical on all machines), |
760 | and the output that Emacs actually sent to the terminal. | |
761 | ||
762 | The way to collect the terminal output is to execute the Lisp expression | |
763 | ||
764 | @example | |
765 | (open-termscript "~/termscript") | |
766 | @end example | |
767 | ||
768 | @noindent | |
1c64e6ed | 769 | using @kbd{M-:} or from the @file{*scratch*} buffer just after |
6bf7aab6 DL |
770 | starting Emacs. From then on, Emacs copies all terminal output to the |
771 | specified termscript file as well, until the Emacs process is killed. | |
772 | If the problem happens when Emacs starts up, put this expression into | |
c61ab18c CY |
773 | your Emacs initialization file so that the termscript file will be |
774 | open when Emacs displays the screen for the first time. | |
6bf7aab6 DL |
775 | |
776 | Be warned: it is often difficult, and sometimes impossible, to fix a | |
777 | terminal-dependent bug without access to a terminal of the type that | |
21c80203 | 778 | stimulates the bug. |
6bf7aab6 | 779 | |
d527b615 | 780 | @item |
76dd3692 | 781 | If non-@acronym{ASCII} text or internationalization is relevant, the locale that |
e6830948 | 782 | was current when you started Emacs. On GNU/Linux and Unix systems, or |
892c6176 | 783 | if you use a Posix-style shell such as Bash, you can use this shell |
e6830948 | 784 | command to view the relevant values: |
d527b615 | 785 | |
520e10f5 | 786 | @smallexample |
d881eade | 787 | echo LC_ALL=$LC_ALL LC_COLLATE=$LC_COLLATE LC_CTYPE=$LC_CTYPE \ |
b72d30a7 | 788 | LC_MESSAGES=$LC_MESSAGES LC_TIME=$LC_TIME LANG=$LANG |
520e10f5 | 789 | @end smallexample |
d527b615 | 790 | |
2cd8b7f6 EZ |
791 | Alternatively, use the @command{locale} command, if your system has it, |
792 | to display your locale settings. | |
793 | ||
794 | You can use the @kbd{M-!} command to execute these commands from | |
1c64e6ed | 795 | Emacs, and then copy the output from the @file{*Messages*} buffer into |
c1cb46c7 | 796 | the bug report. Alternatively, @kbd{M-x getenv @key{RET} LC_ALL |
1ba2ce68 | 797 | @key{RET}} will display the value of @code{LC_ALL} in the echo area, and |
1c64e6ed | 798 | you can copy its output from the @file{*Messages*} buffer. |
d527b615 | 799 | |
6bf7aab6 DL |
800 | @item |
801 | A description of what behavior you observe that you believe is | |
16152b76 | 802 | incorrect. For example, ``The Emacs process gets a fatal signal'', or, |
6bf7aab6 DL |
803 | ``The resulting text is as follows, which I think is wrong.'' |
804 | ||
805 | Of course, if the bug is that Emacs gets a fatal signal, then one can't | |
806 | miss it. But if the bug is incorrect text, the maintainer might fail to | |
807 | notice what is wrong. Why leave it to chance? | |
808 | ||
809 | Even if the problem you experience is a fatal signal, you should still | |
810 | say so explicitly. Suppose something strange is going on, such as, your | |
811 | copy of the source is out of sync, or you have encountered a bug in the | |
812 | C library on your system. (This has happened!) Your copy might crash | |
813 | and the copy here might not. If you @emph{said} to expect a crash, then | |
814 | when Emacs here fails to crash, we would know that the bug was not | |
815 | happening. If you don't say to expect a crash, then we would not know | |
816 | whether the bug was happening---we would not be able to draw any | |
817 | conclusion from our observations. | |
818 | ||
ab26d9a1 RS |
819 | @item |
820 | If the bug is that the Emacs Manual or the Emacs Lisp Reference Manual | |
821 | fails to describe the actual behavior of Emacs, or that the text is | |
822 | confusing, copy in the text from the online manual which you think is | |
823 | at fault. If the section is small, just the section name is enough. | |
824 | ||
6bf7aab6 DL |
825 | @item |
826 | If the manifestation of the bug is an Emacs error message, it is | |
827 | important to report the precise text of the error message, and a | |
828 | backtrace showing how the Lisp program in Emacs arrived at the error. | |
829 | ||
830 | To get the error message text accurately, copy it from the | |
1c64e6ed | 831 | @file{*Messages*} buffer into the bug report. Copy all of it, not just |
6bf7aab6 DL |
832 | part. |
833 | ||
50556a88 | 834 | @findex toggle-debug-on-error |
68b34f99 | 835 | @pindex Edebug |
50556a88 RS |
836 | To make a backtrace for the error, use @kbd{M-x toggle-debug-on-error} |
837 | before the error happens (that is to say, you must give that command | |
21c80203 | 838 | and then make the bug happen). This causes the error to start the Lisp |
50556a88 RS |
839 | debugger, which shows you a backtrace. Copy the text of the |
840 | debugger's backtrace into the bug report. @xref{Debugger,, The Lisp | |
841 | Debugger, elisp, the Emacs Lisp Reference Manual}, for information on | |
68b34f99 | 842 | debugging Emacs Lisp programs with the Edebug package. |
6bf7aab6 DL |
843 | |
844 | This use of the debugger is possible only if you know how to make the | |
845 | bug happen again. If you can't make it happen again, at least copy | |
846 | the whole error message. | |
847 | ||
88ab4340 EZ |
848 | @vindex debug-on-quit |
849 | If Emacs appears to be stuck in an infinite loop or in a very long | |
850 | operation, typing @kbd{C-g} with the variable @code{debug-on-quit} | |
851 | non-@code{nil} will start the Lisp debugger and show a backtrace. | |
852 | This backtrace is useful for debugging such long loops, so if you can | |
853 | produce it, copy it into the bug report. | |
854 | ||
649f602c GM |
855 | @vindex debug-on-event |
856 | If you cannot get Emacs to respond to @kbd{C-g} (e.g., because | |
857 | @code{inhibit-quit} is set), then you can try sending the signal | |
858 | specified by @code{debug-on-event} (default SIGUSR2) from outside | |
859 | Emacs to cause it to enter the debugger. | |
860 | ||
6bf7aab6 DL |
861 | @item |
862 | Check whether any programs you have loaded into the Lisp world, | |
c61ab18c CY |
863 | including your initialization file, set any variables that may affect |
864 | the functioning of Emacs. Also, see whether the problem happens in a | |
865 | freshly started Emacs without loading your initialization file (start | |
866 | Emacs with the @code{-Q} switch to prevent loading the init files). | |
867 | If the problem does @emph{not} occur then, you must report the precise | |
868 | contents of any programs that you must load into the Lisp world in | |
869 | order to cause the problem to occur. | |
6bf7aab6 DL |
870 | |
871 | @item | |
872 | If the problem does depend on an init file or other Lisp programs that | |
873 | are not part of the standard Emacs system, then you should make sure it | |
874 | is not a bug in those programs by complaining to their maintainers | |
875 | first. After they verify that they are using Emacs in a way that is | |
876 | supposed to work, they should report the bug. | |
877 | ||
878 | @item | |
879 | If you wish to mention something in the GNU Emacs source, show the line | |
880 | of code with a few lines of context. Don't just give a line number. | |
881 | ||
882 | The line numbers in the development sources don't match those in your | |
883 | sources. It would take extra work for the maintainers to determine what | |
884 | code is in your version at a given line number, and we could not be | |
885 | certain. | |
886 | ||
887 | @item | |
888 | Additional information from a C debugger such as GDB might enable | |
889 | someone to find a problem on a machine which he does not have available. | |
890 | If you don't know how to use GDB, please read the GDB manual---it is not | |
891 | very long, and using GDB is easy. You can find the GDB distribution, | |
892 | including the GDB manual in online form, in most of the same places you | |
893 | can find the Emacs distribution. To run Emacs under GDB, you should | |
894 | switch to the @file{src} subdirectory in which Emacs was compiled, then | |
895 | do @samp{gdb emacs}. It is important for the directory @file{src} to be | |
896 | current so that GDB will read the @file{.gdbinit} file in this | |
897 | directory. | |
898 | ||
899 | However, you need to think when you collect the additional information | |
900 | if you want it to show what causes the bug. | |
901 | ||
902 | @cindex backtrace for bug reports | |
903 | For example, many people send just a backtrace, but that is not very | |
904 | useful by itself. A simple backtrace with arguments often conveys | |
905 | little about what is happening inside GNU Emacs, because most of the | |
906 | arguments listed in the backtrace are pointers to Lisp objects. The | |
907 | numeric values of these pointers have no significance whatever; all that | |
908 | matters is the contents of the objects they point to (and most of the | |
909 | contents are themselves pointers). | |
910 | ||
911 | @findex debug_print | |
912 | To provide useful information, you need to show the values of Lisp | |
913 | objects in Lisp notation. Do this for each variable which is a Lisp | |
914 | object, in several stack frames near the bottom of the stack. Look at | |
915 | the source to see which variables are Lisp objects, because the debugger | |
916 | thinks of them as integers. | |
917 | ||
918 | To show a variable's value in Lisp syntax, first print its value, then | |
919 | use the user-defined GDB command @code{pr} to print the Lisp object in | |
920 | Lisp syntax. (If you must use another debugger, call the function | |
921 | @code{debug_print} with the object as an argument.) The @code{pr} | |
922 | command is defined by the file @file{.gdbinit}, and it works only if you | |
923 | are debugging a running process (not with a core dump). | |
924 | ||
925 | To make Lisp errors stop Emacs and return to GDB, put a breakpoint at | |
926 | @code{Fsignal}. | |
927 | ||
8389e1e2 | 928 | For a short listing of Lisp functions running, type the GDB |
177c0ea7 | 929 | command @code{xbacktrace}. |
8389e1e2 | 930 | |
6bf7aab6 DL |
931 | The file @file{.gdbinit} defines several other commands that are useful |
932 | for examining the data types and contents of Lisp objects. Their names | |
933 | begin with @samp{x}. These commands work at a lower level than | |
934 | @code{pr}, and are less convenient, but they may work even when | |
935 | @code{pr} does not, such as when debugging a core dump or when Emacs has | |
936 | had a fatal signal. | |
937 | ||
878c3c90 EZ |
938 | @cindex debugging Emacs, tricks and techniques |
939 | More detailed advice and other useful techniques for debugging Emacs | |
940 | are available in the file @file{etc/DEBUG} in the Emacs distribution. | |
941 | That file also includes instructions for investigating problems | |
942 | whereby Emacs stops responding (many people assume that Emacs is | |
16152b76 | 943 | ``hung'', whereas in fact it might be in an infinite loop). |
878c3c90 | 944 | |
ac41be63 RS |
945 | To find the file @file{etc/DEBUG} in your Emacs installation, use the |
946 | directory name stored in the variable @code{data-directory}. | |
6bf7aab6 DL |
947 | @end itemize |
948 | ||
949 | Here are some things that are not necessary in a bug report: | |
950 | ||
951 | @itemize @bullet | |
952 | @item | |
953 | A description of the envelope of the bug---this is not necessary for a | |
954 | reproducible bug. | |
955 | ||
956 | Often people who encounter a bug spend a lot of time investigating | |
957 | which changes to the input file will make the bug go away and which | |
958 | changes will not affect it. | |
959 | ||
960 | This is often time-consuming and not very useful, because the way we | |
ac41be63 RS |
961 | will find the bug is by running a single example under the debugger |
962 | with breakpoints, not by pure deduction from a series of examples. | |
963 | You might as well save time by not searching for additional examples. | |
964 | It is better to send the bug report right away, go back to editing, | |
965 | and find another bug to report. | |
6bf7aab6 DL |
966 | |
967 | Of course, if you can find a simpler example to report @emph{instead} of | |
968 | the original one, that is a convenience. Errors in the output will be | |
969 | easier to spot, running under the debugger will take less time, etc. | |
970 | ||
971 | However, simplification is not vital; if you can't do this or don't have | |
972 | time to try, please report the bug with your original test case. | |
973 | ||
c6fcb73d RS |
974 | @item |
975 | A core dump file. | |
976 | ||
977 | Debugging the core dump might be useful, but it can only be done on | |
978 | your machine, with your Emacs executable. Therefore, sending the core | |
979 | dump file to the Emacs maintainers won't be useful. Above all, don't | |
980 | include the core file in an email bug report! Such a large message | |
981 | can be extremely inconvenient. | |
982 | ||
6bf7aab6 DL |
983 | @item |
984 | A system-call trace of Emacs execution. | |
985 | ||
986 | System-call traces are very useful for certain special kinds of | |
987 | debugging, but in most cases they give little useful information. It is | |
988 | therefore strange that many people seem to think that @emph{the} way to | |
989 | report information about a crash is to send a system-call trace. Perhaps | |
990 | this is a habit formed from experience debugging programs that don't | |
991 | have source code or debugging symbols. | |
992 | ||
993 | In most programs, a backtrace is normally far, far more informative than | |
994 | a system-call trace. Even in Emacs, a simple backtrace is generally | |
995 | more informative, though to give full information you should supplement | |
996 | the backtrace by displaying variable values and printing them as Lisp | |
997 | objects with @code{pr} (see above). | |
998 | ||
999 | @item | |
1000 | A patch for the bug. | |
1001 | ||
1002 | A patch for the bug is useful if it is a good one. But don't omit the | |
1003 | other information that a bug report needs, such as the test case, on the | |
1004 | assumption that a patch is sufficient. We might see problems with your | |
1005 | patch and decide to fix the problem another way, or we might not | |
1006 | understand it at all. And if we can't understand what bug you are | |
1007 | trying to fix, or why your patch should be an improvement, we mustn't | |
1008 | install it. | |
1009 | ||
62fe831c | 1010 | @ifnottex |
6bf7aab6 DL |
1011 | @xref{Sending Patches}, for guidelines on how to make it easy for us to |
1012 | understand and install your patches. | |
62fe831c | 1013 | @end ifnottex |
6bf7aab6 DL |
1014 | |
1015 | @item | |
1016 | A guess about what the bug is or what it depends on. | |
1017 | ||
1018 | Such guesses are usually wrong. Even experts can't guess right about | |
1019 | such things without first using the debugger to find the facts. | |
1020 | @end itemize | |
1021 | ||
1022 | @node Sending Patches | |
1023 | @subsection Sending Patches for GNU Emacs | |
1024 | ||
1025 | @cindex sending patches for GNU Emacs | |
1026 | @cindex patches, sending | |
1027 | If you would like to write bug fixes or improvements for GNU Emacs, | |
1028 | that is very helpful. When you send your changes, please follow these | |
1029 | guidelines to make it easy for the maintainers to use them. If you | |
1030 | don't follow these guidelines, your information might still be useful, | |
1031 | but using it will take extra work. Maintaining GNU Emacs is a lot of | |
1032 | work in the best of circumstances, and we can't keep up unless you do | |
1033 | your best to help. | |
1034 | ||
1035 | @itemize @bullet | |
1036 | @item | |
1037 | Send an explanation with your changes of what problem they fix or what | |
63e1eaa1 GM |
1038 | improvement they bring about. For a fix for an existing bug, it is |
1039 | best to reply to the relevant discussion on the @samp{bug-gnu-emacs} | |
c61ab18c CY |
1040 | list, or the bug entry in the GNU Bug Tracker at |
1041 | @url{http://debbugs.gnu.org}. Explain why your change fixes the bug. | |
6bf7aab6 DL |
1042 | |
1043 | @item | |
1044 | Always include a proper bug report for the problem you think you have | |
1045 | fixed. We need to convince ourselves that the change is right before | |
1046 | installing it. Even if it is correct, we might have trouble | |
1047 | understanding it if we don't have a way to reproduce the problem. | |
1048 | ||
1049 | @item | |
1050 | Include all the comments that are appropriate to help people reading the | |
1051 | source in the future understand why this change was needed. | |
1052 | ||
1053 | @item | |
1054 | Don't mix together changes made for different reasons. | |
1055 | Send them @emph{individually}. | |
1056 | ||
1057 | If you make two changes for separate reasons, then we might not want to | |
1058 | install them both. We might want to install just one. If you send them | |
1059 | all jumbled together in a single set of diffs, we have to do extra work | |
1060 | to disentangle them---to figure out which parts of the change serve | |
1061 | which purpose. If we don't have time for this, we might have to ignore | |
1062 | your changes entirely. | |
1063 | ||
1064 | If you send each change as soon as you have written it, with its own | |
1065 | explanation, then two changes never get tangled up, and we can consider | |
1066 | each one properly without any extra work to disentangle them. | |
1067 | ||
1068 | @item | |
1069 | Send each change as soon as that change is finished. Sometimes people | |
1070 | think they are helping us by accumulating many changes to send them all | |
1071 | together. As explained above, this is absolutely the worst thing you | |
1072 | could do. | |
1073 | ||
1074 | Since you should send each change separately, you might as well send it | |
1075 | right away. That gives us the option of installing it immediately if it | |
1076 | is important. | |
1077 | ||
1078 | @item | |
1079 | Use @samp{diff -c} to make your diffs. Diffs without context are hard | |
1080 | to install reliably. More than that, they are hard to study; we must | |
1081 | always study a patch to decide whether we want to install it. Unidiff | |
1082 | format is better than contextless diffs, but not as easy to read as | |
1083 | @samp{-c} format. | |
1084 | ||
1085 | If you have GNU diff, use @samp{diff -c -F'^[_a-zA-Z0-9$]+ *('} when | |
1086 | making diffs of C code. This shows the name of the function that each | |
1087 | change occurs in. | |
1088 | ||
1089 | @item | |
1090 | Avoid any ambiguity as to which is the old version and which is the new. | |
1091 | Please make the old version the first argument to diff, and the new | |
1092 | version the second argument. And please give one version or the other a | |
1093 | name that indicates whether it is the old version or your new changed | |
1094 | one. | |
1095 | ||
1096 | @item | |
1097 | Write the change log entries for your changes. This is both to save us | |
1098 | the extra work of writing them, and to help explain your changes so we | |
1099 | can understand them. | |
1100 | ||
1101 | The purpose of the change log is to show people where to find what was | |
1102 | changed. So you need to be specific about what functions you changed; | |
1103 | in large functions, it's often helpful to indicate where within the | |
1104 | function the change was. | |
1105 | ||
1106 | On the other hand, once you have shown people where to find the change, | |
1107 | you need not explain its purpose in the change log. Thus, if you add a | |
1108 | new function, all you need to say about it is that it is new. If you | |
1109 | feel that the purpose needs explaining, it probably does---but put the | |
1110 | explanation in comments in the code. It will be more useful there. | |
1111 | ||
21c80203 RS |
1112 | Please read the @file{ChangeLog} files in the @file{src} and |
1113 | @file{lisp} directories to see what sorts of information to put in, | |
1114 | and to learn the style that we use. @xref{Change Log}. | |
6bf7aab6 DL |
1115 | |
1116 | @item | |
1117 | When you write the fix, keep in mind that we can't install a change that | |
1118 | would break other systems. Please think about what effect your change | |
1119 | will have if compiled on another type of system. | |
1120 | ||
1121 | Sometimes people send fixes that @emph{might} be an improvement in | |
1122 | general---but it is hard to be sure of this. It's hard to install | |
1123 | such changes because we have to study them very carefully. Of course, | |
1124 | a good explanation of the reasoning by which you concluded the change | |
1125 | was correct can help convince us. | |
1126 | ||
1127 | The safest changes are changes to the configuration files for a | |
1128 | particular machine. These are safe because they can't create new bugs | |
1129 | on other machines. | |
1130 | ||
1131 | Please help us keep up with the workload by designing the patch in a | |
1132 | form that is clearly safe to install. | |
1133 | @end itemize | |
1134 | ||
abb9615e | 1135 | @node Contributing |
6bf7aab6 | 1136 | @section Contributing to Emacs Development |
16207c0a | 1137 | @cindex contributing to Emacs |
6bf7aab6 DL |
1138 | |
1139 | If you would like to help pretest Emacs releases to assure they work | |
1140 | well, or if you would like to work on improving Emacs, please contact | |
b656e0f4 | 1141 | the maintainers at @email{emacs-devel@@gnu.org}. A pretester |
6bf7aab6 DL |
1142 | should be prepared to investigate bugs as well as report them. If you'd |
1143 | like to work on improving Emacs, please ask for suggested projects or | |
1144 | suggest your own ideas. | |
1145 | ||
1146 | If you have already written an improvement, please tell us about it. If | |
1147 | you have not yet started work, it is useful to contact | |
b656e0f4 | 1148 | @email{emacs-devel@@gnu.org} before you start; it might be |
6bf7aab6 DL |
1149 | possible to suggest ways to make your extension fit in better with the |
1150 | rest of Emacs. | |
1151 | ||
4f3bc373 | 1152 | The development version of Emacs can be downloaded from the |
7e17c3a2 | 1153 | repository where it is actively maintained by a group of developers. |
21c80203 RS |
1154 | See the Emacs project page |
1155 | @url{http://savannah.gnu.org/projects/emacs/} for details. | |
b656e0f4 | 1156 | |
16207c0a GM |
1157 | For more information on how to contribute, see the @file{etc/CONTRIBUTE} |
1158 | file in the Emacs distribution. | |
1159 | ||
abb9615e | 1160 | @node Service |
6bf7aab6 DL |
1161 | @section How To Get Help with GNU Emacs |
1162 | ||
1163 | If you need help installing, using or changing GNU Emacs, there are two | |
1164 | ways to find it: | |
1165 | ||
1166 | @itemize @bullet | |
1167 | @item | |
1168 | Send a message to the mailing list | |
60a96371 | 1169 | @email{help-gnu-emacs@@gnu.org}, or post your request on |
6bf7aab6 DL |
1170 | newsgroup @code{gnu.emacs.help}. (This mailing list and newsgroup |
1171 | interconnect, so it does not matter which one you use.) | |
1172 | ||
1173 | @item | |
1174 | Look in the service directory for someone who might help you for a fee. | |
1175 | The service directory is found in the file named @file{etc/SERVICE} in the | |
1176 | Emacs distribution. | |
1177 | @end itemize | |
ab5796a9 | 1178 | |
0d6e9754 LT |
1179 | @ifnottex |
1180 | @lowersections | |
1181 | @end ifnottex |