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6bf7aab6 | 1 | @c This is part of the Emacs manual. |
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2 | @c Copyright (C) 1985-1987, 1993-1995, 1997, 2001-2013 Free Software |
3 | @c Foundation, Inc. | |
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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 |
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19 | @section Quitting and Aborting |
20 | @cindex quitting | |
21 | ||
22 | @table @kbd | |
23 | @item C-g | |
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24 | @itemx C-@key{BREAK} @r{(MS-DOS only)} |
25 | Quit: cancel running or partially typed command. | |
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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. | |
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33 | @item C-/ |
34 | @itemx C-x u | |
35 | @itemx C-_ | |
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36 | Cancel a previously made change in the buffer contents (@code{undo}). |
37 | @end table | |
38 | ||
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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 | |
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43 | and cancels the command that invoked the recursive edit |
44 | (@pxref{Recursive Edit}). | |
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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 |
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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 |
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58 | successive @kbd{C-g} characters to get out of a search. |
59 | @xref{Incremental Search}, for details. | |
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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 | |
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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 |
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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 | |
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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}. | |
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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 |
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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. | |
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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. | |
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119 | |
120 | @findex top-level | |
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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 | |
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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 |
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133 | finished executing. @xref{Undo}, for more information about the undo |
134 | facility. | |
6bf7aab6 | 135 | |
abb9615e | 136 | @node Lossage |
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137 | @section Dealing with Emacs Trouble |
138 | ||
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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. | |
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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, |
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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 |
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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 | |
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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 |
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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 |
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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 | |
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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: |
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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 | |
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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}. | |
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225 | |
226 | @node Screen Garbled | |
227 | @subsection Garbage on the Screen | |
228 | ||
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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 | |
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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 | |
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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 | ||
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257 | @node Memory Full |
258 | @subsection Running out of Memory | |
259 | @cindex memory full | |
260 | @cindex out of memory | |
261 | ||
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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. | |
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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 |
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279 | itself, and the reserve supply may not be enough. |
280 | ||
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281 | @node Crashing |
282 | @subsection When Emacs Crashes | |
283 | ||
4c1f6a5b | 284 | @cindex crash report |
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285 | @cindex backtrace |
286 | @cindex @file{emacs_backtrace.txt} file, MS-Windows | |
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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. | |
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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: | |
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325 | |
326 | @example | |
327 | sed -n 's/.*\[\(.*\)]$/\1/p' @var{backtrace} | | |
7f102272 | 328 | addr2line -C -f -i -p -e @var{bindir}/@var{emacs-binary} |
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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 | |
ee271528 PE |
336 | systems and @file{emacs.exe} on MS-Windows and MS-DOS. Omit the |
337 | @option{-p} option if your version of @command{addr2line} is too old | |
338 | to have it. | |
cf29dd84 | 339 | |
4c1f6a5b | 340 | @cindex core dump |
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341 | Optionally, Emacs can generate a @dfn{core dump} when it crashes, on |
342 | systems that support core files. A core dump is a file containing | |
343 | voluminous data about the state of the program prior to the crash, | |
d8ad4d3f | 344 | usually examined by loading it into a debugger such as GDB@. On many |
a33da68b EZ |
345 | platforms, core dumps are disabled by default, and you must explicitly |
346 | enable them by running the shell command @samp{ulimit -c unlimited} | |
d8ad4d3f | 347 | (e.g., in your shell startup script). |
4c1f6a5b | 348 | |
6bf7aab6 DL |
349 | @node After a Crash |
350 | @subsection Recovery After a Crash | |
351 | ||
352 | If Emacs or the computer crashes, you can recover the files you were | |
353 | editing at the time of the crash from their auto-save files. To do | |
354 | this, start Emacs again and type the command @kbd{M-x recover-session}. | |
355 | ||
356 | This command initially displays a buffer which lists interrupted | |
357 | session files, each with its date. You must choose which session to | |
358 | recover from. Typically the one you want is the most recent one. Move | |
359 | point to the one you choose, and type @kbd{C-c C-c}. | |
360 | ||
21c80203 RS |
361 | Then @code{recover-session} considers each of the files that you |
362 | were editing during that session; for each such file, it asks whether | |
363 | to recover that file. If you answer @kbd{y} for a file, it shows the | |
364 | dates of that file and its auto-save file, then asks once again | |
365 | whether to recover that file. For the second question, you must | |
366 | confirm with @kbd{yes}. If you do, Emacs visits the file but gets the | |
367 | text from the auto-save file. | |
6bf7aab6 DL |
368 | |
369 | When @code{recover-session} is done, the files you've chosen to | |
370 | recover are present in Emacs buffers. You should then save them. Only | |
371 | this---saving them---updates the files themselves. | |
372 | ||
615cdecf NF |
373 | As a last resort, if you had buffers with content which were not |
374 | associated with any files, or if the autosave was not recent enough to | |
375 | have recorded important changes, you can use the | |
16540869 NF |
376 | @file{etc/emacs-buffer.gdb} script with GDB (the GNU Debugger) to |
377 | retrieve them from a core dump--provided that a core dump was saved, | |
378 | and that the Emacs executable was not stripped of its debugging | |
379 | symbols. | |
380 | ||
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381 | As soon as you get the core dump, rename it to another name such as |
382 | @file{core.emacs}, so that another crash won't overwrite it. | |
383 | ||
5cf98ab4 | 384 | To use this script, run @code{gdb} with the file name of your Emacs |
1df7defd | 385 | executable and the file name of the core dump, e.g., @samp{gdb |
16540869 NF |
386 | /usr/bin/emacs core.emacs}. At the @code{(gdb)} prompt, load the |
387 | recovery script: @samp{source /usr/src/emacs/etc/emacs-buffer.gdb}. | |
5cf98ab4 RS |
388 | Then type the command @code{ybuffer-list} to see which buffers are |
389 | available. For each buffer, it lists a buffer number. To save a | |
390 | buffer, use @code{ysave-buffer}; you specify the buffer number, and | |
391 | the file name to write that buffer into. You should use a file name | |
392 | which does not already exist; if the file does exist, the script does | |
a5cecf92 | 393 | not make a backup of its old contents. |
615cdecf | 394 | |
6bf7aab6 DL |
395 | @node Emergency Escape |
396 | @subsection Emergency Escape | |
397 | ||
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398 | On text terminals, the @dfn{emergency escape} feature suspends Emacs |
399 | immediately if you type @kbd{C-g} a second time before Emacs can | |
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400 | actually respond to the first one by quitting. This is so you can |
401 | always get out of GNU Emacs no matter how badly it might be hung. | |
402 | When things are working properly, Emacs recognizes and handles the | |
403 | first @kbd{C-g} so fast that the second one won't trigger emergency | |
404 | escape. However, if some problem prevents Emacs from handling the | |
405 | first @kbd{C-g} properly, then the second one will get you back to the | |
406 | shell. | |
6bf7aab6 | 407 | |
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408 | When you resume Emacs after a suspension caused by emergency escape, |
409 | it asks two questions before going back to what it had been doing: | |
6bf7aab6 DL |
410 | |
411 | @example | |
412 | Auto-save? (y or n) | |
413 | Abort (and dump core)? (y or n) | |
414 | @end example | |
415 | ||
416 | @noindent | |
417 | Answer each one with @kbd{y} or @kbd{n} followed by @key{RET}. | |
418 | ||
21c80203 RS |
419 | Saying @kbd{y} to @samp{Auto-save?} causes immediate auto-saving of |
420 | all modified buffers in which auto-saving is enabled. Saying @kbd{n} | |
421 | skips this. | |
422 | ||
423 | Saying @kbd{y} to @samp{Abort (and dump core)?} causes Emacs to | |
424 | crash, dumping core. This is to enable a wizard to figure out why | |
425 | Emacs was failing to quit in the first place. Execution does not | |
426 | continue after a core dump. | |
6bf7aab6 | 427 | |
21c80203 RS |
428 | If you answer this question @kbd{n}, Emacs execution resumes. With |
429 | luck, Emacs will ultimately do the requested quit. If not, each | |
430 | subsequent @kbd{C-g} invokes emergency escape again. | |
6bf7aab6 DL |
431 | |
432 | If Emacs is not really hung, just slow, you may invoke the double | |
21c80203 RS |
433 | @kbd{C-g} feature without really meaning to. Then just resume and |
434 | answer @kbd{n} to both questions, and you will get back to the former | |
435 | state. The quit you requested will happen by and by. | |
6bf7aab6 | 436 | |
58af1784 RS |
437 | Emergency escape is active only for text terminals. On graphical |
438 | displays, you can use the mouse to kill Emacs or switch to another | |
439 | program. | |
6bf7aab6 | 440 | |
21c80203 RS |
441 | On MS-DOS, you must type @kbd{C-@key{BREAK}} (twice) to cause |
442 | emergency escape---but there are cases where it won't work, when | |
443 | system call hangs or when Emacs is stuck in a tight loop in C code. | |
6bf7aab6 | 444 | |
abb9615e | 445 | @node Bugs |
6bf7aab6 DL |
446 | @section Reporting Bugs |
447 | ||
448 | @cindex bugs | |
63e1eaa1 GM |
449 | If you think you have found a bug in Emacs, please report it. We |
450 | cannot promise to fix it, or always to agree that it is a bug, but we | |
451 | certainly want to hear about it. The same applies for new features | |
452 | you would like to see added. The following sections will help you to | |
453 | construct an effective bug report. | |
9e25ea70 | 454 | |
6bf7aab6 | 455 | @menu |
63e1eaa1 | 456 | * Known Problems:: How to read about known problems and bugs. |
8838673e GM |
457 | * Criteria: Bug Criteria. Have you really found a bug? |
458 | * Understanding Bug Reporting:: How to report a bug effectively. | |
459 | * Checklist:: Steps to follow for a good bug report. | |
460 | * Sending Patches:: How to send a patch for GNU Emacs. | |
6bf7aab6 DL |
461 | @end menu |
462 | ||
63e1eaa1 GM |
463 | @node Known Problems |
464 | @subsection Reading Existing Bug Reports and Known Problems | |
465 | ||
466 | Before reporting a bug, if at all possible please check to see if it | |
467 | is already known about. Indeed, it may already have been fixed in a | |
468 | later release of Emacs, or in the development version. Here is a list | |
469 | of the main places you can read about known issues: | |
470 | ||
471 | @itemize | |
472 | @item | |
c61ab18c CY |
473 | The @file{etc/PROBLEMS} file; type @kbd{C-h C-p} to read it. This |
474 | file contains a list of particularly well-known issues that have been | |
475 | encountered in compiling, installing and running Emacs. Often, there | |
476 | are suggestions for workarounds and solutions. | |
63e1eaa1 GM |
477 | |
478 | @item | |
479 | Some additional user-level problems can be found in @ref{Bugs and | |
480 | problems, , Bugs and problems, efaq, GNU Emacs FAQ}. | |
481 | ||
c61ab18c CY |
482 | @cindex bug tracker |
483 | @item | |
484 | The GNU Bug Tracker at @url{http://debbugs.gnu.org}. Emacs bugs are | |
485 | filed in the tracker under the @samp{emacs} package. The tracker | |
486 | records information about the status of each bug, the initial bug | |
487 | report, and the follow-up messages by the bug reporter and Emacs | |
488 | developers. You can search for bugs by subject, severity, and other | |
489 | criteria. | |
490 | ||
491 | @cindex debbugs package | |
492 | Instead of browsing the bug tracker as a webpage, you can browse it | |
493 | from Emacs using the @code{debbugs} package, which can be downloaded | |
494 | via the Package Menu (@pxref{Packages}). This package provides the | |
495 | command @kbd{M-x debbugs-gnu} to list bugs, and @kbd{M-x | |
87288971 MA |
496 | debbugs-gnu-search} to search for a specific bug. User tags, applied |
497 | by the Emacs maintainers, are shown by @kbd{M-x debbugs-gnu-usertags}. | |
c61ab18c | 498 | |
63e1eaa1 GM |
499 | @item |
500 | The @samp{bug-gnu-emacs} mailing list (also available as the newsgroup | |
ae742cb5 | 501 | @samp{gnu.emacs.bug}). You can read the list archives at |
c61ab18c CY |
502 | @url{http://lists.gnu.org/mailman/listinfo/bug-gnu-emacs}. This list |
503 | works as a ``mirror'' of the Emacs bug reports and follow-up messages | |
504 | which are sent to the bug tracker. It also contains old bug reports | |
505 | from before the bug tracker was introduced (in early 2008). | |
63e1eaa1 | 506 | |
c61ab18c CY |
507 | If you like, you can subscribe to the list. Be aware that its purpose |
508 | is to provide the Emacs maintainers with information about bugs and | |
509 | feature requests, so reports may contain fairly large amounts of data; | |
510 | spectators should not complain about this. | |
63e1eaa1 GM |
511 | |
512 | @item | |
513 | The @samp{emacs-pretest-bug} mailing list. This list is no longer | |
514 | used, and is mainly of historical interest. At one time, it was used | |
515 | for bug reports in development (i.e., not yet released) versions of | |
516 | Emacs. You can read the archives for 2003 to mid 2007 at | |
c61ab18c CY |
517 | @url{http://lists.gnu.org/archive/html/emacs-pretest-bug/}. Nowadays, |
518 | it is an alias for @samp{bug-gnu-emacs}. | |
63e1eaa1 GM |
519 | |
520 | @item | |
521 | The @samp{emacs-devel} mailing list. Sometimes people report bugs to | |
522 | this mailing list. This is not the main purpose of the list, however, | |
523 | and it is much better to send bug reports to the bug list. You should | |
524 | not feel obliged to read this list before reporting a bug. | |
525 | ||
526 | @end itemize | |
527 | ||
528 | ||
6bf7aab6 DL |
529 | @node Bug Criteria |
530 | @subsection When Is There a Bug | |
531 | ||
21c80203 RS |
532 | If Emacs accesses an invalid memory location (``segmentation |
533 | fault''), or exits with an operating system error message that | |
534 | indicates a problem in the program (as opposed to something like | |
535 | ``disk full''), then it is certainly a bug. | |
6bf7aab6 | 536 | |
c61ab18c CY |
537 | If the Emacs display does not correspond properly to the contents of |
538 | the buffer, then it is a bug. But you should check that features like | |
539 | buffer narrowing (@pxref{Narrowing}), which can hide parts of the | |
540 | buffer or change how it is displayed, are not responsible. | |
6bf7aab6 DL |
541 | |
542 | Taking forever to complete a command can be a bug, but you must make | |
c61ab18c CY |
543 | sure that it is really Emacs's fault. Some commands simply take a |
544 | long time. Type @kbd{C-g} (@kbd{C-@key{BREAK}} on MS-DOS) and then | |
545 | @kbd{C-h l} to see whether the input Emacs received was what you | |
546 | intended to type; if the input was such that you @emph{know} it should | |
547 | have been processed quickly, report a bug. If you don't know whether | |
548 | the command should take a long time, find out by looking in the manual | |
549 | or by asking for assistance. | |
6bf7aab6 DL |
550 | |
551 | If a command you are familiar with causes an Emacs error message in a | |
552 | case where its usual definition ought to be reasonable, it is probably a | |
553 | bug. | |
554 | ||
c61ab18c CY |
555 | If a command does the wrong thing, that is a bug. But be sure you |
556 | know for certain what it ought to have done. If you aren't familiar | |
557 | with the command, it might actually be working right. If in doubt, | |
558 | read the command's documentation (@pxref{Name Help}). | |
6bf7aab6 | 559 | |
c61ab18c CY |
560 | A command's intended definition may not be the best possible |
561 | definition for editing with. This is a very important sort of | |
562 | problem, but it is also a matter of judgment. Also, it is easy to | |
ba3ce288 GM |
563 | come to such a conclusion out of ignorance of some of the existing |
564 | features. It is probably best not to complain about such a problem | |
565 | until you have checked the documentation in the usual ways, feel | |
566 | confident that you understand it, and know for certain that what you | |
21c80203 RS |
567 | want is not available. Ask other Emacs users, too. If you are not |
568 | sure what the command is supposed to do after a careful reading of the | |
569 | manual, check the index and glossary for any terms that may be | |
570 | unclear. | |
6bf7aab6 DL |
571 | |
572 | If after careful rereading of the manual you still do not understand | |
573 | what the command should do, that indicates a bug in the manual, which | |
574 | you should report. The manual's job is to make everything clear to | |
575 | people who are not Emacs experts---including you. It is just as | |
576 | important to report documentation bugs as program bugs. | |
577 | ||
c61ab18c | 578 | If the built-in documentation for a function or variable disagrees |
6bf7aab6 DL |
579 | with the manual, one of them must be wrong; that is a bug. |
580 | ||
581 | @node Understanding Bug Reporting | |
582 | @subsection Understanding Bug Reporting | |
583 | ||
584 | @findex emacs-version | |
c61ab18c CY |
585 | When you decide that there is a bug, it is important to report it |
586 | and to report it in a way which is useful. What is most useful is an | |
587 | exact description of what commands you type, starting with the shell | |
588 | command to run Emacs, until the problem happens. | |
6bf7aab6 DL |
589 | |
590 | The most important principle in reporting a bug is to report | |
c61ab18c CY |
591 | @emph{facts}. Hypotheses and verbal descriptions are no substitute |
592 | for the detailed raw data. Reporting the facts is straightforward, | |
593 | but many people strain to posit explanations and report them instead | |
594 | of the facts. If the explanations are based on guesses about how | |
595 | Emacs is implemented, they will be useless; meanwhile, lacking the | |
596 | facts, we will have no real information about the bug. If you want to | |
597 | actually @emph{debug} the problem, and report explanations that are | |
598 | more than guesses, that is useful---but please include the raw facts | |
599 | as well. | |
6bf7aab6 DL |
600 | |
601 | For example, suppose that you type @kbd{C-x C-f /glorp/baz.ugh | |
21c80203 | 602 | @key{RET}}, visiting a file which (you know) happens to be rather |
c61ab18c CY |
603 | large, and Emacs displays @samp{I feel pretty today}. The bug report |
604 | would need to provide all that information. You should not assume | |
605 | that the problem is due to the size of the file and say, ``I visited a | |
606 | large file, and Emacs displayed @samp{I feel pretty today}.'' This is | |
16152b76 | 607 | what we mean by ``guessing explanations''. The problem might be due |
c61ab18c CY |
608 | to the fact that there is a @samp{z} in the file name. If this is so, |
609 | then when we got your report, we would try out the problem with some | |
16152b76 | 610 | ``large file'', probably with no @samp{z} in its name, and not see any |
c61ab18c | 611 | problem. There is no way we could guess that we should try visiting a |
6bf7aab6 DL |
612 | file with a @samp{z} in its name. |
613 | ||
c61ab18c CY |
614 | You should not even say ``visit a file'' instead of @kbd{C-x C-f}. |
615 | Similarly, rather than saying ``if I have three characters on the | |
16152b76 | 616 | line'', say ``after I type @kbd{@key{RET} A B C @key{RET} C-p}'', if |
c61ab18c CY |
617 | that is the way you entered the text. |
618 | ||
619 | If possible, try quickly to reproduce the bug by invoking Emacs with | |
620 | @command{emacs -Q} (so that Emacs starts with no initial | |
621 | customizations; @pxref{Initial Options}), and repeating the steps that | |
622 | you took to trigger the bug. If you can reproduce the bug this way, | |
623 | that rules out bugs in your personal customizations. Then your bug | |
624 | report should begin by stating that you started Emacs with | |
625 | @command{emacs -Q}, followed by the exact sequence of steps for | |
626 | reproducing the bug. If possible, inform us of the exact contents of | |
627 | any file that is needed to reproduce the bug. | |
628 | ||
629 | Some bugs are not reproducible from @command{emacs -Q}; some are not | |
630 | easily reproducible at all. In that case, you should report what you | |
631 | have---but, as before, please stick to the raw facts about what you | |
632 | did to trigger the bug the first time. | |
6bf7aab6 | 633 | |
65faed73 XF |
634 | Please do not stack multiple issues into one report unless it is |
635 | really necessary. For example, jamming @code{electric-indent-mode} | |
636 | and @code{electric-pair-mode} into one report, reporting multiple key | |
637 | binding problems into one report (e.g., @kbd{C-i} doesn't indent the | |
638 | current line, @code{M-h} doesn't set mark, etc.). Please make one | |
639 | report for each individual problem. | |
640 | ||
6bf7aab6 DL |
641 | @node Checklist |
642 | @subsection Checklist for Bug Reports | |
643 | ||
644 | @cindex reporting bugs | |
63e1eaa1 GM |
645 | |
646 | Before reporting a bug, first try to see if the problem has already | |
647 | been reported (@pxref{Known Problems}). | |
648 | ||
649 | If you are able to, try the latest release of Emacs to see if the | |
650 | problem has already been fixed. Even better is to try the latest | |
651 | development version. We recognize that this is not easy for some | |
652 | people, so do not feel that you absolutely must do this before making | |
653 | a report. | |
6bf7aab6 | 654 | |
6bf7aab6 | 655 | @findex report-emacs-bug |
63e1eaa1 GM |
656 | The best way to write a bug report for Emacs is to use the command |
657 | @kbd{M-x report-emacs-bug}. This sets up a mail buffer | |
658 | (@pxref{Sending Mail}) and automatically inserts @emph{some} of the | |
659 | essential information. However, it cannot supply all the necessary | |
660 | information; you should still read and follow the guidelines below, so | |
661 | you can enter the other crucial information by hand before you send | |
662 | the message. You may feel that some of the information inserted by | |
663 | @kbd{M-x report-emacs-bug} is not relevant, but unless you are | |
664 | absolutely sure it is best to leave it, so that the developers can | |
665 | decide for themselves. | |
666 | ||
667 | When you have finished writing your report, type @kbd{C-c C-c} and it | |
2f3ac208 GM |
668 | will be sent to the Emacs maintainers at |
669 | @ifnothtml | |
670 | @email{bug-gnu-emacs@@gnu.org}. | |
671 | @end ifnothtml | |
672 | @ifhtml | |
673 | @url{http://lists.gnu.org/mailman/listinfo/bug-gnu-emacs, bug-gnu-emacs}. | |
674 | @end ifhtml | |
63e1eaa1 GM |
675 | (If you want to suggest an improvement or new feature, use the same |
676 | address.) If you cannot send mail from inside Emacs, you can copy the | |
91af9d2e | 677 | text of your report to your normal mail client (if your system |
c4af1efc | 678 | supports it, you can type @kbd{C-c M-i} to have Emacs do this for you) |
91af9d2e GM |
679 | and send it to that address. Or you can simply send an email to that |
680 | address describing the problem. | |
63e1eaa1 GM |
681 | |
682 | Your report will be sent to the @samp{bug-gnu-emacs} mailing list, and | |
c61ab18c | 683 | stored in the GNU Bug Tracker at @url{http://debbugs.gnu.org}. Please |
63e1eaa1 GM |
684 | include a valid reply email address, in case we need to ask you for |
685 | more information about your report. Submissions are moderated, so | |
686 | there may be a delay before your report appears. | |
687 | ||
c61ab18c CY |
688 | You do not need to know how the Gnu Bug Tracker works in order to |
689 | report a bug, but if you want to, you can read the tracker's online | |
690 | documentation to see the various features you can use. | |
63e1eaa1 GM |
691 | |
692 | All mail sent to the @samp{bug-gnu-emacs} mailing list is also | |
ffda048b | 693 | gatewayed to the @samp{gnu.emacs.bug} newsgroup. The reverse is also |
da3930f3 GM |
694 | true, but we ask you not to post bug reports (or replies) via the |
695 | newsgroup. It can make it much harder to contact you if we need to ask | |
696 | for more information, and it does not integrate well with the bug | |
697 | tracker. | |
63e1eaa1 GM |
698 | |
699 | If your data is more than 500,000 bytes, please don't include it | |
700 | directly in the bug report; instead, offer to send it on request, or | |
701 | make it available by ftp and say where. | |
6bf7aab6 DL |
702 | |
703 | To enable maintainers to investigate a bug, your report | |
704 | should include all these things: | |
705 | ||
706 | @itemize @bullet | |
707 | @item | |
63e1eaa1 GM |
708 | The version number of Emacs. Without this, we won't know whether there is any |
709 | point in looking for the bug in the current version of GNU Emacs. | |
6bf7aab6 | 710 | |
63e1eaa1 GM |
711 | @kbd{M-x report-emacs-bug} includes this information automatically, |
712 | but if you are not using that command for your report you can get the | |
713 | version number by typing @kbd{M-x emacs-version @key{RET}}. If that | |
714 | command does not work, you probably have something other than GNU | |
715 | Emacs, so you will have to report the bug somewhere else. | |
6bf7aab6 DL |
716 | |
717 | @item | |
718 | The type of machine you are using, and the operating system name and | |
63e1eaa1 GM |
719 | version number (again, automatically included by @kbd{M-x |
720 | report-emacs-bug}). @kbd{M-x emacs-version @key{RET}} provides this | |
1c64e6ed | 721 | information too. Copy its output from the @file{*Messages*} buffer, |
63e1eaa1 | 722 | so that you get it all and get it accurately. |
6bf7aab6 DL |
723 | |
724 | @item | |
725 | The operands given to the @code{configure} command when Emacs was | |
63e1eaa1 | 726 | installed (automatically included by @kbd{M-x report-emacs-bug}). |
6bf7aab6 DL |
727 | |
728 | @item | |
729 | A complete list of any modifications you have made to the Emacs source. | |
730 | (We may not have time to investigate the bug unless it happens in an | |
731 | unmodified Emacs. But if you've made modifications and you don't tell | |
732 | us, you are sending us on a wild goose chase.) | |
733 | ||
734 | Be precise about these changes. A description in English is not | |
735 | enough---send a context diff for them. | |
736 | ||
737 | Adding files of your own, or porting to another machine, is a | |
738 | modification of the source. | |
739 | ||
740 | @item | |
741 | Details of any other deviations from the standard procedure for installing | |
742 | GNU Emacs. | |
743 | ||
744 | @item | |
745 | The complete text of any files needed to reproduce the bug. | |
746 | ||
747 | If you can tell us a way to cause the problem without visiting any files, | |
748 | please do so. This makes it much easier to debug. If you do need files, | |
749 | make sure you arrange for us to see their exact contents. For example, it | |
21c80203 | 750 | can matter whether there are spaces at the ends of lines, or a |
6bf7aab6 DL |
751 | newline after the last line in the buffer (nothing ought to care whether |
752 | the last line is terminated, but try telling the bugs that). | |
753 | ||
754 | @item | |
c61ab18c CY |
755 | The precise commands we need to type to reproduce the bug. If at all |
756 | possible, give a full recipe for an Emacs started with the @samp{-Q} | |
757 | option (@pxref{Initial Options}). This bypasses your personal | |
758 | customizations. | |
6bf7aab6 DL |
759 | |
760 | @findex open-dribble-file | |
761 | @cindex dribble file | |
34a41968 | 762 | @cindex logging keystrokes |
63e1eaa1 | 763 | One way to record the input to Emacs precisely is to write a dribble |
fb23ecc2 LMI |
764 | file. To start the file, use the @kbd{M-x open-dribble-file |
765 | @key{RET}} command. From then on, Emacs copies all your input to the | |
6bf7aab6 DL |
766 | specified dribble file until the Emacs process is killed. |
767 | ||
768 | @item | |
769 | @findex open-termscript | |
770 | @cindex termscript file | |
60a96371 | 771 | @cindex @env{TERM} environment variable |
6bf7aab6 | 772 | For possible display bugs, the terminal type (the value of environment |
60a96371 | 773 | variable @env{TERM}), the complete termcap entry for the terminal from |
6bf7aab6 DL |
774 | @file{/etc/termcap} (since that file is not identical on all machines), |
775 | and the output that Emacs actually sent to the terminal. | |
776 | ||
777 | The way to collect the terminal output is to execute the Lisp expression | |
778 | ||
779 | @example | |
780 | (open-termscript "~/termscript") | |
781 | @end example | |
782 | ||
783 | @noindent | |
1c64e6ed | 784 | using @kbd{M-:} or from the @file{*scratch*} buffer just after |
6bf7aab6 DL |
785 | starting Emacs. From then on, Emacs copies all terminal output to the |
786 | specified termscript file as well, until the Emacs process is killed. | |
787 | If the problem happens when Emacs starts up, put this expression into | |
c61ab18c CY |
788 | your Emacs initialization file so that the termscript file will be |
789 | open when Emacs displays the screen for the first time. | |
6bf7aab6 DL |
790 | |
791 | Be warned: it is often difficult, and sometimes impossible, to fix a | |
792 | terminal-dependent bug without access to a terminal of the type that | |
21c80203 | 793 | stimulates the bug. |
6bf7aab6 | 794 | |
d527b615 | 795 | @item |
76dd3692 | 796 | If non-@acronym{ASCII} text or internationalization is relevant, the locale that |
e6830948 | 797 | was current when you started Emacs. On GNU/Linux and Unix systems, or |
892c6176 | 798 | if you use a Posix-style shell such as Bash, you can use this shell |
e6830948 | 799 | command to view the relevant values: |
d527b615 | 800 | |
520e10f5 | 801 | @smallexample |
d881eade | 802 | echo LC_ALL=$LC_ALL LC_COLLATE=$LC_COLLATE LC_CTYPE=$LC_CTYPE \ |
b72d30a7 | 803 | LC_MESSAGES=$LC_MESSAGES LC_TIME=$LC_TIME LANG=$LANG |
520e10f5 | 804 | @end smallexample |
d527b615 | 805 | |
2cd8b7f6 EZ |
806 | Alternatively, use the @command{locale} command, if your system has it, |
807 | to display your locale settings. | |
808 | ||
809 | You can use the @kbd{M-!} command to execute these commands from | |
1c64e6ed | 810 | Emacs, and then copy the output from the @file{*Messages*} buffer into |
c1cb46c7 | 811 | the bug report. Alternatively, @kbd{M-x getenv @key{RET} LC_ALL |
1ba2ce68 | 812 | @key{RET}} will display the value of @code{LC_ALL} in the echo area, and |
1c64e6ed | 813 | you can copy its output from the @file{*Messages*} buffer. |
d527b615 | 814 | |
6bf7aab6 DL |
815 | @item |
816 | A description of what behavior you observe that you believe is | |
16152b76 | 817 | incorrect. For example, ``The Emacs process gets a fatal signal'', or, |
6bf7aab6 DL |
818 | ``The resulting text is as follows, which I think is wrong.'' |
819 | ||
820 | Of course, if the bug is that Emacs gets a fatal signal, then one can't | |
821 | miss it. But if the bug is incorrect text, the maintainer might fail to | |
822 | notice what is wrong. Why leave it to chance? | |
823 | ||
824 | Even if the problem you experience is a fatal signal, you should still | |
825 | say so explicitly. Suppose something strange is going on, such as, your | |
826 | copy of the source is out of sync, or you have encountered a bug in the | |
827 | C library on your system. (This has happened!) Your copy might crash | |
828 | and the copy here might not. If you @emph{said} to expect a crash, then | |
829 | when Emacs here fails to crash, we would know that the bug was not | |
830 | happening. If you don't say to expect a crash, then we would not know | |
831 | whether the bug was happening---we would not be able to draw any | |
832 | conclusion from our observations. | |
833 | ||
ab26d9a1 RS |
834 | @item |
835 | If the bug is that the Emacs Manual or the Emacs Lisp Reference Manual | |
836 | fails to describe the actual behavior of Emacs, or that the text is | |
837 | confusing, copy in the text from the online manual which you think is | |
838 | at fault. If the section is small, just the section name is enough. | |
839 | ||
6bf7aab6 DL |
840 | @item |
841 | If the manifestation of the bug is an Emacs error message, it is | |
842 | important to report the precise text of the error message, and a | |
843 | backtrace showing how the Lisp program in Emacs arrived at the error. | |
844 | ||
845 | To get the error message text accurately, copy it from the | |
1c64e6ed | 846 | @file{*Messages*} buffer into the bug report. Copy all of it, not just |
6bf7aab6 DL |
847 | part. |
848 | ||
50556a88 | 849 | @findex toggle-debug-on-error |
68b34f99 | 850 | @pindex Edebug |
50556a88 RS |
851 | To make a backtrace for the error, use @kbd{M-x toggle-debug-on-error} |
852 | before the error happens (that is to say, you must give that command | |
21c80203 | 853 | and then make the bug happen). This causes the error to start the Lisp |
50556a88 RS |
854 | debugger, which shows you a backtrace. Copy the text of the |
855 | debugger's backtrace into the bug report. @xref{Debugger,, The Lisp | |
856 | Debugger, elisp, the Emacs Lisp Reference Manual}, for information on | |
68b34f99 | 857 | debugging Emacs Lisp programs with the Edebug package. |
6bf7aab6 DL |
858 | |
859 | This use of the debugger is possible only if you know how to make the | |
860 | bug happen again. If you can't make it happen again, at least copy | |
861 | the whole error message. | |
862 | ||
88ab4340 EZ |
863 | @vindex debug-on-quit |
864 | If Emacs appears to be stuck in an infinite loop or in a very long | |
865 | operation, typing @kbd{C-g} with the variable @code{debug-on-quit} | |
866 | non-@code{nil} will start the Lisp debugger and show a backtrace. | |
867 | This backtrace is useful for debugging such long loops, so if you can | |
868 | produce it, copy it into the bug report. | |
869 | ||
649f602c GM |
870 | @vindex debug-on-event |
871 | If you cannot get Emacs to respond to @kbd{C-g} (e.g., because | |
872 | @code{inhibit-quit} is set), then you can try sending the signal | |
873 | specified by @code{debug-on-event} (default SIGUSR2) from outside | |
874 | Emacs to cause it to enter the debugger. | |
875 | ||
6bf7aab6 DL |
876 | @item |
877 | Check whether any programs you have loaded into the Lisp world, | |
c61ab18c CY |
878 | including your initialization file, set any variables that may affect |
879 | the functioning of Emacs. Also, see whether the problem happens in a | |
880 | freshly started Emacs without loading your initialization file (start | |
881 | Emacs with the @code{-Q} switch to prevent loading the init files). | |
882 | If the problem does @emph{not} occur then, you must report the precise | |
883 | contents of any programs that you must load into the Lisp world in | |
884 | order to cause the problem to occur. | |
6bf7aab6 DL |
885 | |
886 | @item | |
887 | If the problem does depend on an init file or other Lisp programs that | |
888 | are not part of the standard Emacs system, then you should make sure it | |
889 | is not a bug in those programs by complaining to their maintainers | |
890 | first. After they verify that they are using Emacs in a way that is | |
891 | supposed to work, they should report the bug. | |
892 | ||
893 | @item | |
894 | If you wish to mention something in the GNU Emacs source, show the line | |
895 | of code with a few lines of context. Don't just give a line number. | |
896 | ||
897 | The line numbers in the development sources don't match those in your | |
898 | sources. It would take extra work for the maintainers to determine what | |
899 | code is in your version at a given line number, and we could not be | |
900 | certain. | |
901 | ||
902 | @item | |
903 | Additional information from a C debugger such as GDB might enable | |
904 | someone to find a problem on a machine which he does not have available. | |
905 | If you don't know how to use GDB, please read the GDB manual---it is not | |
906 | very long, and using GDB is easy. You can find the GDB distribution, | |
907 | including the GDB manual in online form, in most of the same places you | |
908 | can find the Emacs distribution. To run Emacs under GDB, you should | |
909 | switch to the @file{src} subdirectory in which Emacs was compiled, then | |
910 | do @samp{gdb emacs}. It is important for the directory @file{src} to be | |
911 | current so that GDB will read the @file{.gdbinit} file in this | |
912 | directory. | |
913 | ||
914 | However, you need to think when you collect the additional information | |
915 | if you want it to show what causes the bug. | |
916 | ||
917 | @cindex backtrace for bug reports | |
918 | For example, many people send just a backtrace, but that is not very | |
919 | useful by itself. A simple backtrace with arguments often conveys | |
920 | little about what is happening inside GNU Emacs, because most of the | |
921 | arguments listed in the backtrace are pointers to Lisp objects. The | |
922 | numeric values of these pointers have no significance whatever; all that | |
923 | matters is the contents of the objects they point to (and most of the | |
924 | contents are themselves pointers). | |
925 | ||
926 | @findex debug_print | |
927 | To provide useful information, you need to show the values of Lisp | |
928 | objects in Lisp notation. Do this for each variable which is a Lisp | |
929 | object, in several stack frames near the bottom of the stack. Look at | |
930 | the source to see which variables are Lisp objects, because the debugger | |
931 | thinks of them as integers. | |
932 | ||
933 | To show a variable's value in Lisp syntax, first print its value, then | |
934 | use the user-defined GDB command @code{pr} to print the Lisp object in | |
935 | Lisp syntax. (If you must use another debugger, call the function | |
936 | @code{debug_print} with the object as an argument.) The @code{pr} | |
937 | command is defined by the file @file{.gdbinit}, and it works only if you | |
938 | are debugging a running process (not with a core dump). | |
939 | ||
940 | To make Lisp errors stop Emacs and return to GDB, put a breakpoint at | |
941 | @code{Fsignal}. | |
942 | ||
8389e1e2 | 943 | For a short listing of Lisp functions running, type the GDB |
177c0ea7 | 944 | command @code{xbacktrace}. |
8389e1e2 | 945 | |
6bf7aab6 DL |
946 | The file @file{.gdbinit} defines several other commands that are useful |
947 | for examining the data types and contents of Lisp objects. Their names | |
948 | begin with @samp{x}. These commands work at a lower level than | |
949 | @code{pr}, and are less convenient, but they may work even when | |
950 | @code{pr} does not, such as when debugging a core dump or when Emacs has | |
951 | had a fatal signal. | |
952 | ||
878c3c90 EZ |
953 | @cindex debugging Emacs, tricks and techniques |
954 | More detailed advice and other useful techniques for debugging Emacs | |
955 | are available in the file @file{etc/DEBUG} in the Emacs distribution. | |
956 | That file also includes instructions for investigating problems | |
957 | whereby Emacs stops responding (many people assume that Emacs is | |
16152b76 | 958 | ``hung'', whereas in fact it might be in an infinite loop). |
878c3c90 | 959 | |
ac41be63 RS |
960 | To find the file @file{etc/DEBUG} in your Emacs installation, use the |
961 | directory name stored in the variable @code{data-directory}. | |
6bf7aab6 DL |
962 | @end itemize |
963 | ||
964 | Here are some things that are not necessary in a bug report: | |
965 | ||
966 | @itemize @bullet | |
967 | @item | |
968 | A description of the envelope of the bug---this is not necessary for a | |
969 | reproducible bug. | |
970 | ||
971 | Often people who encounter a bug spend a lot of time investigating | |
972 | which changes to the input file will make the bug go away and which | |
973 | changes will not affect it. | |
974 | ||
975 | This is often time-consuming and not very useful, because the way we | |
ac41be63 RS |
976 | will find the bug is by running a single example under the debugger |
977 | with breakpoints, not by pure deduction from a series of examples. | |
978 | You might as well save time by not searching for additional examples. | |
979 | It is better to send the bug report right away, go back to editing, | |
980 | and find another bug to report. | |
6bf7aab6 DL |
981 | |
982 | Of course, if you can find a simpler example to report @emph{instead} of | |
983 | the original one, that is a convenience. Errors in the output will be | |
984 | easier to spot, running under the debugger will take less time, etc. | |
985 | ||
986 | However, simplification is not vital; if you can't do this or don't have | |
987 | time to try, please report the bug with your original test case. | |
988 | ||
c6fcb73d RS |
989 | @item |
990 | A core dump file. | |
991 | ||
992 | Debugging the core dump might be useful, but it can only be done on | |
993 | your machine, with your Emacs executable. Therefore, sending the core | |
994 | dump file to the Emacs maintainers won't be useful. Above all, don't | |
995 | include the core file in an email bug report! Such a large message | |
996 | can be extremely inconvenient. | |
997 | ||
6bf7aab6 DL |
998 | @item |
999 | A system-call trace of Emacs execution. | |
1000 | ||
1001 | System-call traces are very useful for certain special kinds of | |
1002 | debugging, but in most cases they give little useful information. It is | |
1003 | therefore strange that many people seem to think that @emph{the} way to | |
1004 | report information about a crash is to send a system-call trace. Perhaps | |
1005 | this is a habit formed from experience debugging programs that don't | |
1006 | have source code or debugging symbols. | |
1007 | ||
1008 | In most programs, a backtrace is normally far, far more informative than | |
1009 | a system-call trace. Even in Emacs, a simple backtrace is generally | |
1010 | more informative, though to give full information you should supplement | |
1011 | the backtrace by displaying variable values and printing them as Lisp | |
1012 | objects with @code{pr} (see above). | |
1013 | ||
1014 | @item | |
1015 | A patch for the bug. | |
1016 | ||
1017 | A patch for the bug is useful if it is a good one. But don't omit the | |
1018 | other information that a bug report needs, such as the test case, on the | |
1019 | assumption that a patch is sufficient. We might see problems with your | |
1020 | patch and decide to fix the problem another way, or we might not | |
1021 | understand it at all. And if we can't understand what bug you are | |
1022 | trying to fix, or why your patch should be an improvement, we mustn't | |
1023 | install it. | |
1024 | ||
62fe831c | 1025 | @ifnottex |
6bf7aab6 DL |
1026 | @xref{Sending Patches}, for guidelines on how to make it easy for us to |
1027 | understand and install your patches. | |
62fe831c | 1028 | @end ifnottex |
6bf7aab6 DL |
1029 | |
1030 | @item | |
1031 | A guess about what the bug is or what it depends on. | |
1032 | ||
1033 | Such guesses are usually wrong. Even experts can't guess right about | |
1034 | such things without first using the debugger to find the facts. | |
1035 | @end itemize | |
1036 | ||
1037 | @node Sending Patches | |
1038 | @subsection Sending Patches for GNU Emacs | |
1039 | ||
1040 | @cindex sending patches for GNU Emacs | |
1041 | @cindex patches, sending | |
1042 | If you would like to write bug fixes or improvements for GNU Emacs, | |
1043 | that is very helpful. When you send your changes, please follow these | |
1044 | guidelines to make it easy for the maintainers to use them. If you | |
1045 | don't follow these guidelines, your information might still be useful, | |
1046 | but using it will take extra work. Maintaining GNU Emacs is a lot of | |
1047 | work in the best of circumstances, and we can't keep up unless you do | |
1048 | your best to help. | |
1049 | ||
1050 | @itemize @bullet | |
1051 | @item | |
1052 | Send an explanation with your changes of what problem they fix or what | |
63e1eaa1 GM |
1053 | improvement they bring about. For a fix for an existing bug, it is |
1054 | best to reply to the relevant discussion on the @samp{bug-gnu-emacs} | |
c61ab18c CY |
1055 | list, or the bug entry in the GNU Bug Tracker at |
1056 | @url{http://debbugs.gnu.org}. Explain why your change fixes the bug. | |
6bf7aab6 DL |
1057 | |
1058 | @item | |
1059 | Always include a proper bug report for the problem you think you have | |
1060 | fixed. We need to convince ourselves that the change is right before | |
1061 | installing it. Even if it is correct, we might have trouble | |
1062 | understanding it if we don't have a way to reproduce the problem. | |
1063 | ||
1064 | @item | |
1065 | Include all the comments that are appropriate to help people reading the | |
1066 | source in the future understand why this change was needed. | |
1067 | ||
1068 | @item | |
1069 | Don't mix together changes made for different reasons. | |
1070 | Send them @emph{individually}. | |
1071 | ||
1072 | If you make two changes for separate reasons, then we might not want to | |
1073 | install them both. We might want to install just one. If you send them | |
1074 | all jumbled together in a single set of diffs, we have to do extra work | |
1075 | to disentangle them---to figure out which parts of the change serve | |
1076 | which purpose. If we don't have time for this, we might have to ignore | |
1077 | your changes entirely. | |
1078 | ||
1079 | If you send each change as soon as you have written it, with its own | |
1080 | explanation, then two changes never get tangled up, and we can consider | |
1081 | each one properly without any extra work to disentangle them. | |
1082 | ||
1083 | @item | |
1084 | Send each change as soon as that change is finished. Sometimes people | |
1085 | think they are helping us by accumulating many changes to send them all | |
1086 | together. As explained above, this is absolutely the worst thing you | |
1087 | could do. | |
1088 | ||
1089 | Since you should send each change separately, you might as well send it | |
1090 | right away. That gives us the option of installing it immediately if it | |
1091 | is important. | |
1092 | ||
1093 | @item | |
1094 | Use @samp{diff -c} to make your diffs. Diffs without context are hard | |
1095 | to install reliably. More than that, they are hard to study; we must | |
1096 | always study a patch to decide whether we want to install it. Unidiff | |
1097 | format is better than contextless diffs, but not as easy to read as | |
1098 | @samp{-c} format. | |
1099 | ||
1100 | If you have GNU diff, use @samp{diff -c -F'^[_a-zA-Z0-9$]+ *('} when | |
1101 | making diffs of C code. This shows the name of the function that each | |
1102 | change occurs in. | |
1103 | ||
1104 | @item | |
1105 | Avoid any ambiguity as to which is the old version and which is the new. | |
1106 | Please make the old version the first argument to diff, and the new | |
1107 | version the second argument. And please give one version or the other a | |
1108 | name that indicates whether it is the old version or your new changed | |
1109 | one. | |
1110 | ||
1111 | @item | |
1112 | Write the change log entries for your changes. This is both to save us | |
1113 | the extra work of writing them, and to help explain your changes so we | |
1114 | can understand them. | |
1115 | ||
1116 | The purpose of the change log is to show people where to find what was | |
1117 | changed. So you need to be specific about what functions you changed; | |
1118 | in large functions, it's often helpful to indicate where within the | |
1119 | function the change was. | |
1120 | ||
1121 | On the other hand, once you have shown people where to find the change, | |
1122 | you need not explain its purpose in the change log. Thus, if you add a | |
1123 | new function, all you need to say about it is that it is new. If you | |
1124 | feel that the purpose needs explaining, it probably does---but put the | |
1125 | explanation in comments in the code. It will be more useful there. | |
1126 | ||
21c80203 RS |
1127 | Please read the @file{ChangeLog} files in the @file{src} and |
1128 | @file{lisp} directories to see what sorts of information to put in, | |
1129 | and to learn the style that we use. @xref{Change Log}. | |
6bf7aab6 DL |
1130 | |
1131 | @item | |
1132 | When you write the fix, keep in mind that we can't install a change that | |
1133 | would break other systems. Please think about what effect your change | |
1134 | will have if compiled on another type of system. | |
1135 | ||
1136 | Sometimes people send fixes that @emph{might} be an improvement in | |
1137 | general---but it is hard to be sure of this. It's hard to install | |
1138 | such changes because we have to study them very carefully. Of course, | |
1139 | a good explanation of the reasoning by which you concluded the change | |
1140 | was correct can help convince us. | |
1141 | ||
1142 | The safest changes are changes to the configuration files for a | |
1143 | particular machine. These are safe because they can't create new bugs | |
1144 | on other machines. | |
1145 | ||
1146 | Please help us keep up with the workload by designing the patch in a | |
1147 | form that is clearly safe to install. | |
1148 | @end itemize | |
1149 | ||
412a0972 | 1150 | @c FIXME: Include the node above? |
abb9615e | 1151 | @node Contributing |
6bf7aab6 | 1152 | @section Contributing to Emacs Development |
16207c0a | 1153 | @cindex contributing to Emacs |
6bf7aab6 | 1154 | |
2f3ac208 GM |
1155 | If you would like to work on improving Emacs, please contact the maintainers at |
1156 | @ifnothtml | |
1157 | @email{emacs-devel@@gnu.org}. | |
1158 | @end ifnothtml | |
1159 | @ifhtml | |
1160 | @url{http://lists.gnu.org/mailman/listinfo/emacs-devel, the | |
1161 | emacs-devel mailing list}. | |
1162 | @end ifhtml | |
1163 | You can ask for suggested projects or suggest your own ideas. | |
6bf7aab6 DL |
1164 | |
1165 | If you have already written an improvement, please tell us about it. If | |
1166 | you have not yet started work, it is useful to contact | |
2f3ac208 GM |
1167 | @ifnothtml |
1168 | @email{emacs-devel@@gnu.org} | |
1169 | @end ifnothtml | |
1170 | @ifhtml | |
1171 | @url{http://lists.gnu.org/mailman/listinfo/emacs-devel, emacs-devel} | |
1172 | @end ifhtml | |
1173 | before you start; it might be possible to suggest ways to make your | |
1174 | extension fit in better with the rest of Emacs. | |
6bf7aab6 | 1175 | |
4f3bc373 | 1176 | The development version of Emacs can be downloaded from the |
7e17c3a2 | 1177 | repository where it is actively maintained by a group of developers. |
21c80203 RS |
1178 | See the Emacs project page |
1179 | @url{http://savannah.gnu.org/projects/emacs/} for details. | |
b656e0f4 | 1180 | |
16207c0a GM |
1181 | For more information on how to contribute, see the @file{etc/CONTRIBUTE} |
1182 | file in the Emacs distribution. | |
1183 | ||
abb9615e | 1184 | @node Service |
6bf7aab6 DL |
1185 | @section How To Get Help with GNU Emacs |
1186 | ||
1187 | If you need help installing, using or changing GNU Emacs, there are two | |
1188 | ways to find it: | |
1189 | ||
1190 | @itemize @bullet | |
1191 | @item | |
2f3ac208 GM |
1192 | Send a message to |
1193 | @ifnothtml | |
1194 | the mailing list @email{help-gnu-emacs@@gnu.org}, | |
1195 | @end ifnothtml | |
1196 | @ifhtml | |
1197 | @url{http://lists.gnu.org/mailman/listinfo/help-gnu-emacs, the | |
1198 | help-gnu-emacs mailing list}, | |
1199 | @end ifhtml | |
1200 | or post your request on newsgroup @code{gnu.emacs.help}. (This | |
1201 | mailing list and newsgroup interconnect, so it does not matter which | |
1202 | one you use.) | |
6bf7aab6 DL |
1203 | |
1204 | @item | |
1205 | Look in the service directory for someone who might help you for a fee. | |
1206 | The service directory is found in the file named @file{etc/SERVICE} in the | |
1207 | Emacs distribution. | |
1208 | @end itemize | |
ab5796a9 | 1209 | |
0d6e9754 LT |
1210 | @ifnottex |
1211 | @lowersections | |
1212 | @end ifnottex |