Quitting and Aborting
=====================

C-g
     Quit.  Cancel running or partially typed command.

C-]
     Abort innermost recursive editing level and cancel the command which invoked it (abort-recursive-edit).

M-x top-level
     Abort all recursive editing levels that are currently executing.

C-x u
     Cancel an already-executed command, usually (undo).

There are two ways of cancelling commands which are not finished executing: quitting with C-g, and aborting with C-] or M-x top-level.  Quitting is cancelling a partially typed command or one which is already running.  Aborting is getting out of a recursive editing level and cancelling the command that invoked the recursive edit.

Quitting with C-g is used for getting rid of a partially typed command or a numeric argument that you don't want.  It also stops a running command in the middle in a relatively safe way, so you can use it if you accidentally start executing a command that takes a long time.  In particular, it is safe to quit out of killing; either your text will ALL still be there, or it will ALL be in the kill ring (or maybe both).  Quitting an incremental search does special things documented under searching; in general, it may take two successive C-g characters to get out of a search.  C-g works by setting the variable quit-flag to t the instant C-g is typed; Emacs Lisp checks this variable frequently and quits if it is non-nil.  C-g is only actually executed as a command if it is typed while Emacs is waiting for input.

If you quit twice in a row before the first C-g is recognized, you activate the ``emergency escape'' feature and return to the shell. See Emergency Escape.

You can use C-] (abort-recursive-edit) to get out of a recursive editing level and cancel the command which invoked it. Quitting with C-g does not do this, and could not do this because it is used to cancel a partially typed command within the recursive editing level.  Both operations are useful.  For example, if you are in the Emacs debugger (see Lisp Debug) and have typed C-u 8 to enter a numeric argument, you can cancel that argument with C-g and remain in the debugger.

The command M-x top-level is equivalent to ``enough'' C-] commands to get you out of all the levels of recursive edits that you are in.  C-] only gets you out one level at a time, but M-x top-level goes out all levels at once.  Both C-] and M-x top-level are like all other commands and unlike C-g in that they are effective only when Emacs is ready for a command.  C-] is an ordinary key and has its meaning only because of its binding in the keymap. See Recursive Edit.

C-x u (undo) is not strictly speaking a way of cancelling a command, but you can think of it as cancelling a command already finished executing.  See Undo.

Dealing With Emacs Trouble
==========================

This section describes various conditions in which Emacs fails to work, and how to recognize them and correct them.

Recursive Editing Levels
------------------------

Recursive editing levels are important and useful features of Emacs, but they can seem like malfunctions to the user who does not understand them.

If the mode line has square brackets [...] around the parentheses that contain the names of the major and minor modes, you have entered a recursive editing level.  If you did not do this on purpose, or if you don't understand what that means, you should just get out of the recursive editing level.  To do so, type M-x top-level.  This is called getting back to top level.  See Recursive Edit.

Garbage on the Screen
---------------------

If the data on the screen looks wrong, the first thing to do is see whether the text is actually wrong.  Type C-l, to redisplay the entire screen.  If the text appears correct after this, the problem was entirely in the previous screen update.

Display updating problems often result from an incorrect termcap entry for the terminal you are using.  The file etc/TERMS in the Emacs distribution gives the fixes for known problems of this sort. INSTALL contains general advice for these problems in one of its sections.  Very likely there is simply insufficient padding for certain display operations.  To investigate the possibility that you have this sort of problem, try Emacs on another terminal made by a different manufacturer.  If problems happen frequently on one kind of terminal but not another kind, the real problem is likely to be a bad termcap entry, though it could also be due to a bug in Emacs that appears for terminals that have or lack specific features.

Garbage in the Text
-------------------

If C-l shows that the text is wrong, try undoing the changes to it using C-x u until it gets back to a state you consider correct.  Also try C-h l to find out what command you typed to produce the observed results.

If a large portion of text appears to be missing at the beginning or end of the buffer, check for the word Narrow in the mode line. If it appears, the text is still present, but marked off-limits. To make it visible again, type C-x n w.  See Narrowing.

Spontaneous Entry to Incremental Search
---------------------------------------

If Emacs spontaneously displays I-search: at the bottom of the screen, it means that the terminal is sending C-s and C-q according to the poorly designed xon/xoff ``flow control'' protocol.  You should try to prevent this by putting the terminal in a mode where it will not use flow control, or by giving it enough padding that it will never send a C-s.  If that cannot be done, you must tell Emacs to expect flow control to be used, until you can get a properly designed terminal.

Information on how to do these things can be found in the file INSTALL in the Emacs distribution.

Emergency Escape
----------------

Because at times there have been bugs causing Emacs to loop without checking quit-flag, a special feature causes Emacs to be suspended immediately if you type a second C-g while the flag is already set, so you can always get out of XEmacs.  Normally Emacs recognizes and clears quit-flag (and quits!) quickly enough to prevent this from happening.

When you resume Emacs after a suspension caused by multiple C-g, it asks two questions before going back to what it had been doing:

     Auto-save? (y or n)
     Abort (and dump core)? (y or n)

Answer each one with y or n followed by RET.

Saying y to Auto-save? causes immediate auto-saving of all modified buffers in which auto-saving is enabled.

Saying y to Abort (and dump core)? causes an illegal instruction to be executed, dumping core.  This is to enable a wizard to figure out why Emacs was failing to quit in the first place.  Execution does not continue after a core dump.  If you answer n, execution does continue.  With luck, Emacs will ultimately check quit-flag and quit normally.  If not, and you type another C-g, it is suspended again.

If Emacs is not really hung, but is just being slow, you may invoke the double C-g feature without really meaning to.  In that case, simply resume and answer n to both questions, and you will arrive at your former state.  Presumably the quit you requested will happen soon.

The double-C-g feature may be turned off when Emacs is running under a window system, since the window system always enables you to kill Emacs or to create another window and run another program.

Help for Total Frustration
--------------------------

If using Emacs (or something else) becomes terribly frustrating and none of the techniques described above solve the problem, Emacs can still help you.

First, if the Emacs you are using is not responding to commands, type C-g C-g to get out of it and then start a new one.

Second, type M-x doctor RET.

The doctor will make you feel better.  Each time you say something to the doctor, you must end it by typing RET RET.  This lets the doctor know you are finished.

Reporting Bugs
==============

Sometimes you will encounter a bug in Emacs.  Although we cannot promise we can or will fix the bug, and we might not even agree that it is a bug, we want to hear about bugs you encounter in case we do want to fix them.

To make it possible for us to fix a bug, you must report it.  In order to do so effectively, you must know when and how to do it.

When Is There a Bug
-------------------

If Emacs executes an illegal instruction, or dies with an operating system error message that indicates a problem in the program (as opposed to something like ``disk full''), then it is certainly a bug.

If Emacs updates the display in a way that does not correspond to what is in the buffer, then it is certainly a bug.  If a command seems to do the wrong thing but the problem corrects itself if you type C-l, it is a case of incorrect display updating.

Taking forever to complete a command can be a bug, but you must make certain that it was really Emacs's fault.  Some commands simply take a long time.  Type C-g and then C-h l to see whether the input Emacs received was what you intended to type; if the input was such that you KNOW it should have been processed quickly, report a bug.  If you don't know whether the command should take a long time, find out by looking in the manual or by asking for assistance.

If a command you are familiar with causes an Emacs error message in a case where its usual definition ought to be reasonable, it is probably a bug.

If a command does the wrong thing, that is a bug.  But be sure you know for certain what it ought to have done.  If you aren't familiar with the command, or don't know for certain how the command is supposed to work, then it might actually be working right.  Rather than jumping to conclusions, show the problem to someone who knows for certain.

Finally, a command's intended definition may not be best for editing with.  This is a very important sort of problem, but it is also a matter of judgment.  Also, it is easy to come to such a conclusion out of ignorance of some of the existing features.  It is probably best not to complain about such a problem until you have checked the documentation in the usual ways, feel confident that you understand it, and know for certain that what you want is not available.  If you are not sure what the command is supposed to do after a careful reading of the manual, check the index and glossary for any terms that may be unclear.  If you still do not understand, this indicates a bug in the manual.  The manual's job is to make everything clear.  It is just as important to report documentation bugs as program bugs.

If the online documentation string of a function or variable disagrees with the manual, one of them must be wrong, so report the bug.

How to Report a Bug
-------------------

When you decide that there is a bug, it is important to report it and to report it in a way which is useful.  What is most useful is an exact description of what commands you type, starting with the shell command to run Emacs, until the problem happens.  Always include the version number of Emacs that you are using; type M-x emacs-version to print this.

The most important principle in reporting a bug is to report FACTS, not hypotheses or categorizations.  It is always easier to report the facts, but people seem to prefer to strain to posit explanations and report them instead.  If the explanations are based on guesses about how Emacs is implemented, they will be useless; we will have to try to figure out what the facts must have been to lead to such speculations.  Sometimes this is impossible.  But in any case, it is unnecessary work for us.

For example, suppose that you type C-x C-f /glorp/baz.ugh RET, visiting a file which (you know) happens to be rather large, and Emacs prints out I feel pretty today.  The best way to report the bug is with a sentence like the preceding one, because it gives all the facts and nothing but the facts.

Do not assume that the problem is due to the size of the file and say, ``When I visit a large file, Emacs prints out I feel pretty today.'' This is what we mean by ``guessing explanations''.  The problem is just as likely to be due to the fact that there is a z in the file name.  If this is so, then when we got your report, we would try out the problem with some ``large file'', probably with no z in its name, and not find anything wrong.  There is no way in the world that we could guess that we should try visiting a file with a z in its name.

Alternatively, the problem might be due to the fact that the file starts with exactly 25 spaces.  For this reason, you should make sure that you inform us of the exact contents of any file that is needed to reproduce the bug.  What if the problem only occurs when you have typed the C-x a l command previously?  This is why we ask you to give the exact sequence of characters you typed since starting to use Emacs.

You should not even say ``visit a file'' instead of C-x C-f unless you know that it makes no difference which visiting command is used. Similarly, rather than saying ``if I have three characters on the line,'' say ``after I type RET A B C RET C-p,'' if that is the way you entered the text.

If you are not in Fundamental mode when the problem occurs, you should say what mode you are in.

If the manifestation of the bug is an Emacs error message, it is important to report not just the text of the error message but a backtrace showing how the Lisp program in Emacs arrived at the error.  To make the backtrace, you must execute the Lisp expression (setq debug-on-error t) before the error happens (that is to say, you must execute that expression and then make the bug happen).  This causes the Lisp debugger to run (see Lisp Debug).  The debugger's backtrace can be copied as text into the bug report.  This use of the debugger is possible only if you know how to make the bug happen again.  Do note the error message the first time the bug happens, so if you can't make it happen again, you can report at least that.

Check whether any programs you have loaded into the Lisp world, including your init file, set any variables that may affect the functioning of Emacs.  See Init File.  Also, see whether the problem happens in a freshly started Emacs without loading your init file (start Emacs with the -q switch to prevent loading the init file).  If the problem does NOT occur then, it is essential that we know the contents of any programs that you must load into the Lisp world in order to cause the problem to occur.

If the problem does depend on an init file or other Lisp programs that are not part of the standard Emacs system, then you should make sure it is not a bug in those programs by complaining to their maintainers first. After they verify that they are using Emacs in a way that is supposed to work, they should report the bug.

If you can tell us a way to cause the problem without visiting any files, please do so.  This makes it much easier to debug.  If you do need files, make sure you arrange for us to see their exact contents.  For example, it can often matter whether there are spaces at the ends of lines, or a newline after the last line in the buffer (nothing ought to care whether the last line is terminated, but tell that to the bugs).

The easy way to record the input to Emacs precisely is to write a dribble file; execute the Lisp expression:

     (open-dribble-file "~/dribble")

using Meta-ESC or from the *scratch* buffer just after starting Emacs.  From then on, all Emacs input will be written in the specified dribble file until the Emacs process is killed.

For possible display bugs, it is important to report the terminal type (the value of environment variable TERM), the complete termcap entry for the terminal from /etc/termcap (since that file is not identical on all machines), and the output that Emacs actually sent to the terminal. The way to collect this output is to execute the Lisp expression:

     (open-termscript "~/termscript")

using Meta-ESC or from the *scratch* buffer just after starting Emacs.  From then on, all output from Emacs to the terminal will be written in the specified termscript file as well, until the Emacs process is killed.  If the problem happens when Emacs starts up, put this expression into your init file so that the termscript file will be open when Emacs displays the screen for the first time. See Init File. Be warned: it is often difficult, and sometimes impossible, to fix a terminal-dependent bug without access to a terminal of the type that stimulates the bug.

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