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Diffstat (limited to 'doc/emacs/trouble.texi')
| -rw-r--r-- | doc/emacs/trouble.texi | 175 |
1 files changed, 82 insertions, 93 deletions
diff --git a/doc/emacs/trouble.texi b/doc/emacs/trouble.texi index 93f9c779dbf..887e5c6170f 100644 --- a/doc/emacs/trouble.texi +++ b/doc/emacs/trouble.texi @@ -151,7 +151,6 @@ garbled displays, running out of memory, and crashes and hangs. Emacs. @menu -* DEL Does Not Delete:: What to do if @key{DEL} doesn't delete. * Stuck Recursive:: '[...]' in mode line around the parentheses. * Screen Garbled:: Garbage on the screen. * Text Garbled:: Garbage in the text. @@ -159,66 +158,9 @@ Emacs. * Crashing:: What Emacs does when it crashes. * After a Crash:: Recovering editing in an Emacs session that crashed. * Emergency Escape:: What to do if Emacs stops responding. -* Long Lines:: Mitigating slowness due to extremely long lines. +* DEL Does Not Delete:: What to do if @key{DEL} doesn't delete. @end menu -@node DEL Does Not Delete -@subsection If @key{DEL} Fails to Delete -@cindex @key{DEL} vs @key{BACKSPACE} -@cindex @key{BACKSPACE} vs @key{DEL} -@cindex @key{DEL} does not delete - - Every keyboard has a large key, usually labeled @key{BACKSPACE}, -which is ordinarily used to erase the last character that you typed. -In Emacs, this key is supposed to be equivalent to @key{DEL}. - - When Emacs starts up on a graphical display, it determines -automatically which key should be @key{DEL}. In some unusual cases, -Emacs gets the wrong information from the system, and @key{BACKSPACE} -ends up deleting forwards instead of backwards. - - Some keyboards also have a @key{Delete} key, which is ordinarily -used to delete forwards. If this key deletes backward in Emacs, that -too suggests Emacs got the wrong information---but in the opposite -sense. - - On a text terminal, if you find that @key{BACKSPACE} prompts for a -Help command, like @kbd{Control-h}, instead of deleting a character, -it means that key is actually sending the @samp{BS} character. Emacs -ought to be treating @key{BS} as @key{DEL}, but it isn't. - -@findex normal-erase-is-backspace-mode - In all of those cases, the immediate remedy is the same: use the -command @kbd{M-x normal-erase-is-backspace-mode}. This toggles -between the two modes that Emacs supports for handling @key{DEL}, so -if Emacs starts in the wrong mode, this should switch to the right -mode. On a text terminal, if you want to ask for help when @key{BS} -is treated as @key{DEL}, use @key{F1} instead of @kbd{C-h}; @kbd{C-?} -may also work, if it sends character code 127. - - To fix the problem in every Emacs session, put one of the following -lines into your initialization file (@pxref{Init File}). For the -first case above, where @key{BACKSPACE} deletes forwards instead of -backwards, use this line to make @key{BACKSPACE} act as @key{DEL}: - -@lisp -(normal-erase-is-backspace-mode 0) -@end lisp - -@noindent -For the other two cases, use this line: - -@lisp -(normal-erase-is-backspace-mode 1) -@end lisp - -@vindex normal-erase-is-backspace - Another way to fix the problem for every Emacs session is to -customize the variable @code{normal-erase-is-backspace}: the value -@code{t} specifies the mode where @key{BS} or @key{BACKSPACE} is -@key{DEL}, and @code{nil} specifies the other mode. @xref{Easy -Customization}. - @node Stuck Recursive @subsection Recursive Editing Levels @cindex stuck in recursive editing @@ -296,6 +238,31 @@ editing in the same Emacs session. out of memory, because the Buffer Menu needs a fair amount of memory itself, and the reserve supply may not be enough. +@cindex out of memory killer, GNU/Linux +@cindex OOM killer + On GNU/Linux systems, Emacs does not normally get notified about +out-of-memory situations; instead, the OS can kill the Emacs process +when it runs out of memory. This feature is known as the +@dfn{out-of-memory killer}, or @dfn{@acronym{OOM} killer}. When this +behavior is in effect, Emacs is unable to detect the out-of-memory +situation in time, and won't be able to let you save your buffer as +described above. However, it is possible to turn off this behavior of +the OS, and thus allow Emacs a chance to handle the out-of-memory +situation in a more useful manner, before it is killed. To do that, +become the super user, edit the file @code{/etc/sysctl.conf} to +contain the lines shown below, and then invoke the command +@w{@kbd{sysctl -p}} from the shell prompt: + +@example +vm.overcommit_memory=2 +vm.overcommit_ratio=0 +@end example + +@noindent +Please note that the above setting affects all the processes on the +system, and in general the behavior of the system under memory +pressure, not just the Emacs process alone. + @node Crashing @subsection When Emacs Crashes @@ -465,40 +432,62 @@ program. emergency escape---but there are cases where it won't work, when a system call hangs or when Emacs is stuck in a tight loop in C code. -@node Long Lines -@subsection Long Lines -@cindex long lines - - For a variety of reasons (some of which are fundamental to the Emacs -redisplay code and the complex range of possibilities it handles; -others of which are due to modes and features which do not scale well -in unusual circumstances), Emacs can perform poorly when extremely -long lines are present (where ``extremely long'' usually means at -least many thousands of characters). - -@cindex @code{so-long} mode -@findex global-so-long-mode -@vindex so-long-action - A particular problem is that Emacs may ``hang'' for a long time at -the point of visiting a file with extremely long lines. This can be -mitigated by enabling the @file{so-long} library, which detects when a -visited file contains abnormally long lines, and takes steps to -disable features which are liable to cause slowness in that situation. -To enable this library, type @kbd{M-x global-so-long-mode @key{RET}}, -or turn on the @code{global-so-long-mode} in your init file -(@pxref{Init File}), or customize the @code{global-so-long-mode} -option. You can tailor this mode's operation by customizing the -variable @code{so-long-action}. - - The @file{so-long} library can also significantly improve -performance when moving and editing in a buffer with long lines. -Performance is still likely to degrade as you get deeper into the long -lines, but the improvements from using this library can nevertheless -be substantial. - -@findex so-long-commentary - Use @kbd{M-x so-long-commentary} to view the documentation for this -library and learn more about how to enable and configure it. +@node DEL Does Not Delete +@subsection If @key{DEL} Fails to Delete +@cindex @key{DEL} vs @key{BACKSPACE} +@cindex @key{BACKSPACE} vs @key{DEL} +@cindex @key{DEL} does not delete + + Every keyboard has a large key, usually labeled @key{BACKSPACE}, +which is ordinarily used to erase the last character that you typed. +In Emacs, this key is supposed to be equivalent to @key{DEL}. + + When Emacs starts up on a graphical display, it determines +automatically which key should be @key{DEL}. In some unusual cases, +Emacs gets the wrong information from the system, and @key{BACKSPACE} +ends up deleting forwards instead of backwards. + + Some keyboards also have a @key{Delete} key, which is ordinarily +used to delete forwards. If this key deletes backward in Emacs, that +too suggests Emacs got the wrong information---but in the opposite +sense. + + On a text terminal, if you find that @key{BACKSPACE} prompts for a +Help command, like @kbd{Control-h}, instead of deleting a character, +it means that key is actually sending the @samp{BS} character. Emacs +ought to be treating @key{BS} as @key{DEL}, but it isn't. + +@findex normal-erase-is-backspace-mode + In all of those cases, the immediate remedy is the same: use the +command @kbd{M-x normal-erase-is-backspace-mode}. This toggles +between the two modes that Emacs supports for handling @key{DEL}, so +if Emacs starts in the wrong mode, this should switch to the right +mode. On a text terminal, if you want to ask for help when @key{BS} +is treated as @key{DEL}, use @key{F1} instead of @kbd{C-h}; @kbd{C-?} +may also work, if it sends character code 127. + + To fix the problem in every Emacs session, put one of the following +lines into your initialization file (@pxref{Init File}). For the +first case above, where @key{BACKSPACE} deletes forwards instead of +backwards, use this line to make @key{BACKSPACE} act as @key{DEL}: + +@lisp +(normal-erase-is-backspace-mode 0) +@end lisp + +@noindent +For the other two cases, use this line: + +@lisp +(normal-erase-is-backspace-mode 1) +@end lisp + +@vindex normal-erase-is-backspace + Another way to fix the problem for every Emacs session is to +customize the variable @code{normal-erase-is-backspace}: the value +@code{t} specifies the mode where @key{BS} or @key{BACKSPACE} is +@key{DEL}, and @code{nil} specifies the other mode. @xref{Easy +Customization}. @node Bugs @section Reporting Bugs |