There are two common kinds of [SEGV][1], which is an error that results from an invalid memory access:

 1. A page was accessed which had the wrong permissions. E.g., it was read-only but your code tried to write to it. This will be reported as [`SEGV_ACCERR`][2].
 2. A page was accessed that is not even mapped into the address space of the application at all. This will often result from dereferencing a null pointer or a pointer that was corrupted with a small integer value. This is reported as [`SEGV_MAPERR`][3].

Documentation of a sort (indexed Linux source code) for `SEGV_MAPERR` is here: &lt;http://lxr.free-electrons.com/ident?i=SEGV_MAPERR&gt;.


  [1]: https://elixir.bootlin.com/linux/v5.15.8/source/include/uapi/asm-generic/siginfo.h#L228
  [2]: https://elixir.bootlin.com/linux/v5.15.8/source/include/uapi/asm-generic/siginfo.h#L231
  [3]: https://elixir.bootlin.com/linux/v5.15.8/source/include/uapi/asm-generic/siginfo.h#L230

It&#39;s a segmentation fault. Most probably a dangling pointer issue, or some sort of buffer overflow.

`SIGSSEGV` is the signal that terminates it based on the issue, segmentation fault.

Check for dangling pointers as well as the overflow issue.

Enabling core dumps will help you determine the problem.

What are public, private and protected in object oriented programming?

I have an application which I want to hit the market as a Paid app. I would like to have other version which would be a &quot;trial&quot; version with a time limit of say, 5 days?

How can I go about doing this?

Creating an Android trial application that expires after a fixed time period

What is `SEGV_MAPERR`, why does it always come up with `SIGSEGV`?

What is SEGV_MAPERR?

<p>What is <code>SEGV_MAPERR</code>, why does it always come up with <code>SIGSEGV</code>?</p>


As I make the full switch from Windows to Linux (CentOS 5) I&#39;m in search of the best free GUI SQL Client tool for MSSQL, MySQL, Oracle, etc... any suggestions?

I&#39;ve tried DBVisualizer (The best bet so far but still limited by the free version, not all functionality is there), MySQL GUI Tools (Good but only for MySQL, need other DB&#39;s as well) and Aqua Data Studio (Same as DBVis, it&#39;s good but a lot of the functionality is missing in the free version).

What is the best free SQL GUI for Linux for various DBMS systems

I read that it&#39;s supposedly possible to change the I/O scheduler for a particular device on a running kernel by writing to /sys/block/[disk]/queue/scheduler.  For example I can see on my system:

    anon@anon:~$ cat /sys/block/sda/queue/scheduler 
    noop anticipatory deadline [cfq] 

that the default is the completely fair queuing scheduler.  What I&#39;m wondering is if there is any use in including all four schedulers in my custom kernel.  It would seem that there&#39;s not much point in having more than one scheduler compiled in unless the kernel is smart enough to select the correct scheduler for the correct hardware, specifically the &#39;noop&#39; scheduler for flash based drives and one of the others for a traditional hard drive.

Is this the case?

Selecting a Linux I/O Scheduler

Looking for a command that will return the single most recent file in a directory.

Not seeing a limit parameter to `ls`...

Get most recent file in a directory on Linux

Impressed by [is-latex-worth-learning-today](https://web.archive.org/web/20130816143747/https://stackoverflow.com/questions/874576/is-latex-worth-learning-today#), and many how-to&#39;s on Windows,

How do you have someone started with LaTeX on Linux?

How do you generate a pdf out of it and give up the OOO Word processer?

Update: 

Thanks to all the suggestions given in here. I was able to create an awesome ppt using the Beamer class: http://github.com/becomingGuru/gids-django-ppt. I found this approach too far better than using powerpoint and the like.

Those interested may checkout the [TEX file](http://github.com/becomingGuru/gids-django-ppt/blob/master/contents.tex), with many custom commands and the [corresponding presentation](http://www.slideshare.net/scorpion032/building-pluggable-web-applications-using-django).

Get started with Latex on Linux

Is it possible to use `ls` in Unix to list the total size of a sub-directory and all its contents as opposed to the usual `4K` that (I assume) is just the directory file itself?

    total 12K
    drwxrwxr-x  6 *** *** 4.0K 2009-06-19 10:10 branches
    drwxrwxr-x 13 *** *** 4.0K 2009-06-19 10:52 tags
    drwxrwxr-x 16 *** *** 4.0K 2009-06-19 10:02 trunk

After scouring the man pages I&#39;m coming up empty.


Using ls to list directories and their total sizes


In general, what can we take for granted when we append to a file in UNIX from multiple processes?  Is it possible to lose data (one process overwriting the other&#39;s changes)?  Is it possible for data to get mangled?  (For example, each process is appending one line per append to a log file, is it possible that two lines get mangled?)  If the append is not atomic in the above sense, then what&#39;s the best way of ensuring mutual exclusion?

Is file append atomic in UNIX?

How do I catch a &lt;kbd&gt;Ctrl&lt;/kbd&gt;+&lt;kbd&gt;C&lt;/kbd&gt; event in C++?

How can I catch a ctrl-c event?

What is POSIX? I have read the [Wikipedia article][1] and I read it every time I encounter the term. The fact is that I never really understood what it is.

Can anyone please explain it to me by explaining &quot;the need for POSIX&quot; too?

  [1]: http://en.wikipedia.org/wiki/POSIX

What is the meaning of &quot;POSIX&quot;?

What is the difference between `read()` and `recv()`, and between `send()` and `write()` in socket programming in terms of performances, speed and other behaviors?

What is the Difference Between read() and recv() , and Between send() and write()?

How do I distinguish running Java threads and native threads?

In Linux there will be Parent process for every child process, and they say 0 is the parent of all the process, will there be a Parent thread of all the forked Java threads?

How do I know which Java thread is related to OS thread (if a Java thread forkes a native process thread).

Is there any naming convention of Java threads and OS threads?

Can a running Java threads can be suspended or killed from another Java code?

Distinguishing between Java threads and OS threads?

I&#39;m moving [a project][1] to the new Android Native Development Kit (i.e. JNI) and I&#39;d like to catch SIGSEGV, should it occur (possibly also SIGILL, SIGABRT, SIGFPE) in order to present a nice crash reporting dialog, instead of (or before) what currently happens: the immediate unceremonious death of the process and possibly some attempt by the OS to restart it. (&lt;b&gt;Edit:&lt;/b&gt; The JVM/Dalvik VM catches the signal and logs a stack trace and other useful information; I just want to offer the user the option to email that info to me really.) 

The situation is: a large body of C code which I didn&#39;t write does most of the work in this application (all the game logic) and although it&#39;s well-tested on numerous other platforms, it&#39;s entirely possible that I, in my Android port, will feed it garbage and cause a crash in native code, so I want the crash dumps (both native and Java) that currently show up in the Android log (I guess it would be stderr in a non-Android situation). I&#39;m free to modify both C and Java code arbitrarily, although the callbacks (both going in and coming out of JNI) number about 40 and obviously, bonus points for small diffs.

I&#39;ve heard of the signal chaining library in J2SE, libjsig.so, and if I could safely install a signal handler like that on Android, that would solve the catching part of my question, but I see no such library for Android/Dalvik.


  [1]: http://chris.boyle.name/projects/android-puzzles

How can I catch SIGSEGV (segmentation fault) and get a stack trace under JNI on Android?

I need to know the root cause of the segmentation fault (SIGSEGV), and how to handle it.

What causes a SIGSEGV

The following code gives me a segmentation fault when run on a 2Gb machine, but works on a 4GB machine.


    int main()
    {
       int c[1000000];
       cout &lt;&lt; &quot;done\n&quot;;
       return 0;
    }

The size of the array is just 4Mb. Is there a limit on the size of an array that can be used in c++?



Segmentation fault on large array sizes

This can be a very simple question, I&#39;m am attempting to debug an application which generates the following segfault error in the `kern.log`

`kernel: myapp[15514]: segfault at 794ef0 ip 080513b sp 794ef0 error 6 in myapp[8048000+24000]`

Here are my questions: 

 1. Is there any documentation as to what are the diff error numbers on segfault, in this instance it is error 6, but i&#39;ve seen error 4, 5

 2. What is the meaning of the information `at bf794ef0 ip 0805130b sp bf794ef0 and myapp[8048000+24000]`?

So far i was able to compile with symbols, and when i do a `x 0x8048000+24000` it returns a symbol, is that the correct way of doing it? My assumptions thus far are the following:

- sp = stack pointer?
- ip = instruction pointer
- at = ????
- myapp[8048000+24000] = address of symbol?

How do you read a segfault kernel log message

What is a segmentation fault? Is it different in C and C++? How are segmentation faults and dangling pointers related?

What is a segmentation fault?

While running a C program, It says *&quot;(core dumped)&quot;* but I can&#39;t see any files under the current path.

I have set and verified the `ulimit`:

    ulimit -c unlimited 
    ulimit -a 

I also tried to find a file named &quot;core&quot;, but didn&#39;t get the core dumped file?  
Any help, where is my core file?


Core dumped, but core file is not in the current directory?

On Mac OS X, if I send SIGQUIT to my C program, it terminates, but there is no core dump file.

Do you have to manually enable core dumps on Mac OS X (how?), or are they written to somewhere else instead of the working directory?

Where are core dumps written on Mac?

What are all the things I will need to check while analyzing a core dump file?

Please tell me from scratch.



Core dump file analysis

Every time, my application crash a core dump file is not generated. I remember that few days ago, on another server it **was** generated. I&#39;m running the app using screen in bash like this:

    #!/bin/bash
    ulimit -c unlimited
    while true; do ./server; done

As you can see I&#39;m using `ulimit -c unlimited` which is important if I want to generate a core dump, but it still doesn&#39;t generate it, when I got an segmentation fault.
How can I make it work?

Core dump file is not generated

My program operates like this:

    exe -p param1 -i param2 -o param3

It crashed and generated a core dump file, `core.pid`.

I want to analyze the core dump file by

    gdb ./exe -p param1 -i param2 -o param3 core.pid

But GDB recognizes the parameters of the EXE file as GDB&#39;s input.

How do I analyze a core dump file in this situation?


Content Type	Original Author	Original Content on Stackoverflow
Question	Geek	View Question on Stackoverflow
Solution 1 - Linux	ahcox	View Answer on Stackoverflow
Solution 2 - Linux	Sev	View Answer on Stackoverflow

What is SEGV_MAPERR?

Linux Problem Overview

Linux Solutions

Solution 1 - Linux

Solution 2 - Linux

Creating an Android trial application that expires after a fixed time period

What are public, private and protected in object oriented programming?

Attributions