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

Question

While running a C program, It says "(core dumped)" but I can'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 "core", but didn't get the core dumped file?
Any help, where is my core file?

Undying

Does the program invoke chdir at some point? If so, look there. – Steelmaker

Does the program change its working directory? Look there. – Insurmountable

I would search the entire harddrive for a recent file ;) – Fricandeau

yes..the program uses chdir - I'll check there in few seconds – Undying

oops no its not there... I checked it ..program chdir to /mnt and / i checked both directories but could not find the file. I even did find / -name "*core." even this didn't show me the file. The program uses C + sqlite ,while inserting values it core dumps It said assertion error==0 for the first time and error=101 for the second time.. – Undying

is there a way to redirect core dumped file to specific directory say /tmp – Undying

Yes, if you override /proc/sys/kernel/core_pattern with a string starting with /tmp then that's where your core dumps will go. – Delegacy

Related: [my own Q&A] AskUbuntu: Where do I find core dump files, and how do I view and analyze the backtrace (stack trace) in one? – Kip

Answer 1

Read /usr/src/linux/Documentation/sysctl/kernel.txt.

core_pattern is used to specify a core dumpfile pattern name.

• If the first character of the pattern is a '|', the kernel will treat the rest of the pattern as a command to run. The core dump will be written to the standard input of that program instead of to a file.

Instead of writing the core dump to disk, your system is configured to send it to the abrt (meaning: Automated Bug Reporting Tool, not "abort") program instead. Automated Bug Reporting Tool is possibly not as documented as it should be...

In any case, the quick answer is that you should be able to find your core file in /var/cache/abrt, where abrt stores it after being invoked. Similarly, other systems using Apport may squirrel away cores in /var/crash, and so on.

Delegacy

yes,I have edited core_pattern with following content echo "core.%e.%p" > /proc/sys/kernel/core_pattern ..now it creates the core dump file in current directory itself. with name "core.giis.12344" etc. Thank you all for your answers/comments/hints . – Undying

Just to note that fedora 18 abrt program is storing core dumps in /var/spool/abrt/ instead of /var/cache/abrt – Kulun

Is there a way to allow users to configure this for themselves, rather than everyone having to use the system configuration? – Passageway

When this command is run and process is invoked, are stdout and stderr not opened by default? I see very strange things happenning. when i use dup2 of stderr and stdout into my custom file(applog.txt), Data which i am writing into other file(mycore.BIN) is being redirected to file which i have used to catch stdout & stderr(applog.txt). Is there a good read about this one? Please suggest. Thank you – Blindfish

systemd in archlinux store coredumps in /var/lib/systemd/coredump/ – Piny

systemd in debian as well uses /var/lib/systemd/coredump/ – Gaberlunzie

Answer 2

On recent Ubuntu (12.04 in my case), it's possible for "Segmentation fault (core dumped)" to be printed, but no core file produced where you might expect one (for instance for a locally compiled program).

This can happen if you have a core file size ulimit of 0 (you haven't done ulimit -c unlimited) -- this is the default on Ubuntu. Normally that would suppress the "(core dumped)", cluing you into your mistake, but on Ubuntu, corefiles are piped to Apport (Ubuntu's crash reporting system) via /proc/sys/kernel/core_pattern, and this seems to cause the misleading message.

If Apport discovers that the program in question is not one it should be reporting crashes for (which you can see happening in /var/log/apport.log), it falls back to simulating the default kernel behaviour of putting a core file in the cwd (this is done in the script /usr/share/apport/apport). This includes honouring ulimit, in which case it does nothing. But (I assume) as far as the kernel is concerned, a corefile was generated (and piped to apport), hence the message "Segmentation fault (core dumped)".

Ultimately PEBKAC for forgetting to set ulimit, but the misleading message had me thinking I was going mad for a while, wondering what was eating my corefiles.

(Also, in general, the core(5) manual page -- man 5 core -- is a good reference for where your core file ends up and reasons it might not be written.)

Psalter

Thank you so much -- I ran into the very same problem. Btw, Ubuntu 14.04 exhibits exactly the same behavior as the one you described. – Kairouan

On my Ubuntu install (modified 14.04), there's an easy temporary workaround for this by running sudo service apport stop --- after I ran that, it changed /proc/sys/kernel/core_pattern from the apport pipe to just core. Apport is smart enough to fix up the core_pattern temporarily, I suppose. – Erosion

"ulimit -c unlimited" is exactly what I needed - Thank you! – Karlie

Recently, ubuntu writes the core to ~/temp/core, after you have raised ulimit. Check the log on var/log/apport.log (yes, you need to have su powers to read that file). – Abana

I have tried every applicable answer, and every location in every comment here after doing the ulimit command, but still can't find a core file anywhere on my Ubuntu 16.04 LTS... – Aeroscope

@Nagev, I am facing the same issue with Ubuntu 14.04. Have you ever found a solution? – Magdeburg

@ElectricGoat No I haven't. It's poor UX design, IMO. The system should just print the path, or not print a message at all if it's not being created. I'll add my own answer, when or if I get a chance to investigate this further. – Aeroscope

thanks, solved it this way : echo core | sudo tee /proc/sys/kernel/core_pattern – Brandenbrandenburg

Brilliant! On Ubuntu 16.04, /var/log/apport.log contained host pid [...] crashed in a separate mount namespace, ignoring (a quick search reveals nothing useful regarding this message, nor how to work around it), and stopping the Apport service temporarily with systemctl stop apport allowed the core dump to be written to its expected location. – Haemophiliac

I'm surprised about the many up votes: The OP said core size is unlimited. Besides of that the is *no message core dumped if no core was dumped! Most likely today is that systemd interfered with core dump (redirecting the core file). Easiest way to find out is reading the syslog (which is always a good idea after problems, BTW). – Otherworld

Answer 3

With the launch of systemd, there's another scenario as well. By default systemd will store core dumps in its journal, being accessible with the systemd-coredumpctl command. Defined in the core_pattern-file:

$ cat /proc/sys/kernel/core_pattern 
|/usr/lib/systemd/systemd-coredump %p %u %g %s %t %e

Easiest way to check for stored core dumps is via coredumpctl list (older core dumps may have been removed automatically). This behaviour can be disabled with a simple "hack":

$ ln -s /dev/null /etc/sysctl.d/50-coredump.conf
$ sysctl -w kernel.core_pattern=core      # or just reboot

As always, the size of core dumps has to be equal or higher than the size of the core that is being dumped, as done by for example ulimit -c unlimited.

Mirianmirielle

That "hack" didn't work for me (even after a restart). I'm running Arch Linux and I've already run ulimit -c unlimited. – Gynaeco

@gsingh2011 It might be outdated. I don't run Arch anymore so I can't say if it should work these days. If you figure it out feel free to update me/us with a new comment. – Mirianmirielle

@gsingh2011 Try 50-coredump.conf instead of coredump.conf. This should override /lib/sysctl.d/50-coredump.conf. The default can be restored with sysctl -w kernel.core_pattern=core – Quarantine

I had to turn off appport for this to work sudo service apport stop – Conversational

On Ubuntu 21.10 I had to install systemd-coredump first, before I could get the coredumpctl command to work. After that it was easy ;) – Reaction

Answer 4

Writing instructions to get a core dump under Ubuntu 16.04 LTS:

1. As @jtn has mentioned in his answer, Ubuntu delegates the display of crashes to apport, which in turn refuses to write the dump because the program is not an installed package.

2. To remedy the problem, we need to make sure apport writes core dump files for non-package programs as well. To do so, create a file named ~/.config/apport/settings with the following contents:
   [main] unpackaged=true

3. Now crash your program again, and see your crash files being generated within folder: /var/crash with names like *.1000.crash. Note that these files cannot be read by gdb directly.

4. [Optional] To make the dumps readble by gdb, run the following command:

   apport-unpack <location_of_report> <target_directory>

References: Core_dump – Oracle VM VirtualBox

Selfrestraint

This is the only solution that worked for me in Ubuntu 18.04 – Enzootic

Which user does ~/ pertain to? If process is run by root does that mean /root/.config/apport/settings ? – Platelet

@Platelet I believe it should be the user that executed the program. I'm not sure though. – Selfrestraint

This still works as of Ubuntu 21.04. – Tetartohedral

Worked for Ubuntu 20.04.4 – Locule

Answer 5

I could think of two following possibilities:

1. As others have already pointed out, the program might chdir(). Is the user running the program allowed to write into the directory it chdir()'ed to? If not, it cannot create the core dump.

2. For some weird reason the core dump isn't named core.* You can check /proc/sys/kernel/core_pattern for that. Also, the find command you named wouldn't find a typical core dump. You should use find / -name "*core.*", as the typical name of the coredump is core.$PID

Riparian

here is my pattern - does this mean core file is named something like"PID.signal.userid" instead of core.pid ??? $cat /proc/sys/kernel/core_pattern /usr/lib/hookCCpp /var/char/abrt %p %s %u – Undying

If contents of virtual file /proc/sys/kernel/core_pattern starts with a pipe symbol | the file will not be written to file defined by core_pattern but the command defined after the the pipe symbol is launched and the core file will be written to stdin of that program. It's 100% up to the program to handle the core file contents after that. – Adel

On item 1: No, the program won't core dump; it would see an EPERM. Only if the program fails to handle the error correctly it may be forced to terminate (to prevent even more nonsense to happen). – Otherworld

Answer 6

In Ubuntu18.04, the most easist way to get a core file is inputing the command below to stop the apport service.

sudo service apport stop

Then rerun the application, you will get dump file in current directory.

Classis

I tried this and got /etc/init.d/apport: 68: /etc/init.d/apport: cannot create /proc/sys/fs/suid_dumpable: Operation not permitted still cannot find the crash files. I have already set ulimit -c unlimited. Somebody mentioned the /proc/sys/kernel/core_pattern, I can even not see this file. What else should be done? – Discourse

sorry, since I have not encountered the problem, I cannot give a good answer for you. However, I think you can learn the knowledge of apport service, then you can know where the core dump file. Here is the document of apport: https://wiki.ubuntu.com/Apport. – Classis

Answer 7

I found core files of my Ubuntu 20.04 system at;

/var/lib/apport/coredump 

Correspondent

Answer 8

If you're missing core dumps for binaries on RHEL and when using abrt, make sure that /etc/abrt/abrt-action-save-package-data.conf

contains

ProcessUnpackaged = yes

This enables the creation of crash reports (including core dumps) for binaries which are not part of installed packages (e.g. locally built).

Amylopsin

You miss the fact that when "(core dumped)" is output, a core was dumped; if no core was dumped, you do not see that message. – Otherworld

Answer 9

For fedora25, I could find core file at

/var/spool/abrt/ccpp-2017-02-16-16:36:51-2974/coredump

where ccpp-2017-02-16-16:36:51-2974" is pattern "%s %c %p %u %g %t %P % as per `/proc/sys/kernel/core_pattern'

Alodi

Answer 10

I'm on Linux Mint 19 (Ubuntu 18 based). I wanted to have coredump files in current folder. I had to do two things:

1. Change /proc/sys/kernel/core_pattern (by # echo "core.%p.%s.%c.%d.%P > /proc/sys/kernel/core_pattern or by # sysctl -w kernel.core_pattern=core.%p.%s.%c.%d.%P)
2. Raising limit for core file size by $ ulimit -c unlimited

That was written already in the answers, but I wrote to summarize succinctly. Interestingly changing limit did not require root privileges (as per https://askubuntu.com/questions/162229/how-do-i-increase-the-open-files-limit-for-a-non-root-user non-root can only lower the limit, so that was unexpected - comments about it are welcome).

Gifted

sudo sysctl -w kernel.core_pattern=core command helped me to create the core file in the current dir. Thanks. – Disposition

Answer 11

My efforts in WSL have been unsuccessful.

For those running on Windows Subsystem for Linux (WSL) there seems to be an open issue at this time for missing core dump files.

The comments indicate that

This is a known issue that we are aware of, it is something we are investigating.

Github issue

Windows Developer Feedback

Seventeen

Answer 12

In my case, the reason is that the ulimit command only effect the current terminal.

If I set ulimit -c unlimited on the first terminal. Then I start a new terminal to run the program. It will not generate the core file when core dumped.

You have to confirm the core size of the terminal which runs your program.

The following steps work on ubuntu 20.04 and ubuntu 21.04:

1. stop apport service

sudo service apport stop

2. set core size of the terminal which ready to run your program

ulimit -c unlimited

Elastomer

Answer 13

ulimit -c unlimited made the core file correctly appear in the current directory after a "core dumped".

Thelmathem

Answer 14

If you use Fedora, in order to generate core dump file in the same directory of binary file:

echo "core.%e.%p" > /proc/sys/kernel/core_pattern

And

ulimit -c unlimited

Decastyle

This is fine in itself, but if you want to work with the existing system setup, instead of against it, try to figure out how it is setup and inspect the docs for whatever command is capturing the dumps to get to them. See https://mcmap.net/q/92299/-core-dumped-but-core-file-is-not-in-the-current-directory for details. – Reaction

Answer 15

A one-liner to get the latest core dump path:

ls -t $(cat /proc/sys/kernel/core_pattern | awk -F% '{print $1"*"}') 2>/dev/null | head -1

You can of course modify the last -1 on that line to e.g. -4 to get the last 4 core dumps.

Note: That's not expected to work e.g. in case the path pattern uses variables before the last / or when non core dump files are on that dir.

Demonstration

or you can just use coredumpctl -1 info – Gentlemanly

Answer 16

The most easy way to start debugging a core dump I found is using coredumpctl (man coredumpctl for more info).

To start a debug session using the latest segmentation fault, just type

$ coredumpctl debug

It is also useful to find and extract core dump files.

Hysterics