Core dump file is not generated

Question

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 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 m using ulimit -c unlimited which is important if I want to generate a core dump  but it still doesn t generate it  when I got an segmentation fault  How can I make it work

User · Answer

If you call daemon   and then daemonize a process  by default the current working directory will change to    So if your program is a daemon then you should be looking for a core in   directory and not in the directory of the binary

User · Answer

In centos if you are not root account to generate core file  you must be set the account has a root privilege or login root account      vim  etc security limits conf         account soft core unlimited  account hard core unlimited    then if you in login shell with securecrt or other   logout  and then relogin

User · Answer

Check     sysctl kernel core pattern   to see how your dumps are created   e will be the process name  and  t will be the system time    If you ve Ubuntu  your dumps are created by apport in  var crash  but in different format  edit the file to see it    You can test it by   sleep 10  amp  killall -SIGSEGV sleep   If core dumping is successful  you will see     core dumped     after the segmentation fault indication   Read more   How to generate core dump file in Ubuntu    Ubuntu  Please read more at   https   wiki ubuntu com Apport

User · Answer

Make sure your current directory  at the time of crash -- server may change directories  is writable  If the server calls setuid  the directory has to be writable by that user   Also check  proc sys kernel core pattern  That may redirect core dumps to another directory  and that directory must be writable  More info here

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This link contains a good checklist why core dumps are not generated    The core would have been larger than the current limit  You don t have the necessary permissions to dump core  directory and file   Notice that core dumps are placed in the dumping process  current directory which could be different from the parent process  Verify that the file system is writeable and have sufficient free space  If a sub directory named core exist in the working directory no core will be dumped  If a file named core already exist but has multiple hard links the kernel will not dump core  Verify the permissions on the executable  if the executable has the suid or sgid bit enabled core dumps will by default be disabled  The same will be the case if you have execute permissions but no read permissions on the file  Verify that the process has not changed working directory  core size limit  or dumpable flag  Some kernel versions cannot dump processes with shared address space  AKA threads   Newer kernel versions can dump such processes but will append the pid to the file name  The executable could be in a non-standard format not supporting core dumps  Each executable format must implement a core dump routine  The segmentation fault could actually be a kernel Oops  check the system logs for any Oops messages  The application called exit   instead of using the core dump handler

User · Answer

Although this isn t going to be a problem for the person who asked the question  because they ran the program that was to produce the core file in a script with the ulimit command  I d like to document that the ulimit command is specific to the shell in which you run it  like environment variables    I spent way too much time running ulimit and sysctl and stuff in one shell  and the command that I wanted to dump core in the other shell  and wondering why the core file was not produced   I will be adding it to my bashrc   The sysctl works for all processes once it is issued  but the ulimit only works for the shell in which it is issued  maybe also the descendents too  - but not for other shells that happen to be running

User · Answer

The answers given here cover pretty well most scenarios for which core dump is not created  However  in my instance  none of these applied  I m posting this answer as an addition to the other answers    If your core file is not being created for whatever reason  I recommend looking at the  var log messages  There might be a hint in there to why the core file is not created  In my case there was a line stating the root cause   Executable   path to executable  doesn t belong to any package   To work around this issue edit  etc abrt abrt-action-save-package-data conf and change ProcessUnpackaged from  no  to  yes     ProcessUnpackaged   yes   This setting specifies whether to create core for binaries not installed with package manager

User · Answer

For the record  on Debian 9 Stretch  systemd   I had to install the package systemd-coredump  Afterwards  core dumps were generated in the folder  var lib systemd coredump   Furthermore  these coredumps are compressed in the lz4 format  To decompress  you can use the package liblz4-tool like this  lz4 -d FILE   To be able to debug the decompressed coredump using gdb  I also had to rename the utterly long filename into something shorter

User · Answer

Note  If you have written any crash handler yourself  then the core might not get generated  So search for code with something on the line   signal SIGSEGV   lt handler gt       so the SIGSEGV will be handled by handler and you will not get the core dump

User · Answer

Just in case someone else stumbles on this  I was running someone else s code - make sure they are not handling the signal  so they can gracefully exit   I commented out the handling  and got the core dump

User · Answer

If one is on a Linux distro  e g  CentOS  Debian  then perhaps the most accessible way to find out about core files and related conditions is in the man page  Just run the following command from a terminal   man 5 core

User · Answer

Also  check to make sure you have enough disk space on  var core or wherever your core dumps get written   If the partition is almos full or at 100  disk usage then that would be the problem   My core dumps average a few gigs so you should be sure to have at least 5-10 gig available on the partition

User · Answer

Remember if you are starting the server from a service  it will start a different bash session so the ulimit won t be effective there  Try to put this in your script itself   ulimit -c unlimited

[linux] Core dump file is not generated

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