I've noticed my Debian 9 VM doesn't create a core dump with kill -s 6 <pid>. Looked into ulimit, suid_dumpable, core_pattern - they seem OK to me. The message after kill doesn't show (core dumped), and there is no core file in either the working directory or the one specified in core_pattern. Sudo doesn't help. Any configuration piece I'm missing?
Configuration:
Static hostname: <hostname>
Icon name: computer-vm
Chassis: vm
Machine ID: <redacted>
Boot ID: <redacted>
Virtualization: microsoft
Operating System: Debian GNU/Linux 9 (stretch)
Kernel: Linux 4.19.128-dcc08d126b2b
Architecture: x86-64
<user>@<hostname>:~$ ulimit -Ha
core file size (blocks, -c) unlimited
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 56048
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 1048576
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) unlimited
cpu time (seconds, -t) unlimited
max user processes (-u) 56048
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited
<user>@<hostname>:~$ ulimit -Sa
core file size (blocks, -c) 100000
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 56048
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 1024
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 8192
cpu time (seconds, -t) unlimited
max user processes (-u) 56048
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited
<user>@<hostname>:~$ cat /proc/sys/fs/suid_dumpable
1
<user>@<hostname>:~$ cat /proc/sys/kernel/core_pattern
/opt/core/%e.SIG-%s.%p.core
Example:
<user>@<hostname>:~$ sleep 500 &
[1] 14259
<user>@<hostname>:~$ kill -s 6 14259
[1]+ Aborted sleep 500
<user>@<hostname>:~$ ls -la /opt/core/
total 8
drwxr-xr-x 2 root root 4096 Jun 8 15:27 .
drwxr-xr-x 6 root root 4096 Jun 8 15:27 ..
<user>@<hostname>:~$ ls -la | grep core
<user>@<hostname>:~$
Maybe your system has been messed by systemd. In that case you have to install systemd-coredump:
# apt-get install systemd-coredump
Next you can inspect the core dumps with coredumpctl.
# sleep 100
^\Quit (core dumped)
# coredumpctl list
TIME PID UID GID SIG COREFILE EXE
Tue 2021-06-15 18:00:58 CEST 21065 0 0 3 present /bin/sleep
They are placed in /var/lib/systemd/coredump.
# ll /var/lib/systemd/coredump/
total 68
-rw-r----- 1 root root 26605 Jun 15 18:00 core.sleep.0.af2fa0f571f84f279c4510ee3281a787.21065.1623772857000000.lz4