Core dump
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===From within GDB=== | ===From within GDB=== | ||
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generate-core-file [file] | generate-core-file [file] | ||
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==Naming the core dumps== | ==Naming the core dumps== |
Revision as of 10:13, 28 November 2016
To enable core dumps, do this in a shell:
ulimit -c unlimited
Or this from C:
#include <sys/time.h> #include <sys/resource.h> void coredump_enable(void) { struct rlimit rlim; getrlimit(RLIMIT_CORE,&rlim); rlim.rlim_cur = rlim.rlim_max; setrlimit(RLIMIT_CORE,&rlim); } void coredump_disable(void) { struct rlimit rlim; getrlimit(RLIMIT_CORE,&rlim); rlim.rlim_cur = 0; setrlimit(RLIMIT_CORE,&rlim); }
After you call coredump_enable()
, if your program dies for any reason (Segfault, etc) then a core dump will be taken.
It will often be stored to ./code
but the naming schema can be changed.
BEWARE: once a dump has been taken, if the naming schema does not result in a unique name, then an existing dump (or file) will NOT be overwritten.
Contents |
Creating a core dump
SIGQUIT
is usually bound to ^\
. If it's not being masked and core dumps are enabled, then you should get a dump in your current directory.
Alternatively, use kill -QUIT ${PID}
or kill -ABRT ${PID}
From within GDB
generate-core-file [file]
Naming the core dumps
Run the following to see your current setting:
cat /proc/sys/kernel/core_pattern
And run the following (as root) to update it:
echo "%e.core.%s.%p" > /proc/sys/kernel/core_pattern
Putting a '|
' (pipe) before an executable path and parameters from below in here allows you to run a script on a crash! That is executed before the application is killed!
Be careful, that application is run as root, as a child of 'keventd'.
Info
Pattern replacement
%p | pid |
%% | output one '%' |
%u | uid |
%g | gid |
%s | signal number |
%t | UNIX time of dump |
%h | hostname |
%e | executable filename |
%<OTHER> | both are dropped |
%<NUL> | '%' is dropped |
Permanent Configuration
You can add a line like this to /etc/sysctl.conf
:
kernel.core_pattern = "%e.core.%s.%p"
Analyzing the dump later
Take your executable in the left hand, and the core in the right, and shove them at gdb:
gdb ${EXECUTABLE} ${COREDUMP}
Initiate a dump from C
#include <stdio.h> #include <unistd.h> #include <sys/types.h> #include <sys/wait.h> #include <sys/time.h> #include <sys/resource.h> void dump_core(void) { pid_t cpid, rpid; int status; cpid = fork(); if (cpid == -1) { /* fork failed... */ fprintf(stderr, "dump_core(): failed to fork...\n"); } if (cpid == 0 || cpid == -1) { /* in the child or fork()-failed process... */ struct rlimit rlim; rlim_t t; /* ensure that a dump will be created by setting RLIMIT_CORE... */ if (getrlimit(RLIMIT_CORE, &rlim) == -1) { fprintf(stderr, "dump_core(): failed to query RLIMIT_CORE... continuing to attempt a core dump...\n"); } else { if (rlim.rlim_max == 0) { fprintf(stderr, "dump_core(): rlim_max is set to 0... we can't create a core dump...\n"); if (cpid == -1) return; exit(42); } else if (rlim.rlim_max != RLIM_INFINITY) { fprintf(stderr, "dump_core(): rlim_max is not RLIM_INFINITY... limited to a dump of %ldx 512-byte blocks...\n", rlim.rlim_max); } t = rlim.rlim_cur; rlim.rlim_cur = rlim.rlim_max; if (setrlimit(RLIMIT_CORE, &rlim) == -1) { fprintf(stderr, "dump_core(): failed to set RLIMIT_CORE...\n"); if (t == 0) { fprintf(stderr, "dump_core(): rlim_cur was set to 0... we can't create a core dump...\n"); if (cpid == -1) return; exit(42); } else if (t != RLIM_INFINITY) { fprintf(stderr, "dump_core(): rlim_cur is not RLIM_INFINITY... limited to a dump of %ldx 512-byte blocks...\n", t); } } } /* and crash in your favorite way! */ abort(); (*((int*)0)) = 42; exit(-1); } /* wait for the child to go away (die) */ if ((rpid = waitpid(cpid, &status, 0)) == -1) { fprintf(stderr, "dump_core(): failed to wait for the child...\n"); } else if (rpid == 0) { fprintf(stderr, "dump_core(): somehow waitpid() returned with no notification...\n"); } else if (rpid != cpid) { fprintf(stderr, "dump_core(): somehow waitpid() returned a notification for the wrong child...\n"); } else { if (WIFEXITED(status)) { if (WEXITSTATUS(status) == 42) { fprintf(stderr, "dump_core(): failed to create a core dump...\n"); } else { fprintf(stderr, "dump_core(): child returned with %d (unexpected...)\n", WEXITSTATUS(status)); } } else if (WIFSIGNALED(status)) { if (WCOREDUMP(status)) { /* if everything goes to plan, this should be all you'll see: */ fprintf(stderr, "dump_core(): successfully created a core dump!\n"); } else { fprintf(stderr, "dump_core(): apparently no core dump was created... :-(\n"); } } } }