.\" the source, must acknowledge the copyright and authors of this work.
.\" %%%LICENSE_END
.\"
-.TH CORE 5 2016-10-08 "Linux" "Linux Programmer's Manual"
+.TH CORE 5 2019-03-06 "Linux" "Linux Programmer's Manual"
.SH NAME
core \- core dump file
.SH DESCRIPTION
to inspect the state of the program at the time that it terminated.
A list of the signals which cause a process to dump core can be found in
.BR signal (7).
-
+.PP
A process can set its soft
.B RLIMIT_CORE
resource limit to place an upper limit on the size of the core dump file
that will be produced if it receives a "core dump" signal; see
.BR getrlimit (2)
for details.
-
+.PP
There are various circumstances in which a core dump file is
not produced:
.IP * 3
is the ID of the process that dumped core,
and is created in the current working directory.
See below for details on naming.)
-Writing the core file will fail if the directory in which
+Writing the core file fails if the directory in which
it is to be created is nonwritable,
or if a file with the same name exists and
is not writable
file in
.BR proc (5).)
.IP *
+.I /proc/sys/kernel/core_pattern
+is empty and
+.I /proc/sys/kernel/core_uses_pid
+contains the value 0.
+(These files are described below.)
+Note that if
+.I /proc/sys/kernel/core_pattern
+is empty and
+.I /proc/sys/kernel/core_uses_pid
+contains the value 1,
+core dump files will have names of the form
+.IR .pid ,
+and such files are hidden unless one uses the
+.BR ls (1)
+.I \-a
+option.
+.IP *
(Since Linux 3.7)
.\" commit 046d662f481830e652ac34cd112249adde16452a
The kernel was configured without the
.BR madvise (2)
.B MADV_DONTDUMP
flag was employed.
+.PP
+On systems that employ
+.BR systemd (1)
+as the
+.I init
+framework, core dumps may instead be placed in a location determined by
+.BR systemd (1).
+See below for further details.
+.\"
.SS Naming of core dump files
By default, a core dump file is named
.IR core ,
.I /proc/sys/kernel/core_uses_pid
(see below)
is nonzero, then .PID will be appended to the core filename.
-
+.PP
Paths are interpreted according to the settings that are active for the
crashing process.
That means the crashing process's mount namespace (see
.BR getcwd (2)),
and its root directory (see
.BR chroot (2)).
-
+.PP
Since version 2.4, Linux has also provided
a more primitive method of controlling
the name of the core dump file.
If this file contains a nonzero value, then the core dump file includes
the process ID in a name of the form
.IR core.PID .
-
+.PP
Since Linux 3.6,
.\" 9520628e8ceb69fa9a4aee6b57f22675d9e1b709
if
file.
If the first character of this file is a pipe symbol (\fB|\fP),
then the remainder of the line is interpreted as the command-line for
-a a user-space program (or script) that is to be executed.
+a user-space program (or script) that is to be executed.
Instead of being written to a disk file, the core dump is given as
standard input to the program.
Note the following points:
Command-line arguments can be supplied to the
program (since Linux 2.6.24),
delimited by white space (up to a total line length of 128 bytes).
+.IP *
+The
+.B RLIMIT_CORE
+limit is not enforced for core dumps that are piped to a program
+via this mechanism.
.\"
.SS /proc/sys/kernel/core_pipe_limit
When collecting core dumps via a pipe to a user-space program,
This in turn creates the
possibility that a misbehaving collecting program can block
the reaping of a crashed process by simply never exiting.
-
+.PP
Since Linux 2.6.32,
.\" commit a293980c2e261bd5b0d2a77340dd04f684caff58
the
processes may be piped to user-space programs in parallel.
If this value is exceeded, then those crashing processes above this value
are noted in the kernel log and their core dumps are skipped.
-
+.PP
A value of 0 in this file is special.
It indicates that unlimited processes may be captured in parallel,
but that no waiting will take place (i.e., the collecting
file can be used to control which memory segments are written to the
core dump file in the event that a core dump is performed for the
process with the corresponding process ID.
-
+.PP
The value in the file is a bit mask of memory mapping types (see
.BR mmap (2)).
If a bit is set in the mask, then memory mappings of the
This default can be modified at boot time using the
.I coredump_filter
boot option.
-
+.PP
The value of this file is displayed in hexadecimal.
(The default value is thus displayed as 33.)
-
+.PP
Memory-mapped I/O pages such as frame buffer are never dumped, and
-virtual DSO pages are always dumped, regardless of the
+virtual DSO
+.RB ( vdso (7))
+pages are always dumped, regardless of the
.I coredump_filter
value.
-
+.PP
A child process created via
.BR fork (2)
inherits its parent's
.I coredump_filter
value is preserved across an
.BR execve (2).
-
+.PP
It can be useful to set
.I coredump_filter
in the parent shell before running a program, for example:
-
+.PP
.in +4n
-.nf
+.EX
.RB "$" " echo 0x7 > /proc/self/coredump_filter"
.RB "$" " ./some_program"
-.fi
+.EE
.in
.PP
This file is provided only if the kernel was built with the
.B CONFIG_ELF_CORE
configuration option.
+.\"
+.SS Core dumps and systemd
+On systems using the
+.BR systemd (1)
+.I init
+framework, core dumps may be placed in a location determined by
+.BR systemd (1).
+To do this,
+.BR systemd (1)
+employs the
+.I core_pattern
+feature that allows piping core dumps to a program.
+One can verify this by checking whether core dumps are being piped to the
+.BR systemd\-coredump (8)
+program:
+.PP
+.in +4n
+.EX
+$ \fBcat /proc/sys/kernel/core_pattern\fP
+|/usr/lib/systemd/systemd\-coredump %P %u %g %s %t %c %e
+.EE
+.in
+.PP
+In this case, core dumps will be placed in the location configured for
+.BR systemd\-coredump (8),
+typically as
+.BR lz4 (1)
+compressed files in the directory
+.IR /var/lib/systemd/coredump/ .
+One can list the core dumps that have been recorded by
+.BR systemd\-coredump (8)
+using
+.BR coredumpctl (1):
+.PP
+.in +2n
+.EX
+$ \fBcoredumpctl list | tail -5\fP
+Wed 2017-10-11 22:25:30 CEST 2748 1000 1000 3 present /usr/bin/sleep
+Thu 2017-10-12 06:29:10 CEST 2716 1000 1000 3 present /usr/bin/sleep
+Thu 2017-10-12 06:30:50 CEST 2767 1000 1000 3 present /usr/bin/sleep
+Thu 2017-10-12 06:37:40 CEST 2918 1000 1000 3 present /usr/bin/cat
+Thu 2017-10-12 08:13:07 CEST 2955 1000 1000 3 present /usr/bin/cat
+.EE
+.in
+.PP
+The information shown for each core dump includes the date and time
+of the dump, the PID, UID, and GID of the dumping process,
+the signal number that caused the core dump,
+and the pathname of the executable that was being run by the dumped process.
+Various options to
+.BR coredumpctl (1)
+allow a specified coredump file to be pulled from the
+.BR systemd (1)
+location into a specified file.
+For example, to extract the core dump for PID 2955 shown above to a file named
+.IR core
+in the current directory, one could use:
+.PP
+.in +4n
+.EX
+$ \fBcoredumpctl dump 2955 \-o core\fP
+.EE
+.in
+.PP
+For more extensive details, see the
+.BR coredumpctl (1)
+manual page.
+.PP
+To disable the
+.BR systemd (1)
+mechanism that archives core dumps, restoring to something more like
+traditional Linux behavior, one can set an override for the
+.BR systemd (1)
+mechanism, using something like:
+.PP
+.in +2n
+.EX
+# echo "kernel.core_pattern=core.%p" > /etc/sysctl.d/50\-coredump.conf
+# /lib/systemd/systemd\-sysctl
+.EE
+.in
+.PP
+.\"
.SH NOTES
The
.BR gdb (1)
.I gcore
command can be used to obtain a core dump of a running process.
-
+.PP
In Linux versions up to and including 2.6.27,
.\" Changed with commit 6409324b385f3f63a03645b4422e3be67348d922
if a multithreaded process (or, more precisely, a process that
.IR core_pattern_pipe_test ):
.PP
.in +4n
-.nf
+.EX
.RB "$" " cc \-o core_pattern_pipe_test core_pattern_pipe_test.c"
.RB "$" " su"
Password:
argc[3]=<GID=100>
argc[4]=<sig=3>
Total bytes in core dump: 282624
-.fi
+.EE
.in
.SS Program source
\&
-.nf
+.EX
/* core_pattern_pipe_test.c */
#define _GNU_SOURCE
/* Display command\-line arguments given to core_pattern
pipe program */
- fprintf(fp, "argc=%d\\n", argc);
+ fprintf(fp, "argc=%d\en", argc);
for (j = 0; j < argc; j++)
- fprintf(fp, "argc[%d]=<%s>\\n", j, argv[j]);
+ fprintf(fp, "argc[%d]=<%s>\en", j, argv[j]);
/* Count bytes in standard input (the core dump) */
tot = 0;
while ((nread = read(STDIN_FILENO, buf, BUF_SIZE)) > 0)
tot += nread;
- fprintf(fp, "Total bytes in core dump: %d\\n", tot);
+ fprintf(fp, "Total bytes in core dump: %d\en", tot);
fclose(fp);
exit(EXIT_SUCCESS);
}
-.fi
+.EE
.SH SEE ALSO
.BR bash (1),
+.BR coredumpctl (1),
.BR gdb (1),
.BR getrlimit (2),
.BR mmap (2),
.BR elf (5),
.BR proc (5),
.BR pthreads (7),
-.BR signal (7)
+.BR signal (7),
+.BR systemd\-coredump (8)
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