1 .\" Copyright (c) 2006, 2008 by Michael Kerrisk <mtk.manpages@gmail.com>
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25 .TH CORE 5 2014-03-14 "Linux" "Linux Programmer's Manual"
27 core \- core dump file
29 The default action of certain signals is to cause a process to terminate
31 .IR "core dump file" ,
32 a disk file containing an image of the process's memory at
33 the time of termination.
34 This image can be used in a debugger (e.g.,
36 to inspect the state of the program at the time that it terminated.
37 A list of the signals which cause a process to dump core can be found in
40 A process can set its soft
42 resource limit to place an upper limit on the size of the core dump file
43 that will be produced if it receives a "core dump" signal; see
47 There are various circumstances in which a core dump file is
50 The process does not have permission to write the core file.
51 (By default the core file is called
53 and is created in the current working directory.
54 See below for details on naming.)
55 Writing the core file will fail if the directory in which
56 it is to be created is nonwritable,
57 or if a file with the same name exists and
59 or is not a regular file
60 (e.g., it is a directory or a symbolic link).
62 A (writable, regular) file with the same name as would be used for the
63 core dump already exists, but there is more than one hard link to that
66 The filesystem where the core dump file would be created is full;
67 or has run out of inodes; or is mounted read-only;
68 or the user has reached their quota for the filesystem.
70 The directory in which the core dump file is to be created does
77 (file size) resource limits for the process are set to zero; see
79 and the documentation of the shell's
86 The binary being executed by the process does not have read
89 The process is executing a set-user-ID (set-group-ID) program
90 that is owned by a user (group) other than the real user (group)
92 (However, see the description of the
95 operation, and the description of the
96 .I /proc/sys/fs/suid_dumpable
97 .\" FIXME . Perhaps relocate discussion of /proc/sys/fs/suid_dumpable
98 .\" and PR_SET_DUMPABLE to this page?
103 .\" commit 046d662f481830e652ac34cd112249adde16452a
104 The kernel was configured without the
109 a core dump may exclude part of the address space of the process if the
113 .SS Naming of core dump files
114 By default, a core dump file is named
117 .I /proc/sys/kernel/core_pattern
118 file (since Linux 2.6 and 2.4.21)
119 can be set to define a template that is used to name core dump files.
120 The template can contain % specifiers which are substituted
121 by the following values when a core file is created:
130 core file size soft resource limit of crashing process (since Linux 2.6.24)
133 .\" Added in git commit 12a2b4b2241e318b4f6df31228e4272d2c2968a1
134 dump mode\(emsame as value returned by
140 executable filename (without path prefix)
143 pathname of executable,
144 with slashes (\(aq/\(aq) replaced by exclamation marks (\(aq!\(aq)
148 (numeric) real GID of dumped process
151 hostname (same as \fInodename\fP returned by \fBuname\fP(2))
154 PID of dumped process,
155 as seen in the PID namespace in which the process resides
158 .\" Added in git commit 65aafb1e7484b7434a0c1d4c593191ebe5776a2f
159 PID of dumped process, as seen in the initial PID namespace
163 number of signal causing dump
166 time of dump, expressed as seconds since the
167 Epoch, 1970-01-01 00:00:00 +0000 (UTC)
170 (numeric) real UID of dumped process
174 A single % at the end of the template is dropped from the
175 core filename, as is the combination of a % followed by any
176 character other than those listed above.
177 All other characters in the template become a literal
178 part of the core filename.
179 The template may include \(aq/\(aq characters, which are interpreted
180 as delimiters for directory names.
181 The maximum size of the resulting core filename is 128 bytes (64 bytes
182 in kernels before 2.6.19).
183 The default value in this file is "core".
184 For backward compatibility, if
185 .I /proc/sys/kernel/core_pattern
186 does not include "%p" and
187 .I /proc/sys/kernel/core_uses_pid
189 is nonzero, then .PID will be appended to the core filename.
191 Since version 2.4, Linux has also provided
192 a more primitive method of controlling
193 the name of the core dump file.
195 .I /proc/sys/kernel/core_uses_pid
196 file contains the value 0, then a core dump file is simply named
198 If this file contains a nonzero value, then the core dump file includes
199 the process ID in a name of the form
203 .\" 9520628e8ceb69fa9a4aee6b57f22675d9e1b709
205 .I /proc/sys/fs/suid_dumpable
206 is set to 2 ("suidsafe"), the pattern must be either an absolute pathname
207 (starting with a leading \(aq/\(aq character) or a pipe, as defined below.
208 .SS Piping core dumps to a program
209 Since kernel 2.6.19, Linux supports an alternate syntax for the
210 .I /proc/sys/kernel/core_pattern
212 If the first character of this file is a pipe symbol (\fB|\fP),
213 then the remainder of the line is interpreted as a program to be
215 Instead of being written to a disk file, the core dump is given as
216 standard input to the program.
217 Note the following points:
219 The program must be specified using an absolute pathname (or a
220 pathname relative to the root directory, \fI/\fP),
221 and must immediately follow the '|' character.
223 The process created to run the program runs as user and group
226 Command-line arguments can be supplied to the
227 program (since Linux 2.6.24),
228 delimited by white space (up to a total line length of 128 bytes).
230 The command-line arguments can include any of
231 the % specifiers listed above.
232 For example, to pass the PID of the process that is being dumped, specify
235 .SS Controlling which mappings are written to the core dump
236 Since kernel 2.6.23, the Linux-specific
237 .IR /proc/PID/coredump_filter
238 file can be used to control which memory segments are written to the
239 core dump file in the event that a core dump is performed for the
240 process with the corresponding process ID.
242 The value in the file is a bit mask of memory mapping types (see
244 If a bit is set in the mask, then memory mappings of the
245 corresponding type are dumped; otherwise they are not dumped.
246 The bits in this file have the following meanings:
252 Dump anonymous private mappings.
255 Dump anonymous shared mappings.
258 Dump file-backed private mappings.
261 Dump file-backed shared mappings.
262 .\" file-backed shared mappings of course also update the underlying
265 bit 4 (since Linux 2.6.24)
268 bit 5 (since Linux 2.6.28)
269 Dump private huge pages.
271 bit 6 (since Linux 2.6.28)
272 Dump shared huge pages.
276 By default, the following bits are set: 0, 1, 4 (if the
277 .B CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS
278 kernel configuration option is enabled), and 5.
279 The value of this file is displayed in hexadecimal.
280 (The default value is thus displayed as 33.)
282 Memory-mapped I/O pages such as frame buffer are never dumped, and
283 virtual DSO pages are always dumped, regardless of the
287 A child process created via
289 inherits its parent's
294 value is preserved across an
297 It can be useful to set
299 in the parent shell before running a program, for example:
303 .RB "$" " echo 0x7 > /proc/self/coredump_filter"
304 .RB "$" " ./some_program"
308 This file is provided only if the kernel was built with the
310 configuration option.
315 command can be used to obtain a core dump of a running process.
317 In Linux versions up to and including 2.6.27,
318 .\" Changed with commit 6409324b385f3f63a03645b4422e3be67348d922
319 if a multithreaded process (or, more precisely, a process that
320 shares its memory with another process by being created with the
324 dumps core, then the process ID is always appended to the core filename,
325 unless the process ID was already included elsewhere in the
326 filename via a %p specification in
327 .IR /proc/sys/kernel/core_pattern .
328 (This is primarily useful when employing the obsolete
329 LinuxThreads implementation,
330 where each thread of a process has a different PID.)
331 .\" Always including the PID in the name of the core file made
332 .\" sense for LinuxThreads, where each thread had a unique PID,
333 .\" but doesn't seem to serve any purpose with NPTL, where all the
334 .\" threads in a process share the same PID (as POSIX.1 requires).
335 .\" Probably the behavior is maintained so that applications using
336 .\" LinuxThreads continue appending the PID (the kernel has no easy
337 .\" way of telling which threading implementation the user-space
338 .\" application is using). -- mtk, April 2006
340 The program below can be used to demonstrate the use of the
342 .I /proc/sys/kernel/core_pattern
344 The following shell session demonstrates the use of this program
345 (compiled to create an executable named
346 .IR core_pattern_pipe_test ):
350 .RB "$" " cc \-o core_pattern_pipe_test core_pattern_pipe_test.c"
353 .RB "#" " echo \(dq|$PWD/core_pattern_pipe_test %p \
354 UID=%u GID=%g sig=%s\(dq > \e"
355 .B " /proc/sys/kernel/core_pattern"
358 .BR "^\e" " # type control-backslash"
360 .RB "$" " cat core.info"
362 argc[0]=</home/mtk/core_pattern_pipe_test>
367 Total bytes in core dump: 282624
373 /* core_pattern_pipe_test.c */
376 #include <sys/stat.h>
383 #define BUF_SIZE 1024
386 main(int argc, char *argv[])
394 /* Change our current working directory to that of the
397 snprintf(cwd, PATH_MAX, "/proc/%s/cwd", argv[1]);
400 /* Write output to file "core.info" in that directory */
402 fp = fopen("core.info", "w+");
406 /* Display command\-line arguments given to core_pattern
409 fprintf(fp, "argc=%d\\n", argc);
410 for (j = 0; j < argc; j++)
411 fprintf(fp, "argc[%d]=<%s>\\n", j, argv[j]);
413 /* Count bytes in standard input (the core dump) */
416 while ((nread = read(STDIN_FILENO, buf, BUF_SIZE)) > 0)
418 fprintf(fp, "Total bytes in core dump: %d\\n", tot);
435 This page is part of release 3.67 of the Linux
438 A description of the project,
439 information about reporting bugs,
440 and the latest version of this page,
442 \%http://www.kernel.org/doc/man\-pages/.