1 .\" Copyright (c) 2006, 2008 by Michael Kerrisk <mtk.manpages@gmail.com>
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23 .TH CORE 5 2012-07-16 "Linux" "Linux Programmer's Manual"
25 core \- core dump file
27 The default action of certain signals is to cause a process to terminate
29 .IR "core dump file" ,
30 a disk file containing an image of the process's memory at
31 the time of termination.
32 This image can be used in a debugger (e.g.,
34 to inspect the state of the program at the time that it terminated.
35 A list of the signals which cause a process to dump core can be found in
38 A process can set its soft
40 resource limit to place an upper limit on the size of the core dump file
41 that will be produced if it receives a "core dump" signal; see
45 There are various circumstances in which a core dump file is
48 The process does not have permission to write the core file.
49 (By default the core file is called
51 and is created in the current working directory.
52 See below for details on naming.)
53 Writing the core file will fail if the directory in which
54 it is to be created is nonwritable,
55 or if a file with the same name exists and
57 or is not a regular file
58 (e.g., it is a directory or a symbolic link).
60 A (writable, regular) file with the same name as would be used for the
61 core dump already exists, but there is more than one hard link to that
64 The file system where the core dump file would be created is full;
65 or has run out of inodes; or is mounted read-only;
66 or the user has reached their quota for the file system.
68 The directory in which the core dump file is to be created does
75 (file size) resource limits for the process are set to zero; see
77 and the documentation of the shell's
84 The binary being executed by the process does not have read
87 The process is executing a set-user-ID (set-group-ID) program
88 that is owned by a user (group) other than the real user (group)
90 (However, see the description of the
93 operation, and the description of the
94 .I /proc/sys/fs/suid_dumpable
95 .\" FIXME . Perhaps relocate discussion of /proc/sys/fs/suid_dumpable
96 .\" and PR_SET_DUMPABLE to this page?
101 a core dump may exclude part of the address space of the process if the
105 .SS Naming of core dump files
106 By default, a core dump file is named
109 .I /proc/sys/kernel/core_pattern
110 file (since Linux 2.6 and 2.4.21)
111 can be set to define a template that is used to name core dump files.
112 The template can contain % specifiers which are substituted
113 by the following values when a core file is created:
122 PID of dumped process
125 (numeric) real UID of dumped process
128 (numeric) real GID of dumped process
131 number of signal causing dump
134 time of dump, expressed as seconds since the
135 Epoch, 1970-01-01 00:00:00 +0000 (UTC)
138 hostname (same as \fInodename\fP returned by \fBuname\fP(2))
141 executable filename (without path prefix)
144 pathname of executable,
145 with slashes (\(aq/\(aq) replaced by exclamation marks (\(aq!\(aq).
148 core file size soft resource limit of crashing process (since Linux 2.6.24)
152 A single % at the end of the template is dropped from the
153 core filename, as is the combination of a % followed by any
154 character other than those listed above.
155 All other characters in the template become a literal
156 part of the core filename.
157 The template may include \(aq/\(aq characters, which are interpreted
158 as delimiters for directory names.
159 The maximum size of the resulting core filename is 128 bytes (64 bytes
160 in kernels before 2.6.19).
161 The default value in this file is "core".
162 For backward compatibility, if
163 .I /proc/sys/kernel/core_pattern
164 does not include "%p" and
165 .I /proc/sys/kernel/core_uses_pid
167 is nonzero, then .PID will be appended to the core filename.
169 Since version 2.4, Linux has also provided
170 a more primitive method of controlling
171 the name of the core dump file.
173 .I /proc/sys/kernel/core_uses_pid
174 file contains the value 0, then a core dump file is simply named
176 If this file contains a nonzero value, then the core dump file includes
177 the process ID in a name of the form
179 .SS Piping core dumps to a program
180 Since kernel 2.6.19, Linux supports an alternate syntax for the
181 .I /proc/sys/kernel/core_pattern
183 If the first character of this file is a pipe symbol (\fB|\fP),
184 then the remainder of the line is interpreted as a program to be
186 Instead of being written to a disk file, the core dump is given as
187 standard input to the program.
188 Note the following points:
190 The program must be specified using an absolute pathname (or a
191 pathname relative to the root directory, \fI/\fP),
192 and must immediately follow the '|' character.
194 The process created to run the program runs as user and group
197 Command-line arguments can be supplied to the
198 program (since kernel 2.6.24),
199 delimited by white space (up to a total line length of 128 bytes).
201 The command-line arguments can include any of
202 the % specifiers listed above.
203 For example, to pass the PID of the process that is being dumped, specify
206 .SS Controlling which mappings are written to the core dump
207 Since kernel 2.6.23, the Linux-specific
208 .IR /proc/PID/coredump_filter
209 file can be used to control which memory segments are written to the
210 core dump file in the event that a core dump is performed for the
211 process with the corresponding process ID.
213 The value in the file is a bit mask of memory mapping types (see
215 If a bit is set in the mask, then memory mappings of the
216 corresponding type are dumped; otherwise they are not dumped.
217 The bits in this file have the following meanings:
223 Dump anonymous private mappings.
226 Dump anonymous shared mappings.
229 Dump file-backed private mappings.
232 Dump file-backed shared mappings.
233 .\" file-backed shared mappings of course also update the underlying
236 bit 4 (since Linux 2.6.24)
239 bit 5 (since Linux 2.6.28)
240 Dump private huge pages.
242 bit 6 (since Linux 2.6.28)
243 Dump shared huge pages.
247 By default, the following bits are set: 0, 1, 4 (if the
248 .B CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS
249 kernel configuration option is enabled), and 5.
250 The value of this file is displayed in hexadecimal.
251 (The default value is thus displayed as 33.)
253 Memory-mapped I/O pages such as frame buffer are never dumped, and
254 virtual DSO pages are always dumped, regardless of the
258 A child process created via
260 inherits its parent's
265 value is preserved across an
268 It can be useful to set
270 in the parent shell before running a program, for example:
274 .RB "$" " echo 0x7 > /proc/self/coredump_filter"
275 .RB "$" " ./some_program"
279 This file is only provided if the kernel was built with the
281 configuration option.
286 command can be used to obtain a core dump of a running process.
288 If a multithreaded process (or, more precisely, a process that
289 shares its memory with another process by being created with the
293 dumps core, then the process ID is always appended to the core filename,
294 unless the process ID was already included elsewhere in the
295 filename via a %p specification in
296 .IR /proc/sys/kernel/core_pattern .
297 (This is primarily useful when employing the LinuxThreads implementation,
298 where each thread of a process has a different PID.)
299 .\" Always including the PID in the name of the core file made
300 .\" sense for LinuxThreads, where each thread had a unique PID,
301 .\" but doesn't seem to serve any purpose with NPTL, where all the
302 .\" threads in a process share the same PID (as POSIX.1 requires).
303 .\" Probably the behavior is maintained so that applications using
304 .\" LinuxThreads continue appending the PID (the kernel has no easy
305 .\" way of telling which threading implementation the userspace
306 .\" application is using). -- mtk, April 2006
308 The program below can be used to demonstrate the use of the
310 .I /proc/sys/kernel/core_pattern
312 The following shell session demonstrates the use of this program
313 (compiled to create an executable named
314 .IR core_pattern_pipe_test ):
318 .RB "$" " cc \-o core_pattern_pipe_test core_pattern_pipe_test.c"
321 .RB "#" " echo \(dq|$PWD/core_pattern_pipe_test %p \
322 UID=%u GID=%g sig=%s\(dq > \e"
323 .B " /proc/sys/kernel/core_pattern"
326 .BR "^\e" " # type control-backslash"
328 .RB "$" " cat core.info"
330 argc[0]=</home/mtk/core_pattern_pipe_test>
335 Total bytes in core dump: 282624
341 /* core_pattern_pipe_test.c */
344 #include <sys/stat.h>
351 #define BUF_SIZE 1024
354 main(int argc, char *argv[])
362 /* Change our current working directory to that of the
365 snprintf(cwd, PATH_MAX, "/proc/%s/cwd", argv[1]);
368 /* Write output to file "core.info" in that directory */
370 fp = fopen("core.info", "w+");
374 /* Display command\-line arguments given to core_pattern
377 fprintf(fp, "argc=%d\\n", argc);
378 for (j = 0; j < argc; j++)
379 fprintf(fp, "argc[%d]=<%s>\\n", j, argv[j]);
381 /* Count bytes in standard input (the core dump) */
384 while ((nread = read(STDIN_FILENO, buf, BUF_SIZE)) > 0)
386 fprintf(fp, "Total bytes in core dump: %d\\n", tot);