1 .\" Copyright (c) 2006, 2008 by Michael Kerrisk <mtk.manpages@gmail.com>
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23 .TH CORE 5 2012-01-17 "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?
99 .SS Naming of core dump files
100 By default, a core dump file is named
103 .I /proc/sys/kernel/core_pattern
104 file (since Linux 2.6 and 2.4.21)
105 can be set to define a template that is used to name core dump files.
106 The template can contain % specifiers which are substituted
107 by the following values when a core file is created:
116 PID of dumped process
119 (numeric) real UID of dumped process
122 (numeric) real GID of dumped process
125 number of signal causing dump
128 time of dump, expressed as seconds since the
129 Epoch, 1970-01-01 00:00:00 +0000 (UTC)
132 hostname (same as \fInodename\fP returned by \fBuname\fP(2))
135 executable filename (without path prefix)
138 pathname of executable,
139 with slashes (\(aq/\(aq) replaced by exclamation marks (\(aq!\(aq).
142 core file size soft resource limit of crashing process (since Linux 2.6.24)
146 A single % at the end of the template is dropped from the
147 core filename, as is the combination of a % followed by any
148 character other than those listed above.
149 All other characters in the template become a literal
150 part of the core filename.
151 The template may include \(aq/\(aq characters, which are interpreted
152 as delimiters for directory names.
153 The maximum size of the resulting core filename is 128 bytes (64 bytes
154 in kernels before 2.6.19).
155 The default value in this file is "core".
156 For backward compatibility, if
157 .I /proc/sys/kernel/core_pattern
158 does not include "%p" and
159 .I /proc/sys/kernel/core_uses_pid
161 is nonzero, then .PID will be appended to the core filename.
163 Since version 2.4, Linux has also provided
164 a more primitive method of controlling
165 the name of the core dump file.
167 .I /proc/sys/kernel/core_uses_pid
168 file contains the value 0, then a core dump file is simply named
170 If this file contains a nonzero value, then the core dump file includes
171 the process ID in a name of the form
173 .SS Piping core dumps to a program
174 Since kernel 2.6.19, Linux supports an alternate syntax for the
175 .I /proc/sys/kernel/core_pattern
177 If the first character of this file is a pipe symbol (\fB|\fP),
178 then the remainder of the line is interpreted as a program to be
180 Instead of being written to a disk file, the core dump is given as
181 standard input to the program.
182 Note the following points:
184 The program must be specified using an absolute pathname (or a
185 pathname relative to the root directory, \fI/\fP),
186 and must immediately follow the '|' character.
188 The process created to run the program runs as user and group
191 Command-line arguments can be supplied to the
192 program (since kernel 2.6.24),
193 delimited by white space (up to a total line length of 128 bytes).
195 The command-line arguments can include any of
196 the % specifiers listed above.
197 For example, to pass the PID of the process that is being dumped, specify
200 .SS Controlling which mappings are written to the core dump
201 Since kernel 2.6.23, the Linux-specific
202 .IR /proc/PID/coredump_filter
203 file can be used to control which memory segments are written to the
204 core dump file in the event that a core dump is performed for the
205 process with the corresponding process ID.
207 The value in the file is a bit mask of memory mapping types (see
209 If a bit is set in the mask, then memory mappings of the
210 corresponding type are dumped; otherwise they are not dumped.
211 The bits in this file have the following meanings:
217 Dump anonymous private mappings.
220 Dump anonymous shared mappings.
223 Dump file-backed private mappings.
226 Dump file-backed shared mappings.
227 .\" file-backed shared mappings of course also update the underlying
230 bit 4 (since Linux 2.6.24)
233 bit 5 (since Linux 2.6.28)
234 Dump private huge pages.
236 bit 6 (since Linux 2.6.28)
237 Dump shared huge pages.
241 By default, the following bits are set: 0, 1, 4 (if the
242 .B CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS
243 kernel configuration option is enabled), and 5.
244 The value of this file is displayed in hexadecimal.
245 (The default value is thus displayed as 33.)
247 Memory-mapped I/O pages such as frame buffer are never dumped, and
248 virtual DSO pages are always dumped, regardless of the
252 A child process created via
254 inherits its parent's
259 value is preserved across an
262 It can be useful to set
264 in the parent shell before running a program, for example:
268 .RB "$" " echo 0x7 > /proc/self/coredump_filter"
269 .RB "$" " ./some_program"
273 This file is only provided if the kernel was built with the
275 configuration option.
280 command can be used to obtain a core dump of a running process.
282 If a multithreaded process (or, more precisely, a process that
283 shares its memory with another process by being created with the
287 dumps core, then the process ID is always appended to the core filename,
288 unless the process ID was already included elsewhere in the
289 filename via a %p specification in
290 .IR /proc/sys/kernel/core_pattern .
291 (This is primarily useful when employing the LinuxThreads implementation,
292 where each thread of a process has a different PID.)
293 .\" Always including the PID in the name of the core file made
294 .\" sense for LinuxThreads, where each thread had a unique PID,
295 .\" but doesn't seem to serve any purpose with NPTL, where all the
296 .\" threads in a process share the same PID (as POSIX.1 requires).
297 .\" Probably the behavior is maintained so that applications using
298 .\" LinuxThreads continue appending the PID (the kernel has no easy
299 .\" way of telling which threading implementation the userspace
300 .\" application is using). -- mtk, April 2006
302 The program below can be used to demonstrate the use of the
304 .I /proc/sys/kernel/core_pattern
306 The following shell session demonstrates the use of this program
307 (compiled to create an executable named
308 .IR core_pattern_pipe_test ):
312 .RB "$" " cc \-o core_pattern_pipe_test core_pattern_pipe_test.c"
315 .RB "#" " echo \(dq|$PWD/core_pattern_pipe_test %p \
316 UID=%u GID=%g sig=%s\(dq > \e"
317 .B " /proc/sys/kernel/core_pattern"
320 .BR "^\e" " # type control-backslash"
322 .RB "$" " cat core.info"
324 argc[0]=</home/mtk/core_pattern_pipe_test>
329 Total bytes in core dump: 282624
335 /* core_pattern_pipe_test.c */
338 #include <sys/stat.h>
345 #define BUF_SIZE 1024
348 main(int argc, char *argv[])
356 /* Change our current working directory to that of the
359 snprintf(cwd, PATH_MAX, "/proc/%s/cwd", argv[1]);
362 /* Write output to file "core.info" in that directory */
364 fp = fopen("core.info", "w+");
368 /* Display command\-line arguments given to core_pattern
371 fprintf(fp, "argc=%d\\n", argc);
372 for (j = 0; j < argc; j++)
373 fprintf(fp, "argc[%d]=<%s>\\n", j, argv[j]);
375 /* Count bytes in standard input (the core dump) */
378 while ((nread = read(STDIN_FILENO, buf, BUF_SIZE)) > 0)
380 fprintf(fp, "Total bytes in core dump: %d\\n", tot);