man5/core.5

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  23 .TH CORE 5 2006-04-03 "Linux" "Linux Programmer's Manual"
  24 .SH NAME
  25 core \- core dump file
  26 .SH DESCRIPTION
  27 The default action of certain signals is to cause a process to terminate
  28 and produce a
  29 .IR "core dump file" ,
  30 a disk file containing an image of the process's memory at
  31 the time of termination.
  32 A list of the signals which cause a process to dump core can be found in
  33 .BR signal (7).
  34
  35 A process can set its soft
  36 .B RLIMIT_CORE
  37 resource limit to place an upper limit on the size of the core dump file
  38 that will be produced if it receives a "core dump" signal; see
  39 .BR getrlimit (2)
  40 for details.
  41
  42 There are various circumstances in which a core dump file is
  43 not produced:
  44 .IP * 3
  45 The process does not have permission to write the core file.
  46 (By default the core file is called
  47 .IR core ,
  48 and is created in the current working directory.
  49 See below for details on naming.)
  50 Writing the core file will fail if the directory in which
  51 it is to be created is non-writable,
  52 or if a file with the same name exists and
  53 is not writable
  54 or is not a regular file
  55 (e.g., it is a directory or a symbolic link).
  56 .IP *
  57 A (writable, regular) file with the same name as would be used for the
  58 core dump already exists, but there is more than one hard link to that
  59 file.
  60 .IP *
  61 The file system where the core dump file would be created is full;
  62 or has run out of inodes; or is mounted read-only;
  63 or the user has reached their quota for the file system.
  64 .IP *
  65 The directory in which the core dump file is to be created does
  66 not exist.
  67 .IP *
  68 .B RLIMIT_CORE
  69 or
  70 .B RLIMIT_FSIZE
  71 resource limits for a process are set to zero (see
  72 .BR getrlimit (2)).
  73 .IP *
  74 The binary being executed by the process does not have read
  75 permission enabled.
  76 .IP *
  77 The process is executing a set-user-ID (set-group-ID) program
  78 that is owned by a user (group) other than the real user (group)
  79 ID of the process.
  80 (However, see the description of the
  81 .BR prctl (2)
  82 .B PR_SET_DUMPABLE
  83 operation, and the description of the
  84 .I /proc/sys/fs/suid_dumpable
  85 file in
  86 .BR proc (5).)
  87 .SS Naming of core dump files
  88 By default, a core dump file is named
  89 .IR core ,
  90 but the
  91 .I /proc/sys/kernel/core_pattern
  92 file
  93 (since Linux 2.6 and 2.4.21)
  94 can be set to define a template that is used to name core dump files.
  95 The template can contain % specifiers which are substituted
  96 by the following values when a core file is created:
  97 .nf
  98
  99   %%  A single % character
 100   %p  PID of dumped process
 101   %u  real UID of dumped process
 102   %g  real GID of dumped process
 103   %s  number of signal causing dump
 104   %t  time of dump (seconds since 0:00h, 1 Jan 1970)
 105   %h  hostname (same as \fInodename\fP returned by \fBuname\fP(2))
 106   %e  executable filename
 107
 108 .fi
 109 A single % at the end of the template is dropped from the
 110 core filename, as is the combination of a % followed by any
 111 character other than those listed above.
 112 All other characters in the template become a literal
 113 part of the core filename.
 114 The template may include \'/\' characters, which are interpreted
 115 as delimiters for directory names.
 116 The maximum size of the resulting core filename is 64 bytes.
 117 The default value in this file is "core".
 118 For backward compatibility, if
 119 .I /proc/sys/kernel/core_pattern
 120 does not include "%p" and
 121 .I /proc/sys/kernel/core_uses_pid
 122 (see below)
 123 is non-zero, then .PID will be appended to the core filename.
 124
 125 Since version 2.4, Linux has also provided
 126 a more primitive method of controlling
 127 the name of the core dump file.
 128 If the
 129 .I /proc/sys/kernel/core_uses_pid
 130 file contains the value 0, then a core dump file is simply named
 131 .IR core .
 132 If this file contains a non-zero value, then the core dump file includes
 133 the process ID in a name of the form
 134 .IR core.PID .
 135 .SH NOTES
 136 The
 137 .BR gdb (1)
 138 .I gcore
 139 command can be used to obtain a core dump of a running process.
 140
 141 If a multithreaded process (or, more precisely, a process that
 142 shares its memory with another process by being created with the
 143 .B CLONE_VM
 144 flag of
 145 .BR clone (2))
 146 dumps core, then the process ID is always appended to the core filename,
 147 unless the process ID was already included elsewhere in the
 148 filename via a %p specification in
 149 .IR /proc/sys/kernel/core_pattern .
 150 (This is primarily useful when employing the LinuxThreads implementation,
 151 where each thread of a process has a different PID.)
 152 .\" Always including the PID in the name of the core file made
 153 .\" sense for LinuxThreads, where each thread had a unique PID,
 154 .\" but doesn't seem to serve any purpose with NPTL, where all the
 155 .\" threads in a process share the same PID (as POSIX.1 requires).
 156 .\" Probably the behavior is maintained so that applications using
 157 .\" LinuxThreads continue appending the PID (the kernel has no easy
 158 .\" way of telling which threading implementation the userspace
 159 .\" application is using). -- mtk, April 2006
 160 .SH SEE ALSO
 161 .BR gdb (1),
 162 .BR getrlimit (2),
 163 .BR prctl (2),
 164 .BR sigaction (2),
 165 .BR elf (5),
 166 .BR proc (5),
 167 .BR pthreads (7),
 168 .BR signal (7)