\n| <\/td>\n | \n *<\/p>\n<\/td>\n | <\/td>\n | \n The process does not have permission to write the core file. (By default, the core file is called core<\/i> or core.pid<\/i>, where pid<\/i> 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 fails if the directory in which it is to be created is not writable, or if a file with the same name exists and is not writable or is not a regular file (e.g., it is a directory or a symbolic link).<\/p>\n<\/td>\n<\/tr>\n\n| <\/td>\n | \n *<\/p>\n<\/td>\n | <\/td>\n | \n A (writable, regular) file with the same name as would be used for the core dump already exists, but there is more than one hard link to that file.<\/p>\n<\/td>\n<\/tr>\n | \n| <\/td>\n | \n *<\/p>\n<\/td>\n | <\/td>\n | \n The filesystem where the core dump file would be created is full; or has run out of inodes; or is mounted read-only; or the user has reached their quota for the filesystem.<\/p>\n<\/td>\n<\/tr>\n | \n| <\/td>\n | \n *<\/p>\n<\/td>\n | <\/td>\n | \n The directory in which the core dump file is to be created does not exist.<\/p>\n<\/td>\n<\/tr>\n | \n| <\/td>\n | \n *<\/p>\n<\/td>\n | <\/td>\n | \n The RLIMIT_CORE<\/b> (core file size) or RLIMIT_FSIZE<\/b> (file size) resource limits for the process are set to zero; see getrlimit<\/b>(2) and the documentation of the shell\u2019s ulimit<\/i> command (limit<\/i> in csh<\/b>(1)).<\/p>\n<\/td>\n<\/tr>\n\n| <\/td>\n | \n *<\/p>\n<\/td>\n | <\/td>\n | \n The binary being executed by the process does not have read permission enabled. (This is a security measure to ensure that an executable whose contents are not readable does not produce a\u2014possibly readable\u2014core dump containing an image of the executable.)<\/p>\n<\/td>\n<\/tr>\n | \n| <\/td>\n | \n *<\/p>\n<\/td>\n | <\/td>\n | \n The process is executing a set-user-ID (set-group-ID) program that is owned by a user (group) other than the real user (group) ID of the process, or the process is executing a program that has file capabilities (see capabilities<\/b>(7)). (However, see the description of the prctl<\/b>(2) PR_SET_DUMPABLE<\/b> operation, and the description of the \/proc\/sys\/fs\/suid_dumpable<\/i> file in proc<\/b>(5).)<\/p>\n<\/td>\n<\/tr>\n\n| <\/td>\n | \n *<\/p>\n<\/td>\n | <\/td>\n | \n \/proc\/sys\/kernel\/core_pattern<\/i> is empty and \/proc\/sys\/kernel\/core_uses_pid<\/i> contains the value 0. (These files are described below.) Note that if \/proc\/sys\/kernel\/core_pattern<\/i> is empty and \/proc\/sys\/kernel\/core_uses_pid<\/i> contains the value 1, core dump files will have names of the form .pid<\/i>, and such files are hidden unless one uses the ls<\/b>(1) \u2212a<\/i> option.<\/p>\n<\/td>\n<\/tr>\n\n| <\/td>\n | \n *<\/p>\n<\/td>\n | <\/td>\n | \n (Since Linux 3.7) The kernel was configured without the CONFIG_COREDUMP<\/b> option.<\/p>\n<\/td>\n<\/tr>\n<\/table>\n In addition, a core dump may exclude part of the address space of the process if the madvise<\/b>(2) MADV_DONTDUMP<\/b> flag was employed.<\/p>\n On systems that employ systemd<\/b>(1) as the init<\/i> framework, core dumps may instead be placed in a location determined by systemd<\/b>(1). See below for further details.<\/p>\n Naming of core dump files<\/b>
By default, a core dump file is named core<\/i>, but the \/proc\/sys\/kernel\/core_pattern<\/i> file (since Linux 2.6 and 2.4.21) can be set to define a template that is used to name core dump files. The template can contain % specifiers which are substituted by the following values when a core file is created:<\/p>\n\n\n| <\/td>\n | \n %%<\/p>\n<\/td>\n | <\/td>\n | \n A single % character.<\/p>\n<\/td>\n<\/tr>\n | \n| <\/td>\n | \n %c<\/p>\n<\/td>\n | <\/td>\n | \n Core file size soft resource limit of crashing process (since Linux 2.6.24).<\/p>\n<\/td>\n<\/tr>\n | \n| <\/td>\n | \n %d<\/p>\n<\/td>\n | <\/td>\n | \n Dump mode\u2014same as value returned by prctl<\/b>(2) PR_GET_DUMPABLE<\/b> (since Linux 3.7).<\/p>\n<\/td>\n<\/tr>\n\n| <\/td>\n | \n %e<\/p>\n<\/td>\n | <\/td>\n | \n The process or thread\u2019s comm<\/i> value, which typically is the same as the executable filename (without path prefix, and truncated to a maximum of 15 characters), but may have been modified to be something different; see the discussion of \/proc\/[pid]\/comm<\/i> and \/proc\/[pid]\/task\/[tid]\/comm<\/i> in proc<\/b>(5).<\/p>\n<\/td>\n<\/tr>\n\n| <\/td>\n | \n %E<\/p>\n<\/td>\n | <\/td>\n | \n Pathname of executable, with slashes (‘\/’) replaced by exclamation marks (‘!’) (since Linux 3.0).<\/p>\n<\/td>\n<\/tr>\n | \n| <\/td>\n | \n %g<\/p>\n<\/td>\n | <\/td>\n | \n Numeric real GID of dumped process.<\/p>\n<\/td>\n<\/tr>\n | \n| <\/td>\n | \n %h<\/p>\n<\/td>\n | <\/td>\n | \n Hostname (same as nodename<\/i> returned by uname<\/b>(2)).<\/p>\n<\/td>\n<\/tr>\n\n| <\/td>\n | \n %i<\/p>\n<\/td>\n | <\/td>\n | \n TID of thread that triggered core dump, as seen in the PID namespace in which the thread resides (since Linux 3.18).<\/p>\n<\/td>\n<\/tr>\n | \n| <\/td>\n | \n %I<\/p>\n<\/td>\n | <\/td>\n | \n TID of thread that triggered core dump, as seen in the initial PID namespace (since Linux 3.18).<\/p>\n<\/td>\n<\/tr>\n | \n| <\/td>\n | \n %p<\/p>\n<\/td>\n | <\/td>\n | \n PID of dumped process, as seen in the PID namespace in which the process resides.<\/p>\n<\/td>\n<\/tr>\n | \n| <\/td>\n | \n %P<\/p>\n<\/td>\n | <\/td>\n | \n PID of dumped process, as seen in the initial PID namespace (since Linux 3.12).<\/p>\n<\/td>\n<\/tr>\n | \n| <\/td>\n | \n %s<\/p>\n<\/td>\n | <\/td>\n | \n Number of signal causing dump.<\/p>\n<\/td>\n<\/tr>\n | \n| <\/td>\n | \n %t<\/p>\n<\/td>\n | <\/td>\n | \n Time of dump, expressed as seconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC).<\/p>\n<\/td>\n<\/tr>\n | \n| <\/td>\n | \n %u<\/p>\n<\/td>\n | <\/td>\n | \n Numeric real UID of dumped process.<\/p>\n<\/td>\n<\/tr>\n<\/table>\n A single % at the end of the template is dropped from the core filename, as is the combination of a % followed by any character other than those listed above. All other characters in the template become a literal part of the core filename. The template may include ‘\/’ characters, which are interpreted as delimiters for directory names. The maximum size of the resulting core filename is 128 bytes (64 bytes in kernels before 2.6.19). The default value in this file is “core”. For backward compatibility, if \/proc\/sys\/kernel\/core_pattern<\/i> does not include %p<\/i> and \/proc\/sys\/kernel\/core_uses_pid<\/i> (see below) is nonzero, then .PID will be appended to the core filename.<\/p>\n Paths are interpreted according to the settings that are active for the crashing process. That means the crashing process\u2019s mount namespace (see mount_namespaces<\/b>(7)), its current working directory (found via getcwd<\/b>(2)), and its root directory (see chroot<\/b>(2)).<\/p>\n Since version 2.4, Linux has also provided a more primitive method of controlling the name of the core dump file. If the \/proc\/sys\/kernel\/core_uses_pid<\/i> file contains the value 0, then a core dump file is simply named core<\/i>. If this file contains a nonzero value, then the core dump file includes the process ID in a name of the form core.PID<\/i>.<\/p>\n Since Linux 3.6, if \/proc\/sys\/fs\/suid_dumpable<\/i> is set to 2 (“suidsafe”), the pattern must be either an absolute pathname (starting with a leading ‘\/’ character) or a pipe, as defined below.<\/p>\n Piping core dumps to a program<\/b>
Since kernel 2.6.19, Linux supports an alternate syntax for the \/proc\/sys\/kernel\/core_pattern<\/i> file. If the first character of this file is a pipe symbol (|<\/b>), then the remainder of the line is interpreted as the command-line for a user-space program (or script) that is to be executed.<\/p>\n Since kernel 5.3.0, the pipe template is split on spaces into an argument list before<\/i> the template parameters are expanded. In earlier kernels, the template parameters are expanded first and the resulting string is split on spaces into an argument list. This means that in earlier kernels executable names added by the %e<\/i> and %E<\/i> template parameters could get split into multiple arguments. So the core dump handler needs to put the executable names as the last argument and ensure it joins all parts of the executable name using spaces. Executable names with multiple spaces in them are not correctly represented in earlier kernels, meaning that the core dump handler needs to use mechanisms to find the executable name.<\/p>\n Instead of being written to a file, the core dump is given as standard input to the program. Note the following points:<\/p>\n \n\n| <\/td>\n | \n *<\/p>\n<\/td>\n | <\/td>\n | \n The program must be specified using an absolute pathname (or a pathname relative to the root directory, \/<\/i>), and must immediately follow the \u2019|\u2019 character.<\/p>\n<\/td>\n<\/tr>\n\n| <\/td>\n | \n *<\/p>\n<\/td>\n | <\/td>\n | \n The command-line arguments can include any of the % specifiers listed above. For example, to pass the PID of the process that is being dumped, specify %p<\/i> in an argument.<\/p>\n<\/td>\n<\/tr>\n\n| <\/td>\n | \n *<\/p>\n<\/td>\n | <\/td>\n | \n The process created to run the program runs as user and group root<\/i>.<\/p>\n<\/td>\n<\/tr>\n\n| <\/td>\n | \n *<\/p>\n<\/td>\n | <\/td>\n | \n Running as root<\/i> does not confer any exceptional security bypasses. Namely, LSMs (e.g., SELinux) are still active and may prevent the handler from accessing details about the crashed process via \/proc\/[pid]<\/i>.<\/p>\n<\/td>\n<\/tr>\n\n| <\/td>\n | \n *<\/p>\n<\/td>\n | <\/td>\n | \n The program pathname is interpreted with respect to the initial mount namespace as it is always executed there. It is not affected by the settings (e.g., root directory, mount namespace, current working directory) of the crashing process.<\/p>\n<\/td>\n<\/tr>\n | \n| <\/td>\n | \n *<\/p>\n<\/td>\n | <\/td>\n | \n The process runs in the initial namespaces (PID, mount, user, and so on) and not in the namespaces of the crashing process. One can utilize specifiers such as %P<\/i> to find the right \/proc\/[pid]<\/i> directory and probe\/enter the crashing process\u2019s namespaces if needed.<\/p>\n<\/td>\n<\/tr>\n\n| <\/td>\n | \n *<\/p>\n<\/td>\n | <\/td>\n | \n The process starts with its current working directory as the root directory. If desired, it is possible change to the working directory of the dumping process by employing the value provided by the %P<\/i> specifier to change to the location of the dumping process via \/proc\/[pid]\/cwd<\/i>.<\/p>\n<\/td>\n<\/tr>\n\n| <\/td>\n | \n *<\/p>\n<\/td>\n | <\/td>\n | \n 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).<\/p>\n<\/td>\n<\/tr>\n | \n| <\/td>\n | \n *<\/p>\n<\/td>\n | <\/td>\n | \n The RLIMIT_CORE<\/b> limit is not enforced for core dumps that are piped to a program via this mechanism.<\/p>\n<\/td>\n<\/tr>\n<\/table>\n \/proc\/sys\/kernel\/core_pipe_limit<\/b>
When collecting core dumps via a pipe to a user-space program, it can be useful for the collecting program to gather data about the crashing process from that process\u2019s \/proc\/[pid]<\/i> directory. In order to do this safely, the kernel must wait for the program collecting the core dump to exit, so as not to remove the crashing process\u2019s \/proc\/[pid]<\/i> files prematurely. This in turn creates the possibility that a misbehaving collecting program can block the reaping of a crashed process by simply never exiting.<\/p>\n Since Linux 2.6.32, the \/proc\/sys\/kernel\/core_pipe_limit<\/i> can be used to defend against this possibility. The value in this file defines how many concurrent crashing 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.<\/p>\n 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 program is not guaranteed access to \/proc\/<\/i>). The default value for this file is 0.<\/p>\nControlling which mappings are written to the core dump<\/b>
Since kernel 2.6.23, the Linux-specific \/proc\/[pid]\/coredump_filter<\/i> 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.<\/p>\n The value in the file is a bit mask of memory mapping types (see mmap<\/b>(2)). If a bit is set in the mask, then memory mappings of the corresponding type are dumped; otherwise they are not dumped. The bits in this file have the following meanings:<\/p>\n | | | | | | | | | | | | | | | |