core(4) File Formats core(4)NAMEcore - process core file
DESCRIPTION
The operating system writes out a core file for a process when the
process is terminated due to receiving certain signals. A core file is
a disk copy of the contents of the process address space at the time
the process received the signal, along with additional information
about the state of the process. This information can be consumed by a
debugger. Core files can also be generated by applying the gcore(1)
utility to a running process.
Typically, core files are produced following abnormal termination of a
process resulting from a bug in the corresponding application. Whatever
the cause, the core file itself provides invaluable information to the
programmer or support engineer to aid in diagnosing the problem. The
core file can be inspected using a debugger such as dbx(1) or mdb(1) or
by applying one of the proc(1) tools.
The operating system attempts to create up to two core files for each
abnormally terminating process, using a global core file name pattern
and a per-process core file name pattern. These patterns are expanded
to determine the pathname of the resulting core files, and can be con‐
figured by coreadm(1M). By default, the global core file pattern is
disabled and not used, and the per-process core file pattern is set to
core. Therefore, by default, the operating system attempts to create a
core file named core in the process's current working directory.
A process terminates and produces a core file whenever it receives one
of the signals whose default disposition is to cause a core dump. The
list of signals that result in generating a core file is shown in sig‐
nal.h(3HEAD). Therefore, a process might not produce a core file if it
has blocked or modified the behavior of the corresponding signal. Addi‐
tionally, no core dump can be created under the following conditions:
o If normal file and directory access permissions prevent the
creation or modification of the per-process core file path‐
name by the current process user and group ID. This test
does not apply to the global core file pathname because,
regardless of the UID of the process dumping core, the
attempt to write the global core file is made as the supe‐
ruser.
o Core files owned by the user nobody will not be produced.
For example, core files generated for the superuser on an
NFS directory are owned by nobody and are, therefore, not
written.
o If the core file pattern expands to a pathname that contains
intermediate directory components that do not exist. For
example, if the global pattern is set to
/var/core/%n/core.%p, and no directory /var/core/`uname -n`
has been created, no global core files are produced.
o If the destination directory is part of a filesystem that is
mounted read-only.
o If the resource limit RLIMIT_CORE has been set to 0 for the
process, no per-process core file is produced. Refer to
setrlimit(2) and ulimit(1) for more information on resource
limits.
o If the core file name already exists in the destination
directory and is not a regular file (that is, is a symlink,
block or character special-file, and so forth).
o If the kernel cannot open the destination file O_EXCL, which
can occur if same file is being created by another process
simultaneously.
o If the process's effective user ID is different from its
real user ID or if its effective group ID is different from
its real group ID. Similarly, set-user-ID and set-group-ID
programs do not produce core files as this could potentially
compromise system security. These processes can be explic‐
itly granted permission to produce core files using core‐
adm(1M), at the risk of exposing secure information.
The core file contains all the process information pertinent to debug‐
ging: contents of hardware registers, process status, and process data.
The format of a core file is object file specific.
For ELF executable programs (see a.out(4)), the core file generated is
also an ELF file, containing ELF program and file headers. The e_type
field in the file header has type ET_CORE. The program header contains
an entry for every segment that was part of the process address space,
including shared library segments. The contents of the mappings speci‐
fied by coreadm(1M) are also part of the core image. Each program
header has its p_memsz field set to the size of the mapping. The pro‐
gram headers that represent mappings whose data is included in the core
file have their p_filesz field set the same as p_memsz, otherwise
p_filesz is zero.
A mapping's data can be excluded due to the core file content settings
(see coreadm(1M)), or due to some failure. If the data is excluded
because of a failure, the program header entry will have the
PF_SUNW_FAILURE flag set in its p_flags field.
The program headers of an ELF core file also contain entries for two
NOTE segments, each containing several note entries as described below.
The note entry header and core file note type (n_type) definitions are
contained in <sys/elf.h>. The first NOTE segment exists for binary com‐
patibility with old programs that deal with core files. It contains
structures defined in <sys/old_procfs.h>. New programs should recognize
and skip this NOTE segment, advancing instead to the new NOTE segment.
The old NOTE segment is deleted from core files in a future release.
The old NOTE segment contains the following entries. Each has entry
name "CORE" and presents the contents of a system structure:
prpsinfo_t n_type: NT_PRPSINFO. This entry contains information of
interest to the ps(1) command, such as process status,
CPU usage, nice value, controlling terminal, user-ID,
process-ID, the name of the executable, and so forth.
The prpsinfo_t structure is defined in
<sys/old_procfs.h>.
char array n_type: NT_PLATFORM. This entry contains a string
describing the specific model of the hardware platform
on which this core file was created. This information
is the same as provided by sysinfo(2) when invoked with
the command SI_PLATFORM.
auxv_t array n_type: NT_AUXV. This entry contains the array of
auxv_t structures that was passed by the operating sys‐
tem as startup information to the dynamic linker. Aux‐
iliary vector information is defined in <sys/auxv.h>.
Following these entries, for each active (non-zombie) light-weight
process (LWP) in the process, the old NOTE segment contains an entry
with a prstatus_t structure, plus other optionally-present entries
describing the LWP, as follows:
prstatus_t n_type: NT_PRSTATUS. This structure contains things of
interest to a debugger from the operating system, such
as the general registers, signal dispositions, state,
reason for stopping, process-ID, and so forth. The
prstatus_t structure is defined in <sys/old_procfs.h>.
prfpregset_t n_type: NT_PRFPREG. This entry is present only if the
LWP used the floating-point hardware. It contains the
floating-point registers. The prfpregset_t structure is
defined in <sys/procfs_isa.h>.
gwindows_t n_type: NT_GWINDOWS. This entry is present only on a
SPARC machine and only if the system was unable to
flush all of the register windows to the stack. It con‐
tains all of the unspilled register windows. The gwin‐
dows_t structure is defined in <sys/regset.h>.
prxregset_t n_type: NT_PRXREG. This entry is present only if the
machine has extra register state associated with it. It
contains the extra register state. The prxregset_t
structure is defined in <sys/procfs_isa.h>.
The new NOTE segment contains the following entries. Each has entry
name "CORE" and presents the contents of a system structure:
psinfo_t n_type: NT_PSINFO. This structure contains informa‐
tion of interest to the ps(1) command, such as
process status, CPU usage, nice value, controlling
terminal, user-ID, process-ID, the name of the exe‐
cutable, and so forth. The psinfo_t structure is
defined in <sys/procfs.h>.
pstatus_t n_type: NT_PSTATUS. This structure contains things
of interest to a debugger from the operating sys‐
tem, such as pending signals, state, process-ID,
and so forth. The pstatus_t structure is defined in
<sys/procfs.h>.
char array n_type: NT_PLATFORM. This entry contains a string
describing the specific model of the hardware plat‐
form on which this core file was created. This
information is the same as provided by sysinfo(2)
when invoked with the command SI_PLATFORM.
auxv_t array n_type: NT_AUXV. This entry contains the array of
auxv_t structures that was passed by the operating
system as startup information to the dynamic
linker. Auxiliary vector information is defined in
<sys/auxv.h>.
struct utsname n_type: NT_UTSNAME. This structure contains the
system information that would have been returned to
the process if it had performed a uname(2) system
call prior to dumping core. The utsname structure
is defined in <sys/utsname.h>.
prcred_t n_type: NT_PRCRED. This structure contains the
process credentials, including the real, saved, and
effective user and group IDs. The prcred_t struc‐
ture is defined in <aasys/procfs.h>. Following the
structure is an optional array of supplementary
group IDs. The total number of supplementary group
IDs is given by the pr_ngroups member of the
prcred_t structure, and the structure includes
space for one supplementary group. If pr_ngroups is
greater than 1, there is pr_ngroups - 1 gid_t items
following the structure; otherwise, there is no
additional data.
char array n_type: NT_ZONENAME. This entry contains a string
which describes the name of the zone in which the
process was running. See zones(5). The information
is the same as provided by getzonenamebyid(3C) when
invoked with the numerical ID returned by get‐
zoneid(3C).
struct ssd array n_type: NT_LDT. This entry is present only on an
32-bit x86 machine and only if the process has set
up a Local Descriptor Table (LDT). It contains an
array of structures of type struct ssd, each of
which was typically used to set up the %gs segment
register to be used to fetch the address of the
current thread information structure in a multi‐
threaded process. The ssd structure is defined in
<sys/sysi86.h>.
core_content_t n_type: NT_CONTENT. This optional entry indicates
which parts of the process image are specified to
be included in the core file. See coreadm(1M).
Following these entries, for each active and zombie LWP in the process,
the new NOTE segment contains an entry with an lwpsinfo_t structure
plus, for a non-zombie LWP, an entry with an lwpstatus_t structure,
plus other optionally-present entries describing the LWP, as follows. A
zombie LWP is a non-detached LWP that has terminated but has not yet
been reaped by another LWP in the same process.
lwpsinfo_t n_type: NT_LWPSINFO. This structure contains information
of interest to the ps(1) command, such as LWP status,
CPU usage, nice value, LWP-ID, and so forth. The
lwpsinfo_t structure is defined in <sys/procfs.h>. This
is the only entry present for a zombie LWP.
lwpstatus_t n_type: NT_LWPSTATUS. This structure contains things of
interest to a debugger from the operating system, such
as the general registers, the floating point registers,
state, reason for stopping, LWP-ID, and so forth. The
lwpstatus_t structure is defined in <sys/procfs.h>>.
gwindows_t n_type: NT_GWINDOWS. This entry is present only on a
SPARC machine and only if the system was unable to flush
all of the register windows to the stack. It contains
all of the unspilled register windows. The gwindows_t
structure is defined in <sys/regset.h>.
prxregset_t n_type: NT_PRXREG. This entry is present only if the
machine has extra register state associated with it. It
contains the extra register state. The prxregset_t
structure is defined in <sys/procfs_isa.h>.
asrset_t n_type: NT_ASRS. This entry is present only on a SPARC
V9 machine and only if the process is a 64-bit process.
It contains the ancillary state registers for the LWP.
The asrset_t structure is defined in <sys/regset.h>.
Depending on the coreadm(1M) settings, the section header of an ELF
core file can contain entries for CTF, symbol table, and string table
sections. The sh_addr fields are set to the base address of the first
mapping of the load object that they came from to. This can be used to
match those sections with the corresponding load object.
The size of the core file created by a process can be controlled by the
user (see getrlimit(2)).
SEE ALSOelfdump(1), gcore(1), mdb(1), proc(1), ps(1), coreadm(1M), getr‐
limit(2), setrlimit(2), setuid(2), sysinfo(2), uname(2), getzonename‐
byid(3C), getzoneid(3C), elf(3ELF), signal.h(3HEAD), a.out(4), proc(4),
zones(5)
ANSI C Programmer's Guide
SunOS 5.11 13 May 2008 core(4)
