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File Formats                                              core(4)



NAME
     core - process core file

DESCRIPTION
     The operating system writes out a core file  for  a  process
     when the process is terminated due to the receipt of 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 termi-
     nation  of a process resulting from a bug in the correspond-
     ing 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 configured 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 work-
     ing directory.

     A process will terminate and produce 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  gen-
     erating  a core file is shown in signal(3HEAD). Therefore, a
     process might not produce a core file if it has  blocked  or
     modified the behavior of the corresponding signal. Addition-
     ally, no core dump can be created under the following condi-
     tions:

        o  If  normal  file  and  directory  access   permissions
           prevent  the  creation  or  modification  of  the per-
           process core file pathname by the current process user
           and  group  ID. This test does not apply to the global
           core file pathname because the  global  core  file  is
           always written as the superuser.

        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



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File Formats                                              core(4)



           /var/core/`uname -n` has been created, no global  core
           files will be 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. Refer to setrlimit(2) and ulimit(1)
           for more information on resource limits.

        o  If the core file name already exists in  the  destina-
           tion  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 dif-
           ferent 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 explicitly granted permission
           to produce core files using coreadm(1M), at  the  risk
           of exposing secure information.

     The core file contains all the process information pertinent
     to   debugging:  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 seg-
     ment that was part of the process address  space,  including
     shared  library  segments. The contents of the writable seg-
     ments are also part of the core image.

     The program header of an ELF core file also contains 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 compatibility 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 will be deleted from core
     files in a future release.




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File Formats                                              core(4)



     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
           system as startup information to the  dynamic  linker.
           Auxiliary    vector    information   is   defined   in
           <sys/auxv.h>.

     Following these entries, for each 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
           contains  all  of  the unspilled register windows. The
           gwindows_t structure is defined in <sys/regset.h>.

     prxregset_t



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File Formats                                              core(4)



           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 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  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 system, 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 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
           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 pro-
           cess 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 structure 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



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File Formats                                              core(4)



           structure  includes space for one supplementary group.
           If  pr_ngroups  is  greater  than  1,  there  will  be
           pr_ngroups  -  1  gid_t items following the structure;
           otherwise, there will be no additional data.

     struct ssd array
           n_type: NT_LDT. This entry is present only on an  IA32
           (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 multithreaded process.  The
           ssd structure is defined in <sys/sysi86.h>.

     Following these entries, for each LWP in  the  process,  the
     new NOTE segment contains an entry with an lwpsinfo_t struc-
     ture plus an entry with an lwpstatus_t structure, plus other
     optionally-present entries describing the LWP, as follows:

     lwpsinfo_t
           n_type: NT_LWPSINFO. This structure contains  informa-
           tion  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>.

     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 pro-
           cess. It contains the ancillary  state  registers  for
           the   LWP.   The  asrset_t  structure  is  defined  in



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File Formats                                              core(4)



           <sys/regset.h>.

     The size of the core file created by a process may  be  con-
     trolled by the user (see getrlimit(2)).

SEE ALSO
     gcore(1), mdb(1), proc(1), ps(1), coreadm(1M), getrlimit(2),
     setrlimit(2),  setuid(2),  sysinfo(2),  uname(2), elf(3ELF),
     signal(3HEAD), a.out(4), proc(4)

     ANSI C Programmer's Guide












































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