prctl

       #include <sys/prctl.h>

       int prctl(int option, unsigned long arg2, unsigned long arg3,
                 unsigned long arg4, unsigned long arg5);

DESCRIPTION
       prctl()  is  called  with  a first argument describing what to do (with
       values defined in <linux/prctl.h>), and further arguments with  a  sig-
       nificance depending on the first one.  The first argument can be:

       PR_CAP_AMBIENT (since Linux 4.3)
              Reads  or  changes  the ambient capability set, according to the
              value of arg2, which must be one of the following:

              PR_CAP_AMBIENT_RAISE
                     The capability specified in arg3 is added to the  ambient
                     set.  The specified capability must already be present in
                     both the  permitted  and  the  inheritable  sets  of  the
                     process.    This   operation  is  not  permitted  if  the
                     SECBIT_NO_CAP_AMBIENT_RAISE securebit is set.

              PR_CAP_AMBIENT_LOWER
                     The capability specified in  arg3  is  removed  from  the
                     ambient set.

              PR_CAP_AMBIENT_IS_SET
                     The  prctl(2) call returns 1 if the capability in arg3 is
                     in the ambient set and 0 if it is not.

              PR_CAP_AMBIENT_CLEAR_ALL
                     All capabilities will be removed from  the  ambient  set.
                     This operation requires setting arg3 to zero.

              In  all of the above operations, arg4 and arg5 must be specified
              as 0.

       PR_CAPBSET_READ (since Linux 2.6.25)
              Return (as the function result) 1 if the capability specified in
              arg2 is in the calling thread's capability bounding set, or 0 if
              it  is  not.   (The  capability   constants   are   defined   in
              <linux/capability.h>.)   The  capability  bounding  set dictates
              whether the process can receive the capability through a  file's
              permitted capability set on a subsequent call to execve(2).

              If  the capability specified in arg2 is not valid, then the call
              fails with the error EINVAL.

       PR_CAPBSET_DROP (since Linux 2.6.25)
              If the calling thread has the CAP_SETPCAP capability, then  drop
              the capability specified by arg2 from the calling thread's capa-
              bility bounding set.  Any children of the  calling  thread  will
              inherit the newly reduced bounding set.

              The  call fails with the error: EPERM if the calling thread does
              nated)  and marked as having a subreaper, the nearest still liv-
              ing ancestor subreaper will receive a SIGCHLD signal and be able
              to wait(2) on the process to discover its termination status.

       PR_GET_CHILD_SUBREAPER (since Linux 3.4)
              Return the "child subreaper" setting of the caller, in the loca-
              tion pointed to by (int *) arg2.

       PR_SET_DUMPABLE (since Linux 2.3.20)
              Set the state of the "dumpable" flag, which  determines  whether
              core dumps are produced for the calling process upon delivery of
              a signal whose default behavior is to produce a core dump.

              In kernels up to and including 2.6.12, arg2  must  be  either  0
              (SUID_DUMP_DISABLE,    process    is    not   dumpable)   or   1
              (SUID_DUMP_USER, process is dumpable).  Between  kernels  2.6.13
              and  2.6.17,  the  value  2 was also permitted, which caused any
              binary which normally would not be dumped to be dumped  readable
              by  root  only;  for  security  reasons,  this  feature has been
              removed.    (See   also   the   description   of   /proc/sys/fs/
              suid_dumpable in proc(5).)

              Normally,  this  flag  is set to 1.  However, it is reset to the
              current value contained in the  file  /proc/sys/fs/suid_dumpable
              (which  by  default  has  the  value 0), if any of the following
              attributes of the process are changed by the  operations  listed
              below:

              *  The effective user or group ID is changed.

              *  The  filesystem  user  or  group  ID  is changed (see creden-
                 tials(7)).

              *  The process's set of permitted  capabilities  (see  capabili-
                 ties(7))  is changed such that its new set of capabilities is
                 not a subset of its previous set of capabilities.

              The operations that may trigger changes  to  the  dumpable  flag
              include:

              *  execution  (execve(2))  of a set-user-ID or set-group-ID pro-
                 gram, or a  program  that  has  capabilities  (see  capabili-
                 ties(7));

              *  capset(2); and

              *  system  calls that change process credentials (setuid(2) set-
                 gid(2), setresuid(2), setresgid(2), setgroups(2), and so on).

              Processes  that  are  not  dumpable  can  not  be  attached  via
              ptrace(2) PTRACE_ATTACH.

       PR_GET_DUMPABLE (since Linux 2.3.20)
              Return (as the function result) the current state of the calling

       PR_SET_FPEMU (since Linux 2.4.18, 2.5.9, only on ia64)
              Set  floating-point  emulation  control  bits  to  arg2.    Pass
              PR_FPEMU_NOPRINT  to  silently  emulate floating-point operation
              accesses, or PR_FPEMU_SIGFPE to not emulate floating-point oper-
              ations and send SIGFPE instead.

       PR_GET_FPEMU (since Linux 2.4.18, 2.5.9, only on ia64)
              Return  floating-point  emulation  control bits, in the location
              pointed to by (int *) arg2.

       PR_SET_FPEXC (since Linux 2.4.21, 2.5.32, only on PowerPC)
              Set   floating-point   exception    mode    to    arg2.     Pass
              PR_FP_EXC_SW_ENABLE  to  use  FPEXC  for  FP  exception enables,
              PR_FP_EXC_DIV for floating-point divide by  zero,  PR_FP_EXC_OVF
              for  floating-point  overflow,  PR_FP_EXC_UND for floating-point
              underflow,  PR_FP_EXC_RES  for  floating-point  inexact  result,
              PR_FP_EXC_INV     for    floating-point    invalid    operation,
              PR_FP_EXC_DISABLED for FP exceptions disabled,  PR_FP_EXC_NONRE-
              COV for async nonrecoverable exception mode, PR_FP_EXC_ASYNC for
              async recoverable exception mode, PR_FP_EXC_PRECISE for  precise
              exception mode.

       PR_GET_FPEXC (since Linux 2.4.21, 2.5.32, only on PowerPC)
              Return floating-point exception mode, in the location pointed to
              by (int *) arg2.

       PR_SET_KEEPCAPS (since Linux 2.2.18)
              Set the state of the thread's "keep  capabilities"  flag,  which
              determines  whether  the  threads's  permitted capability set is
              cleared when a change is made to the  threads's  user  IDs  such
              that  the threads's real UID, effective UID, and saved set-user-
              ID all become nonzero when at least one of them  previously  had
              the  value  0.   By  default,  the  permitted  capability set is
              cleared when such a change is made; setting the "keep  capabili-
              ties"  flag prevents it from being cleared.  arg2 must be either
              0 (permitted capabilities are cleared) or 1 (permitted capabili-
              ties  are kept).  (A thread's effective capability set is always
              cleared when such a credential change is made, regardless of the
              setting  of  the "keep capabilities" flag.)  The "keep capabili-
              ties" value will be reset to 0 on subsequent calls to execve(2).

       PR_GET_KEEPCAPS (since Linux 2.2.18)
              Return (as the function result) the current state of the calling
              threads's "keep capabilities" flag.

       PR_MCE_KILL (since Linux 2.6.32)
              Set the machine check memory corruption kill policy for the cur-
              rent thread.  If arg2 is  PR_MCE_KILL_CLEAR,  clear  the  thread
              memory  corruption  kill policy and use the system-wide default.
              (The system-wide default is defined by /proc/sys/vm/memory_fail-
              ure_early_kill; see proc(5).)  If arg2 is PR_MCE_KILL_SET, use a
              thread-specific memory corruption kill policy.   In  this  case,
              arg3    defines    whether    the    policy    is   early   kill
              (PR_MCE_KILL_EARLY), late kill (PR_MCE_KILL_LATE), or  the  sys-

       PR_SET_MM (since Linux 3.3)
              Modify certain kernel memory map descriptor fields of the  call-
              ing  process.   Usually  these  fields are set by the kernel and
              dynamic loader (see ld.so(8) for more information) and a regular
              application  should  not  use  this feature.  However, there are
              cases, such as self-modifying programs, where  a  program  might
              find  it  useful  to change its own memory map.  This feature is
              available only if the kernel is  built  with  the  CONFIG_CHECK-
              POINT_RESTORE option enabled.  The calling process must have the
              CAP_SYS_RESOURCE capability.  The value in arg2 is  one  of  the
              options below, while arg3 provides a new value for the option.

              PR_SET_MM_START_CODE
                     Set  the  address  above  which the program text can run.
                     The corresponding memory area must be readable  and  exe-
                     cutable,  but  not  writable or sharable (see mprotect(2)
                     and mmap(2) for more information).

              PR_SET_MM_END_CODE
                     Set the address below which the  program  text  can  run.
                     The  corresponding  memory area must be readable and exe-
                     cutable, but not writable or sharable.

              PR_SET_MM_START_DATA
                     Set the address above which initialized and uninitialized
                     (bss)  data  are  placed.   The corresponding memory area
                     must be readable and  writable,  but  not  executable  or
                     sharable.

              PR_SET_MM_END_DATA
                     Set the address below which initialized and uninitialized
                     (bss) data are placed.   The  corresponding  memory  area
                     must  be  readable  and  writable,  but not executable or
                     sharable.

              PR_SET_MM_START_STACK
                     Set the start address of the  stack.   The  corresponding
                     memory area must be readable and writable.

              PR_SET_MM_START_BRK
                     Set  the  address  above  which  the  program heap can be
                     expanded with brk(2) call.  The address must  be  greater
                     than  the ending address of the current program data seg-
                     ment.  In addition, the combined size  of  the  resulting
                     heap  and  the  size of the data segment can't exceed the
                     RLIMIT_DATA resource limit (see setrlimit(2)).

              PR_SET_MM_BRK
                     Set the current brk(2) value.  The requirements  for  the
                     address  are  the  same  as  for  the PR_SET_MM_START_BRK
                     option.

              The following options are available since Linux 3.5.

              PR_SET_MM_ENV_END
                     Set  the  address  below which the program environment is
                     placed.

                     The    address    passed    with     PR_SET_MM_ARG_START,
                     PR_SET_MM_ARG_END,        PR_SET_MM_ENV_START,        and
                     PR_SET_MM_ENV_END should belong to a process stack  area.
                     Thus,  the  corresponding  memory  area must be readable,
                     writable, and (depending  on  the  kernel  configuration)
                     have the MAP_GROWSDOWN attribute set (see mmap(2)).

              PR_SET_MM_AUXV
                     Set  a  new  auxiliary  vector.  The arg3 argument should
                     provide the address of the vector.  The arg4 is the  size
                     of the vector.

              PR_SET_MM_EXE_FILE
                     Supersede  the /proc/pid/exe symbolic link with a new one
                     pointing to a new executable file identified by the  file
                     descriptor  provided in arg3 argument.  The file descrip-
                     tor should be obtained with a regular open(2) call.

                     To change the symbolic  link,  one  needs  to  unmap  all
                     existing executable memory areas, including those created
                     by the kernel itself (for example the kernel usually cre-
                     ates  at  least  one  executable  memory area for the ELF
                     .text section).

                     The second limitation is that  such  transitions  can  be
                     done  only  once  in  a  process  life time.  Any further
                     attempts will  be  rejected.   This  should  help  system
                     administrators  monitor unusual symbolic-link transitions
                     over all processes running on a system.

       PR_MPX_ENABLE_MANAGEMENT, PR_MPX_DISABLE_MANAGEMENT (since Linux 3.19)
              Enable or disable kernel management of Memory Protection  eXten-
              sions (MPX) bounds tables.  The arg2, arg3, arg4, and arg5 argu-
              ments must be zero.

              MPX is  a  hardware-assisted  mechanism  for  performing  bounds
              checking on pointers.  It consists of a set of registers storing
              bounds information and a set  of  special  instruction  prefixes
              that  tell  the  CPU  on  which instructions it should do bounds
              enforcement.  There is a limited number of these  registers  and
              when there are more pointers than registers, their contents must
              be "spilled" into a set of  tables.   These  tables  are  called
              "bounds  tables"  and the MPX prctl() operations control whether
              the kernel manages their allocation and freeing.

              When management is enabled, the kernel will take over allocation
              and  freeing of the bounds tables.  It does this by trapping the
              #BR exceptions that result at first use of missing bounds tables
              and  instead of delivering the exception to user space, it allo-
              cates the table and populates  the  bounds  directory  with  the
              MPX  by looking for the 'mpx' CPUID bit, like with the following
              command:

                   cat /proc/cpuinfo | grep ' mpx '

              A thread may not switch in or out of long  (64-bit)  mode  while
              MPX is enabled.

              All threads in a process are affected by these calls.

              The  child  of  a  fork(2) inherits the state of MPX management.
              During execve(2), MPX management is  reset  to  a  state  as  if
              PR_MPX_DISABLE_MANAGEMENT had been called.

              For further information on Intel MPX, see the kernel source file
              Documentation/x86/intel_mpx.txt.

       PR_SET_NAME (since Linux 2.6.9)
              Set the name of the calling thread, using the value in the loca-
              tion  pointed  to  by  (char *)  arg2.  The name can be up to 16
              bytes long, including the terminating null byte.  (If the length
              of  the  string, including the terminating null byte, exceeds 16
              bytes, the string is silently  truncated.)   This  is  the  same
              attribute   that   can  be  set  via  pthread_setname_np(3)  and
              retrieved using pthread_getname_np(3).  The attribute  is  like-
              wise accessible via /proc/self/task/[tid]/comm, where tid is the
              name of the calling thread.

       PR_GET_NAME (since Linux 2.6.11)
              Return the name of the calling thread, in the buffer pointed  to
              by  (char *)  arg2.   The buffer should allow space for up to 16
              bytes; the returned string will be null-terminated.

       PR_SET_NO_NEW_PRIVS (since Linux 3.5)
              Set the calling process's no_new_privs bit to the value in arg2.
              With  no_new_privs  set  to  1,  execve(2) promises not to grant
              privileges to do anything that could not have been done  without
              the  execve(2)  call (for example, rendering the set-user-ID and
              set-group-ID mode bits, and file  capabilities  non-functional).
              Once  set, this bit cannot be unset.  The setting of this bit is
              inherited by children created by fork(2) and clone(2), and  pre-
              served across execve(2).

              For  more  information,  see  the  kernel source file Documenta-
              tion/prctl/no_new_privs.txt.

       PR_GET_NO_NEW_PRIVS (since Linux 3.5)
              Return (as the function result) the value  of  the  no_new_privs
              bit for the current process.  A value of 0 indicates the regular
              execve(2) behavior.  A value of 1 indicates execve(2) will oper-
              ate in the privilege-restricting mode described above.

       PR_SET_PDEATHSIG (since Linux 2.1.57)
              Set  the  parent  death  signal  of  the calling process to arg2
              parent process terminate.

       PR_GET_PDEATHSIG (since Linux 2.3.15)
              Return the current value of the parent process death signal,  in
              the location pointed to by (int *) arg2.

       PR_SET_PTRACER (since Linux 3.4)
              This is meaningful only when the Yama LSM is enabled and in mode
              1   ("restricted    ptrace",    visible    via    /proc/sys/ker-
              nel/yama/ptrace_scope).   When  a "ptracer process ID" is passed
              in arg2, the caller is declaring that the  ptracer  process  can
              ptrace(2)  the  calling  process  as if it were a direct process
              ancestor.  Each PR_SET_PTRACER operation replaces  the  previous
              "ptracer process ID".  Employing PR_SET_PTRACER with arg2 set to
              0  clears  the  caller's  "ptracer  process  ID".   If  arg2  is
              PR_SET_PTRACER_ANY,  the  ptrace restrictions introduced by Yama
              are effectively disabled for the calling process.

              For further information, see the kernel source  file  Documenta-
              tion/security/Yama.txt.

       PR_SET_SECCOMP (since Linux 2.6.23)
              Set  the secure computing (seccomp) mode for the calling thread,
              to limit the available system calls.  The more recent seccomp(2)
              system   call  provides  a  superset  of  the  functionality  of
              PR_SET_SECCOMP.

              The seccomp mode is selected via arg2.  (The  seccomp  constants
              are defined in <linux/seccomp.h>.)

              With arg2 set to SECCOMP_MODE_STRICT, the only system calls that
              the thread is permitted to make are read(2), write(2),  _exit(2)
              (but  not  exit_group(2)), and sigreturn(2).  Other system calls
              result in the delivery of a SIGKILL signal.  Strict secure  com-
              puting mode is useful for number-crunching applications that may
              need to execute untrusted byte code, perhaps obtained by reading
              from  a pipe or socket.  This operation is available only if the
              kernel is configured with CONFIG_SECCOMP enabled.

              With arg2 set to SECCOMP_MODE_FILTER (since Linux 3.5), the sys-
              tem  calls allowed are defined by a pointer to a Berkeley Packet
              Filter passed in arg3.  This argument is  a  pointer  to  struct
              sock_fprog;  it can be designed to filter arbitrary system calls
              and system call arguments.  This mode is available only  if  the
              kernel is configured with CONFIG_SECCOMP_FILTER enabled.

              If  SECCOMP_MODE_FILTER filters permit fork(2), then the seccomp
              mode is inherited by children created by fork(2);  if  execve(2)
              is   permitted,  then  the  seccomp  mode  is  preserved  across
              execve(2).  If the filters permit prctl() calls, then additional
              filters can be added; they are run in order until the first non-
              allow result is seen.

              For further information, see the kernel source  file  Documenta-

              Since  Linux  3.8,  the  Seccomp field of the /proc/[pid]/status
              file provides a method of obtaining the same information,  with-
              out the risk that the process is killed; see proc(5).

       PR_SET_SECUREBITS (since Linux 2.6.26)
              Set  the  "securebits"  flags of the calling thread to the value
              supplied in arg2.  See capabilities(7).

       PR_GET_SECUREBITS (since Linux 2.6.26)
              Return (as the function result) the "securebits"  flags  of  the
              calling thread.  See capabilities(7).

       PR_SET_THP_DISABLE (since Linux 3.15)
              Set  the state of the "THP disable" flag for the calling thread.
              If arg2 has a nonzero value, the flag is set,  otherwise  it  is
              cleared.   Setting  this  flag  provides  a method for disabling
              transparent huge pages for jobs where the code cannot  be  modi-
              fied,  and  using a malloc hook with madvise(2) is not an option
              (i.e., statically allocated data).  The setting of the "THP dis-
              able"  flag  is  inherited by a child created via fork(2) and is
              preserved across execve(2).

       PR_TASK_PERF_EVENTS_DISABLE (since Linux 2.6.31)
              Disable  all  performance  counters  attached  to  the   calling
              process, regardless of whether the counters were created by this
              process or another process.  Performance counters created by the
              calling  process  for  other processes are unaffected.  For more
              information on performance counters, see the Linux kernel source
              file tools/perf/design.txt.

              Originally  called  PR_TASK_PERF_COUNTERS_DISABLE; renamed (with
              same numerical value) in Linux 2.6.32.

       PR_TASK_PERF_EVENTS_ENABLE (since Linux 2.6.31)
              The converse of PR_TASK_PERF_EVENTS_DISABLE; enable  performance
              counters attached to the calling process.

              Originally called PR_TASK_PERF_COUNTERS_ENABLE; renamed in Linux
              2.6.32.

       PR_GET_THP_DISABLE (since Linux 3.15)
              Return (via the function result) the current setting of the "THP
              disable"  flag  for the calling thread: either 1, if the flag is
              set, or 0, if it is not.

       PR_GET_TID_ADDRESS (since Linux 3.5)
              Retrieve the clear_child_tid address set  by  set_tid_address(2)
              and  the  clone(2)  CLONE_CHILD_CLEARTID  flag,  in the location
              pointed to by (int **) arg2.  This feature is available only  if
              the  kernel  is  built with the CONFIG_CHECKPOINT_RESTORE option
              enabled.

       PR_SET_TIMERSLACK (since Linux 2.6.28)
              epoll_pwait(2), clock_nanosleep(2), nanosleep(2),  and  futex(2)
              (and thus the library functions implemented via futexes, includ-
              ing    pthread_cond_timedwait(3),    pthread_mutex_timedlock(3),
              pthread_rwlock_timedrdlock(3),    pthread_rwlock_timedwrlock(3),
              and sem_timedwait(3)).

              Timer slack is not applied to threads that are scheduled under a
              real-time scheduling policy (see sched_setscheduler(2)).

              Each  thread  has two associated timer slack values: a "default"
              value, and a "current" value.  The current value is the one that
              governs  grouping  of  timer  expirations.  When a new thread is
              created, the two timer slack values are made  the  same  as  the
              current  value of the creating thread.  Thereafter, a thread can
              adjust its current timer slack value via PR_SET_TIMERSLACK  (the
              default value can't be changed).  The timer slack values of init
              (PID 1), the ancestor of all processes, are  50,000  nanoseconds
              (50  microseconds).  The timer slack values are preserved across
              execve(2).

       PR_GET_TIMERSLACK (since Linux 2.6.28)
              Return (as the function result) the current timer slack value of
              the calling thread.

       PR_SET_TIMING (since Linux 2.6.0-test4)
              Set  whether  to  use  (normal, traditional) statistical process
              timing or accurate timestamp-based process  timing,  by  passing
              PR_TIMING_STATISTICAL  or  PR_TIMING_TIMESTAMP to arg2.  PR_TIM-
              ING_TIMESTAMP is not currently implemented  (attempting  to  set
              this mode will yield the error EINVAL).

       PR_GET_TIMING (since Linux 2.6.0-test4)
              Return  (as  the function result) which process timing method is
              currently in use.

       PR_SET_TSC (since Linux 2.6.26, x86 only)
              Set the state of the  flag  determining  whether  the  timestamp
              counter  can be read by the process.  Pass PR_TSC_ENABLE to arg2
              to allow it to be read, or PR_TSC_SIGSEGV to generate a  SIGSEGV
              when the process tries to read the timestamp counter.

       PR_GET_TSC (since Linux 2.6.26, x86 only)
              Return  the  state of the flag determining whether the timestamp
              counter can be read, in the location pointed to by (int *) arg2.

       PR_SET_UNALIGN
              (Only on: ia64, since Linux 2.3.48; parisc, since Linux  2.6.15;
              PowerPC,  since  Linux  2.6.18;  Alpha,  since Linux 2.6.22) Set
              unaligned access control bits to arg2.  Pass  PR_UNALIGN_NOPRINT
              to silently fix up unaligned user accesses, or PR_UNALIGN_SIGBUS
              to generate SIGBUS on unaligned user access.

       PR_GET_UNALIGN
              (see PR_SET_UNALIGN for information on  versions  and  architec-

       EACCES option is PR_SET_MM, and arg3 is PR_SET_MM_EXE_FILE, the file is
              not executable.

       EBADF  option is PR_SET_MM, arg3 is PR_SET_MM_EXE_FILE,  and  the  file
              descriptor passed in arg4 is not valid.

       EBUSY  option  is  PR_SET_MM,  arg3 is PR_SET_MM_EXE_FILE, and this the
              second attempt to change the /proc/pid/exe symbolic link,  which
              is prohibited.

       EFAULT arg2 is an invalid address.

       EFAULT option  is PR_SET_SECCOMP, arg2 is SECCOMP_MODE_FILTER, the sys-
              tem was built with CONFIG_SECCOMP_FILTER, and arg3 is an invalid
              address.

       EINVAL The value of option is not recognized.

       EINVAL option  is  PR_MCE_KILL  or  PR_MCE_KILL_GET  or  PR_SET_MM, and
              unused prctl() arguments were not specified as zero.

       EINVAL arg2 is not valid value for this option.

       EINVAL option is PR_SET_SECCOMP or PR_GET_SECCOMP, and the  kernel  was
              not configured with CONFIG_SECCOMP.

       EINVAL option  is  PR_SET_SECCOMP, arg2 is SECCOMP_MODE_FILTER, and the
              kernel was not configured with CONFIG_SECCOMP_FILTER.

       EINVAL option is PR_SET_MM, and one of the following is true

              *  arg4 or arg5 is nonzero;

              *  arg3 is greater than TASK_SIZE (the limit on the size of  the
                 user address space for this architecture);

              *  arg2     is     PR_SET_MM_START_CODE,     PR_SET_MM_END_CODE,
                 PR_SET_MM_START_DATA,         PR_SET_MM_END_DATA,          or
                 PR_SET_MM_START_STACK, and the permissions of the correspond-
                 ing memory area are not as required;

              *  arg2 is PR_SET_MM_START_BRK or  PR_SET_MM_BRK,  and  arg3  is
                 less  than  or equal to the end of the data segment or speci-
                 fies a value that would cause the RLIMIT_DATA resource  limit
                 to be exceeded.

       EINVAL option  is PR_SET_PTRACER and arg2 is not 0, PR_SET_PTRACER_ANY,
              or the PID of an existing process.

       EINVAL option is PR_SET_PDEATHSIG and arg2 is not a valid  signal  num-
              ber.

       EINVAL option  is PR_SET_DUMPABLE and arg2 is neither SUID_DUMP_DISABLE
              nor SUID_DUMP_USER.
              nonzero.

       EINVAL option is PR_CAP_AMBIENT and an unused argument (arg4, arg5, or,
              in the case of PR_CAP_AMBIENT_CLEAR_ALL, arg3)  is  nonzero;  or
              arg2  has  an  invalid  value;  or arg2 is PR_CAP_AMBIENT_LOWER,
              PR_CAP_AMBIENT_RAISE, or PR_CAP_AMBIENT_IS_SET and arg3 does not
              specify a valid capability.

       ENXIO  option was PR_MPX_ENABLE_MANAGEMENT or PR_MPX_DISABLE_MANAGEMENT
              and the kernel or the  CPU  does  not  support  MPX  management.
              Check that the kernel and processor have MPX support.

       EPERM  option  is  PR_SET_SECUREBITS,  and the caller does not have the
              CAP_SETPCAP capability, or tried to unset a  "locked"  flag,  or
              tried to set a flag whose corresponding locked flag was set (see
              capabilities(7)).

       EPERM  option     is     PR_SET_KEEPCAPS,     and     the      caller's
              SECURE_KEEP_CAPS_LOCKED flag is set (see capabilities(7)).

       EPERM  option  is  PR_CAPBSET_DROP,  and  the  caller does not have the
              CAP_SETPCAP capability.

       EPERM  option  is  PR_SET_MM,  and  the  caller  does  not   have   the
              CAP_SYS_RESOURCE capability.

       EPERM  option  is  PR_CAP_AMBIENT and arg2 is PR_CAP_AMBIENT_RAISE, but
              either the capability specified in arg3 is not  present  in  the
              process's  permitted  and  inheritable  capability  sets, or the
              PR_CAP_AMBIENT_LOWER securebit has been set.

VERSIONS
       The prctl() system call was introduced in Linux 2.1.57.

CONFORMING TO
       This call is Linux-specific.  IRIX has  a  prctl()  system  call  (also
       introduced  in  Linux  2.1.44  as irix_prctl on the MIPS architecture),
       with prototype

       ptrdiff_t prctl(int option, int arg2, int arg3);

       and options to get the maximum number of processes per  user,  get  the
       maximum  number  of  processors  the  calling process can use, find out
       whether a specified process is currently blocked, get or set the  maxi-
       mum stack size, and so on.

SEE ALSO
       signal(2), core(5)

COLOPHON
       This  page  is  part of release 4.04 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at
       http://www.kernel.org/doc/man-pages/.
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