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NAME

       prctl - operations on a process

SYNOPSIS

       #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
       significance depending on the first one.  The first argument can be:

       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
              capability  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
              not  have  the  CAP_SETPCAP; EINVAL if arg2 does not represent a
              valid capability; or EINVAL if file capabilities are not enabled
              in the kernel, in which case bounding sets are not supported.

       PR_SET_CHILD_SUBREAPER (since Linux 3.4)
              If  arg2  is nonzero, set the "child subreaper" attribute of the
              calling process; if arg2 is zero, unset the attribute.   When  a
              process is marked as a child subreaper, all of the children that
              it creates, and their descendants, will be marked  as  having  a
              subreaper.   In effect, a subreaper fulfills the role of init(1)
              for its descendant processes.  Upon  termination  of  a  process
              that  is  orphaned  (i.e.,  its  immediate  parent  has  already
              terminated) and marked as having a subreaper, the nearest  still
              living  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
              location pointed to by (int *) arg2.

       PR_SET_DUMPABLE (since Linux 2.3.20)
              Set the state of the flag determining  whether  core  dumps  are
              produced for the calling process upon delivery of a signal whose
              default behavior is to produce a  core  dump.   (Normally,  this
              flag  is  set for a process by default, but it is cleared when a
              set-user-ID or set-group-ID program  is  executed  and  also  by
              various system calls that manipulate process UIDs and GIDs).  In
              kernels up to and  including  2.6.12,  arg2  must  be  either  0
              (process  is  not dumpable) or 1 (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).)  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
              process's dumpable flag.

       PR_SET_ENDIAN (since Linux 2.6.18, PowerPC only)
              Set the endian-ness of the calling process to the value given in
              arg2,  which  should  be  one  of  the following: PR_ENDIAN_BIG,
              PR_ENDIAN_LITTLE, or PR_ENDIAN_PPC_LITTLE (PowerPC pseudo little
              endian).

       PR_GET_ENDIAN (since Linux 2.6.18, PowerPC only)
              Return  the  endian-ness of the calling process, in the location
              pointed to by (int *) arg2.

       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 fp operations accesses, or
              PR_FPEMU_SIGFPE to not emulate fp  operations  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_NONRECOV  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
              capabilities" flag prevents it from being cleared.  arg2 must be
              either 0 (permitted capabilities are cleared)  or  1  (permitted
              capabilities 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
              capabilities" 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_SET_NAME (since Linux 2.6.9)
              Set the name of the calling  thread,  using  the  value  in  the
              location  pointed to by (char *) arg2.  The name can be up to 16
              bytes long, and should be null-terminated if it  contains  fewer
              bytes.   This  is  the  same  attribute  that  can  be  set  via
              pthread_setname_np(3) and retrieved using pthread_getname_np(3).
              The      attribute      is      likewise      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 if it is
              shorter than that.

       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  permission  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 preserved across execve(2).

              For    more    information,   see   the   kernel   source   file
              Documentation/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
              operate in the privilege-restricting mode described above.

       PR_SET_PDEATHSIG (since Linux 2.1.57)
              Set  the  parent  process death signal of the calling process to
              arg2 (either a signal value in the  range  1..maxsig,  or  0  to
              clear).   This  is  the signal that the calling process will get
              when its parent dies.  This value is cleared for the child of  a
              fork(2)  and (since Linux 2.4.36 / 2.6.23) when executing a set-
              user-ID or set-group-ID binary.  This value is preserved  across
              execve(2).

       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/kernel/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
              Documentation/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  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),
              and  sigreturn(2).  Other system calls result in the delivery of
              a SIGKILL signal.  Strict secure computing 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
              system  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
              Documentation/prctl/seccomp_filter.txt.

       PR_GET_SECCOMP (since Linux 2.6.23)
              Return (as the function result) the secure computing mode of the
              calling thread.  If the caller is not in secure computing  mode,
              this  operation  returns  0;  if  the caller is in strict secure
              computing mode, then the  prctl()  call  will  cause  a  SIGKILL
              signal  to  be  sent to the process.  If the caller is in filter
              mode, and this system call is allowed by the seccomp filters, it
              returns  2.   This  operation is available only if the kernel is
              configured with CONFIG_SECCOMP enabled.

       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
              modified, and using a malloc hook  with  madvise(2)  is  not  an
              option  (i.e.,  statically  allocated data).  The setting of the
              "THP disable" flag is inherited by a child created  via  fork(2)
              and is preserved across execve(2).

       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)
              Set  the  current  timer  slack  for  the  calling thread to the
              nanosecond value supplied in arg2.  If  arg2  is  less  than  or
              equal  to  zero,  reset  the current timer slack to the thread's
              default timer slack value.  The  timer  slack  is  used  by  the
              kernel  to  group  timer expirations for the calling thread that
              are close to one another; as a  consequence,  timer  expirations
              for  the thread may be up to the specified number of nanoseconds
              late (but will never expire early).  Grouping timer  expirations
              can help reduce system power consumption by minimizing CPU wake-
              ups.

              The timer expirations affected by timer slack are those  set  by
              select(2),   pselect(2),   poll(2),   ppoll(2),   epoll_wait(2),
              epoll_pwait(2), clock_nanosleep(2), nanosleep(2),  and  futex(2)
              (and   thus  the  library  functions  implemented  via  futexes,
              including 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_TIMING_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_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_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
              architectures)  Return  unaligned  access  control  bits, in the
              location pointed to by (int *) arg2.

       PR_MCE_KILL (since Linux 2.6.32)
              Set the machine check memory  corruption  kill  policy  for  the
              current  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_failure_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
              system-wide default  (PR_MCE_KILL_DEFAULT).   Early  kill  means
              that  the  thread  receives  a SIGBUS signal as soon as hardware
              memory corruption is detected inside its address space.  In late
              kill  mode,  the  process  is  killed  only  when  it accesses a
              corrupted page.  See sigaction(2) for more  information  on  the
              SIGBUS  signal.   The  policy  is  inherited  by  children.  The
              remaining unused prctl()  arguments  must  be  zero  for  future
              compatibility.

       PR_MCE_KILL_GET (since Linux 2.6.32)
              Return  the  current per-process machine check kill policy.  All
              unused prctl() arguments must be zero.

       PR_SET_MM (since Linux 3.3)
              Modify certain  kernel  memory  map  descriptor  fields  of  the
              calling 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_CHECKPOINT_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
                     executable, 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
                     executable, 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
                     segment.  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_ARG_START
                     Set  the  address above which the program command line is
                     placed.

              PR_SET_MM_ARG_END
                     Set the address below which the program command  line  is
                     placed.

              PR_SET_MM_ENV_START
                     Set  the  address  above which the program environment is
                     placed.

              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
                     descriptor  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
                     creates  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.

RETURN VALUE

       On  success,  PR_GET_DUMPABLE,  PR_GET_KEEPCAPS,   PR_GET_NO_NEW_PRIVS,
       PR_GET_THP_DISABLE,  PR_CAPBSET_READ, PR_GET_TIMING, PR_GET_TIMERSLACK,
       PR_GET_SECUREBITS, PR_MCE_KILL_GET, and (if it returns)  PR_GET_SECCOMP
       return the nonnegative values described above.  All other option values
       return 0 on success.  On error,  -1  is  returned,  and  errno  is  set
       appropriately.

ERRORS

       EFAULT arg2 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_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
                 corresponding 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
                 specifies  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
              number.

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

       EINVAL option is PR_SET_TIMING and arg2 is not PR_TIMING_STATISTICAL.

       EINVAL option  is  PR_SET_NO_NEW_PRIVS  and  arg2  is not equal to 1 or
              arg3, arg4, or arg5 is nonzero.

       EINVAL option is PR_GET_NO_NEW_PRIVS and arg2, arg3, arg4, or  arg5  is
              nonzero.

       EINVAL option is PR_SET_THP_DISABLE and arg3, arg4, or arg5 is nonzero.

       EINVAL option  is  PR_GET_THP_DISABLE  and arg2, arg3, arg4, or arg5 is
              nonzero.

       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     callers'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.

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

       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.

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

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
       maximum stack size, and so on.

SEE ALSO

       signal(2), core(5)

COLOPHON

       This  page  is  part of release 3.65 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.



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