• 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_DUMPABLE " (since Linux 2.3.20)"
  

  Set the state of the flag determining whether core dumps are produced
  for this 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) .)
  

  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 non-recoverable 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 effective and permitted
  capability sets are 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 non-zero when at least one of them previously had the value 0.
  (By default, these credential sets are cleared).
  arg2
  must be either 0 (capabilities are cleared) or 1 (capabilities are kept).
  This 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 process name for the calling process,
  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.
  

  PR_GET_NAME " (since Linux 2.6.11)"
  

  Return the process name for the calling process,
  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_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) .
  

  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_SECCOMP " (since Linux 2.6.23)"
  

  
  
  
  Set the secure computing mode for the calling thread.
  In the current implementation,
  arg2
  must be 1.
  After the secure computing mode has been set to 1,
  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.
  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 only available
  if the kernel is configured with CONFIG_SECCOMP enabled.
  

  PR_GET_SECCOMP " (since Linux 2.6.23)"
  

  Return the secure computing mode of the calling thread.
  Not very useful for the current implementation (mode equals 1),
  but may be useful for other possible future modes:
  if the caller is not in secure computing mode, this operation returns 0;
  if the caller is in secure computing mode, then the
  prctl ()
  call will cause a
  SIGKILL signal to be sent to the process.
  This operation is only available
  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_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_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" .
  

• RETURN VALUE
  
  On success,
  PR_GET_DUMPABLE ,
  PR_GET_KEEPCAPS ,
  PR_CAPBSET_READ ,
  PR_GET_TIMING ,
  PR_GET_SECUREBITS ,
  and (if it returns)
  PR_GET_SECCOMP
  return the non-negative 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

  arg2
  is not valid value for this
  option .
  

  EINVAL

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

  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.
  
  
  
  
  
  
  
  
  

• 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, etc.
  
• SEE ALSO
  
  signal(2) ,
  core(5)
  
• COLOPHON
  
  This page is part of release 3.19 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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