1PRCTL(2)                   Linux Programmer's Manual                  PRCTL(2)


6       prctl - operations on a process or thread


9       #include <sys/prctl.h>
11       int prctl(int option, unsigned long arg2, unsigned long arg3,
12                 unsigned long arg4, unsigned long arg5);


15       prctl()  manipulates  various  aspects  of  the behavior of the calling
16       thread or process.
18       Note that careless use of some prctl() operations can confuse the user-
19       space  run-time  environment,  so  these operations should be used with
20       care.
22       prctl() is called with a first argument describing  what  to  do  (with
23       values  defined  in <linux/prctl.h>), and further arguments with a sig‐
24       nificance depending on the first one.  The first argument can be:
26       PR_CAP_AMBIENT (since Linux 4.3)
27              Reads or changes the  ambient  capability  set  of  the  calling
28              thread, according to the value of arg2, which must be one of the
29              following:
31              PR_CAP_AMBIENT_RAISE
32                     The capability specified in arg3 is added to the  ambient
33                     set.  The specified capability must already be present in
34                     both the  permitted  and  the  inheritable  sets  of  the
35                     process.    This   operation  is  not  permitted  if  the
36                     SECBIT_NO_CAP_AMBIENT_RAISE securebit is set.
38              PR_CAP_AMBIENT_LOWER
39                     The capability specified in arg3 is removed from the  am‐
40                     bient set.
42              PR_CAP_AMBIENT_IS_SET
43                     The  prctl()  call returns 1 if the capability in arg3 is
44                     in the ambient set and 0 if it is not.
46              PR_CAP_AMBIENT_CLEAR_ALL
47                     All capabilities will be removed from  the  ambient  set.
48                     This operation requires setting arg3 to zero.
50              In  all of the above operations, arg4 and arg5 must be specified
51              as 0.
53              Higher-level interfaces layered on top of the  above  operations
54              are provided in the libcap(3) library in the form of cap_get_am‐
55              bient(3), cap_set_ambient(3), and cap_reset_ambient(3).
57       PR_CAPBSET_READ (since Linux 2.6.25)
58              Return (as the function result) 1 if the capability specified in
59              arg2 is in the calling thread's capability bounding set, or 0 if
60              it is not.  (The capability constants are defined in  <linux/ca‐
61              pability.h>.)   The capability bounding set dictates whether the
62              process can receive the capability through  a  file's  permitted
63              capability set on a subsequent call to execve(2).
65              If  the capability specified in arg2 is not valid, then the call
66              fails with the error EINVAL.
68              A higher-level interface layered on top  of  this  operation  is
69              provided   in   the   libcap(3)   library   in   the   form   of
70              cap_get_bound(3).
72       PR_CAPBSET_DROP (since Linux 2.6.25)
73              If the calling thread has the CAP_SETPCAP capability within  its
74              user  namespace, then drop the capability specified by arg2 from
75              the calling thread's capability bounding set.  Any  children  of
76              the calling thread will inherit the newly reduced bounding set.
78              The  call fails with the error: EPERM if the calling thread does
79              not have the CAP_SETPCAP; EINVAL if arg2 does  not  represent  a
80              valid capability; or EINVAL if file capabilities are not enabled
81              in the kernel, in which case bounding sets are not supported.
83              A higher-level interface layered on top  of  this  operation  is
84              provided   in   the   libcap(3)   library   in   the   form   of
85              cap_drop_bound(3).
87       PR_SET_CHILD_SUBREAPER (since Linux 3.4)
88              If arg2 is nonzero, set the "child subreaper" attribute  of  the
89              calling process; if arg2 is zero, unset the attribute.
91              A subreaper fulfills the role of init(1) for its descendant pro‐
92              cesses.  When a process becomes orphaned  (i.e.,  its  immediate
93              parent  terminates), then that process will be reparented to the
94              nearest still living ancestor subreaper.  Subsequently, calls to
95              getppid(2)  in  the  orphaned process will now return the PID of
96              the subreaper process, and when the orphan terminates, it is the
97              subreaper process that will receive a SIGCHLD signal and will be
98              able to wait(2) on the process to discover its termination  sta‐
99              tus.
101              The  setting of the "child subreaper" attribute is not inherited
102              by children created by fork(2) and  clone(2).   The  setting  is
103              preserved across execve(2).
105              Establishing a subreaper process is useful in session management
106              frameworks where a hierarchical group of processes is managed by
107              a  subreaper  process  that needs to be informed when one of the
108              processes—for example, a double-forked  daemon—terminates  (per‐
109              haps  so that it can restart that process).  Some init(1) frame‐
110              works (e.g., systemd(1)) employ a subreaper process for  similar
111              reasons.
113       PR_GET_CHILD_SUBREAPER (since Linux 3.4)
114              Return the "child subreaper" setting of the caller, in the loca‐
115              tion pointed to by (int *) arg2.
117       PR_SET_DUMPABLE (since Linux 2.3.20)
118              Set the state of  the  "dumpable"  attribute,  which  determines
119              whether core dumps are produced for the calling process upon de‐
120              livery of a signal whose default behavior is to produce  a  core
121              dump.
123              In  kernels  up  to  and including 2.6.12, arg2 must be either 0
124              (SUID_DUMP_DISABLE,   process   is   not    dumpable)    or    1
125              (SUID_DUMP_USER,  process  is dumpable).  Between kernels 2.6.13
126              and 2.6.17, the value 2 was also permitted, which caused any bi‐
127              nary which normally would not be dumped to be dumped readable by
128              root only; for security reasons, this feature has been  removed.
129              (See  also  the  description  of  /proc/sys/fs/suid_dumpable  in
130              proc(5).)
132              Normally, the "dumpable" attribute is set to 1.  However, it  is
133              reset  to  the current value contained in the file /proc/sys/fs/
134              suid_dumpable (which by default has the value 0), in the follow‐
135              ing circumstances:
137              *  The process's effective user or group ID is changed.
139              *  The  process's  filesystem  user  or group ID is changed (see
140                 credentials(7)).
142              *  The process executes (execve(2)) a set-user-ID or  set-group-
143                 ID  program,  resulting  in  a change of either the effective
144                 user ID or the effective group ID.
146              *  The process executes (execve(2)) a program that has file  ca‐
147                 pabilities  (see  capabilities(7)), but only if the permitted
148                 capabilities gained exceed those already  permitted  for  the
149                 process.
151              Processes  that  are  not  dumpable  can  not  be  attached  via
152              ptrace(2) PTRACE_ATTACH; see ptrace(2) for further details.
154              If a process is not dumpable, the  ownership  of  files  in  the
155              process's  /proc/[pid]  directory  is  affected  as described in
156              proc(5).
158       PR_GET_DUMPABLE (since Linux 2.3.20)
159              Return (as the function result) the current state of the calling
160              process's dumpable attribute.
162       PR_SET_ENDIAN (since Linux 2.6.18, PowerPC only)
163              Set the endian-ness of the calling process to the value given in
164              arg2, which should  be  one  of  the  following:  PR_ENDIAN_BIG,
165              PR_ENDIAN_LITTLE, or PR_ENDIAN_PPC_LITTLE (PowerPC pseudo little
166              endian).
168       PR_GET_ENDIAN (since Linux 2.6.18, PowerPC only)
169              Return the endian-ness of the calling process, in  the  location
170              pointed to by (int *) arg2.
172       PR_SET_FP_MODE (since Linux 4.0, only on MIPS)
173              On  the MIPS architecture, user-space code can be built using an
174              ABI which permits linking with code that  has  more  restrictive
175              floating-point  (FP) requirements.  For example, user-space code
176              may be built to target the O32 FPXX ABI  and  linked  with  code
177              built  for either one of the more restrictive FP32 or FP64 ABIs.
178              When more restrictive code is linked in, the overall requirement
179              for  the  process  is to use the more restrictive floating-point
180              mode.
182              Because the kernel has no means of knowing in advance which mode
183              the  process  should  be executed in, and because these restric‐
184              tions  can  change  over  the  lifetime  of  the  process,   the
185              PR_SET_FP_MODE  operation  is  provided  to allow control of the
186              floating-point mode from user space.
188              The (unsigned int) arg2 argument is a bit  mask  describing  the
189              floating-point mode used:
191              PR_FP_MODE_FR
192                     When  this bit is unset (so called FR=0 or FR0 mode), the
193                     32 floating-point registers are 32 bits wide, and  64-bit
194                     registers  are  represented as a pair of registers (even-
195                     and odd- numbered, with the even-numbered  register  con‐
196                     taining  the lower 32 bits, and the odd-numbered register
197                     containing the higher 32 bits).
199                     When this bit is set  (on  supported  hardware),  the  32
200                     floating-point registers are 64 bits wide (so called FR=1
201                     or FR1 mode).   Note  that  modern  MIPS  implementations
202                     (MIPS R6 and newer) support FR=1 mode only.
204                     Applications  that  use the O32 FP32 ABI can operate only
205                     when this bit is unset (FR=0; or they can  be  used  with
206                     FRE  enabled,  see below).  Applications that use the O32
207                     FP64 ABI (and the O32 FP64A ABI, which exists to  provide
208                     the  ability  to operate with existing FP32 code; see be‐
209                     low) can operate only when this bit is set  (FR=1).   Ap‐
210                     plications that use the O32 FPXX ABI can operate with ei‐
211                     ther FR=0 or FR=1.
213              PR_FP_MODE_FRE
214                     Enable emulation of  32-bit  floating-point  mode.   When
215                     this  mode  is enabled, it emulates 32-bit floating-point
216                     operations by raising a reserved-instruction exception on
217                     every instruction that uses 32-bit formats and the kernel
218                     then handles the instruction in software.   (The  problem
219                     lies  in  the discrepancy of handling odd-numbered regis‐
220                     ters which are the high 32 bits of 64-bit registers  with
221                     even  numbers  in FR=0 mode and the lower 32-bit parts of
222                     odd-numbered 64-bit registers in  FR=1  mode.)   Enabling
223                     this  bit  is  necessary  when code with the O32 FP32 ABI
224                     should operate with code with compatible the O32 FPXX  or
225                     O32  FP64A  ABIs (which require FR=1 FPU mode) or when it
226                     is executed on newer hardware  (MIPS  R6  onwards)  which
227                     lacks  FR=0  mode support when a binary with the FP32 ABI
228                     is used.
230                     Note that this mode makes sense only when the FPU  is  in
231                     64-bit mode (FR=1).
233                     Note  that the use of emulation inherently has a signifi‐
234                     cant performance hit and should be avoided if possible.
236              In the N32/N64 ABI, 64-bit floating-point mode is  always  used,
237              so  FPU emulation is not required and the FPU always operates in
238              FR=1 mode.
240              This option is mainly intended for use  by  the  dynamic  linker
241              (ld.so(8)).
243              The arguments arg3, arg4, and arg5 are ignored.
245       PR_GET_FP_MODE (since Linux 4.0, only on MIPS)
246              Return  (as the function result) the current floating-point mode
247              (see the description of PR_SET_FP_MODE for details).
249              On success, the call returns a bit  mask  which  represents  the
250              current floating-point mode.
252              The arguments arg2, arg3, arg4, and arg5 are ignored.
254       PR_SET_FPEMU (since Linux 2.4.18, 2.5.9, only on ia64)
255              Set   floating-point  emulation  control  bits  to  arg2.   Pass
256              PR_FPEMU_NOPRINT to silently  emulate  floating-point  operation
257              accesses, or PR_FPEMU_SIGFPE to not emulate floating-point oper‐
258              ations and send SIGFPE instead.
260       PR_GET_FPEMU (since Linux 2.4.18, 2.5.9, only on ia64)
261              Return floating-point emulation control bits,  in  the  location
262              pointed to by (int *) arg2.
264       PR_SET_FPEXC (since Linux 2.4.21, 2.5.32, only on PowerPC)
265              Set    floating-point    exception    mode    to   arg2.    Pass
266              PR_FP_EXC_SW_ENABLE to  use  FPEXC  for  FP  exception  enables,
267              PR_FP_EXC_DIV  for  floating-point divide by zero, PR_FP_EXC_OVF
268              for floating-point overflow,  PR_FP_EXC_UND  for  floating-point
269              underflow,  PR_FP_EXC_RES  for  floating-point  inexact  result,
270              PR_FP_EXC_INV    for    floating-point    invalid     operation,
271              PR_FP_EXC_DISABLED  for FP exceptions disabled, PR_FP_EXC_NONRE‐
272              COV for async nonrecoverable exception mode, PR_FP_EXC_ASYNC for
273              async  recoverable exception mode, PR_FP_EXC_PRECISE for precise
274              exception mode.
276       PR_GET_FPEXC (since Linux 2.4.21, 2.5.32, only on PowerPC)
277              Return floating-point exception mode, in the location pointed to
278              by (int *) arg2.
280       PR_SET_IO_FLUSHER (since Linux 5.6)
281              If  a  user process is involved in the block layer or filesystem
282              I/O path, and can allocate memory while processing I/O  requests
283              it  must  set  arg2  to  1.   This  will  put the process in the
284              IO_FLUSHER state, which allows  it  special  treatment  to  make
285              progress when allocating memory.  If arg2 is 0, the process will
286              clear the IO_FLUSHER state, and the  default  behavior  will  be
287              used.
289              The calling process must have the CAP_SYS_RESOURCE capability.
291              arg3, arg4, and arg5 must be zero.
293              The IO_FLUSHER state is inherited by a child process created via
294              fork(2) and is preserved across execve(2).
296              Examples of IO_FLUSHER applications are FUSE daemons,  SCSI  de‐
297              vice  emulation daemons, and daemons that perform error handling
298              like multipath path recovery applications.
300       PR_GET_IO_FLUSHER (Since Linux 5.6)
301              Return (as the function result)  the  IO_FLUSHER  state  of  the
302              caller.   A  value  of  1  indicates  that  the caller is in the
303              IO_FLUSHER state; 0 indicates that the  caller  is  not  in  the
304              IO_FLUSHER state.
306              The calling process must have the CAP_SYS_RESOURCE capability.
308              arg2, arg3, arg4, and arg5 must be zero.
310       PR_SET_KEEPCAPS (since Linux 2.2.18)
311              Set  the state of the calling thread's "keep capabilities" flag.
312              The effect of this flag is described in  capabilities(7).   arg2
313              must  be  either  0  (clear  the flag) or 1 (set the flag).  The
314              "keep capabilities" value will be reset to 0 on subsequent calls
315              to execve(2).
317       PR_GET_KEEPCAPS (since Linux 2.2.18)
318              Return (as the function result) the current state of the calling
319              thread's "keep capabilities" flag.  See  capabilities(7)  for  a
320              description of this flag.
322       PR_MCE_KILL (since Linux 2.6.32)
323              Set  the  machine  check  memory  corruption kill policy for the
324              calling thread.  If arg2 is PR_MCE_KILL_CLEAR, clear the  thread
325              memory  corruption  kill policy and use the system-wide default.
326              (The system-wide default is defined by /proc/sys/vm/memory_fail‐
327              ure_early_kill; see proc(5).)  If arg2 is PR_MCE_KILL_SET, use a
328              thread-specific memory corruption kill policy.   In  this  case,
329              arg3    defines    whether    the    policy    is   early   kill
330              (PR_MCE_KILL_EARLY), late kill (PR_MCE_KILL_LATE), or  the  sys‐
331              tem-wide  default  (PR_MCE_KILL_DEFAULT).  Early kill means that
332              the thread receives a SIGBUS signal as soon as  hardware  memory
333              corruption  is  detected inside its address space.  In late kill
334              mode, the process is killed only when it  accesses  a  corrupted
335              page.   See sigaction(2) for more information on the SIGBUS sig‐
336              nal.  The policy is inherited by children.  The remaining unused
337              prctl() arguments must be zero for future compatibility.
339       PR_MCE_KILL_GET (since Linux 2.6.32)
340              Return  (as the function result) the current per-process machine
341              check kill policy.  All unused prctl() arguments must be zero.
343       PR_SET_MM (since Linux 3.3)
344              Modify certain kernel memory map descriptor fields of the  call‐
345              ing process.  Usually these fields are set by the kernel and dy‐
346              namic loader (see ld.so(8) for more information) and  a  regular
347              application  should  not  use  this feature.  However, there are
348              cases, such as self-modifying programs, where  a  program  might
349              find it useful to change its own memory map.
351              The  calling  process must have the CAP_SYS_RESOURCE capability.
352              The value in arg2 is one of the options below, while  arg3  pro‐
353              vides  a  new value for the option.  The arg4 and arg5 arguments
354              must be zero if unused.
356              Before Linux 3.10, this feature is available only if the  kernel
357              is built with the CONFIG_CHECKPOINT_RESTORE option enabled.
359              PR_SET_MM_START_CODE
360                     Set  the  address  above  which the program text can run.
361                     The corresponding memory area must be readable  and  exe‐
362                     cutable,  but  not writable or shareable (see mprotect(2)
363                     and mmap(2) for more information).
365              PR_SET_MM_END_CODE
366                     Set the address below which the  program  text  can  run.
367                     The  corresponding  memory area must be readable and exe‐
368                     cutable, but not writable or shareable.
370              PR_SET_MM_START_DATA
371                     Set the address above which initialized and uninitialized
372                     (bss)  data  are  placed.   The corresponding memory area
373                     must be readable and  writable,  but  not  executable  or
374                     shareable.
376              PR_SET_MM_END_DATA
377                     Set the address below which initialized and uninitialized
378                     (bss) data are placed.   The  corresponding  memory  area
379                     must  be  readable  and  writable,  but not executable or
380                     shareable.
382              PR_SET_MM_START_STACK
383                     Set the start address of the  stack.   The  corresponding
384                     memory area must be readable and writable.
386              PR_SET_MM_START_BRK
387                     Set  the  address above which the program heap can be ex‐
388                     panded with brk(2) call.  The  address  must  be  greater
389                     than  the ending address of the current program data seg‐
390                     ment.  In addition, the combined size  of  the  resulting
391                     heap  and  the  size of the data segment can't exceed the
392                     RLIMIT_DATA resource limit (see setrlimit(2)).
394              PR_SET_MM_BRK
395                     Set the current brk(2) value.  The requirements  for  the
396                     address  are  the same as for the PR_SET_MM_START_BRK op‐
397                     tion.
399              The following options are available since Linux 3.5.
401              PR_SET_MM_ARG_START
402                     Set the address above which the program command  line  is
403                     placed.
405              PR_SET_MM_ARG_END
406                     Set  the  address below which the program command line is
407                     placed.
409              PR_SET_MM_ENV_START
410                     Set the address above which the  program  environment  is
411                     placed.
413              PR_SET_MM_ENV_END
414                     Set  the  address  below which the program environment is
415                     placed.
417                     The    address    passed    with     PR_SET_MM_ARG_START,
418                     PR_SET_MM_ARG_END,        PR_SET_MM_ENV_START,        and
419                     PR_SET_MM_ENV_END should belong to a process stack  area.
420                     Thus,  the  corresponding  memory  area must be readable,
421                     writable, and (depending  on  the  kernel  configuration)
422                     have the MAP_GROWSDOWN attribute set (see mmap(2)).
424              PR_SET_MM_AUXV
425                     Set  a  new  auxiliary  vector.  The arg3 argument should
426                     provide the address of the vector.  The arg4 is the  size
427                     of the vector.
429              PR_SET_MM_EXE_FILE
430                     Supersede  the /proc/pid/exe symbolic link with a new one
431                     pointing to a new executable file identified by the  file
432                     descriptor  provided in arg3 argument.  The file descrip‐
433                     tor should be obtained with a regular open(2) call.
435                     To change the symbolic link, one needs to unmap  all  ex‐
436                     isting  executable  memory areas, including those created
437                     by the kernel itself (for example the kernel usually cre‐
438                     ates  at  least  one  executable  memory area for the ELF
439                     .text section).
441                     In Linux 4.9 and earlier, the  PR_SET_MM_EXE_FILE  opera‐
442                     tion  can be performed only once in a process's lifetime;
443                     attempting to perform the operation a second time results
444                     in  the  error  EPERM.  This restriction was enforced for
445                     security reasons that were subsequently deemed  specious,
446                     and  the  restriction  was  removed in Linux 4.10 because
447                     some user-space applications needed to perform this oper‐
448                     ation more than once.
450              The following options are available since Linux 3.18.
452              PR_SET_MM_MAP
453                     Provides  one-shot access to all the addresses by passing
454                     in a struct prctl_mm_map (as defined in <linux/prctl.h>).
455                     The arg4 argument should provide the size of the struct.
457                     This  feature  is  available  only if the kernel is built
458                     with the CONFIG_CHECKPOINT_RESTORE option enabled.
460              PR_SET_MM_MAP_SIZE
461                     Returns the size of the struct  prctl_mm_map  the  kernel
462                     expects.   This  allows  user  space to find a compatible
463                     struct.  The arg4 argument should be a pointer to an  un‐
464                     signed int.
466                     This  feature  is  available  only if the kernel is built
467                     with the CONFIG_CHECKPOINT_RESTORE option enabled.
470       removed in Linux 5.4; only on x86)
471              Enable  or disable kernel management of Memory Protection eXten‐
472              sions (MPX) bounds tables.  The arg2, arg3, arg4, and arg5 argu‐
473              ments must be zero.
475              MPX  is  a  hardware-assisted  mechanism  for  performing bounds
476              checking on pointers.  It consists of a set of registers storing
477              bounds  information  and  a  set of special instruction prefixes
478              that tell the CPU on which instructions it should do bounds  en‐
479              forcement.   There  is  a  limited number of these registers and
480              when there are more pointers than registers, their contents must
481              be  "spilled"  into  a  set  of tables.  These tables are called
482              "bounds tables" and the MPX prctl() operations  control  whether
483              the kernel manages their allocation and freeing.
485              When management is enabled, the kernel will take over allocation
486              and freeing of the bounds tables.  It does this by trapping  the
487              #BR exceptions that result at first use of missing bounds tables
488              and instead of delivering the exception to user space, it  allo‐
489              cates  the table and populates the bounds directory with the lo‐
490              cation of the new table.  For freeing, the kernel checks to  see
491              if  bounds tables are present for memory which is not allocated,
492              and frees them if so.
494              Before enabling MPX management  using  PR_MPX_ENABLE_MANAGEMENT,
495              the  application  must  first have allocated a user-space buffer
496              for the bounds directory and placed the location of that  direc‐
497              tory in the bndcfgu register.
499              These  calls  fail  if  the  CPU or kernel does not support MPX.
500              Kernel support for MPX is enabled via  the  CONFIG_X86_INTEL_MPX
501              configuration  option.   You  can check whether the CPU supports
502              MPX by looking for the mpx CPUID bit, like  with  the  following
503              command:
505                  cat /proc/cpuinfo | grep ' mpx '
507              A  thread  may  not switch in or out of long (64-bit) mode while
508              MPX is enabled.
510              All threads in a process are affected by these calls.
512              The child of a fork(2) inherits the  state  of  MPX  management.
513              During  execve(2),  MPX  management  is  reset  to a state as if
514              PR_MPX_DISABLE_MANAGEMENT had been called.
516              For further information on Intel MPX, see the kernel source file
517              Documentation/x86/intel_mpx.txt.
519              Due to a lack of toolchain support, PR_MPX_ENABLE_MANAGEMENT and
520              PR_MPX_DISABLE_MANAGEMENT are not supported  in  Linux  5.4  and
521              later.
523       PR_SET_NAME (since Linux 2.6.9)
524              Set the name of the calling thread, using the value in the loca‐
525              tion pointed to by (char *) arg2.  The name  can  be  up  to  16
526              bytes long, including the terminating null byte.  (If the length
527              of the string, including the terminating null byte,  exceeds  16
528              bytes,  the string is silently truncated.)  This is the same at‐
529              tribute that can be set via pthread_setname_np(3) and  retrieved
530              using pthread_getname_np(3).  The attribute is likewise accessi‐
531              ble via /proc/self/task/[tid]/comm (see proc(5)), where [tid] is
532              the thread ID of the calling thread, as returned by gettid(2).
534       PR_GET_NAME (since Linux 2.6.11)
535              Return  the name of the calling thread, in the buffer pointed to
536              by (char *) arg2.  The buffer should allow space for  up  to  16
537              bytes; the returned string will be null-terminated.
539       PR_SET_NO_NEW_PRIVS (since Linux 3.5)
540              Set  the calling thread's no_new_privs attribute to the value in
541              arg2.  With no_new_privs set to 1,  execve(2)  promises  not  to
542              grant  privileges  to  do anything that could not have been done
543              without the execve(2) call (for example, rendering the set-user-
544              ID  and  set-group-ID mode bits, and file capabilities non-func‐
545              tional).  Once set, the no_new_privs attribute cannot be  unset.
546              The  setting  of this attribute is inherited by children created
547              by fork(2) and clone(2), and preserved across execve(2).
549              Since Linux 4.10, the value of a thread's no_new_privs attribute
550              can be viewed via the NoNewPrivs field in the /proc/[pid]/status
551              file.
553              For more information, see  the  kernel  source  file  Documenta‐
554              tion/userspace-api/no_new_privs.rst        (or        Documenta‐
555              tion/prctl/no_new_privs.txt before Linux 4.13).  See  also  sec‐
556              comp(2).
558       PR_GET_NO_NEW_PRIVS (since Linux 3.5)
559              Return  (as  the  function result) the value of the no_new_privs
560              attribute for the calling thread.  A value of  0  indicates  the
561              regular  execve(2)  behavior.   A value of 1 indicates execve(2)
562              will operate in the privilege-restricting mode described above.
564       PR_PAC_RESET_KEYS (since Linux 5.0, only on arm64)
565              Securely reset the thread's pointer authentication keys to fresh
566              random values generated by the kernel.
568              The  set of keys to be reset is specified by arg2, which must be
569              a logical OR of zero or more of the following:
571              PR_PAC_APIAKEY
572                     instruction authentication key A
574              PR_PAC_APIBKEY
575                     instruction authentication key B
577              PR_PAC_APDAKEY
578                     data authentication key A
580              PR_PAC_APDBKEY
581                     data authentication key B
583              PR_PAC_APGAKEY
584                     generic authentication “A” key.
586                     (Yes folks, there really is no generic B key.)
588              As a special case, if arg2 is zero, then all the keys are reset.
589              Since new keys could be added in future, this is the recommended
590              way to completely wipe the existing  keys  when  establishing  a
591              clean  execution  context.   Note  that  there is no need to use
592              PR_PAC_RESET_KEYS in preparation for  calling  execve(2),  since
593              execve(2) resets all the pointer authentication keys.
595              The remaining arguments arg3, arg4, and arg5 must all be zero.
597              If the arguments are invalid, and in particular if arg2 contains
598              set bits that are unrecognized or that correspond to a  key  not
599              available  on this platform, then the call fails with error EIN‐
600              VAL.
602              Warning: Because the compiler or run-time environment may be us‐
603              ing  some or all of the keys, a successful PR_PAC_RESET_KEYS may
604              crash the calling process.  The conditions for using  it  safely
605              are  complex and system-dependent.  Don't use it unless you know
606              what you are doing.
608              For more information, see  the  kernel  source  file  Documenta‐
609              tion/arm64/pointer-authentication.rst       (or       Documenta‐
610              tion/arm64/pointer-authentication.txt before Linux 5.3).
612       PR_SET_PDEATHSIG (since Linux 2.1.57)
613              Set the parent-death signal of the calling process to arg2  (ei‐
614              ther  a  signal  value  in  the range 1..NSIG-1, or 0 to clear).
615              This is the signal that the calling process will  get  when  its
616              parent dies.
618              Warning:  the  "parent"  in  this  case  is considered to be the
619              thread that created this process.  In other  words,  the  signal
620              will  be  sent  when  that  thread terminates (via, for example,
621              pthread_exit(3)), rather than after all of the  threads  in  the
622              parent process terminate.
624              The  parent-death  signal is sent upon subsequent termination of
625              the parent thread and also upon termination  of  each  subreaper
626              process (see the description of PR_SET_CHILD_SUBREAPER above) to
627              which the caller is  subsequently  reparented.   If  the  parent
628              thread  and  all  ancestor subreapers have already terminated by
629              the time of the PR_SET_PDEATHSIG operation, then no parent-death
630              signal is sent to the caller.
632              The parent-death signal is process-directed (see signal(7)) and,
633              if the child installs a handler using the  sigaction(2)  SA_SIG‐
634              INFO  flag,  the  si_pid  field of the siginfo_t argument of the
635              handler contains the PID of the terminating parent process.
637              The parent-death signal setting is cleared for the  child  of  a
638              fork(2).   It is also (since Linux 2.4.36 / 2.6.23) cleared when
639              executing a set-user-ID or set-group-ID binary, or a binary that
640              has  associated  capabilities  (see capabilities(7)); otherwise,
641              this value is preserved across execve(2).  The parent-death sig‐
642              nal setting is also cleared upon changes to any of the following
643              thread credentials:  effective  user  ID,  effective  group  ID,
644              filesystem user ID, or filesystem group ID.
646       PR_GET_PDEATHSIG (since Linux 2.3.15)
647              Return  the current value of the parent process death signal, in
648              the location pointed to by (int *) arg2.
650       PR_SET_PTRACER (since Linux 3.4)
651              This is meaningful only when the Yama LSM is enabled and in mode
652              1    ("restricted    ptrace",    visible    via   /proc/sys/ker‐
653              nel/yama/ptrace_scope).  When a "ptracer process ID"  is  passed
654              in  arg2,  the  caller is declaring that the ptracer process can
655              ptrace(2) the calling process as if it were a direct process an‐
656              cestor.   Each  PR_SET_PTRACER  operation  replaces the previous
657              "ptracer process ID".  Employing PR_SET_PTRACER with arg2 set to
658              0  clears  the  caller's  "ptracer  process  ID".   If  arg2  is
659              PR_SET_PTRACER_ANY, the ptrace restrictions introduced  by  Yama
660              are effectively disabled for the calling process.
662              For  further  information, see the kernel source file Documenta‐
663              tion/admin-guide/LSM/Yama.rst      (or       Documentation/secu‐
664              rity/Yama.txt before Linux 4.13).
666       PR_SET_SECCOMP (since Linux 2.6.23)
667              Set  the secure computing (seccomp) mode for the calling thread,
668              to limit the available system calls.  The more recent seccomp(2)
669              system   call  provides  a  superset  of  the  functionality  of
670              PR_SET_SECCOMP.
672              The seccomp mode is selected via arg2.  (The  seccomp  constants
673              are defined in <linux/seccomp.h>.)
675              With arg2 set to SECCOMP_MODE_STRICT, the only system calls that
676              the thread is permitted to make are read(2), write(2),  _exit(2)
677              (but  not  exit_group(2)), and sigreturn(2).  Other system calls
678              result in the delivery of a SIGKILL signal.  Strict secure  com‐
679              puting mode is useful for number-crunching applications that may
680              need to execute untrusted byte code, perhaps obtained by reading
681              from  a pipe or socket.  This operation is available only if the
682              kernel is configured with CONFIG_SECCOMP enabled.
684              With arg2 set to SECCOMP_MODE_FILTER (since Linux 3.5), the sys‐
685              tem  calls allowed are defined by a pointer to a Berkeley Packet
686              Filter passed in arg3.  This argument is  a  pointer  to  struct
687              sock_fprog;  it can be designed to filter arbitrary system calls
688              and system call arguments.  This mode is available only  if  the
689              kernel is configured with CONFIG_SECCOMP_FILTER enabled.
691              If  SECCOMP_MODE_FILTER filters permit fork(2), then the seccomp
692              mode is inherited by children created by fork(2);  if  execve(2)
693              is  permitted,  then  the  seccomp  mode is preserved across ex‐
694              ecve(2).  If the filters permit prctl() calls,  then  additional
695              filters can be added; they are run in order until the first non-
696              allow result is seen.
698              For further information, see the kernel source  file  Documenta‐
699              tion/userspace-api/seccomp_filter.rst       (or       Documenta‐
700              tion/prctl/seccomp_filter.txt before Linux 4.13).
702       PR_GET_SECCOMP (since Linux 2.6.23)
703              Return (as the function result) the secure computing mode of the
704              calling  thread.  If the caller is not in secure computing mode,
705              this operation returns 0; if the caller is in strict secure com‐
706              puting  mode,  then the prctl() call will cause a SIGKILL signal
707              to be sent to the process.  If the caller is in filter mode, and
708              this  system  call is allowed by the seccomp filters, it returns
709              2; otherwise, the process is killed with a SIGKILL signal.  This
710              operation  is  available  only  if the kernel is configured with
711              CONFIG_SECCOMP enabled.
713              Since Linux 3.8, the Seccomp  field  of  the  /proc/[pid]/status
714              file  provides a method of obtaining the same information, with‐
715              out the risk that the process is killed; see proc(5).
717       PR_SET_SECUREBITS (since Linux 2.6.26)
718              Set the "securebits" flags of the calling thread  to  the  value
719              supplied in arg2.  See capabilities(7).
721       PR_GET_SECUREBITS (since Linux 2.6.26)
722              Return  (as  the  function result) the "securebits" flags of the
723              calling thread.  See capabilities(7).
725       PR_GET_SPECULATION_CTRL (since Linux 4.17)
726              Return (as the function result) the  state  of  the  speculation
727              misfeature  specified  in  arg2.   Currently, the only permitted
728              value for this argument is PR_SPEC_STORE_BYPASS  (otherwise  the
729              call fails with the error ENODEV).
731              The return value uses bits 0-3 with the following meaning:
733              PR_SPEC_PRCTL
734                     Mitigation  can be controlled per thread by PR_SET_SPECU‐
735                     LATION_CTRL.
737              PR_SPEC_ENABLE
738                     The speculation feature is enabled,  mitigation  is  dis‐
739                     abled.
741              PR_SPEC_DISABLE
742                     The  speculation  feature  is disabled, mitigation is en‐
743                     abled.
745              PR_SPEC_FORCE_DISABLE
746                     Same as PR_SPEC_DISABLE but cannot be undone.
748              PR_SPEC_DISABLE_NOEXEC (since Linux 5.1)
749                     Same as PR_SPEC_DISABLE, but the state will be cleared on
750                     execve(2).
752              If  all bits are 0, then the CPU is not affected by the specula‐
753              tion misfeature.
755              If PR_SPEC_PRCTL is set, then per-thread control of the  mitiga‐
756              tion is available.  If not set, prctl() for the speculation mis‐
757              feature will fail.
759              The arg3, arg4, and arg5 arguments must be specified as 0;  oth‐
760              erwise the call fails with the error EINVAL.
762       PR_SET_SPECULATION_CTRL (since Linux 4.17)
763              Sets  the state of the speculation misfeature specified in arg2.
764              The speculation-misfeature settings are per-thread attributes.
766              Currently, arg2 must be one of:
768              PR_SPEC_STORE_BYPASS
769                     Set the state of the speculative store bypass misfeature.
771              PR_SPEC_INDIRECT_BRANCH (since Linux 4.20)
772                     Set the state of the indirect branch speculation  misfea‐
773                     ture.
775              If  arg2  does  not  have one of the above values, then the call
776              fails with the error ENODEV.
778              The arg3 argument is used to hand in the control value, which is
779              one of the following:
781              PR_SPEC_ENABLE
782                     The  speculation  feature  is enabled, mitigation is dis‐
783                     abled.
785              PR_SPEC_DISABLE
786                     The speculation feature is disabled,  mitigation  is  en‐
787                     abled.
789              PR_SPEC_FORCE_DISABLE
790                     Same  as PR_SPEC_DISABLE, but cannot be undone.  A subse‐
791                     quent prctl(arg2, PR_SPEC_ENABLE) with the same value for
792                     arg2 will fail with the error EPERM.
794              PR_SPEC_DISABLE_NOEXEC (since Linux 5.1)
795                     Same as PR_SPEC_DISABLE, but the state will be cleared on
796                     execve(2).  Currently only supported for  arg2  equal  to
797                     PR_SPEC_STORE_BYPASS.
799              Any  unsupported  value  in arg3 will result in the call failing
800              with the error ERANGE.
802              The arg4 and arg5 arguments must be specified  as  0;  otherwise
803              the call fails with the error EINVAL.
805              The   speculation   feature   can  also  be  controlled  by  the
806              spec_store_bypass_disable boot parameter.   This  parameter  may
807              enforce a read-only policy which will result in the prctl() call
808              failing with the error ENXIO.  For further details, see the ker‐
809              nel source file Documentation/admin-guide/kernel-parameters.txt.
811       PR_SVE_SET_VL (since Linux 4.15, only on arm64)
812              Configure  the thread's SVE vector length, as specified by (int)
813              arg2.  Arguments arg3, arg4, and arg5 are ignored.
815              The bits of arg2 corresponding to PR_SVE_VL_LEN_MASK must be set
816              to  the  desired vector length in bytes.  This is interpreted as
817              an upper bound: the kernel will select  the  greatest  available
818              vector length that does not exceed the value specified.  In par‐
819              ticular, specifying SVE_VL_MAX (defined  in  <asm/sigcontext.h>)
820              for  the  PR_SVE_VL_LEN_MASK bits requests the maximum supported
821              vector length.
823              In addition, the other bits of arg2 must be set to  one  of  the
824              following combinations of flags:
826              0      Perform the change immediately.  At the next execve(2) in
827                     the thread, the vector length will be reset to the  value
828                     configured in /proc/sys/abi/sve_default_vector_length.
830              PR_SVE_VL_INHERIT
831                     Perform  the  change  immediately.   Subsequent execve(2)
832                     calls will preserve the new vector length.
834              PR_SVE_SET_VL_ONEXEC
835                     Defer the change, so that it is performed at the next ex‐
836                     ecve(2)  in the thread.  Further execve(2) calls will re‐
837                     set  the  vector  length  to  the  value  configured   in
838                     /proc/sys/abi/sve_default_vector_length.
841                     Defer the change, so that it is performed at the next ex‐
842                     ecve(2) in the thread.  Further execve(2) calls will pre‐
843                     serve the new vector length.
845              In  all  cases,  any  previously pending deferred change is can‐
846              celed.
848              The call fails with error EINVAL if SVE is not supported on  the
849              platform,  if  arg2  is unrecognized or invalid, or the value in
850              the bits of arg2 corresponding to PR_SVE_VL_LEN_MASK is  outside
851              the range SVE_VL_MIN..SVE_VL_MAX or is not a multiple of 16.
853              On  success,  a nonnegative value is returned that describes the
854              selected configuration.  If PR_SVE_SET_VL_ONEXEC was included in
855              arg2,  then the configuration described by the return value will
856              take effect at the next execve().  Otherwise, the  configuration
857              is  already  in  effect when the PR_SVE_SET_VL call returns.  In
858              either case, the value is encoded in the same way as the  return
859              value  of PR_SVE_GET_VL.  Note that there is no explicit flag in
860              the return value corresponding to PR_SVE_SET_VL_ONEXEC.
862              The configuration (including any pending deferred change) is in‐
863              herited across fork(2) and clone(2).
865              For  more  information,  see  the  kernel source file Documenta‐
866              tion/arm64/sve.rst (or Documentation/arm64/sve.txt before  Linux
867              5.3).
869              Warning: Because the compiler or run-time environment may be us‐
870              ing SVE, using this call without the  PR_SVE_SET_VL_ONEXEC  flag
871              may  crash  the  calling  process.   The conditions for using it
872              safely are complex and system-dependent.  Don't  use  it  unless
873              you really know what you are doing.
875       PR_SVE_GET_VL (since Linux 4.15, only on arm64)
876              Get the thread's current SVE vector length configuration.
878              Arguments arg2, arg3, arg4, and arg5 are ignored.
880              Provided  that  the kernel and platform support SVE, this opera‐
881              tion always succeeds, returning a  nonnegative  value  that  de‐
882              scribes  the  current  configuration.  The bits corresponding to
883              PR_SVE_VL_LEN_MASK  contain  the  currently  configured   vector
884              length in bytes.  The bit corresponding to PR_SVE_VL_INHERIT in‐
885              dicates whether the vector length will be inherited  across  ex‐
886              ecve(2).
888              Note  that there is no way to determine whether there is a pend‐
889              ing vector length change that has not yet taken effect.
891              For more information, see  the  kernel  source  file  Documenta‐
892              tion/arm64/sve.rst  (or Documentation/arm64/sve.txt before Linux
893              5.3).
895       PR_SET_TAGGED_ADDR_CTRL (since Linux 5.4, only on arm64)
896              Controls support for passing tagged user-space addresses to  the
897              kernel (i.e., addresses where bits 56—63 are not all zero).
899              The  level  of  support is selected by arg2, which can be one of
900              the following:
902              0      Addresses that are passed for the purpose of being deref‐
903                     erenced by the kernel must be untagged.
905              PR_TAGGED_ADDR_ENABLE
906                     Addresses that are passed for the purpose of being deref‐
907                     erenced by the kernel may be tagged, with the  exceptions
908                     summarized below.
910              The remaining arguments arg3, arg4, and arg5 must all be zero.
912              On  success,  the  mode specified in arg2 is set for the calling
913              thread and the return value is 0.  If the arguments are invalid,
914              the  mode  specified in arg2 is unrecognized, or if this feature
915              is   unsupported    by    the    kernel    or    disabled    via
916              /proc/sys/abi/tagged_addr_disabled,  the call fails with the er‐
917              ror EINVAL.
919              In particular, if prctl(PR_SET_TAGGED_ADDR_CTRL,  0,  0,  0,  0)
920              fails  with EINVAL, then all addresses passed to the kernel must
921              be untagged.
923              Irrespective of which mode is set, addresses passed  to  certain
924              interfaces must always be untagged:
926brk(2), mmap(2), shmat(2), shmdt(2), and the new_address argu‐
927                ment of mremap(2).
929                (Prior to Linux 5.6 these accepted tagged addresses,  but  the
930                behaviour may not be what you expect.  Don't rely on it.)
932              • ‘polymorphic’  interfaces  that  accept  pointers to arbitrary
933                types cast to a void * or  other  generic  type,  specifically
934                prctl(),  ioctl(2), and in general setsockopt(2) (only certain
935                specific setsockopt(2) options allow tagged addresses).
937              This list of exclusions may shrink when moving from  one  kernel
938              version  to  a  later kernel version.  While the kernel may make
939              some guarantees for backwards  compatibility  reasons,  for  the
940              purposes  of new software the effect of passing tagged addresses
941              to these interfaces is unspecified.
943              The mode set by  this  call  is  inherited  across  fork(2)  and
944              clone(2).  The mode is reset by execve(2) to 0 (i.e., tagged ad‐
945              dresses not permitted in the user/kernel ABI).
947              For more information, see  the  kernel  source  file  Documenta‐
948              tion/arm64/tagged-address-abi.rst.
950              Warning: This call is primarily intended for use by the run-time
951              environment.  A successful  PR_SET_TAGGED_ADDR_CTRL  call  else‐
952              where  may  crash the calling process.  The conditions for using
953              it safely are complex and system-dependent.  Don't use it unless
954              you know what you are doing.
956       PR_GET_TAGGED_ADDR_CTRL (since Linux 5.4, only on arm64)
957              Returns the current tagged address mode for the calling thread.
959              Arguments arg2, arg3, arg4, and arg5 must all be zero.
961              If  the arguments are invalid or this feature is disabled or un‐
962              supported by the kernel, the call fails with EINVAL.  In partic‐
963              ular,  if  prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0) fails with
964              EINVAL, then this feature is definitely either  unsupported,  or
965              disabled  via /proc/sys/abi/tagged_addr_disabled.  In this case,
966              all addresses passed to the kernel must be untagged.
968              Otherwise, the call returns a nonnegative value  describing  the
969              current tagged address mode, encoded in the same way as the arg2
970              argument of PR_SET_TAGGED_ADDR_CTRL.
972              For more information, see  the  kernel  source  file  Documenta‐
973              tion/arm64/tagged-address-abi.rst.
975       PR_TASK_PERF_EVENTS_DISABLE (since Linux 2.6.31)
976              Disable   all  performance  counters  attached  to  the  calling
977              process, regardless of whether the counters were created by this
978              process or another process.  Performance counters created by the
979              calling process for other processes are  unaffected.   For  more
980              information on performance counters, see the Linux kernel source
981              file tools/perf/design.txt.
983              Originally called  PR_TASK_PERF_COUNTERS_DISABLE;  renamed  (re‐
984              taining the same numerical value) in Linux 2.6.32.
986       PR_TASK_PERF_EVENTS_ENABLE (since Linux 2.6.31)
987              The  converse of PR_TASK_PERF_EVENTS_DISABLE; enable performance
988              counters attached to the calling process.
990              Originally called PR_TASK_PERF_COUNTERS_ENABLE; renamed in Linux
991              2.6.32.
993       PR_SET_THP_DISABLE (since Linux 3.15)
994              Set  the state of the "THP disable" flag for the calling thread.
995              If arg2 has a nonzero value, the flag is set,  otherwise  it  is
996              cleared.   Setting  this  flag  provides  a method for disabling
997              transparent huge pages for jobs where the code cannot  be  modi‐
998              fied,  and  using a malloc hook with madvise(2) is not an option
999              (i.e., statically allocated data).  The setting of the "THP dis‐
1000              able"  flag  is  inherited by a child created via fork(2) and is
1001              preserved across execve(2).
1003       PR_GET_THP_DISABLE (since Linux 3.15)
1004              Return (as the function result) the current setting of the  "THP
1005              disable"  flag  for the calling thread: either 1, if the flag is
1006              set, or 0, if it is not.
1008       PR_GET_TID_ADDRESS (since Linux 3.5)
1009              Return the clear_child_tid address set by set_tid_address(2) and
1010              the  clone(2) CLONE_CHILD_CLEARTID flag, in the location pointed
1011              to by (int **) arg2.  This feature is available only if the ker‐
1012              nel  is built with the CONFIG_CHECKPOINT_RESTORE option enabled.
1013              Note that since the prctl() system call does not have  a  compat
1014              implementation for the AMD64 x32 and MIPS n32 ABIs, and the ker‐
1015              nel writes out a pointer using the kernel's pointer  size,  this
1016              operation  expects  a  user-space  buffer  of 8 (not 4) bytes on
1017              these ABIs.
1019       PR_SET_TIMERSLACK (since Linux 2.6.28)
1020              Each thread has two associated timer slack values:  a  "default"
1021              value, and a "current" value.  This operation sets the "current"
1022              timer slack value for the calling thread.  arg2 is  an  unsigned
1023              long  value,  then  maximum "current" value is ULONG_MAX and the
1024              minimum "current" value is 1.  If the nanosecond value  supplied
1025              in arg2 is greater than zero, then the "current" value is set to
1026              this value.  If arg2 is equal to zero, the "current" timer slack
1027              is reset to the thread's "default" timer slack value.
1029              The  "current"  timer slack is used by the kernel to group timer
1030              expirations for the calling thread that are  close  to  one  an‐
1031              other; as a consequence, timer expirations for the thread may be
1032              up to the specified number of nanoseconds late (but  will  never
1033              expire  early).  Grouping timer expirations can help reduce sys‐
1034              tem power consumption by minimizing CPU wake-ups.
1036              The timer expirations affected by timer slack are those  set  by
1037              select(2),   pselect(2),   poll(2),   ppoll(2),   epoll_wait(2),
1038              epoll_pwait(2), clock_nanosleep(2), nanosleep(2),  and  futex(2)
1039              (and thus the library functions implemented via futexes, includ‐
1040              ing    pthread_cond_timedwait(3),    pthread_mutex_timedlock(3),
1041              pthread_rwlock_timedrdlock(3),    pthread_rwlock_timedwrlock(3),
1042              and sem_timedwait(3)).
1044              Timer slack is not applied to threads that are scheduled under a
1045              real-time scheduling policy (see sched_setscheduler(2)).
1047              When  a  new  thread  is created, the two timer slack values are
1048              made the same as the "current" value  of  the  creating  thread.
1049              Thereafter,  a thread can adjust its "current" timer slack value
1050              via PR_SET_TIMERSLACK.  The "default" value  can't  be  changed.
1051              The timer slack values of init (PID 1), the ancestor of all pro‐
1052              cesses, are 50,000 nanoseconds  (50  microseconds).   The  timer
1053              slack  value is inherited by a child created via fork(2), and is
1054              preserved across execve(2).
1056              Since Linux 4.6, the "current" timer slack value of any  process
1057              can  be  examined  and  changed  via the file /proc/[pid]/timer‐
1058              slack_ns.  See proc(5).
1060       PR_GET_TIMERSLACK (since Linux 2.6.28)
1061              Return (as the function result) the "current" timer slack  value
1062              of the calling thread.
1064       PR_SET_TIMING (since Linux 2.6.0)
1065              Set  whether  to  use  (normal, traditional) statistical process
1066              timing or accurate timestamp-based process  timing,  by  passing
1067              PR_TIMING_STATISTICAL  or  PR_TIMING_TIMESTAMP to arg2.  PR_TIM‐
1068              ING_TIMESTAMP is not currently implemented  (attempting  to  set
1069              this mode will yield the error EINVAL).
1071       PR_GET_TIMING (since Linux 2.6.0)
1072              Return  (as  the function result) which process timing method is
1073              currently in use.
1075       PR_SET_TSC (since Linux 2.6.26, x86 only)
1076              Set the state of the  flag  determining  whether  the  timestamp
1077              counter  can be read by the process.  Pass PR_TSC_ENABLE to arg2
1078              to allow it to be read, or PR_TSC_SIGSEGV to generate a  SIGSEGV
1079              when the process tries to read the timestamp counter.
1081       PR_GET_TSC (since Linux 2.6.26, x86 only)
1082              Return  the  state of the flag determining whether the timestamp
1083              counter can be read, in the location pointed to by (int *) arg2.
1085       PR_SET_UNALIGN
1086              (Only on: ia64, since Linux 2.3.48; parisc, since Linux  2.6.15;
1087              PowerPC,  since  Linux  2.6.18;  Alpha,  since Linux 2.6.22; sh,
1088              since Linux 2.6.34; tile, since Linux 3.12) Set unaligned access
1089              control  bits  to arg2.  Pass PR_UNALIGN_NOPRINT to silently fix
1090              up unaligned user accesses,  or  PR_UNALIGN_SIGBUS  to  generate
1091              SIGBUS  on  unaligned user access.  Alpha also supports an addi‐
1092              tional flag with the value of 4 and no corresponding named  con‐
1093              stant,  which  instructs kernel to not fix up unaligned accesses
1094              (it is analogous to providing the UAC_NOFIX flag in  SSI_NVPAIRS
1095              operation of the setsysinfo() system call on Tru64).
1097       PR_GET_UNALIGN
1098              (See  PR_SET_UNALIGN  for  information on versions and architec‐
1099              tures.)  Return unaligned access control bits, in  the  location
1100              pointed to by (unsigned int *) arg2.


1107       PR_GET_THP_DISABLE,  PR_GET_TIMING,  PR_GET_TIMERSLACK,  and (if it re‐
1108       turns) PR_GET_SECCOMP return the nonnegative  values  described  above.
1109       All other option values return 0 on success.  On error, -1 is returned,
1110       and errno is set appropriately.


1113       EACCES option is PR_SET_SECCOMP and arg2  is  SECCOMP_MODE_FILTER,  but
1114              the  process  does  not have the CAP_SYS_ADMIN capability or has
1115              not set  the  no_new_privs  attribute  (see  the  discussion  of
1116              PR_SET_NO_NEW_PRIVS above).
1118       EACCES option is PR_SET_MM, and arg3 is PR_SET_MM_EXE_FILE, the file is
1119              not executable.
1121       EBADF  option is PR_SET_MM, arg3 is PR_SET_MM_EXE_FILE,  and  the  file
1122              descriptor passed in arg4 is not valid.
1124       EBUSY  option  is  PR_SET_MM,  arg3 is PR_SET_MM_EXE_FILE, and this the
1125              second attempt to change the /proc/pid/exe symbolic link,  which
1126              is prohibited.
1128       EFAULT arg2 is an invalid address.
1130       EFAULT option  is PR_SET_SECCOMP, arg2 is SECCOMP_MODE_FILTER, the sys‐
1131              tem was built with CONFIG_SECCOMP_FILTER, and arg3 is an invalid
1132              address.
1134       EINVAL The  value of option is not recognized, or not supported on this
1135              system.
1137       EINVAL option is PR_MCE_KILL or PR_MCE_KILL_GET or PR_SET_MM,  and  un‐
1138              used prctl() arguments were not specified as zero.
1140       EINVAL arg2 is not valid value for this option.
1142       EINVAL option  is  PR_SET_SECCOMP or PR_GET_SECCOMP, and the kernel was
1143              not configured with CONFIG_SECCOMP.
1145       EINVAL option is PR_SET_SECCOMP, arg2 is SECCOMP_MODE_FILTER,  and  the
1146              kernel was not configured with CONFIG_SECCOMP_FILTER.
1148       EINVAL option is PR_SET_MM, and one of the following is true
1150              *  arg4 or arg5 is nonzero;
1152              *  arg3  is greater than TASK_SIZE (the limit on the size of the
1153                 user address space for this architecture);
1155              *  arg2     is     PR_SET_MM_START_CODE,     PR_SET_MM_END_CODE,
1156                 PR_SET_MM_START_DATA,          PR_SET_MM_END_DATA,         or
1157                 PR_SET_MM_START_STACK, and the permissions of the correspond‐
1158                 ing memory area are not as required;
1160              *  arg2  is  PR_SET_MM_START_BRK  or  PR_SET_MM_BRK, and arg3 is
1161                 less than or equal to the end of the data segment  or  speci‐
1162                 fies  a value that would cause the RLIMIT_DATA resource limit
1163                 to be exceeded.
1165       EINVAL option is PR_SET_PTRACER and arg2 is not 0,  PR_SET_PTRACER_ANY,
1166              or the PID of an existing process.
1168       EINVAL option  is  PR_SET_PDEATHSIG and arg2 is not a valid signal num‐
1169              ber.
1171       EINVAL option is PR_SET_DUMPABLE and arg2 is neither  SUID_DUMP_DISABLE
1172              nor SUID_DUMP_USER.
1174       EINVAL option is PR_SET_TIMING and arg2 is not PR_TIMING_STATISTICAL.
1176       EINVAL option  is  PR_SET_NO_NEW_PRIVS  and  arg2  is not equal to 1 or
1177              arg3, arg4, or arg5 is nonzero.
1179       EINVAL option is PR_GET_NO_NEW_PRIVS and arg2, arg3, arg4, or  arg5  is
1180              nonzero.
1182       EINVAL option is PR_SET_THP_DISABLE and arg3, arg4, or arg5 is nonzero.
1184       EINVAL option  is  PR_GET_THP_DISABLE  and arg2, arg3, arg4, or arg5 is
1185              nonzero.
1187       EINVAL option is PR_CAP_AMBIENT and an unused argument (arg4, arg5, or,
1188              in  the  case  of PR_CAP_AMBIENT_CLEAR_ALL, arg3) is nonzero; or
1189              arg2 has an invalid  value;  or  arg2  is  PR_CAP_AMBIENT_LOWER,
1190              PR_CAP_AMBIENT_RAISE, or PR_CAP_AMBIENT_IS_SET and arg3 does not
1191              specify a valid capability.
1194              and  unused  arguments  to  prctl() are not 0.  EINVAL option is
1195              PR_PAC_RESET_KEYS and the arguments are invalid or  unsupported.
1196              See the description of PR_PAC_RESET_KEYS above for details.
1198       EINVAL option  is PR_SVE_SET_VL and the arguments are invalid or unsup‐
1199              ported, or SVE is not available on this platform.  See  the  de‐
1200              scription of PR_SVE_SET_VL above for details.
1202       EINVAL option  is  PR_SVE_GET_VL and SVE is not available on this plat‐
1203              form.
1205       EINVAL option is PR_SET_TAGGED_ADDR_CTRL and the arguments are  invalid
1206              or  unsupported.  See the description of PR_SET_TAGGED_ADDR_CTRL
1207              above for details.
1209       EINVAL option is PR_GET_TAGGED_ADDR_CTRL and the arguments are  invalid
1210              or  unsupported.  See the description of PR_GET_TAGGED_ADDR_CTRL
1211              above for details.
1213       ENODEV option was PR_SET_SPECULATION_CTRL the kernel or  CPU  does  not
1214              support the requested speculation misfeature.
1217              and the kernel or the  CPU  does  not  support  MPX  management.
1218              Check that the kernel and processor have MPX support.
1220       ENXIO  option  was  PR_SET_SPECULATION_CTRL implies that the control of
1221              the  selected  speculation  misfeature  is  not  possible.   See
1222              PR_GET_SPECULATION_CTRL  for  the  bit fields to determine which
1223              option is available.
1225       EOPNOTSUPP
1226              option is PR_SET_FP_MODE and arg2 has an invalid or  unsupported
1227              value.
1229       EPERM  option  is  PR_SET_SECUREBITS,  and the caller does not have the
1230              CAP_SETPCAP capability, or tried to unset a  "locked"  flag,  or
1231              tried to set a flag whose corresponding locked flag was set (see
1232              capabilities(7)).
1234       EPERM  option is PR_SET_SPECULATION_CTRL wherein  the  speculation  was
1235              disabled  with  PR_SPEC_FORCE_DISABLE and caller tried to enable
1236              it again.
1238       EPERM  option     is     PR_SET_KEEPCAPS,     and     the      caller's
1239              SECBIT_KEEP_CAPS_LOCKED flag is set (see capabilities(7)).
1241       EPERM  option  is  PR_CAPBSET_DROP,  and  the  caller does not have the
1242              CAP_SETPCAP capability.
1244       EPERM  option  is  PR_SET_MM,  and  the  caller  does  not   have   the
1245              CAP_SYS_RESOURCE capability.
1247       EPERM  option  is  PR_CAP_AMBIENT and arg2 is PR_CAP_AMBIENT_RAISE, but
1248              either the capability specified in arg3 is not  present  in  the
1249              process's  permitted  and  inheritable  capability  sets, or the
1250              PR_CAP_AMBIENT_LOWER securebit has been set.
1252       ERANGE option was PR_SET_SPECULATION_CTRL and arg3 is  not  PR_SPEC_EN‐
1254              ABLE_NOEXEC.


1257       The prctl() system call was introduced in Linux 2.1.57.


1260       This call is Linux-specific.  IRIX has a prctl() system call (also  in‐
1261       troduced  in Linux 2.1.44 as irix_prctl on the MIPS architecture), with
1262       prototype
1264           ptrdiff_t prctl(int option, int arg2, int arg3);
1266       and options to get the maximum number of processes per  user,  get  the
1267       maximum  number  of  processors  the  calling process can use, find out
1268       whether a specified process is currently blocked, get or set the  maxi‐
1269       mum stack size, and so on.


1272       signal(2), core(5)


1275       This  page  is  part of release 5.10 of the Linux man-pages project.  A
1276       description of the project, information about reporting bugs,  and  the
1277       latest     version     of     this    page,    can    be    found    at
1278       https://www.kernel.org/doc/man-pages/.
1282Linux                             2020-08-13                          PRCTL(2)