getauxval - retrieve a value from the auxiliary vector


   #include <sys/auxv.h>

   unsigned long getauxval(unsigned long type);


   The  getauxval() function retrieves values from the auxiliary vector, a
   mechanism that the kernel's ELF binary  loader  uses  to  pass  certain
   information to user space when a program is executed.

   Each entry in the auxiliary vector consists of a pair of values: a type
   that identifies what this entry represents, and a value for that  type.
   Given the argument type, getauxval() returns the corresponding value.

   The  value  returned for each type is given in the following list.  Not
   all type values are present on all architectures.

          The base  address  of  the  program  interpreter  (usually,  the
          dynamic linker).

          A   string  identifying  the  real  platform;  may  differ  from
          AT_PLATFORM (PowerPC only).

          The frequency with which times(2) counts.  This value  can  also
          be obtained via sysconf(_SC_CLK_TCK).

          The data cache block size.

          The effective group ID of the thread.

          The entry address of the executable.

          The effective user ID of the thread.

          File descriptor of program.

          Pathname used to execute program.

          Flags (unused).

          Used  FPU  control  word (SuperH architecture only).  This gives
          some information about the FPU initialization performed  by  the

   AT_GID The real group ID of the thread.

          An  architecture  and  ABI  dependent  bit-mask  whose  settings
          indicate detailed processor capabilities.  The contents  of  the
          bit  mask  are  hardware  dependent (for example, see the kernel
          source  file   arch/x86/include/asm/cpufeature.h   for   details
          relating  to  the  Intel x86 architecture; the value returned is
          the first 32-bit word of the array described there).   A  human-
          readable  version  of  the  same  information  is  available via

   AT_HWCAP2 (since glibc 2.18)
          Further machine-dependent hints about processor capabilities.

          The instruction cache block size.

          The   system   page   size   (the   same   value   returned   by

          The address of the program headers of the executable.

          The size of program header entry.

          The number of program headers.

          A pointer to a string that identifies the hardware platform that
          the program is running on.  The dynamic linker uses this in  the
          interpretation of rpath values.

          The address of sixteen bytes containing a random value.

          Has  a  nonzero  value  if  this  executable  should  be treated
          securely.  Most commonly, a nonzero  value  indicates  that  the
          process  is  executing  a set-user-ID or set-group-ID binary (so
          that its real  and  effective  UIDs  or  GIDs  differ  from  one
          another),  or  that it gained capabilities by executing a binary
          file    that    has    capabilities    (see    capabilities(7)).
          Alternatively,  a  nonzero  value  may  be  triggered by a Linux
          Security Module.  When this value is nonzero, the dynamic linker
          disables  the  use  of  certain  environment  variables (see ld-
 and glibc changes other aspects  of  its  behavior.
          (See also secure_getenv(3).)

          The  entry  point  to the system call function in the vDSO.  Not
          present/needed on all architectures (e.g., absent on x86-64).

          The address of a page  containing  the  virtual  Dynamic  Shared
          Object  (vDSO)  that the kernel creates in order to provide fast
          implementations of certain system calls.

          The unified cache block size.

   AT_UID The real user ID of the thread.


   On success, getauxval() returns the value corresponding  to  type.   If
   type is not found, 0 is returned.


   ENOENT (since glibc 2.19)
          No  entry  corresponding to type could be found in the auxiliary


   The getauxval() function was added to glibc in version 2.16.


   For  an  explanation  of  the  terms  used   in   this   section,   see

   Interface    Attribute      Value   
   getauxval()  Thread safety  MT-Safe 


   This function is a nonstandard glibc extension.


   The  primary consumer of the information in the auxiliary vector is the
   dynamic linker  The auxiliary vector  is  a  convenient
   and  efficient shortcut that allows the kernel to communicate a certain
   set of standard information that the dynamic linker usually  or  always
   needs.  In some cases, the same information could be obtained by system
   calls, but using the auxiliary vector is cheaper.

   The  auxiliary  vector  resides  just  above  the  argument  list   and
   environment  in  the  process  address  space.   The  auxiliary  vector
   supplied to a  program  can  be  viewed  by  setting  the  LD_SHOW_AUXV
   environment variable when running a program:

       $ LD_SHOW_AUXV=1 sleep 1

   The  auxiliary  vector of any process can (subject to file permissions)
   be obtained via /proc/[pid]/auxv; see proc(5) for more information.


   Before the addition of the ENOENT error in glibc 2.19, there was no way
   to  unambiguously  distinguish  the  case where type could not be found
   from the case where the value corresponding to type was zero.


   secure_getenv(3), vdso(7),


   This page is part of release 4.09 of the Linux  man-pages  project.   A
   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at


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