#include <unistd.h>

       int execve(const char *filename, char *const argv[],
                  char *const envp[]);

       execve() executes the program pointed to by filename.  filename must be
       either a binary executable, or a script starting with  a  line  of  the

           #! interpreter [optional-arg]

       For details of the latter case, see "Interpreter scripts" below.

       argv  is  an  array  of argument strings passed to the new program.  By
       convention, the first of these  strings  should  contain  the  filename
       associated  with the file being executed.  envp is an array of strings,
       conventionally of the form key=value, which are passed  as  environment
       to  the  new  program.  Both argv and envp must be terminated by a NULL
       pointer.  The argument vector and environment can be  accessed  by  the
       called program's main function, when it is defined as:

           int main(int argc, char *argv[], char *envp[])

       execve() does not return on success, and the text, data, bss, and stack
       of the calling process are overwritten by that of the program loaded.

       If the current program is being ptraced, a SIGTRAP is sent to it  after
       a successful execve().

       If  the  set-user-ID bit is set on the program file pointed to by file-
       name, and the  underlying  file  system  is  not  mounted  nosuid  (the
       MS_NOSUID  flag  for  mount(2)),  and  the calling process is not being
       ptraced, then the effective user ID of the calling process  is  changed
       to  that  of  the  owner of the program file.  Similarly, when the set-
       group-ID bit of the program file is set the effective group ID  of  the
       calling process is set to the group of the program file.

       The  effective  user ID of the process is copied to the saved set-user-
       ID; similarly, the effective group ID is copied to the saved set-group-
       ID.  This copying takes place after any effective ID changes that occur
       because of the set-user-ID and set-group-ID permission bits.

       If the executable is an a.out dynamically linked binary executable con-
       taining  shared-library  stubs,  the  Linux  dynamic linker ld.so(8) is
       called at the start of execution to bring needed shared libraries  into
       memory and link the executable with them.

       If  the  executable  is a dynamically linked ELF executable, the inter-
       preter named in the PT_INTERP segment is used to load the needed shared
       libraries.   This interpreter is typically /lib/ld-linux.so.1 for bina-
       ries linked with the Linux libc 5, or /lib/ld-linux.so.2  for  binaries
       *      Attached   System   V   shared   memory  segments  are  detached

       *      POSIX shared memory regions are unmapped (shm_open(3)).

       *      Open  POSIX  message  queue  descriptors  are  closed  (mq_over-

       *      Any open POSIX named semaphores are closed (sem_overview(7)).

       *      POSIX timers are not preserved (timer_create(2)).

       *      Any open directory streams are closed (opendir(3)).

       *      Memory locks are not preserved (mlock(2), mlockall(2)).

       *      Exit handlers are not preserved (atexit(3), on_exit(3)).

       *      The  floating-point  environment  is  reset  to the default (see

       The process attributes in the  preceding  list  are  all  specified  in
       POSIX.1-2001.  The following Linux-specific process attributes are also
       not preserved during an execve():

       *  The prctl(2) PR_SET_DUMPABLE flag is set, unless  a  set-user-ID  or
          set-group ID program is being executed, in which case it is cleared.

       *  The prctl(2) PR_SET_KEEPCAPS flag is cleared.

       *  The  process  name, as set by prctl(2) PR_SET_NAME (and displayed by
          ps -o comm), is reset to the name of the new executable file.

       *  The termination signal is reset to SIGCHLD (see clone(2)).

       Note the following further points:

       *  All threads other than the calling thread are  destroyed  during  an
          execve().   Mutexes, condition variables, and other pthreads objects
          are not preserved.

       *  The equivalent of setlocale(LC_ALL,  "C")  is  executed  at  program

       *  POSIX.1-2001 specifies that the dispositions of any signals that are
          ignored or set to the  default  are  left  unchanged.   POSIX.1-2001
          specifies one exception: if SIGCHLD is being ignored, then an imple-
          mentation may leave the disposition unchanged or  reset  it  to  the
          default; Linux does the former.

       *  Any   outstanding   asynchronous   I/O   operations   are   canceled
          (aio_read(3), aio_write(3)).

       *  For the handling of  capabilities  during  execve(),  see  capabili-
          principle,  no  portable  program,  whether  privileged  or not, can
          assume that these three file descriptors will remain  closed  across
          an execve().

   Interpreter scripts
       An  interpreter  script  is  a  text  file  that has execute permission
       enabled and whose first line is of the form:

           #! interpreter [optional-arg]

       The interpreter must be a valid pathname for an executable which is not
       itself  a  script.   If  the filename argument of execve() specifies an
       interpreter script, then interpreter will be invoked with the following

           interpreter [optional-arg] filename arg...

       where arg...  is the series of words pointed to by the argv argument of

       For portable use, optional-arg should either be absent, or be specified
       as  a  single word (i.e., it should not contain white space); see NOTES

   Limits on size of arguments and environment
       Most UNIX implementations impose some limit on the total  size  of  the
       command-line argument (argv) and environment (envp) strings that may be
       passed to a new program.  POSIX.1 allows an implementation to advertise
       this  limit using the ARG_MAX constant (either defined in <limits.h> or
       available at run time using the call sysconf(_SC_ARG_MAX)).

       On Linux prior to kernel 2.6.23, the memory used to store the  environ-
       ment  and argument strings was limited to 32 pages (defined by the ker-
       nel constant MAX_ARG_PAGES).  On architectures with a 4-kB  page  size,
       this yields a maximum size of 128 kB.

       On  kernel  2.6.23  and  later, most architectures support a size limit
       derived from the soft RLIMIT_STACK resource  limit  (see  getrlimit(2))
       that is in force at the time of the execve() call.  (Architectures with
       no memory management unit are excepted: they maintain  the  limit  that
       was  in  effect  before kernel 2.6.23.)  This change allows programs to
       have a much larger argument and/or environment list.  For these  archi-
       tectures,  the  total size is limited to 1/4 of the allowed stack size.
       (Imposing the 1/4-limit ensures that the new program  always  has  some
       stack  space.)   Since  Linux  2.6.25,  the kernel places a floor of 32
       pages on this size limit, so that, even when RLIMIT_STACK is  set  very
       low,  applications are guaranteed to have at least as much argument and
       environment space as was provided by Linux 2.6.23 and  earlier.   (This
       guarantee  was not provided in Linux 2.6.23 and 2.6.24.)  Additionally,
       the limit per string is 32 pages (the kernel constant  MAX_ARG_STRLEN),
       and the maximum number of strings is 0x7FFFFFFF.

       On  success,  execve()  does  not  return, on error -1 is returned, and
       EACCES Execute  permission  is  denied  for the file or a script or ELF

       EACCES The file system is mounted noexec.

       EFAULT filename points outside your accessible address space.

       EINVAL An ELF executable had more than  one  PT_INTERP  segment  (i.e.,
              tried to name more than one interpreter).

       EIO    An I/O error occurred.

       EISDIR An ELF interpreter was a directory.

              An ELF interpreter was not in a recognized format.

       ELOOP  Too  many  symbolic links were encountered in resolving filename
              or the name of a script or ELF interpreter.

       EMFILE The process has the maximum number of files open.

              filename is too long.

       ENFILE The system limit on the total number  of  open  files  has  been

       ENOENT The file filename or a script or ELF interpreter does not exist,
              or a shared library needed for file  or  interpreter  cannot  be

              An  executable  is  not in a recognized format, is for the wrong
              architecture, or has some other format error that means it  can-
              not be executed.

       ENOMEM Insufficient kernel memory was available.

              A  component  of  the path prefix of filename or a script or ELF
              interpreter is not a directory.

       EPERM  The file system is mounted nosuid, the user  is  not  the  supe-
              ruser, and the file has the set-user-ID or set-group-ID bit set.

       EPERM  The  process  is being traced, the user is not the superuser and
              the file has the set-user-ID or set-group-ID bit set.

              Executable was open for writing by one or more processes.

       SVr4, 4.3BSD, POSIX.1-2001.  POSIX.1-2001  does  not  document  the  #!

       A  maximum  line length of 127 characters is allowed for the first line
       in a #! executable shell script.

       The semantics of the optional-arg argument  of  an  interpreter  script
       vary across implementations.  On Linux, the entire string following the
       interpreter name is passed as a single argument to the interpreter, and
       this string can include white space.  However, behavior differs on some
       other systems.  Some systems use the first  white  space  to  terminate
       optional-arg.  On some systems, an interpreter script can have multiple
       arguments, and white spaces in optional-arg are  used  to  delimit  the

       On  Linux,  argv can be specified as NULL, which has the same effect as
       specifying this argument as a pointer to a  list  containing  a  single
       NULL  pointer.   Do  not take advantage of this misfeature!  It is non-
       standard and nonportable: on most other UNIX systems  doing  this  will
       result in an error (EFAULT).

       POSIX.1-2001  says that values returned by sysconf(3) should be invari-
       ant over the lifetime of a process.  However, since  Linux  2.6.23,  if
       the  RLIMIT_STACK  resource  limit  changes, then the value reported by
       _SC_ARG_MAX will also change, to reflect the fact  that  the  limit  on
       space  for holding command-line arguments and environment variables has

       With UNIX V6 the argument list of an exec() call was ended by 0,  while
       the  argument  list  of main was ended by -1.  Thus, this argument list
       was not directly usable in a further exec() call.  Since UNIX  V7  both
       are NULL.

       The  following  program  is designed to be execed by the second program
       below.  It just echoes its command-line one per line.

           /* myecho.c */

           #include <stdio.h>
           #include <stdlib.h>

           main(int argc, char *argv[])
               int j;

               for (j = 0; j < argc; j++)
                   printf("argv[%d]: %s\n", j, argv[j]);


       This program can be used to exec the program named in its  command-line

               if (argc != 2) {
                fprintf(stderr, "Usage: %s <file-to-exec>\n", argv[0]);

               newargv[0] = argv[1];

               execve(argv[1], newargv, newenviron);
               perror("execve");   /* execve() only returns on error */

       We can use the second program to exec the first as follows:

           $ cc myecho.c -o myecho
           $ cc execve.c -o execve
           $ ./execve ./myecho
           argv[0]: ./myecho
           argv[1]: hello
           argv[2]: world

       We  can  also  use  these  programs  to demonstrate the use of a script
       interpreter.  To do this we create a script whose "interpreter" is  our
       myecho program:

           $ cat > script.sh
           #! ./myecho script-arg
           $ chmod +x script.sh

       We can then use our program to exec the script:

           $ ./execve ./script.sh
           argv[0]: ./myecho
           argv[1]: script-arg
           argv[2]: ./script.sh
           argv[3]: hello
           argv[4]: world

       chmod(2),  fork(2), ptrace(2), execl(3), fexecve(3), getopt(3), creden-
       tials(7), environ(7), path_resolution(7), ld.so(8)

       This page is part of release 3.35 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://man7.org/linux/man-pages/.

Linux                             2011-09-14                         EXECVE(2)
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