EXECVE(2)                  Linux Programmer's Manual                 EXECVE(2)

       execve - execute program

       #include <unistd.h>

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

       execve() executes the program referred to by pathname.  This causes the
       program that is currently being run by the calling process  to  be  re-
       placed  with  a  new  program,  with newly initialized stack, heap, and
       (initialized and uninitialized) data segments.

       pathname must be either a binary executable, or a script starting  with
       a line of the form:

           #!interpreter [optional-arg]

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

       argv  is  an  array of pointers to strings passed to the new program as
       its command-line arguments.  By convention, the first of these  strings
       (i.e.,  argv[0])  should  contain the filename associated with the file
       being executed.  The argv array must be terminated by  a  NULL  pointer
       (Thus, in the new program, argv[argc] will be NULL.)

       envp  is  an  array  of pointers to strings, conventionally of the form
       key=value, which are passed as the environment of the new program.  The
       envp array must be terminated by a NULL pointer

       The  argument  vector  and  environment can be accessed by the new pro-
       gram's main function, when it is defined as:

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

       Note, however, that the use of a third argument to the main function is
       not  specified in POSIX.1; according to POSIX.1, the environment should
       be accessed via the external variable environ(7).

       execve() does not return on success, and the  text,  initialized  data,
       uninitialized  data  (bss),  and stack of the calling process are over-
       written according to the contents of the newly loaded program.

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

       If  the set-user-ID bit is set on the program file referred to by path-
       name, then the effective user ID of the calling process is  changed  to
       that  of the owner of the program file.  Similarly, if the set-group-ID
       bit is set on the program file, then the  effective  group  ID  of  the
       calling process is set to the group of the program file.

       The  aforementioned  transformations  of the effective IDs are not per-
       formed (i.e., the set-user-ID and set-group-ID bits are ignored) if any
       of the following is true:

       *  the  no_new_privs  attribute  is  set  for  the  calling thread (see

       *  the underlying filesystem is mounted nosuid (the MS_NOSUID flag  for
          mount(2)); or

       *  the calling process is being ptraced.

       The capabilities of the program file (see capabilities(7)) are also ig-
       nored if any of the above are true.

       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 mode bits.

       The  process's  real  UID and real GID, as well its supplementary group
       IDs, are unchanged by a call to execve().

       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  objects  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
       objects.  This interpreter is typically /lib/ld-linux.so.2 for binaries
       linked with glibc (see ld-linux.so(8)).

   Effect on process attributes
       All process attributes are preserved during  an  execve(),  except  the

       *  The  dispositions  of any signals that are being caught are reset to
          the default (signal(7)).

       *  Any alternate signal stack is not preserved (sigaltstack(2)).

       *  Memory mappings are not preserved (mmap(2)).

       *  Attached System V shared memory segments are detached (shmat(2)).

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

       *  Open POSIX message queue descriptors are closed (mq_overview(7)).

       *  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.  The following Linux-specific process attributes are also  not
       preserved during an execve():

       *  The  process's  "dumpable" attribute is set to the value 1, unless a
          set-user-ID program, a set-group-ID program, or a program with capa-
          bilities  is being executed, in which case the dumpable flag may in-
          stead be reset to the value in  /proc/sys/fs/suid_dumpable,  in  the
          circumstances  described  under  PR_SET_DUMPABLE  in prctl(2).  Note
          that changes to the "dumpable"  attribute  may  cause  ownership  of
          files in the process's /proc/[pid] directory to change to root:root,
          as described in proc(5).

       *  The prctl(2) PR_SET_KEEPCAPS flag is cleared.

       *  (Since Linux 2.4.36 / 2.6.23) If a set-user-ID or set-group-ID  pro-
          gram is being executed, then the parent death signal set by prctl(2)
          PR_SET_PDEATHSIG 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  SECBIT_KEEP_CAPS  securebits  flag  is  cleared.  See capabili-

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

       *  The file descriptor table is unshared, undoing  the  effect  of  the
          CLONE_FILES flag of 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 specifies that the dispositions of any signals that are  ig-
          nored  or  set to the default are left unchanged.  POSIX.1 specifies
          one exception: if SIGCHLD is being ignored, then  an  implementation
          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-

       *  By default, file descriptors remain open across an  execve().   File
          descriptors  that  are  marked close-on-exec are closed; see the de-
          scription of FD_CLOEXEC in  fcntl(2).   (If  a  file  descriptor  is
          closed,  this will cause the release of all record locks obtained on
          the underlying file by this process.   See  fcntl(2)  for  details.)
          POSIX.1 says that if file descriptors 0, 1, and 2 would otherwise be
          closed after a successful execve(), and the process would gain priv-
          ilege  because  the  set-user-ID or set-group-ID mode bit was set on
          the executed file, then the system may open an unspecified file  for
          each of these file descriptors.  As a general 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 en-
       abled and whose first line is of the form:

           #!interpreter [optional-arg]

       The interpreter must be a valid pathname for an executable file.

       If the pathname argument of execve() specifies an  interpreter  script,
       then interpreter will be invoked with the following arguments:

           interpreter [optional-arg] pathname arg...

       where  pathname  is  the absolute pathname of the file specified as the
       first argument of execve(), and arg...  is the series of words  pointed
       to  by  the  argv argument of execve(), starting at argv[1].  Note that
       there is no way to get the argv[0] that  was  passed  to  the  execve()

       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

       Since  Linux  2.6.28, the kernel permits the interpreter of a script to
       itself be a script.  This permission is recursive, up  to  a  limit  of
       four  recursions,  so that the interpreter may be a script which is in-
       terpreted by a script, and so on.

   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 de-
       rived 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 architectures,
       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.)  Additionally, the total size is limited to 3/4 of the value of
       the kernel constant _STK_LIM (8 Mibibytes).  Since  Linux  2.6.25,  the
       kernel  also  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 er-
       rno is set appropriately.

       E2BIG  The total number of bytes in the environment (envp) and argument
              list (argv) is too large.

       EACCES Search permission is denied on a component of the path prefix of
              pathname or  the  name  of  a  script  interpreter.   (See  also

       EACCES The file or a script interpreter is not a regular file.

       EACCES Execute permission is denied for the file or a script or ELF in-

       EACCES The filesystem is mounted noexec.

       EAGAIN (since Linux 3.1)
              Having changed its real UID using one of  the  set*uid()  calls,
              the  caller  was--and  is  now still--above its RLIMIT_NPROC re-
              source limit (see setrlimit(2)).  For a more  detailed  explana-
              tion of this error, see NOTES.

       EFAULT pathname  or  one  of  the  pointers in the vectors argv or envp
              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 pathname
              or the name of a script or ELF interpreter.

       ELOOP  The maximum recursion limit was reached during recursive  script
              interpretation (see "Interpreter scripts", above).  Before Linux
              3.8, the error produced for this case was ENOEXEC.

       EMFILE The per-process limit on the number of open file descriptors has
              been reached.

              pathname is too long.

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

       ENOENT The file pathname or a script or ELF interpreter does not exist.

              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 pathname or a  script  or  ELF
              interpreter is not a directory.

       EPERM  The filesystem is mounted nosuid, the user is not the superuser,
              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.

       EPERM  A  "capability-dumb"  applications would not obtain the full set
              of permitted capabilities granted by the executable  file.   See

              The  specified  executable  was  open for writing by one or more

       POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.  POSIX does not document  the
       #!  behavior,  but  it exists (with some variations) on other UNIX sys-

       One sometimes sees execve() (and the  related  functions  described  in
       exec(3))  described as "executing a new process" (or similar).  This is
       a highly misleading description: there is  no  new  process;  many  at-
       tributes  of  the  calling process remain unchanged (in particular, its
       PID).  All that execve() does is arrange for an existing  process  (the
       calling process) to execute a new program.

       Set-user-ID and set-group-ID processes can not be ptrace(2)d.

       The  result  of mounting a filesystem nosuid varies across Linux kernel
       versions: some will refuse execution of  set-user-ID  and  set-group-ID
       executables  when this would give the user powers they did not have al-
       ready (and return EPERM), some will just  ignore  the  set-user-ID  and
       set-group-ID bits and exec() successfully.

       On  Linux, argv and envp can be specified as NULL.  In both cases, this
       has the same effect as specifying the argument as a pointer to  a  list
       containing  a  single null pointer.  Do not take advantage of this non-
       standard and nonportable misfeature!  On many other UNIX systems, spec-
       ifying  argv as NULL will result in an error (EFAULT).  Some other UNIX
       systems treat the envp==NULL case the same as Linux.

       POSIX.1 says that values returned by  sysconf(3)  should  be  invariant
       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

       In most cases where execve() fails, control returns to the original ex-
       ecutable image, and the caller of execve() can then handle  the  error.
       However,  in  (rare)  cases  (typically caused by resource exhaustion),
       failure may occur past the point of no return: the original  executable
       image  has  been  torn  down, but the new image could not be completely
       built.  In such cases, the kernel kills  the  process  with  a  SIGSEGV
       (SIGKILL until Linux 3.17) signal.

   Interpreter scripts
       The  kernel  imposes a maximum length on the text that follows the "#!"
       characters at the start of a script; characters beyond  the  limit  are
       ignored.   Before  Linux 5.1, the limit is 127 characters.  Since Linux
       5.1, the limit is 255 characters.

       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 op-
       tional-arg.   On  some systems, an interpreter script can have multiple
       arguments, and white spaces in optional-arg are used to delimit the ar-

       Linux (like most other modern UNIX systems) ignores the set-user-ID and
       set-group-ID bits on scripts.

   execve() and EAGAIN
       A more detailed explanation of the EAGAIN error that can  occur  (since
       Linux 3.1) when calling execve() is as follows.

       The  EAGAIN  error  can  occur  when a preceding call to setuid(2), se-
       treuid(2), or setresuid(2) caused the real user ID of  the  process  to
       change,  and  that change caused the process to exceed its RLIMIT_NPROC
       resource limit (i.e., the number of processes belonging to the new real
       UID  exceeds the resource limit).  From Linux 2.6.0 to 3.0, this caused
       the set*uid() call to fail.  (Prior to 2.6, the resource limit was  not
       imposed on processes that changed their user IDs.)

       Since  Linux  3.1,  the  scenario  just  described no longer causes the
       set*uid() call to fail, because it too  often  led  to  security  holes
       where  buggy  applications  didn't  check the return status and assumed
       that--if the caller had root privileges--the call would always succeed.
       Instead,  the set*uid() calls now successfully change the real UID, but
       the kernel sets an internal flag, named PF_NPROC_EXCEEDED, to note that
       the RLIMIT_NPROC resource limit has been exceeded.  If the PF_NPROC_EX-
       CEEDED flag is set and the resource limit is still exceeded at the time
       of  a  subsequent execve() call, that call fails with the error EAGAIN.
       This kernel logic ensures that the RLIMIT_NPROC resource limit is still
       enforced  for  the common privileged daemon workflow--namely, fork(2) +
       set*uid() + execve().

       If the resource limit was not still exceeded at the  time  of  the  ex-
       ecve()  call (because other processes belonging to this real UID termi-
       nated between the set*uid() call and the execve() call), then  the  ex-
       ecve()  call  succeeds  and  the  kernel  clears  the PF_NPROC_EXCEEDED
       process flag.  The flag is also cleared if a subsequent call to fork(2)
       by this process succeeds.

       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 arguments, 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

           /* execve.c */

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

           main(int argc, char *argv[])
               char *newargv[] = { NULL, "hello", "world", NULL };
               char *newenviron[] = { NULL };

               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() returns only 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  in-
       terpreter.   To  do  this we create a script whose "interpreter" is our
       myecho program:

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

       We can then use our program to exec the script:

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

       chmod(2), execveat(2), fork(2), get_robust_list(2), ptrace(2), exec(3),
       fexecve(3), getopt(3), system(3), capabilities(7), credentials(7), env-
       iron(7), path_resolution(7), ld.so(8)

       This page is part of release 5.07 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

Linux                             2020-04-11                         EXECVE(2)

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