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EXEC(2)								       EXEC(2)

NAME
       exec, execl, execle, execlp, execv, execve, execvp - execute a file

SYNOPSIS
       #include <unistd.h>

       int execl(const char *path, const char *arg0, ...
	    /* const char *argn, (char *)0 */);

       int execv(const char *path, char *const argv[]);

       int execle(const char *path, const char *arg0, ...
	    /* const char *argn, (char *)0,char *const envp[]*/);

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

       int execlp(const char *file, const char *arg0, ...
	    /* const char *argn, (char *)0 */);

       int execvp(const char *file, char *const argv[]);

DESCRIPTION
       Each  of	 the functions in the exec family replaces the current process
       image with a new process image. The new image  is  constructed  from  a
       regular,	 executable  file called the new process image file. This file
       is either an executable object file or a file of	 data  for  an	inter‐
       preter. There is no return from a successful call to one of these func‐
       tions because the calling process image is overlaid by the new  process
       image.

       An interpreter file begins with a line of the form

	 #! pathname [arg]

       where  pathname	is the path of the interpreter, and arg is an optional
       argument. When an interpreter file is executed, the system invokes  the
       specified  interpreter.	The pathname specified in the interpreter file
       is passed as arg0 to the interpreter.  If  arg  was  specified  in  the
       interpreter  file, it is passed as arg1 to the interpreter. The remain‐
       ing arguments to the interpreter are arg0 through argn  of  the	origi‐
       nally  exec'd  file.  The  interpreter named by pathname must not be an
       interpreter file.

       When a C-language program is executed as a result of this call,	it  is
       entered as a C-language function call as follows:

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

       where  argc  is	the  argument  count and argv is an array of character
       pointers to the arguments themselves. In addition, the following	 vari‐
       able:

	 extern char **environ;

       is  initialized	as  a pointer to an array of character pointers to the
       environment strings. The argv and environ arrays are each terminated by
       a  null	pointer.  The  null  pointer terminating the argv array is not
       counted in argc.

       The value of argc is non-negative,  and	if  greater  than  0,  argv[0]
       points  to  a  string  containing  the  name of the file. If argc is 0,
       argv[0] is a null pointer,  in  which  case  there  are	no  arguments.
       Applications  should verify that argc is greater than 0 or that argv[0]
       is not a null pointer before dereferencing argv[0].

       The arguments specified by a program with one of the exec functions are
       passed on to the new process image in the main() arguments.

       The path argument points to a path name that identifies the new process
       image file.

       The file argument is used to construct a pathname that  identifies  the
       new  process  image file. If the file argument contains a slash charac‐
       ter, it is used as the pathname for this file. Otherwise, the path pre‐
       fix  for this file is obtained by a search of the directories passed in
       the PATH environment variable (see environ(5)). The environment is sup‐
       plied  typically by the shell. If the process image file is not a valid
       executable object file, execlp() and execvp() use the contents of  that
       file  as	 standard  input to the shell. In this case, the shell becomes
       the new process image. The standard to which the caller conforms deter‐
       mines which shell is used. See standards(5).

       The  arguments  represented  by arg0... are pointers to null-terminated
       character strings. These strings constitute the argument list available
       to  the	new  process  image. The list is terminated by a null pointer.
       The arg0 argument should point to a filename that  is  associated  with
       the process being started by one of the exec functions.

       The  argv argument is an array of character pointers to null-terminated
       strings. The last member of this array must be a	 null  pointer.	 These
       strings	constitute  the	 argument  list	 available  to the new process
       image. The value in argv[0] should point to a filename that is  associ‐
       ated with the process being started by one of the exec functions.

       The  envp argument is an array of character pointers to null-terminated
       strings. These strings constitute the environment for the  new  process
       image.	The  envp  array is terminated by a null pointer. For execl(),
       execv(), execvp(), and execlp(), the C-language run-time start-off rou‐
       tine  places a pointer to the environment of the calling process in the
       global object extern char **environ, and it is used to pass  the	 envi‐
       ronment of the calling process to the new process image.

       The  number  of bytes available for the new process's combined argument
       and  environment	 lists	is  ARG_MAX.  It  is  implementation-dependent
       whether	null  terminators,  pointers,  and/or  any alignment bytes are
       included in this total.

       File descriptors open in the calling process image remain open  in  the
       new process image, except for those whose close-on-exec flag FD_CLOEXEC
       is set; see fcntl(2). For those file descriptors that remain open,  all
       attributes  of  the open file description, including file locks, remain
       unchanged.

       The preferred hardware address translation size	(see  memcntl(2))  for
       the stack and heap of the new process image are set to the default sys‐
       tem page size.

       Directory streams open in the calling process image are closed  in  the
       new process image.

       The  state  of conversion descriptors and message catalogue descriptors
       in the new process image is undefined. For the new process, the equiva‐
       lent of:

	 setlocale(LC_ALL, "C")

       is executed at startup.

       Signals	set  to	 the  default  action (SIG_DFL) in the calling process
       image are set to the default action in the new process image (see  sig‐
       nal(3C)).   Signals  set to be ignored (SIG_IGN) by the calling process
       image are set to be ignored by the new process image. Signals set to be
       caught  by  the	calling process image are set to the default action in
       the new process image (see signal.h(3HEAD)). After a successful call to
       any  of	the  exec functions, alternate signal stacks are not preserved
       and the SA_ONSTACK flag is cleared for all signals.

       After a successful call to any of the  exec  functions,	any  functions
       previously registered by atexit(3C) are no longer registered.

       The saved resource limits in the new process image are set to be a copy
       of the process's corresponding hard and soft resource limits.

       If the ST_NOSUID bit is set for the  file  system  containing  the  new
       process	image  file, then the effective user ID and effective group ID
       are unchanged in the new process image. If the set-user-ID mode bit  of
       the new process image file is set (see chmod(2)), the effective user ID
       of the new process image is set to the owner  ID	 of  the  new  process
       image  file. Similarly, if the set-group-ID mode bit of the new process
       image file is set, the effective group ID of the new process  image  is
       set to the group ID of the new process image file. The real user ID and
       real group ID of the new process image remain the same as those of  the
       calling	process image. The effective user ID and effective group ID of
       the new process image are saved (as the saved set-user-ID and the saved
       set-group-ID for use by setuid(2).

       The privilege sets are changed according to the following rules:

	   1.	  The  inheritable  set, I, is intersected with the limit set,
		  L.  This mechanism enforces the limit set for processes.

	   2.	  The effective set, E, and the permitted  set,	 P,  are  made
		  equal to the new inheritable set.

       The  system  attempts  to  set the privilege-aware state to non-PA both
       before performing any modifications to the process  IDs	and  privilege
       sets  as well as after completing the transition to new UIDs and privi‐
       lege sets, following the rules outlined in privileges(5).

       If the {PRIV_PROC_OWNER} privilege is asserted in  the  effective  set,
       the  set-user-ID and set-group-ID bits will be honored when the process
       is being controlled by ptrace(3C).  Additional  restriction  can	 apply
       when the traced process has an effective UID of 0. See privileges(5).

       Any  shared  memory segments attached to the calling process image will
       not be attached to the new process image (see shmop(2)).	 Any  mappings
       established  through  mmap()  are  not preserved across an exec. Memory
       mappings created in the process are unmapped before the	address	 space
       is rebuilt for the new process image. See mmap(2).

       Memory  locks  established  by  the calling process via calls to mlock‐
       all(3C) or mlock(3C) are removed. If locked pages in the address	 space
       of  the	calling	 process  are  also mapped into the address spaces the
       locks established by the other processes will be unaffected by the call
       by  this	 process to the exec function. If the exec function fails, the
       effect on memory locks is unspecified.

       If _XOPEN_REALTIME is defined and has a value other than −1, any	 named
       semaphores  open in the calling process are closed as if by appropriate
       calls to sem_close(3C)

       Profiling is disabled for the new process; see profil(2).

       Timers created by the calling process with timer_create(3C) are deleted
       before replacing the current process image with the new process image.

       For  the	 SCHED_FIFO  and  SCHED_RR scheduling policies, the policy and
       priority settings are not changed by a call to an exec function.

       All open message queue descriptors in the calling process  are  closed,
       as described in mq_close(3C).

       Any  outstanding	 asynchronous  I/O  operations may be cancelled. Those
       asynchronous I/O operations that are not canceled will complete	as  if
       the exec function had not yet occurred, but any associated signal noti‐
       fications are suppressed. It is unspecified whether the	exec  function
       itself  blocks awaiting such I/O completion. In no event, however, will
       the new process image created by the exec function be affected  by  the
       presence	 of  outstanding  asynchronous	I/O operations at the time the
       exec function is called.

       All active contract templates are cleared (see contract(4)).

       The new process also inherits the following attributes from the calling
       process:

	   o	  controlling terminal

	   o	  current working directory

	   o	  file-locks (see fcntl(2) and lockf(3C))

	   o	  file mode creation mask (see umask(2))

	   o	  file size limit (see ulimit(2))

	   o	  limit privilege set

	   o	  nice value (see nice(2))

	   o	  parent process ID

	   o	  pending signals (see sigpending(2))

	   o	  privilege    debugging    flag    (see   privileges(5)   and
		  getpflags(2))

	   o	  process ID

	   o	  process contract (see contract(4) and process(4))

	   o	  process group ID

	   o	  process signal mask (see sigprocmask(2))

	   o	  processor bindings (see processor_bind(2))

	   o	  processor set bindings (see pset_bind(2))

	   o	  project ID

	   o	  real group ID

	   o	  real user ID

	   o	  resource limits (see getrlimit(2))

	   o	  root directory

	   o	  scheduler class and priority (see priocntl(2))

	   o	  semadj values (see semop(2))

	   o	  session membership (see exit(2) and signal(3C))

	   o	  supplementary group IDs

	   o	  task ID

	   o	  time left until an alarm clock signal (see alarm(2))

	   o	  tms_utime,  tms_stime,  tms_cutime,  and   tms_cstime	  (see
		  times(2))

	   o	  trace flag (see ptrace(3C) request 0)

       A  call	to  any exec function from a process with more than one thread
       results in all threads being terminated and the	new  executable	 image
       being loaded and executed. No destructor functions will be called.

       Upon  successful	 completion,  each of the functions in the exec family
       marks for update the st_atime field of the file.	 If an	exec  function
       failed  but  was	 able  to  locate  the process image file, whether the
       st_atime field is marked for update is unspecified. Should the function
       succeed,	 the process image file is considered to have been opened with
       open(2). The corresponding close(2) is considered to occur  at  a  time
       after  this  open, but before process termination or successful comple‐
       tion of a subsequent call to one of the exec functions. The argv[]  and
       envp[]  arrays  of pointers and the strings to which those arrays point
       will not be modified by a call to one of the exec functions, except  as
       a consequence of replacing the process image.

       The saved resource limits in the new process image are set to be a copy
       of the process's corresponding hard and soft limits.

RETURN VALUES
       If a function in the exec family returns to the calling process	image,
       an error has occurred; the return value is −1 and errno is set to indi‐
       cate the error.

ERRORS
       The exec functions will fail if:

       E2BIG
		       The number of bytes in the new process's argument  list
		       is  greater  than the system-imposed limit of {ARG_MAX}
		       bytes. The argument list limit is sum of	 the  size  of
		       the  argument  list  plus the size of the environment's
		       exported shell variables.

       EACCES
		       Search permission is denied for a directory  listed  in
		       the new process file's path prefix.

		       The new process file is not an ordinary file.

		       The new process file mode denies execute permission.

		       The  {FILE_DAC_SEARCH} privilege overrides the restric‐
		       tion on directory searches.

		       The {FILE_DAC_EXECUTE} privilege overrides the lack  of
		       execute permission.

       EAGAIN
		       Total  amount  of  system memory available when reading
		       using raw I/O is temporarily insufficient.

       EFAULT
		       An argument points to an illegal address.

       EINVAL
		       The new process image file has the appropriate  permis‐
		       sion and has a recognized executable binary format, but
		       the system does not support execution of	 a  file  with
		       this format.

       EINTR
		       A  signal was caught during the execution of one of the
		       functions in the exec family.

       ELOOP
		       Too many symbolic links were encountered in translating
		       path or file.

       ENAMETOOLONG
		       The  length  of	the  file  or  path  argument  exceeds
		       {PATH_MAX}, or the length of a file or  path  component
		       exceeds	 {NAME_MAX}   while  {_POSIX_NO_TRUNC}	is  in
		       effect.

       ENOENT
		       One or more components of the new process path name  of
		       the file do not exist or is a null pathname.

       ENOLINK
		       The  path  argument  points to a remote machine and the
		       link to that machine is no longer active.

       ENOTDIR
		       A component of the new process path of the file	prefix
		       is not a directory.

       The exec functions, except for execlp() and execvp(), will fail if:

       ENOEXEC
		  The  new  process image file has the appropriate access per‐
		  mission but is not in the proper format.

       The exec functions may fail if:

       ENAMETOOLONG
		       Pathname resolution of  a  symbolic  link  produced  an
		       intermediate result whose length exceeds {PATH_MAX}.

       ENOMEM
		       The  new	 process  image	 requires  more memory than is
		       allowed by the hardware	or  system-imposed  by	memory
		       management constraints. See brk(2).

       ETXTBSY
		       The  new process image file is a pure procedure (shared
		       text) file that is currently open for writing  by  some
		       process.

USAGE
       As  the	state of conversion descriptors and message catalogue descrip‐
       tors in the new	process	 image	is  undefined,	portable  applications
       should not rely on their use and should close them prior to calling one
       of the exec functions.

       Applications that require other than the default	 POSIX	locale	should
       call  setlocale(3C)  with  the  appropriate parameters to establish the
       locale of thenew process.

       The environ array should not be accessed directly by the application.

ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:

       ┌────────────────────┬───────────────────┐
       │  ATTRIBUTE TYPE    │  ATTRIBUTE VALUE	│
       ├────────────────────┼───────────────────┤
       │Interface Stability │ Committed		│
       ├────────────────────┼───────────────────┤
       │MT-Level	    │ See below.	│
       ├────────────────────┼───────────────────┤
       │Standard	    │ See standards(5). │
       └────────────────────┴───────────────────┘

       The execle() and execve() fucntions are Async-Signal-Safe.

SEE ALSO
       ksh(1), ps(1), sh(1), alarm(2), brk(2),	chmod(2),  exit(2),  fcntl(2),
       fork(2), getpflags(2), getrlimit(2), memcntl(2), mmap(2), nice(2), pri‐
       ocntl(2), profil(2), semop(2), shmop(2), sigpending(2), sigprocmask(2),
       times(2),  umask(2),  lockf(3C), ptrace(3C), setlocale(3C), signal(3C),
       system(3C),  timer_create(3C),	a.out(4),   contract(4),   process(4),
       attributes(5), environ(5), privileges(5), standards(5)

WARNINGS
       If  a  program is setuid to a user ID other than the superuser, and the
       program is executed when the real user ID is super-user, then the  pro‐
       gram has some of the powers of a super-user as well.

				 Jun 16, 2008			       EXEC(2)
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