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exec(2)				 System	Calls			       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[],	char *envp[]);

       where argc is the argument count, argv is an array of character	point-
       ers  to	the  arguments	themselves,  and envp is 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 tranlation size (see memcntl(2)) for the
       stack and heap of the new process image are set to the  default	system
       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(3RT)

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

       Timers  created	by  the	 calling  process  with	 timer_create(3RT) 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(3RT).

       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  nice value (see nice(2))

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

	 o  process ID

	 o  parent process ID

	 o  process group ID

	 o  task ID

	 o  supplementary group	IDs

	 o  semadj values (see semop(2))

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

	 o  real user ID

	 o  real group ID

	 o  project ID

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

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

	 o  current working directory

	 o  root directory

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

	 o  file size limit (see ulimit(2))

	 o  resource limits (see getrlimit(2))

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

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

	 o  controlling	terminal

	 o
	    process signal mask	(see sigprocmask(2))

	 o  pending signals (see sigpending(2))

	 o  processor bindings (see processor_bind(2))

	 o  processor set bindings (see	pset_bind(2))

	 o  limit privilege set

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

       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 permission but is	not in the proper for-
			       mat.

       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	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |See below.		   |
       +-----------------------------+-----------------------------+

       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(3RT),	a.out(4),  contract(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.

SunOS 5.10			  18 Dec 2003			       exec(2)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | USAGE | ATTRIBUTES | SEE ALSO | WARNINGS

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