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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:


       tab()     allbox;     cw(2.750000i)|    cw(2.750000i)    lw(2.750000i)|
       lw(2.750000i).  ATTRIBUTE TYPEATTRIBUTE VALUE Interface  StabilityStan-
       dard MT-LevelSee 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)