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EXECVE(2)		    BSD	System Calls Manual		     EXECVE(2)

     execve -- execute a file

     #include <unistd.h>

     execve(const char *path, char *const *argv, char *const *envp);

     Execve() transforms the calling process into a new	process.  The new
     process is	constructed from an ordinary file, whose name is pointed to by
     path, called the new process file.	 This file is either an	executable ob-
     ject file,	or a file of data for an interpreter.  An executable object
     file consists of an identifying header, followed by pages of data repre-
     senting the initial program (text)	and initialized	data pages.  Addi-
     tional pages may be specified by the header to be initialized with	zero
     data;  see	a.out(5).

     An	interpreter file begins	with a line of the form:

	   #! interpreter [arg]

     When an interpreter file is execve()'d, the system	execve()'s the speci-
     fied interpreter.	If the optional	arg is specified, it becomes the first
     argument to the interpreter, and the name of the originally execve()'d
     file becomes the second argument; otherwise, the name of the originally
     execve()'d	file becomes the first argument.  The original arguments are
     shifted over to become the	subsequent arguments.  The zeroth argument,
     normally the name of the execve()'d file, is left unchanged.

     The argument argv is a pointer to a null-terminated array of character
     pointers to null-terminated character strings.  These strings construct
     the argument list to be made available to the new process.	 At least one
     argument must be present in the array; by custom, the first element
     should be the name	of the executed	program	(for example, the last compo-
     nent of path).

     The argument envp is also a pointer to a null-terminated array of charac-
     ter pointers to null-terminated strings.  A pointer to this array is nor-
     mally stored in the global	variable environ. These	strings	pass informa-
     tion to the new process that is not directly an argument to the command
     (see environ(7)).

     File descriptors open in the calling process image	remain open in the new
     process image, except for those for which the close-on-exec flag is set
     (see close(2) and fcntl(2)).  Descriptors that remain open	are unaffected
     by	execve().

     Signals set to be ignored in the calling process are set to be ignored in
     the new process. Signals which are	set to be caught in the	calling
     process image are set to default action in	the new	process	image.
     Blocked signals remain blocked regardless of changes to the signal	ac-
     tion.  The	signal stack is	reset to be undefined (see sigaction(2)	for
     more information).

     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.  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, real	group ID and supplementary group IDs of	the new
     process image remain the same as the calling process image.  In either
     case, the SUGID process flag bit is set, and remains set until cleared by
     another call to execve which does not execute a set-id executable.	 This
     flag can be inspected by the ps(1)	utility.

     The new process also inherits the following attributes from the calling

	   process ID		see getpid(2)
	   parent process ID	see getppid(2)
	   process group ID	see getpgrp(2)
	   access groups	see getgroups(2)
	   working directory	see chdir(2)
	   root	directory	see chroot(2)
	   control terminal	see termios(4)
	   resource usages	see getrusage(2)
	   interval timers	see getitimer(2)
	   resource limits	see getrlimit(2)
	   file	mode mask	see umask(2)
	   signal mask		see sigvec(2), sigsetmask(2)

     When a program is executed	as a result of an execve() call, it is entered
     as	follows:

	   main(argc, argv, envp)
	   int argc;
	   char	**argv,	**envp;

     where argc	is the number of elements in argv (the ``arg count'') and argv
     points to the array of character pointers to the arguments	themselves.

     As	the execve() function overlays the current process image with a	new
     process image the successful call has no process to return	to.  If
     execve() does return to the calling process an error has occurred;	the
     return value will be -1 and the global variable errno is set to indicate
     the error.

     Execve() will fail	and return to the calling process if:

     [ENOTDIR]	     A component of the	path prefix is not a directory.

     [EINVAL]	     The pathname contains a character with the	high-order bit

     [ENAMETOOLONG]  A component of a pathname exceeded	255 characters,	or an
		     entire path name exceeded 1023 characters.

     [ENOENT]	     The new process file does not exist.

     [ELOOP]	     Too many symbolic links were encountered in translating
		     the pathname.

     [EACCES]	     Search permission is denied for a component of the	path

     [EACCES]	     The new process file is not an ordinary file.

     [EACCES]	     The new process file mode denies execute permission.

     [EACCES]	     The new process file is on	a filesystem mounted with exe-
		     cution disabled (MNT_NOEXEC in <sys/mount.h>).

     [ENOEXEC]	     The new process file has the appropriate access permis-
		     sion, but has an invalid magic number in its header.

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

     [ENOMEM]	     The new process requires more virtual memory than is al-
		     lowed by the imposed maximum (getrlimit(2)).

     [E2BIG]	     The number	of bytes in the	new process's argument list is
		     larger than the system-imposed limit.  The	limit in the
		     system as released	is 32768 bytes (ARG_MAX	in

     [EFAULT]	     The new process file is not as long as indicated by the
		     size values in its	header.

     [EFAULT]	     Path, argv, or envp point to an illegal address.

     [EIO]	     An	I/O error occurred while reading from the file system.

     If	a program is setuid to a non-super-user, but is	executed when the real
     uid is ``root'', then the program has some	of the powers of a super-user
     as	well.

     ps(1), exit(2), fork(2), execl(3),	environ(7)

     The execve	function call appeared in 4.2BSD.

BSD				March 16, 1994				   BSD


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