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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 actually execve's	the
     specified 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	argu-
     ments 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
     effective group ID	is the first element of	the group list.)  The real
     user ID, real group ID and	other group IDs	of the new process image re-
     main the same as the calling process image.  After	any set-user-ID	and
     set-group-ID processing, the effective user ID is recorded	as the saved
     set-user-ID, and the effective group ID is	recorded as the	saved set-
     group-ID.	These values may be used in changing the effective IDs later
     (see setuid(2)).

     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.

     In	the non-threaded library execve() is implemented as the	execve

     In	the threaded library, the execve syscall is assembled to
     _thread_sys_execve() and execve() is implemented as a function which per-
     forms user-thread library re-initialization and then calls

     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.

     [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.

     [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' argument list is
		     larger than the system-imposed limit.  This limit is
		     specified by the sysctl(3)	MIB variable KERN_ARGMAX.

     [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.

     _exit(2), fork(2),	execl(3), exit(3), sysctl(3), environ(7)

     The execve() function call	appeared in 4.2BSD.

4th Berkeley Distribution	 June 1, 1994	     4th Berkeley Distribution


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