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BSD 2.11 - man page for execve (bsd section 2)

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EXECVE(2) 										  EXECVE(2) 

NAME
       execve - execute a file

SYNOPSIS
       execve(name, argv, envp)
       char *name, *argv[], *envp[];

DESCRIPTION
       Execve  transforms the calling process into a new process.  The new process is constructed
       from an ordinary file called the new process file.  This  file  is  either  an  executable
       object  file, or a file of data for an interpreter.  An executable object file consists of
       an identifying header, followed by pages of data representing the initial  program  (text)
       and  initialized  data  pages.  Additional pages may be specified by the header to be ini-
       tialized with zero data.  See   a.out(5) .

       An interpreter file begins with a line of the form ``#!	interpreter''.	 When  an  inter-
       preter file is execve'd, the system execve's the specified interpreter, giving it the name
       of the originally exec'd file as an argument and shifting over the rest	of  the  original
       arguments.

       There  can  be  no return from a successful execve because the calling core image is lost.
       This is the mechanism whereby different process images become active.

       The argument argv is a null-terminated array  of  character  pointers  to  null-terminated
       character strings.  These strings constitute the argument list to be made available to the
       new process.  By convention, at least one argument must be present in this array, and  the
       first  element  of  this  array should be the name of the executed program (i.e., the last
       component of name).

       The argument envp is also a null-terminated array of character pointers to null-terminated
       strings.   These strings pass information to the new process that is not directly an argu-
       ment to the command (see   environ(7) ).

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

       Ignored signals remain ignored across an execve, but signals that are caught are reset  to
       their  default values.  Blocked signals remain blocked regardless of changes to the signal
       action.	The signal stack is reset to be undefined (see   sigvec(2)  for more information).

       Each process has real user and group IDs and an effective user and group IDs.  The real ID
       identifies the person using the system; the effective ID determines his access privileges.
       Execve changes the effective user and group ID to the owner of the executed  file  if  the
       file has the "set-user-ID" or "set-group-ID" modes.  The real user ID is not affected.

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

	    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   tty(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) ,   sigmask(2) 

       When the executed program begins, it is called 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 is the array of
       character pointers to the arguments themselves.

       Envp is a pointer to an array of strings that constitute the environment of  the  process.
       A  pointer  to  this array is also stored in the global variable ``environ''.  Each string
       consists of a name, an "=", and a null-terminated value.  The array of pointers is  termi-
       nated  by  a  null  pointer.   The shell   sh(1)  passes an environment entry for each global
       shell variable defined when the program is called.  See   environ(7)  for some conventionally
       used names.

RETURN VALUE
       If  execve  returns to the calling process an error has occurred; the return value will be
       -1 and the global variable errno will contain an error code.

ERRORS
       Execve will fail and return to the calling process if one or more  of  the  following  are
       true:

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

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

       [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 prefix.

       [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	permission,  but  has  an
		      invalid magic number in its header.

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

       [ENOMEM]       The new process requires more virtual memory than is allowed 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  20480  bytes
		      (NCARGS in <sys/param.h>.

       [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.

CAVEATS
       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.

SEE ALSO
         exit(2) ,   fork(2) ,   execl(3) ,   environ(7) 

4th Berkeley Distribution		   May 22, 1986 				  EXECVE(2)
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