Fresh Fish 4/FreshFish_May-June1994.bin/gnu/man/cat2/execve.0

Text File | 1993-12-07 | 8KB | 199 lines

EXECVE(2)                  UNIX Programmer's Manual                  EXECVE(2)

NNAAMMEE
     eexxeeccvvee - execute a file

SSYYNNOOPPSSIISS
     ##iinncclluuddee <<uunniissttdd..hh>>

     _i_n_t
     eexxeeccvvee(_c_o_n_s_t _c_h_a_r _*_p_a_t_h, _c_o_n_s_t _* _c_h_a_r _*_a_r_g_v, _c_o_n_s_t _* _c_h_a_r _*_e_n_v_p)

DDEESSCCRRIIPPTTIIOONN
     EExxeeccvvee() transforms the calling process into a new process.  The new pro­
     cess is constructed from an ordinary file, whose name is pointed to by
     _p_a_t_h, called the _n_e_w _p_r_o_c_e_s_s _f_i_l_e. 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.  Addition­
     al 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:

           ##!! _i_n_t_e_r_p_r_e_t_e_r [_a_r_g]

     When an interpreter file is eexxeeccvvee()'d, the system eexxeeccvvee()'s the speci­
     fied _i_n_t_e_r_p_r_e_t_e_r. If the optional _a_r_g is specified, it becomes the first
     argument to the _i_n_t_e_r_p_r_e_t_e_r, and the name of the originally eexxeeccvvee()'d
     file becomes the second argument; otherwise, the name of the originally
     eexxeeccvvee()'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 eexxeeccvvee()'d file, is left unchanged.

     The argument _a_r_g_v is a pointer to a null­terminated array of character
     pointers to null­terminated 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 _p_a_t_h).

     The argument _e_n_v_p is also a pointer to a null­terminated array of charac­
     ter pointers to null­terminated strings.  A pointer to this array is nor­
     mally stored in the global variable _e_n_v_i_r_o_n_. 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 close­on­exec flag is set
     (see close(2) and fcntl(2)).  Descriptors that remain open are unaffected
     by eexxeeccvvee().

     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 pro­
     cess image are set to default action in the new process image.  Blocked
     signals remain blocked regardless of changes to the signal action.  The
     signal stack is reset to be undefined (see sigaction(2) for more informa­
     tion).

     If the set­user­ID 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 set­group­ID mode bit of
     the new process image file is set, the effective group ID of the new pro­
     cess image is set to the group ID of the new process image file.  The re­
     al user ID, real group ID and supplementary group IDs of the new process
     image remain the same as the calling process image.

     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 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 eexxeeccvvee() call, it is entered
     as follows:

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

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

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

EERRRROORRSS
     EExxeeccvvee() 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 high­order 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 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 system­imposed limit.  The limit in the
                     system as released is 20480 bytes (NCARGS in
                     <_s_y_s_/_p_a_r_a_m_._h>.

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

     [EFAULT]        _P_a_t_h, _a_r_g_v, or _e_n_v_p point to an illegal address.

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

CCAAVVEEAATT
     If a program is _s_e_t_u_i_d to a non­super­user, but is executed when the real
     _u_i_d is ``root'', then the program has some of the powers of a super­user
     as well.

SSEEEE AALLSSOO
     exit(2),  fork(2),  execl(3),  environ(7)

HHIISSTTOORRYY
     The eexxeeccvvee function call appeared in 4.2BSD.

4th Berkeley Distribution       March 10, 1991                               3