4.3BSD-UWisc/man/cat2/execve.2
EXECVE(2) UNIX Programmer's Manual EXECVE(2)
NAME
execve - execute a file
SYNOPSIS
execve(name, argv, envp)
char *name, *argv[], *envp[];
DESCRIPTION
_E_x_e_c_v_e transforms the calling process into a new process.
The new process is constructed from an ordinary file called
the _n_e_w _p_r_o_c_e_s_s _f_i_l_e. This file is either an executable
object file, or a file of data for an interpreter. An exe-
cutable object file consists of an identifying header, fol-
lowed by pages of data representing the initial program
(text) and initialized data pages. Additional pages may be
specified by the header to be initialized with zero data.
See _a._o_u_t(5).
An interpreter file begins with a line of the form ``#!
_i_n_t_e_r_p_r_e_t_e_r''. When an interpreter file is _e_x_e_c_v_e'd, the
system _e_x_e_c_v_e's the specified _i_n_t_e_r_p_r_e_t_e_r, giving it the
name of the originally exec'd file as an argument and shift-
ing over the rest of the original arguments.
There can be no return from a successful _e_x_e_c_v_e because the
calling core image is lost. This is the mechanism whereby
different process images become active.
The argument _a_r_g_v 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 _n_a_m_e).
The argument _e_n_v_p is also a null-terminated array of charac-
ter pointers to null-terminated strings. These strings pass
information to the new process that is not directly an argu-
ment to the command (see _e_n_v_i_r_o_n(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 _c_l_o_s_e(2)). Descriptors that remain open
are unaffected by _e_x_e_c_v_e.
Ignored signals remain ignored across an _e_x_e_c_v_e, 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
_s_i_g_v_e_c(2) for more information).
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EXECVE(2) UNIX Programmer's Manual EXECVE(2)
Each process has _r_e_a_l user and group IDs and an _e_f_f_e_c_t_i_v_e
user and group IDs. The _r_e_a_l ID identifies the person using
the system; the _e_f_f_e_c_t_i_v_e ID determines his access
privileges. _E_x_e_c_v_e 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 _r_e_a_l user ID is not
affected.
The new process also inherits the following attributes from
the calling process:
process ID see _g_e_t_p_i_d(2)
parent process ID see _g_e_t_p_p_i_d(2)
process group ID see _g_e_t_p_g_r_p(2)
access groups see _g_e_t_g_r_o_u_p_s(2)
working directory see _c_h_d_i_r(2)
root directory see _c_h_r_o_o_t(2)
control terminal see _t_t_y(4)
resource usages see _g_e_t_r_u_s_a_g_e(2)
interval timers see _g_e_t_i_t_i_m_e_r(2)
resource limits see _g_e_t_r_l_i_m_i_t(2)
file mode mask see _u_m_a_s_k(2)
signal mask see _s_i_g_v_e_c(2), _s_i_g_m_a_s_k(2)
When the executed program begins, it is called 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 is the array of character pointers to the
arguments themselves.
_E_n_v_p is a pointer to an array of strings that constitute the
_e_n_v_i_r_o_n_m_e_n_t of the process. A pointer to this array is also
stored in the global variable ``environ''. Each string con-
sists of a name, an "=", and a null-terminated value. The
array of pointers is terminated by a null pointer. The
shell _s_h(1) passes an environment entry for each global
shell variable defined when the program is called. See
_e_n_v_i_r_o_n(7) for some conventionally used names.
RETURN VALUE
If _e_x_e_c_v_e returns to the calling process an error has
occurred; the return value will be -1 and the global vari-
able _e_r_r_n_o will contain an error code.
ERRORS
_E_x_e_c_v_e will fail and return to the calling process if one or
more of the following are true:
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EXECVE(2) UNIX Programmer's Manual EXECVE(2)
[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 char-
acters, 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 per-
mission.
[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 currently open for
writing or reading by some process.
[ENOMEM] The new process requires more virtual memory
than is allowed by the imposed maximum
(_g_e_t_r_l_i_m_i_t(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
<_s_y_s/_p_a_r_a_m._h>.
[EFAULT] The new process file is not as long as indi-
cated 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.
CAVEATS
If a program is _s_e_t_u_i_d to a non-super-user, but is executed
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EXECVE(2) UNIX Programmer's Manual EXECVE(2)
when the real _u_i_d 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)
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