NAME
execve - execute a file

SYNOPSIS
execve(name, argv, envp)
const char *name; char * const *argv; char * const *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 initialized with zero
data. See a.out(5).

An interpreter file begins with a line of the form "#!
interpreter". When an interpreter 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 argument 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 terminated 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 currently 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)

__________
* Not currently supported under MachTen Personal Unix