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transforms
the calling process into a new process. The new process is constructed from
an ordinary file, whose name is pointed to by called the 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 An interpreter file begins with a line of the form:
When an interpreter file is the system runs the specified If
the optional is specified, it becomes the first argument to the and the
name of the originally file becomes the second argument; otherwise, the
name of the originally file becomes the first argument. The original arguments
are shifted over to become the subsequent arguments. The zeroth argument,
normally the name of the file, is left unchanged. The argument 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 component of The argument is also a pointer to
a null-terminated array of character pointers to null-terminated strings.
A pointer to this array is normally stored in the global variable These
strings pass information to the new process that is not directly an argument
to the command (see 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 and Descriptors that remain open are unaffected by
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 action. The signal stack
is reset to be undefined (see for more information). If the set-user-ID
mode bit of the new process image file is set (see 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 remain 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 The new process also inherits the following attributes from the
calling process: When a program is executed as a result
of an call, it is entered as follows: main(argc, argv, envp) int argc;
char **argv, **envp; where is the number of elements in (the ‘‘arg count’’)
and points to the array of character pointers to the arguments themselves.
As the function overlays the current process image with
a new process image the successful call has no process to return to. If
does return to the calling process an error has occurred; the return value
will be -1 and the global variable is set to indicate the error.
will fail and return to the calling process if: A component of the path
prefix is not a directory. A component of a pathname exceeded characters,
or an entire path name exceeded characters. The new process file does
not exist. Too many symbolic links were encountered in translating the
pathname. Search permission is denied for a component of the path prefix.
The new process file is not an ordinary file. The new process file mode
denies execute permission. The new process file is on a filesystem mounted
with execution disabled in The new process file has the appropriate
access permission, but has an invalid magic number in its header. The new
process file is a pure procedure (shared text) file that is currently open
for writing or reading by some process. The new process requires more virtual
memory than is allowed by the imposed maximum 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 in The new process file
is not as long as indicated by the size values in its header. or point
to an illegal address. An I/O error occurred while reading from the file
system.
If a program is to a non-super-user, but is executed when
the real is ‘‘root’’, then the program has some of the powers of a super-user
as well.
The function call appeared in
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