|EXECVE(2)||System Calls Manual||EXECVE(2)|
execve — execute a
char *path, char *const
argv, char *const
execve() transforms the calling process
into a new process. The new process is constructed from an ordinary file,
whose name is pointed to by path, 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
An interpreter file begins with a line of the form:
When an interpreter file is passed to
execve() the system instead calls
execve() with the specified
interpreter. If the optional arg is
specified, it becomes the first argument to the
interpreter, and the original path
becomes the second argument; otherwise, path becomes
the first argument. The original arguments are shifted over to become the
subsequent arguments. The zeroth argument, normally the name of the file
being executed, is left unchanged.
The argument argv is a pointer to a null-terminated array of character pointers to NUL-terminated character strings. These strings construct the argument list to be made available to the new process. At least one non-null 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 path).
The argument envp is also a pointer to a null-terminated array of character pointers to NUL-terminated strings. A pointer to this array is normally stored in the global variable environ. These strings pass information 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 close-on-exec flag is
set (see close(2) and
fcntl(2)). Descriptors that remain open
are unaffected by
execve(). In the case of a new
setuid or setgid executable being executed, if file descriptors 0, 1, or 2
(representing stdin, stdout, and stderr) are currently unallocated, these
descriptors will be opened to point to some system file like
/dev/null. The intent is to ensure these descriptors
are not unallocated, since many libraries make assumptions about the use of
these 3 file descriptors.
Signals set to be ignored in the calling process, with the
SIGCHLD, are set to be ignored in the
new process. Other signals 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
If the set-user-ID 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 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 setuid(2)). The set-user-ID and set-group-ID bits have no effect if the new process image file is located on a file system mounted with the nosuid flag. The process will be started without the new permissions.
The new process also inherits the following attributes from the calling process:
When a program is executed as a result of an
execve() call, it is entered as follows:
main(int argc, char **argv, char **envp)
where argc is the number of elements in argv (the “arg count”) and argv points to the array of character pointers to the arguments themselves.
execve() function overlays the
current process image with a new process image the successful call has no
process to return to. If
execve() does return to the
calling process an error has occurred; the return value will be -1 and the
global variable errno is set to indicate the
execve() will fail and return to the
calling process if:
NAME_MAXcharacters, or an entire pathname (including the terminating NUL) exceeded
wxneededto perform W^X violating operations, but it is located on a file system not allowing such operations, being mounted without the mount(8)
execve() function is expected to
conform to IEEE Std 1003.1-2008
The predecessor of these functions, the former
exec() system call, first appeared in
Version 1 AT&T UNIX. The
execve() function first appeared in
Version 7 AT&T UNIX.
If a program is setuid to a non-superuser, but is executed when the real uid is “root”, then the process has some of the powers of a superuser as well.
IEEE Std 1003.1-2008
SIGCHLD as ignored in the new process;
portable programs cannot rely on
execve resetting it
to the default disposition.
|July 29, 2019||OpenBSD-current|