EXECVE(2) System Calls Manual EXECVE(2)
execve - execute a file
execve(const char *path, char *const argv, char *const envp);
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 elf(5).
An interpreter file begins with a line of the form:
#! interpreter [arg]
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 exception of
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 information).
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 ID see getpid(2)
parent process ID see getppid(2)
process group ID see getpgrp(2)
session ID see getsid(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) (unless process image file is
setuid or setgid, in which case all timers are
resource limits see getrlimit(2)
file mode mask see umask(2)
signal mask see sigaction(2), sigprocmask(2)
When a program is executed as a result of an execve() call, it is entered
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.
As the 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
execve() will fail and return to the calling process if:
[ENOTDIR] A component of the path prefix is not a directory.
[ENAMETOOLONG] A component of a pathname exceeded NAME_MAX
characters, or an entire pathname (including the
terminating NUL) exceeded PATH_MAX bytes.
[ENOENT] The new process file does not exist.
[ELOOP] Too many symbolic links were encountered in
translating the pathname.
[EISDIR] The new process file is a directory.
[EACCES] Search permission is denied for a component of the
[EACCES] The new process file is not an ordinary file.
[EACCES] The new process file mode denies execute permission.
[EACCES] The new process file is on a filesystem mounted with
execution disabled (MNT_NOEXEC in <sys/mount.h>).
[EACCES] The new process file is marked with ld(1) -z wxneeded
to perform W^X violating operations, but it is located
on a file system not allowing such operations, being
mounted without the mount(8) -o wxallowed flag.
[ENOEXEC] The new process file has the appropriate access
permission, but has an invalid magic number in its
[ETXTBSY] The new process file is a pure procedure (shared text)
file that is currently open for writing by some
[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 262144 bytes (ARG_MAX).
[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.
[EINVAL] argv did not contain at least one element.
[EIO] An I/O error occurred while reading from the file
[ENFILE] During startup of an interpreter, the system file
table was found to be full.
_exit(2), fork(2), execl(3), exit(3), elf(5), environ(7)
The 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
IEEE Std 1003.1-2008 ("POSIX.1") permits execve to leave SIGCHLD as
ignored in the new process; portable programs cannot rely on execve
resetting it to the default disposition.
OpenBSD 6.2 April 13, 2017 OpenBSD 6.2
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