execveat — execute program relative to a directory file descriptor
#include <unistd.h>
int
execveat( |
int dirfd, |
| const char *pathname, | |
| char *const argv[], | |
| char *const envp[], | |
int flags); |
The execveat() system call
executes the program referred to by the combination of
dirfd and pathname. It operates in
exactly the same way as execve(2), except for the
differences described in this manual page.
If the pathname given in pathname is relative, then it
is interpreted relative to the directory referred to by the
file descriptor dirfd
(rather than relative to the current working directory of the
calling process, as is done by execve(2) for a relative
pathname).
If pathname is
relative and dirfd is
the special value AT_FDCWD,
then pathname is
interpreted relative to the current working directory of the
calling process (like execve(2)).
If pathname is
absolute, then dirfd
is ignored.
If pathname is an
empty string and the AT_EMPTY_PATH flag is specified, then the
file descriptor dirfd
specifies the file to be executed (i.e., dirfd refers to an executable
file, rather than a directory).
The flags argument
is a bit mask that can include zero or more of the following
flags:
AT_EMPTY_PATHIf pathname
is an empty string, operate on the file referred to by
dirfd (which
may have been obtained using the open(2) O_PATH flag).
AT_SYMLINK_NOFOLLOWIf the file identified by dirfd and a non-NULL
pathname is a
symbolic link, then the call fails with the error
ELOOP.
On success, execveat() does
not return. On error, −1 is returned, and errno is set appropriately.
The same errors that occur for execve(2) can also occur
for execveat(). The following
additional errors can occur for execveat():
dirfd is not
a valid file descriptor.
Invalid flag specified in flags.
flags
includes AT_SYMLINK_NOFOLLOW and the file
identified by dirfd and a non-NULL
pathname is a
symbolic link.
The program identified by dirfd and pathname requires the use
of an interpreter program (such as a script starting
with "#!"), but the file descriptor dirfd was opened with the
O_CLOEXEC flag, with the
result that the program file is inaccessible to the
launched interpreter. See BUGS.
pathname is
relative and dirfd is a file
descriptor referring to a file other than a
directory.
In addition to the reasons explained in openat(2), the execveat() system call is also needed to
allow fexecve(3) to be
implemented on systems that do not have the /proc filesystem mounted.
When asked to execute a script file, the argv[0] that is passed to the
script interpreter is a string of the form /dev/fd/N or /dev/fd/N/P, where N is the number of the file descriptor
passed via the dirfd
argument. A string of the first form occurs when AT_EMPTY_PATH is employed. A string of the
second form occurs when the script is specified via both
dirfd and pathname; in this case,
P is the value given in
pathname.
For the same reasons described in fexecve(3), the natural
idiom when using execveat(2) is to set the
close-on-exec flag on dirfd. (But see BUGS.)
The ENOENT error described above means that it is not possible to set the close-on-exec flag on the file descriptor given to a call of the form:
execveat(fd, "", argv, envp, AT_EMPTY_PATH);
However, the inability to set the close-on-exec flag means
that a file descriptor referring to the script leaks through
to the script itself. As well as wasting a file descriptor,
this leakage can lead to file-descriptor exhaustion in
scenarios where scripts recursively employ execveat().
This page is part of release 4.07 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
|
Copyright (c) 2014 Google, Inc., written by David Drysdale and Copyright (c) 2015, Michael Kerrisk <mtk.manpagesgmail.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END |