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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | NOTES | BUGS | SEE ALSO | COLOPHON |
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execveat(2) System Calls Manual execveat(2)
execveat - execute program relative to a directory file
descriptor
Standard C library (libc, -lc)
#include <linux/fcntl.h> /* Definition of AT_* constants */
#include <unistd.h>
int execveat(int dirfd, const char *pathname,
char *const _Nullable argv[],
char *const _Nullable 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_PATH
If 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_NOFOLLOW
If 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 to indicate the error.
The same errors that occur for execve(2) can also occur for
execveat(). The following additional errors can occur for
execveat():
pathname
is relative but dirfd is neither AT_FDCWD nor a valid file
descriptor.
EINVAL Invalid flag specified in flags.
ELOOP flags includes AT_SYMLINK_NOFOLLOW and the file identified
by dirfd and a non-NULL pathname is a symbolic link.
ENOENT 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.
ENOTDIR
pathname is relative and dirfd is a file descriptor
referring to a file other than a directory.
Linux.
Linux 3.19, glibc 2.34.
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() 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().
execve(2), openat(2), fexecve(3)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.9.1.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2024-06-26. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.9.1 2024-05-02 execveat(2)
Pages that refer to this page: execve(2), fanotify_mark(2), open(2), syscalls(2), exec(3), fexecve(3)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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