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:
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).
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 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.
execveat() was added to Linux in kernel 3.19. GNU C library support is pending.
The execveat() system call is Linux-specific.
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().
This page is part of release 5.10 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/.