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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON |
EXECVEAT(2) Linux Programmer's Manual EXECVEAT(2)
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_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 appropriately.
The same errors that occur for execve(2) can also occur for
execveat(). The following additional errors can occur for
execveat():
EBADF dirfd is not 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.
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().
execve(2), openat(2), fexecve(3)
This page is part of release 4.12 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/.
Linux 2016-10-08 EXECVEAT(2)
Pages that refer to this page: execve(2), open(2), syscalls(2), exec(3), fexecve(3)