NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON

EXECVEAT(2)               Linux Programmer's Manual              EXECVEAT(2)

NAME         top

       execveat - execute program relative to a directory file descriptor

SYNOPSIS         top

       #include <unistd.h>

       int execveat(int dirfd, const char *pathname,
                    char *const argv[], char *const envp[],
                    int flags);

DESCRIPTION         top

       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.

RETURN VALUE         top

       On success, execveat() does not return.  On error, -1 is returned,
       and errno is set appropriately.

ERRORS         top

       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.

VERSIONS         top

       execveat() was added to Linux in kernel 3.19.  GNU C library support
       is pending.

CONFORMING TO         top

       The execveat() system call is Linux-specific.

NOTES         top

       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.)

BUGS         top

       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().

SEE ALSO         top

       execve(2), openat(2), fexecve(3)

COLOPHON         top

       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)