execveat

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



NAME
       execveat - execute program relative to a directory file descriptor

SYNOPSIS
       #include <unistd.h>

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

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

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

CONFORMING TO
       The execveat() system call is Linux-specific.

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

COLOPHON
       This page is part of release 5.03 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                             2017-09-15                       EXECVEAT(2)