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(2) 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  4.04  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
       http://www.kernel.org/doc/man-pages/.