NAME

       execveat - execute program relative to a directory file descriptor

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <linux/fcntl.h>      /* Definition of AT_* constants */
       #include <unistd.h>

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

DESCRIPTION

       The  execveat()  system  call  executes the program referred to by the combination of dirfd and path.  It
       operates in exactly the same way as execve(2), except for the differences described in this manual page.

       If path 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 path is relative and dirfd is the special value AT_FDCWD, then path is  interpreted  relative  to  the
       current working directory of the calling process (like execve(2)).

       If path is absolute, then dirfd is ignored.

       If  path  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 path 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 path 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 to indicate the
       error.

ERRORS

       The same errors that occur for execve(2) can also occur for execveat().  The following additional  errors
       can occur for execveat():

       path   is relative but dirfd is neither AT_FDCWD nor 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 path is a
              symbolic link.

       ENOENT The program identified by dirfd and path 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
              path is relative and dirfd is a file descriptor referring to a file other than a directory.

STANDARDS

       Linux.

HISTORY

       Linux 3.19, glibc 2.34.

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 path; in this case, P is the value given in path.

       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)

Linux man-pages 6.16                               2025-05-17                                        execveat(2)