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

NAME
       execveat - execute program relative to a directory file descriptor

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

       int execveat(int dirfd, const char *pathname,
                    const char *const argv[], const 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 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():

       pathname
              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 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.  Library support was added to glibc in version 2.34.

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)

Linux                                                                          2021-08-27                                                                    EXECVEAT(2)

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