execveat(2) — Linux manual page

execveat(2)                System Calls Manual               execveat(2)

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 *pathname,
                    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 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.

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 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

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Linux man-pages 6.9.1          2024-05-02                    execveat(2)

Pages that refer to this page: execve(2), fanotify_mark(2), open(2), syscalls(2), exec(3), fexecve(3)

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