MKNOD(3)                   POSIX Programmer's Manual                  MKNOD(3)



PPRROOLLOOGG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NNAAMMEE
       mknod, mknodat -- make directory, special file, or regular file

SSYYNNOOPPSSIISS
       #include <sys/stat.h>

       int mknod(const char *_p_a_t_h, mode_t _m_o_d_e, dev_t _d_e_v);

       #include <fcntl.h>

       int mknodat(int _f_d, const char *_p_a_t_h, mode_t _m_o_d_e, dev_t _d_e_v);

DDEESSCCRRIIPPTTIIOONN
       The _m_k_n_o_d() function shall create a new file named by the pathname to
       which the argument _p_a_t_h points.

       The file type for _p_a_t_h is OR'ed into the _m_o_d_e argument, and the
       application shall select one of the following symbolic constants:

                   +-----------+----------------------------------+
                   |   NNaammee    |           DDeessccrriippttiioonn            |
                   +-----------+----------------------------------+
                   |S_IFIFO    | FIFO-special                     |
                   |S_IFCHR    | Character-special (non-portable) |
                   |S_IFDIR    | Directory (non-portable)         |
                   |S_IFBLK    | Block-special (non-portable)     |
                   |S_IFREG    | Regular (non-portable)           |
                   +-----------+----------------------------------+
       The only portable use of _m_k_n_o_d() is to create a FIFO-special file. If
       _m_o_d_e is not S_IFIFO or _d_e_v is not 0, the behavior of _m_k_n_o_d() is
       unspecified.

       The permissions for the new file are OR'ed into the _m_o_d_e argument, and
       may be selected from any combination of the following symbolic
       constants:

             +-----------+---------------------------------------------+
             |   NNaammee    |                 DDeessccrriippttiioonn                 |
             +-----------+---------------------------------------------+
             |S_ISUID    | Set user ID on execution.                   |
             |S_ISGID    | Set group ID on execution.                  |
             |S_IRWXU    | Read, write, or execute (search) by owner.  |
             |S_IRUSR    | Read by owner.                              |
             |S_IWUSR    | Write by owner.                             |
             |S_IXUSR    | Execute (search) by owner.                  |
             |S_IRWXG    | Read, write, or execute (search) by group.  |
             |S_IRGRP    | Read by group.                              |
             |S_IWGRP    | Write by group.                             |
             |S_IXGRP    | Execute (search) by group.                  |
             |S_IRWXO    | Read, write, or execute (search) by others. |
             |S_IROTH    | Read by others.                             |
             |S_IWOTH    | Write by others.                            |
             |S_IXOTH    | Execute (search) by others.                 |
             |S_ISVTX    | On directories, restricted deletion flag.   |
             +-----------+---------------------------------------------+
       The user ID of the file shall be initialized to the effective user ID
       of the process. The group ID of the file shall be initialized to either
       the effective group ID of the process or the group ID of the parent
       directory. Implementations shall provide a way to initialize the file's
       group ID to the group ID of the parent directory. Implementations may,
       but need not, provide an implementation-defined way to initialize the
       file's group ID to the effective group ID of the calling process. The
       owner, group, and other permission bits of _m_o_d_e shall be modified by
       the file mode creation mask of the process. The _m_k_n_o_d() function shall
       clear each bit whose corresponding bit in the file mode creation mask
       of the process is set.

       If _p_a_t_h names a symbolic link, _m_k_n_o_d() shall fail and set _e_r_r_n_o to
       [[EEEEXXIISSTT]].

       Upon successful completion, _m_k_n_o_d() shall mark for update the last data
       access, last data modification, and last file status change timestamps
       of the file. Also, the last data modification and last file status
       change timestamps of the directory that contains the new entry shall be
       marked for update.

       Only a process with appropriate privileges may invoke _m_k_n_o_d() for file
       types other than FIFO-special.

       The _m_k_n_o_d_a_t() function shall be equivalent to the _m_k_n_o_d() function
       except in the case where _p_a_t_h specifies a relative path. In this case
       the newly created directory, special file, or regular file is located
       relative to the directory associated with the file descriptor _f_d
       instead of the current working directory. If the access mode of the
       open file description associated with the file descriptor is not
       O_SEARCH, the function shall check whether directory searches are
       permitted using the current permissions of the directory underlying the
       file descriptor. If the access mode is O_SEARCH, the function shall not
       perform the check.

       If _m_k_n_o_d_a_t() is passed the special value AT_FDCWD in the _f_d parameter,
       the current working directory shall be used and the behavior shall be
       identical to a call to _m_k_n_o_d().

RREETTUURRNN VVAALLUUEE
       Upon successful completion, these functions shall return 0.  Otherwise,
       these functions shall return -1 and set _e_r_r_n_o to indicate the error. If
       -1 is returned, the new file shall not be created.

EERRRROORRSS
       These functions shall fail if:

       EEAACCCCEESS A component of the path prefix denies search permission, or
              write permission is denied on the parent directory.

       EEEEXXIISSTT The named file exists.

       EEIINNVVAALL An invalid argument exists.

       EEIIOO    An I/O error occurred while accessing the file system.

       EELLOOOOPP  A loop exists in symbolic links encountered during resolution of
              the _p_a_t_h argument.

       EENNAAMMEETTOOOOLLOONNGG
              The length of a component of a pathname is longer than
              {NAME_MAX}.

       EENNOOEENNTT A component of the path prefix of _p_a_t_h does not name an existing
              file or _p_a_t_h is an empty string.

       EENNOOEENNTT or EENNOOTTDDIIRR
              The _p_a_t_h argument contains at least one non-<slash> character
              and ends with one or more trailing <slash> characters. If _p_a_t_h
              without the trailing <slash> characters would name an existing
              file, an [[EENNOOEENNTT]] error shall not occur.

       EENNOOSSPPCC The directory that would contain the new file cannot be extended
              or the file system is out of file allocation resources.

       EENNOOTTDDIIRR
              A component of the path prefix names an existing file that is
              neither a directory nor a symbolic link to a directory.

       EEPPEERRMM  The invoking process does not have appropriate privileges and
              the file type is not FIFO-special.

       EERROOFFSS  The directory in which the file is to be created is located on a
              read-only file system.

       The _m_k_n_o_d_a_t() function shall fail if:

       EEAACCCCEESS The access mode of the open file description associated with _f_d
              is not O_SEARCH and the permissions of the directory underlying
              _f_d do not permit directory searches.

       EEBBAADDFF  The _p_a_t_h argument does not specify an absolute path and the _f_d
              argument is neither AT_FDCWD nor a valid file descriptor open
              for reading or searching.

       EENNOOTTDDIIRR
              The _p_a_t_h argument is not an absolute path and _f_d is a file
              descriptor associated with a non-directory file.

       These functions may fail if:

       EELLOOOOPP  More than {SYMLOOP_MAX} symbolic links were encountered during
              resolution of the _p_a_t_h argument.

       EENNAAMMEETTOOOOLLOONNGG
              The length of a pathname exceeds {PATH_MAX}, or pathname
              resolution of a symbolic link produced an intermediate result
              with a length that exceeds {PATH_MAX}.

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

EEXXAAMMPPLLEESS
   CCrreeaattiinngg aa FFIIFFOO SSppeecciiaall FFiillee
       The following example shows how to create a FIFO special file named
       //hhoommee//ccnndd//mmoodd__ddoonnee, with read/write permissions for owner, and with
       read permissions for group and others.


           #include <sys/types.h>
           #include <sys/stat.h>

           dev_t dev;
           int   status;
           ...
           status  = mknod("/home/cnd/mod_done", S_IFIFO | S_IWUSR |
               S_IRUSR | S_IRGRP | S_IROTH, dev);

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       The _m_k_f_i_f_o() function is preferred over this function for making FIFO
       special files.

RRAATTIIOONNAALLEE
       The POSIX.1-1990 standard required that the group ID of a newly created
       file be set to the group ID of its parent directory or to the effective
       group ID of the creating process. FIPS 151-2 required that
       implementations provide a way to have the group ID be set to the group
       ID of the containing directory, but did not prohibit implementations
       also supporting a way to set the group ID to the effective group ID of
       the creating process.  Conforming applications should not assume which
       group ID will be used. If it matters, an application can use _c_h_o_w_n() to
       set the group ID after the file is created, or determine under what
       conditions the implementation will set the desired group ID.

       The purpose of the _m_k_n_o_d_a_t() function is to create directories, special
       files, or regular files in directories other than the current working
       directory without exposure to race conditions. Any part of the path of
       a file could be changed in parallel to a call to _m_k_n_o_d(), resulting in
       unspecified behavior. By opening a file descriptor for the target
       directory and using the _m_k_n_o_d_a_t() function it can be guaranteed that
       the newly created directory, special file, or regular file is located
       relative to the desired directory.

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       _c_h_m_o_d(), _c_r_e_a_t(), _e_x_e_c, _f_s_t_a_t_a_t(), _m_k_d_i_r(), _m_k_f_i_f_o(), _o_p_e_n(), _u_m_a_s_k()

       The Base Definitions volume of POSIX.1-2017, <<ffccnnttll..hh>>, <<ssyyss__ssttaatt..hh>>

CCOOPPYYRRIIGGHHTT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                             MKNOD(3)
