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PROLOG

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

NAME

       mknod, mknodat — make directory, special file, or regular file

SYNOPSIS

       #include <sys/stat.h>

       int mknod(const char *path, mode_t mode, dev_t dev);
       int mknodat(int fd, const char *path, mode_t mode, dev_t dev);

DESCRIPTION

       The  mknod()  function shall create a new file named by the pathname to which the argument
       path points.

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

                            ┌───────────┬──────────────────────────────────┐
                            │   NameDescription            │
                            ├───────────┼──────────────────────────────────┤
                            │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 mknod() is to create a FIFO-special file. If mode is not S_IFIFO
       or dev is not 0, the behavior of mknod() is unspecified.

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

                       ┌───────────┬─────────────────────────────────────────────┐
                       │   NameDescription                 │
                       ├───────────┼─────────────────────────────────────────────┤
                       │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
       mode shall be modified by the file mode creation mask of the process. The mknod() function
       shall clear each bit whose corresponding bit in the file mode creation mask of the process
       is set.

       If path names a symbolic link, mknod() shall fail and set errno to [EEXIST].

       Upon  successful completion, mknod() 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 mknod() for file  types  other  than
       FIFO-special.

       The  mknodat()  function  shall  be  equivalent to the mknod() function except in the case
       where path 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 fd instead of the current working directory. If the file descriptor was  opened
       without  O_SEARCH, the function shall check whether directory searches are permitted using
       the current permissions of the directory underlying  the  file  descriptor.  If  the  file
       descriptor was opened with O_SEARCH, the function shall not perform the check.

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

RETURN VALUE

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

ERRORS

       These functions shall fail if:

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

       EEXIST The named file exists.

       EINVAL An invalid argument exists.

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

       ELOOP  A loop exists in symbolic links encountered during resolution of the path argument.

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

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

       ENOENT or ENOTDIR
              The path argument contains at least one non-<slash> character and ends with one  or
              more trailing <slash> characters. If path names an existing file, an [ENOENT] error
              shall not occur.

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

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

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

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

       The mknodat() function shall fail if:

       EACCES fd was not opened with O_SEARCH and the permissions of the directory underlying  fd
              do not permit directory searches.

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

       ENOTDIR
              The path argument is not an absolute path and fd is a  file  descriptor  associated
              with a non-directory file.

       These functions may fail if:

       ELOOP  More  than  {SYMLOOP_MAX}  symbolic links were encountered during resolution of the
              path argument.

       ENAMETOOLONG
              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}.

       The following sections are informative.

EXAMPLES

   Creating a FIFO Special File
       The  following  example  shows how to create a FIFO special file named /home/cnd/mod_done,
       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);

APPLICATION USAGE

       The mkfifo() function is preferred over this function for making FIFO special files.

RATIONALE

       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 chown() 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 mknodat() 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
       mknod(), resulting in unspecified behavior. By opening a file descriptor  for  the  target
       directory  and  using  the  mknodat() function it can be guaranteed that the newly created
       directory, special file, or regular file is located relative to the desired directory.

FUTURE DIRECTIONS

       None.

SEE ALSO

       chmod(), creat(), exec, fstatat(), mkdir(), mkfifo(), open(), umask()

       The Base Definitions volume of POSIX.1‐2008, <sys_stat.h>

COPYRIGHT

       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1,  2013  Edition,  Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013  by  the
       Institute  of  Electrical  and  Electronics  Engineers,  Inc and The Open Group.  (This is
       POSIX.1-2008 with the  2013  Technical  Corrigendum  1  applied.)  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.unix.org/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 .