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       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);

       #include <fcntl.h>

       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:

┌───────────┬──────────────────────────────────┐
│ Name │ Description │
├───────────┼──────────────────────────────────┤
│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:

┌───────────┬─────────────────────────────────────────────┐
│ Name │ Description │
├───────────┼─────────────────────────────────────────────┤
│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 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 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 without the trailing <slash> characters
would name 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 The access mode of the open file description associated with fd is not 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.

COPYRIGHT

       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 .