The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.

#### NAME

> mknod - make a directory, a special file, or a regular file

#### SYNOPSIS

> ``[XSI] #include <sys/stat.h>
> int mknod(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 st_atime, st_ctime, and st_mtime fields of the file. Also, the st_ctime and st_mtime fields 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.

#### RETURN VALUE

> Upon successful completion, mknod() shall return 0. Otherwise, it shall return -1, the new file shall not be created, and errno shall be set to indicate the error.

#### ERRORS

> The mknod() function 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 pathname exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}.
> [ENOENT]
>   A component of the path prefix specified by path does not name an existing directory or path is an empty string.
> [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 is not 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 mknod() function may fail if:

> [ELOOP]
>   More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path argument.
> [ENAMETOOLONG]
>   Pathname resolution of a symbolic link produced an intermediate result whose length 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.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> chmod(), creat(), exec(), mkdir(), mkfifo(), open(), stat(), umask(), the Base Definitions volume of IEEE Std 1003.1-2001, <sys/stat.h>

#### CHANGE HISTORY

> First released in Issue 4, Version 2.

#### Issue 5

> Moved from X/OPEN UNIX extension to BASE.

#### Issue 6

> The DESCRIPTION is updated to avoid use of the term "must" for application requirements.

> The wording of the mandatory [ELOOP] error condition is updated, and a second optional [ELOOP] error condition is added.

End of informative text.

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