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MKNOD
Section: POSIX Programmer's Manual (3P)Updated: 2013
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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 fileSYNOPSIS
#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:
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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.
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#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 .