mknod.3p (9731B)
- '\" et
- .TH MKNOD "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
- .\"
- .SH 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.
- .\"
- .SH NAME
- mknod, mknodat
- \(em make directory, special file, or regular file
- .SH SYNOPSIS
- .LP
- .nf
- #include <sys/stat.h>
- .P
- int mknod(const char *\fIpath\fP, mode_t \fImode\fP, dev_t \fIdev\fP);
- .P
- #include <fcntl.h>
- .P
- int mknodat(int \fIfd\fP, const char *\fIpath\fP, mode_t \fImode\fP, dev_t \fIdev\fP);
- .fi
- .SH DESCRIPTION
- The
- \fImknod\fR()
- function shall create a new file named by the pathname to which the
- argument
- .IR path
- points.
- .P
- The file type for
- .IR path
- is OR'ed into the
- .IR mode
- argument, and the application shall select one of the following
- symbolic constants:
- .TS
- tab(!) box center;
- cB | cB
- lw(1i) | lw(3i).
- 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)
- .TE
- .P
- The only portable use of
- \fImknod\fR()
- is to create a FIFO-special file. If
- .IR mode
- is not S_IFIFO or
- .IR dev
- is not 0, the behavior of
- \fImknod\fR()
- is unspecified.
- .P
- The permissions for the new file are OR'ed into the
- .IR mode
- argument, and may be selected from any combination of the following
- symbolic constants:
- .TS
- tab(!) box center;
- cB | cB
- lw(1i) | lw(3i).
- 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.
- .TE
- .P
- 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
- .IR mode
- shall be modified by the file mode creation mask of the process. The
- \fImknod\fR()
- function shall clear each bit whose corresponding bit in the file mode
- creation mask of the process is set.
- .P
- If
- .IR path
- names a symbolic link,
- \fImknod\fR()
- shall fail and set
- .IR errno
- to
- .BR [EEXIST] .
- .P
- Upon successful completion,
- \fImknod\fR()
- 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.
- .P
- Only a process with appropriate privileges may invoke
- \fImknod\fR()
- for file types other than FIFO-special.
- .P
- The
- \fImknodat\fR()
- function shall be equivalent to the
- \fImknod\fR()
- function except in the case where
- .IR 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
- .IR 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.
- .P
- If
- \fImknodat\fR()
- is passed the special value AT_FDCWD in the
- .IR fd
- parameter, the current working directory shall be used and the behavior
- shall be identical to a call to
- \fImknod\fR().
- .SH "RETURN VALUE"
- Upon successful completion, these functions shall return 0.
- Otherwise, these functions shall return \-1 and set
- .IR errno
- to indicate the error. If \-1 is returned, the new file shall
- not be created.
- .SH ERRORS
- These functions shall fail if:
- .TP
- .BR EACCES
- A component of the path prefix denies search permission, or write
- permission is denied on the parent directory.
- .TP
- .BR EEXIST
- The named file exists.
- .TP
- .BR EINVAL
- An invalid argument exists.
- .TP
- .BR EIO
- An I/O error occurred while accessing the file system.
- .TP
- .BR ELOOP
- A loop exists in symbolic links encountered during resolution of the
- .IR path
- argument.
- .TP
- .BR ENAMETOOLONG
- .br
- The length of a component of a pathname is longer than
- {NAME_MAX}.
- .TP
- .BR ENOENT
- A component of the path prefix of
- .IR path
- does not name an existing file or
- .IR path
- is an empty string.
- .TP
- .BR ENOENT " or " ENOTDIR
- .br
- The
- .IR path
- argument contains at least one non-\c
- <slash>
- character and ends with one or more trailing
- <slash>
- characters. If
- .IR path
- without the trailing
- <slash>
- characters would name an existing file, an
- .BR [ENOENT]
- error shall not occur.
- .TP
- .BR ENOSPC
- The directory that would contain the new file cannot be extended or the
- file system is out of file allocation resources.
- .TP
- .BR ENOTDIR
- A component of the path prefix names an existing file that is neither
- a directory nor a symbolic link to a directory.
- .TP
- .BR EPERM
- The invoking process does not have appropriate privileges and the
- file type is not FIFO-special.
- .TP
- .BR EROFS
- The directory in which the file is to be created is located on a
- read-only file system.
- .br
- .P
- The
- \fImknodat\fR()
- function shall fail if:
- .TP
- .BR EACCES
- The access mode of the open file description associated with
- .IR fd
- is not O_SEARCH and the permissions of the directory underlying
- .IR fd
- do not permit directory searches.
- .TP
- .BR EBADF
- The
- .IR path
- argument does not specify an absolute path and the
- .IR fd
- argument is neither AT_FDCWD nor a valid file descriptor open
- for reading or searching.
- .TP
- .BR ENOTDIR
- The
- .IR path
- argument is not an absolute path and
- .IR fd
- is a file descriptor associated with a non-directory file.
- .P
- These functions may fail if:
- .TP
- .BR ELOOP
- More than
- {SYMLOOP_MAX}
- symbolic links were encountered during resolution of the
- .IR path
- argument.
- .TP
- .BR ENAMETOOLONG
- .br
- 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}.
- .LP
- .IR "The following sections are informative."
- .SH EXAMPLES
- .SS "Creating a FIFO Special File"
- .P
- The following example shows how to create a FIFO special file named
- .BR /home/cnd/mod_done ,
- with read/write permissions for owner, and with read permissions for
- group and others.
- .sp
- .RS 4
- .nf
- #include <sys/types.h>
- #include <sys/stat.h>
- .P
- dev_t dev;
- int status;
- \&...
- status = mknod("/home/cnd/mod_done", S_IFIFO | S_IWUSR |
- S_IRUSR | S_IRGRP | S_IROTH, dev);
- .fi
- .P
- .RE
- .SH "APPLICATION USAGE"
- The
- \fImkfifo\fR()
- function is preferred over this function for making FIFO special files.
- .SH RATIONALE
- The POSIX.1\(hy1990 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\(hy2 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
- \fIchown\fR()
- to set the group ID after the file is created, or determine under
- what conditions the implementation will set the desired group ID.
- .P
- The purpose of the
- \fImknodat\fR()
- 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
- \fImknod\fR(),
- resulting in unspecified behavior. By opening a file descriptor for
- the target directory and using the
- \fImknodat\fR()
- function it can be guaranteed that the newly created directory, special
- file, or regular file is located relative to the desired directory.
- .SH "FUTURE DIRECTIONS"
- None.
- .SH "SEE ALSO"
- .IR "\fIchmod\fR\^(\|)",
- .IR "\fIcreat\fR\^(\|)",
- .IR "\fIexec\fR\^",
- .IR "\fIfstatat\fR\^(\|)",
- .IR "\fImkdir\fR\^(\|)",
- .IR "\fImkfifo\fR\^(\|)",
- .IR "\fIopen\fR\^(\|)",
- .IR "\fIumask\fR\^(\|)"
- .P
- The Base Definitions volume of POSIX.1\(hy2017,
- .IR "\fB<fcntl.h>\fP",
- .IR "\fB<sys_stat.h>\fP"
- .\"
- .SH 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 .
- .PP
- 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 .