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MKNOD(2) System Calls Manual MKNOD(2)

mknod, mknodat — make a special file node

#include <sys/stat.h>

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

#include <sys/stat.h>
#include <fcntl.h>

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

The () function creates path with a file type and mode of mode, as modified by umask(2). Only FIFO and device special files are supported by this implementation.

If mode is the bitwise OR of S_IFIFO and zero or more file permissions, and dev is zero, then a FIFO is created. If mode is the bitwise OR of S_IFCHR or S_IFBLK and zero or more file permissions, then a character or block device special (respectively) is created with major and minor device numbers extracted from dev.

The () function is equivalent to mknod() except that where path specifies a relative path, the newly created device special file is created relative to the directory associated with file descriptor fd instead of the current working directory.

If () is passed the special value AT_FDCWD (defined in <fcntl.h>) in the fd parameter, the current working directory is used and the behavior is identical to a call to mknod().

Creating a device special file with () or mknodat() requires superuser privileges.

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

mknod() and mknodat() will fail and the file will be not created if:

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mode is an invalid file type or dev is an invalid value for that file type.
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A component of the path prefix is not a directory.
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A component of a pathname exceeded NAME_MAX characters, or an entire pathname (including the terminating NUL) exceeded PATH_MAX bytes.
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A component of the path prefix does not exist.
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Search permission is denied for a component of the path prefix.
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Too many symbolic links were encountered in translating the pathname.
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mode is a device special and the process's effective user ID is not superuser.
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An I/O error occurred while making the directory entry or allocating the inode.
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The directory in which the entry for the new node is being placed cannot be extended because there is no space left on the file system containing the directory.
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There are no free inodes on the file system on which the node is being created.
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The directory in which the entry for the new node is being placed cannot be extended because the user's quota of disk blocks on the file system containing the directory has been exhausted.
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The user's quota of inodes on the file system on which the node is being created has been exhausted.
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The named file resides on a read-only file system.
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The named file exists.
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path points outside the process's allocated address space.
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The process is running within an alternate root directory, as created by chroot(2).

Additionally, mknodat() will fail if:

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The path argument specifies a relative path and the fd argument is neither AT_FDCWD nor a valid file descriptor.
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The path argument specifies a relative path and the fd argument is a valid file descriptor but it does not reference a directory.
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The path argument specifies a relative path but search permission is denied for the directory which the fd file descriptor references.

chmod(2), chroot(2), mkfifo(2), stat(2), umask(2)

The mknod() and mknodat() functions conform to IEEE Std 1003.1-2008 (“POSIX.1”).

The mknod() system call first appeared in Version 4 AT&T UNIX, and mknodat() has been available since OpenBSD 5.0.

September 10, 2015 OpenBSD-7.0