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MKNOD(2) System Calls Manual MKNOD(2)

mknod, mknodat — make a special file node

library “libc”

#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);

The file system node path is created with the file type and access permissions specified in mode. The access permissions are modified by the process's umask value.

If mode indicates a block or character special file, dev is a configuration dependent specification denoting a particular device on the system. Otherwise, dev is ignored.

The () system call requires super-user privileges.

The () system call is equivalent to mknod() except in the case where path specifies a relative path. In this case the newly created device node is created relative to the directory associated with the file descriptor fd instead of the current working directory. If mknodat() is passed the special value AT_FDCWD in the fd parameter, the current working directory is used and the behavior is identical to a call to mknod().

The mknod() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

The mknod() system call will fail and the file will be not created if:

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A component of the path prefix is not a directory.
[]
A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.
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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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The process's effective user ID is not super-user.
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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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The path argument points outside the process's allocated address space.
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Creating anything else than a block or character special file (or a ) is not supported.

In addition to the errors returned by the mknod(), the mknodat() may fail if:

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The path argument does not specify an absolute path and the fd argument is neither AT_FDCWD nor a valid file descriptor open for searching.
[]
The path argument is not an absolute path and fd is neither AT_FDCWD nor a file descriptor associated with a directory.

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

The mknodat() system call follows The Open Group Extended API Set 2 specification.

The mknod() function appeared in Version 4 AT&T UNIX. The mknodat() system call appeared in FreeBSD 8.0.

December 1, 2017 FreeBSD-12.0