Manpage of MKNOD
MKNODSection: Linux Programmer's Manual (2)
NAMEmknod, mknodat - create a special or ordinary file
#include <sys/types.h>#include <sys/stat.h>#include <fcntl.h>#include <unistd.h>int mknod(const char *pathname, mode_t mode, dev_t dev);#include <fcntl.h> /* Definition of AT_* constants */ #include <sys/stat.h>int mknodat(int dirfd, const char *pathname, mode_t mode, dev_t dev);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
- _XOPEN_SOURCE >= 500
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
DESCRIPTIONThe system call mknod() creates a filesystem node (file, device special file, or named pipe) named pathname, with attributes specified by modeand dev.
The modeargument specifies both the file mode to use and the type of node to be created. It should be a combination (using bitwise OR) of one of the file types listed below and zero or more of the file mode bits listed in stat(2).
The file mode is modified by the process's umaskin the usual way: in the absence of a default ACL, the permissions of the created node are (mode & ~umask).
The file type must be one of S_IFREG, S_IFCHR, S_IFBLK, S_IFIFO, or S_IFSOCKto specify a regular file (which will be created empty), character special file, block special file, FIFO (named pipe), or UNIX domain socket, respectively. (Zero file type is equivalent to type S_IFREG.)
If the file type is S_IFCHRor S_IFBLK, then devspecifies the major and minor numbers of the newly created device special file (makedev(3) may be useful to build the value for dev); otherwise it is ignored.
If pathnamealready exists, or is a symbolic link, this call fails with an EEXISTerror.
The newly created node will be owned by the effective user ID of the process. If the directory containing the node has the set-group-ID bit set, or if the filesystem is mounted with BSD group semantics, the new node will inherit the group ownership from its parent directory; otherwise it will be owned by the effective group ID of the process.
mknodat()The mknodat() system call operates in exactly the same way as mknod(), except for the differences described here.
If the pathname given in pathnameis relative, then it is interpreted relative to the directory referred to by the file descriptor dirfd(rather than relative to the current working directory of the calling process, as is done by mknod() for a relative pathname).
If pathnameis relative and dirfdis the special value AT_FDCWD, then pathnameis interpreted relative to the current working directory of the calling process (like mknod()).
If pathnameis absolute, then dirfdis ignored.
See openat(2) for an explanation of the need for mknodat().
RETURN VALUEmknod() and mknodat() return zero on success, or -1 if an error occurred (in which case, errnois set appropriately).
- The parent directory does not allow write permission to the process, or one of the directories in the path prefix of pathnamedid not allow search permission. (See also path_resolution(7).)
- The user's quota of disk blocks or inodes on the filesystem has been exhausted.
- pathnamealready exists. This includes the case where pathnameis a symbolic link, dangling or not.
- pathname points outside your accessible address space.
- moderequested creation of something other than a regular file, device special file, FIFO or socket.
- Too many symbolic links were encountered in resolving pathname.
- pathname was too long.
- A directory component in pathnamedoes not exist or is a dangling symbolic link.
- Insufficient kernel memory was available.
- The device containing pathnamehas no room for the new node.
- A component used as a directory in pathnameis not, in fact, a directory.
- moderequested creation of something other than a regular file, FIFO (named pipe), or UNIX domain socket, and the caller is not privileged (Linux: does not have the CAP_MKNODcapability); also returned if the filesystem containing pathnamedoes not support the type of node requested.
- pathnamerefers to a file on a read-only filesystem.
The following additional errors can occur for mknodat():
- dirfdis not a valid file descriptor.
- pathnameis relative and dirfdis a file descriptor referring to a file other than a directory.
VERSIONSmknodat() was added to Linux in kernel 2.6.16; library support was added to glibc in version 2.4.
CONFORMING TOmknod(): SVr4, 4.4BSD, POSIX.1-2001 (but see below), POSIX.1-2008.
NOTESPOSIX.1-2001 says: "The only portable use of mknod() is to create a FIFO-special file. If modeis not S_IFIFOor devis not 0, the behavior of mknod() is unspecified." However, nowadays one should never use mknod() for this purpose; one should use mkfifo(3), a function especially defined for this purpose.
Under Linux, mknod() cannot be used to create directories. One should make directories with mkdir(2).
There are many infelicities in the protocol underlying NFS. Some of these affect mknod() and mknodat(2).
SEE ALSOmknod(1), chmod(2), chown(2), fcntl(2), mkdir(2), mount(2), socket(2), stat(2), umask(2), unlink(2), makedev(3), mkfifo(3), acl(5) path_resolution(7)
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