Ubuntu Manpage: mknod, mknodat - create a special or ordinary file

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NAME

       mknod, mknodat - create a special or ordinary file

SYNOPSIS

       #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)):

       mknod():
           _XOPEN_SOURCE >= 500
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

       The  system  call  mknod()  creates  a  filesystem  node (file, device special file, or named pipe) named
       pathname, with attributes specified by mode and dev.

       The mode argument 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 inode(7).

       The  file  mode is modified by the process's umask in 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_IFSOCK to 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_IFCHR or S_IFBLK, then dev specifies 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 pathname already exists, or is a symbolic link, this call fails with an EEXIST error.

       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 pathname is 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 pathname is relative and dirfd is the special value AT_FDCWD, then pathname is interpreted relative to
       the current working directory of the calling process (like mknod()).

       If pathname is absolute, then dirfd is ignored.

       See openat(2) for an explanation of the need for mknodat().

RETURN VALUE

       mknod() and mknodat() return zero on success, or -1 if an error occurred (in which  case,  errno  is  set
       appropriately).

ERRORS

EACCES The parent directory does not allow write permission to the process, or one of the directories in
the path prefix of pathname did not allow search permission. (See also path_resolution(7).)

EDQUOT The user's quota of disk blocks or inodes on the filesystem has been exhausted.

EEXIST pathname already exists. This includes the case where pathname is a symbolic link, dangling or
not.

EFAULT pathname points outside your accessible address space.

EINVAL mode requested creation of something other than a regular file, device special file, FIFO or
socket.

ELOOP Too many symbolic links were encountered in resolving pathname.

ENAMETOOLONG
pathname was too long.

ENOENT A directory component in pathname does not exist or is a dangling symbolic link.

ENOMEM Insufficient kernel memory was available.

ENOSPC The device containing pathname has no room for the new node.

ENOTDIR
A component used as a directory in pathname is not, in fact, a directory.

EPERM mode requested 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_MKNOD capability); also
returned if the filesystem containing pathname does not support the type of node requested.

EROFS pathname refers to a file on a read-only filesystem.

The following additional errors can occur for mknodat():

EBADF dirfd is not a valid file descriptor.

ENOTDIR
pathname is relative and dirfd is a file descriptor referring to a file other than a directory.

VERSIONS

       mknodat() was added to Linux in kernel 2.6.16; library support was added to glibc in version 2.4.

CONFORMING TO

       mknod(): SVr4, 4.4BSD, POSIX.1-2001 (but see below), POSIX.1-2008.

       mknodat(): POSIX.1-2008.

NOTES

       POSIX.1-2001 says: "The only portable use of mknod() is to create a FIFO-special file.  If  mode  is  not
       S_IFIFO or dev is 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().

COLOPHON

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Linux                                              2020-08-13                                           MKNOD(2)