1MKNOD(2) Linux Programmer's Manual MKNOD(2)
2
6 mknod, mknodat - create a special or ordinary file
7
9 #include <sys/types.h>
10 #include <sys/stat.h>
11 #include <fcntl.h>
12 #include <unistd.h>
13 int mknod(const char *pathname, mode_t mode, dev_t dev);
15 #include <fcntl.h> /* Definition of AT_* constants */
17 #include <sys/stat.h>
18 int mknodat(int dirfd, const char *pathname, mode_t mode, dev_t dev);
20 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
22 mknod():
24 _XOPEN_SOURCE >= 500
25 || /* Since glibc 2.19: */ _DEFAULT_SOURCE
26 || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
27
29 The system call mknod() creates a filesystem node (file, device special
30 file, or named pipe) named pathname, with attributes specified by mode
31 and dev.
32 The mode argument specifies both the file mode to use and the type of
34 node to be created. It should be a combination (using bitwise OR) of
35 one of the file types listed below and zero or more of the file mode
36 bits listed in inode(7).
37 The file mode is modified by the process's umask in the usual way: in
39 the absence of a default ACL, the permissions of the created node are
40 (mode & ~umask).
41 The file type must be one of S_IFREG, S_IFCHR, S_IFBLK, S_IFIFO, or
43 S_IFSOCK to specify a regular file (which will be created empty), char‐
44 acter special file, block special file, FIFO (named pipe), or UNIX
45 domain socket, respectively. (Zero file type is equivalent to type
46 S_IFREG.)
47 If the file type is S_IFCHR or S_IFBLK, then dev specifies the major
49 and minor numbers of the newly created device special file (makedev(3)
50 may be useful to build the value for dev); otherwise it is ignored.
51 If pathname already exists, or is a symbolic link, this call fails with
53 an EEXIST error.
54 The newly created node will be owned by the effective user ID of the
56 process. If the directory containing the node has the set-group-ID bit
57 set, or if the filesystem is mounted with BSD group semantics, the new
58 node will inherit the group ownership from its parent directory; other‐
59 wise it will be owned by the effective group ID of the process.
60 mknodat()
62 The mknodat() system call operates in exactly the same way as mknod(),
63 except for the differences described here.
64 If the pathname given in pathname is relative, then it is interpreted
66 relative to the directory referred to by the file descriptor dirfd
67 (rather than relative to the current working directory of the calling
68 process, as is done by mknod() for a relative pathname).
69 If pathname is relative and dirfd is the special value AT_FDCWD, then
71 pathname is interpreted relative to the current working directory of
72 the calling process (like mknod()).
73 If pathname is absolute, then dirfd is ignored.
75 See openat(2) for an explanation of the need for mknodat().
77
79 mknod() and mknodat() return zero on success, or -1 if an error
80 occurred (in which case, errno is set appropriately).
81
83 EACCES The parent directory does not allow write permission to the
84 process, or one of the directories in the path prefix of path‐
85 name did not allow search permission. (See also path_resolu‐
86 tion(7).)
87 EDQUOT The user's quota of disk blocks or inodes on the filesystem has
89 been exhausted.
90 EEXIST pathname already exists. This includes the case where pathname
92 is a symbolic link, dangling or not.
93 EFAULT pathname points outside your accessible address space.
95 EINVAL mode requested creation of something other than a regular file,
97 device special file, FIFO or socket.
98 ELOOP Too many symbolic links were encountered in resolving pathname.
100 ENAMETOOLONG
102 pathname was too long.
103 ENOENT A directory component in pathname does not exist or is a dan‐
105 gling symbolic link.
106 ENOMEM Insufficient kernel memory was available.
108 ENOSPC The device containing pathname has no room for the new node.
110 ENOTDIR
112 A component used as a directory in pathname is not, in fact, a
113 directory.
114 EPERM mode requested creation of something other than a regular file,
116 FIFO (named pipe), or UNIX domain socket, and the caller is not
117 privileged (Linux: does not have the CAP_MKNOD capability); also
118 returned if the filesystem containing pathname does not support
119 the type of node requested.
120 EROFS pathname refers to a file on a read-only filesystem.
122 The following additional errors can occur for mknodat():
124 EBADF dirfd is not a valid file descriptor.
126 ENOTDIR
128 pathname is relative and dirfd is a file descriptor referring to
129 a file other than a directory.
130
132 mknodat() was added to Linux in kernel 2.6.16; library support was
133 added to glibc in version 2.4.
134
136 mknod(): SVr4, 4.4BSD, POSIX.1-2001 (but see below), POSIX.1-2008.
137 mknodat(): POSIX.1-2008.
139
141 POSIX.1-2001 says: "The only portable use of mknod() is to create a
142 FIFO-special file. If mode is not S_IFIFO or dev is not 0, the behav‐
143 ior of mknod() is unspecified." However, nowadays one should never use
144 mknod() for this purpose; one should use mkfifo(3), a function espe‐
145 cially defined for this purpose.
146 Under Linux, mknod() cannot be used to create directories. One should
148 make directories with mkdir(2).
149 There are many infelicities in the protocol underlying NFS. Some of
151 these affect mknod() and mknodat().
152
154 mknod(1), chmod(2), chown(2), fcntl(2), mkdir(2), mount(2), socket(2),
155 stat(2), umask(2), unlink(2), makedev(3), mkfifo(3), acl(5) path_reso‐
156 lution(7)
157
159 This page is part of release 4.16 of the Linux man-pages project. A
160 description of the project, information about reporting bugs, and the
161 latest version of this page, can be found at
162 https://www.kernel.org/doc/man-pages/.
163Linux 2017-09-15 MKNOD(2)