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14.10 Making Special Files

The mknod function is the primitive for making special files, such as files that correspond to devices. The GNU C Library includes this function for compatibility with BSD.

The prototype for mknod is declared in sys/stat.h.

Function: int mknod (const char *filename, mode_t mode, dev_t dev)

Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.

The mknod function makes a special file with name filename. The mode specifies the mode of the file, and may include the various special file bits, such as S_IFCHR (for a character special file) or S_IFBLK (for a block special file). See Testing the Type of a File.

The dev argument specifies which device the special file refers to. Its exact interpretation depends on the kind of special file being created.

The return value is 0 on success and -1 on error. In addition to the usual file name errors (see File Name Errors), the following errno error conditions are defined for this function:


The calling process is not privileged. Only the superuser can create special files.


The directory or file system that would contain the new file is full and cannot be extended.


The directory containing the new file can’t be modified because it’s on a read-only file system.


There is already a file named filename. If you want to replace this file, you must remove the old file explicitly first.

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