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mknod(3p) — Linux manual page

PROLOG \|NAME \|SYNOPSIS \|DESCRIPTION \|RETURN VALUE \|ERRORS \|EXAMPLES \|APPLICATION USAGE \|RATIONALE \|FUTURE DIRECTIONS \|SEE ALSO \|COPYRIGHT

MKNOD(3P)               POSIX Programmer's ManualMKNOD(3P)

PROLOG top

       This manual page is part of the POSIX Programmer's Manual.  The       Linux implementation of this interface may differ (consult the       corresponding Linux manual page for details of Linux behavior), or       the interface may not be implemented on Linux.

NAME top

       mknod, mknodat — make directory, special file, or regular file

SYNOPSIS top

       #include <sys/stat.h>       int mknod(const char *path, mode_tmode, dev_tdev);       #include <fcntl.h>       int mknodat(intfd, const char *path, mode_tmode, dev_tdev);

DESCRIPTION top

       Themknod() function shall create a new file named by the pathname       to which the argumentpath points.       The file type forpath is OR'ed into themode argument, and the       application shall select one of the following symbolic constants:               ┌────────────┬──────────────────────────────────┐               │Name│Description│               ├────────────┼──────────────────────────────────┤               │ S_IFIFO    │ FIFO-special                     │               │ S_IFCHR    │ Character-special (non-portable) │               │ S_IFDIR    │ Directory (non-portable)         │               │ S_IFBLK    │ Block-special (non-portable)     │               │ S_IFREG    │ Regular (non-portable)           │               └────────────┴──────────────────────────────────┘       The only portable use ofmknod() is to create a FIFO-special file.       Ifmode is not S_IFIFO ordev is not 0, the behavior ofmknod() is       unspecified.       The permissions for the new file are OR'ed into themode argument,       and may be selected from any combination of the following symbolic       constants:         ┌────────────┬─────────────────────────────────────────────┐         │Name│Description│         ├────────────┼─────────────────────────────────────────────┤         │ S_ISUID    │ Set user ID on execution.                   │         │ S_ISGID    │ Set group ID on execution.                  │         │ S_IRWXU    │ Read, write, or execute (search) by owner.  │         │ S_IRUSR    │ Read by owner.                              │         │ S_IWUSR    │ Write by owner.                             │         │ S_IXUSR    │ Execute (search) by owner.                  │         │ S_IRWXG    │ Read, write, or execute (search) by group.  │         │ S_IRGRP    │ Read by group.                              │         │ S_IWGRP    │ Write by group.                             │         │ S_IXGRP    │ Execute (search) by group.                  │         │ S_IRWXO    │ Read, write, or execute (search) by others. │         │ S_IROTH    │ Read by others.                             │         │ S_IWOTH    │ Write by others.                            │         │ S_IXOTH    │ Execute (search) by others.                 │         │ S_ISVTX    │ On directories, restricted deletion flag.   │         └────────────┴─────────────────────────────────────────────┘       The user ID of the file shall be initialized to the effective user       ID of the process. The group ID of the file shall be initialized       to either the effective group ID of the process or the group ID of       the parent directory. Implementations shall provide a way to       initialize the file's group ID to the group ID of the parent       directory. Implementations may, but need not, provide an       implementation-defined way to initialize the file's group ID to       the effective group ID of the calling process. The owner, group,       and other permission bits ofmode shall be modified by the file       mode creation mask of the process. Themknod() function shall       clear each bit whose corresponding bit in the file mode creation       mask of the process is set.       Ifpath names a symbolic link,mknod() shall fail and seterrno to[EEXIST].       Upon successful completion,mknod() shall mark for update the last       data access, last data modification, and last file status change       timestamps of the file. Also, the last data modification and last       file status change timestamps of the directory that contains the       new entry shall be marked for update.       Only a process with appropriate privileges may invokemknod() for       file types other than FIFO-special.       Themknodat() function shall be equivalent to themknod() function       except in the case wherepath specifies a relative path. In this       case the newly created directory, special file, or regular file is       located relative to the directory associated with the file       descriptorfd instead of the current working directory. If the       access mode of the open file description associated with the file       descriptor is not O_SEARCH, the function shall check whether       directory searches are permitted using the current permissions of       the directory underlying the file descriptor. If the access mode       is O_SEARCH, the function shall not perform the check.       Ifmknodat() is passed the special value AT_FDCWD in thefd       parameter, the current working directory shall be used and the       behavior shall be identical to a call tomknod().

RETURN VALUE top

       Upon successful completion, these functions shall return 0.       Otherwise, these functions shall return -1 and seterrno to       indicate the error. If -1 is returned, the new file shall not be       created.

ERRORS top

       These functions shall fail if:EACCESA component of the path prefix denies search permission, or              write permission is denied on the parent directory.EEXISTThe named file exists.EINVALAn invalid argument exists.EIOAn I/O error occurred while accessing the file system.ELOOPA loop exists in symbolic links encountered during              resolution of thepath argument.ENAMETOOLONG              The length of a component of a pathname is longer than              {NAME_MAX}.ENOENTA component of the path prefix ofpath does not name an              existing file orpath is an empty string.ENOENTorENOTDIR              Thepath argument contains at least one non-<slash>              character and ends with one or more trailing <slash>              characters. Ifpath without the trailing <slash> characters              would name an existing file, an[ENOENT]error shall not              occur.ENOSPCThe directory that would contain the new file cannot be              extended or the file system is out of file allocation              resources.ENOTDIR              A component of the path prefix names an existing file that              is neither a directory nor a symbolic link to a directory.EPERMThe invoking process does not have appropriate privileges              and the file type is not FIFO-special.EROFSThe directory in which the file is to be created is located              on a read-only file system.       Themknodat() function shall fail if:EACCESThe access mode of the open file description associated              withfd is not O_SEARCH and the permissions of the              directory underlyingfd do not permit directory searches.EBADFThepath argument does not specify an absolute path and thefd argument is neither AT_FDCWD nor a valid file descriptor              open for reading or searching.ENOTDIR              Thepath argument is not an absolute path andfd is a file              descriptor associated with a non-directory file.       These functions may fail if:ELOOPMore than {SYMLOOP_MAX} symbolic links were encountered              during resolution of thepath argument.ENAMETOOLONG              The length of a pathname exceeds {PATH_MAX}, or pathname              resolution of a symbolic link produced an intermediate              result with a length that exceeds {PATH_MAX}.The following sections are informative.

EXAMPLES top

Creating a FIFO Special File       The following example shows how to create a FIFO special file       named/home/cnd/mod_done, with read/write permissions for owner,       and with read permissions for group and others.           #include <sys/types.h>           #include <sys/stat.h>           dev_t dev;           int   status;           ...           status  = mknod("/home/cnd/mod_done", S_IFIFO | S_IWUSR |               S_IRUSR | S_IRGRP | S_IROTH, dev);

APPLICATION USAGE top

       Themkfifo() function is preferred over this function for making       FIFO special files.

RATIONALE top

       The POSIX.1‐1990 standard required that the group ID of a newly       created file be set to the group ID of its parent directory or to       the effective group ID of the creating process. FIPS 151‐2       required that implementations provide a way to have the group ID       be set to the group ID of the containing directory, but did not       prohibit implementations also supporting a way to set the group ID       to the effective group ID of the creating process.  Conforming       applications should not assume which group ID will be used. If it       matters, an application can usechown() to set the group ID after       the file is created, or determine under what conditions the       implementation will set the desired group ID.       The purpose of themknodat() function is to create directories,       special files, or regular files in directories other than the       current working directory without exposure to race conditions. Any       part of the path of a file could be changed in parallel to a call       tomknod(), resulting in unspecified behavior. By opening a file       descriptor for the target directory and using themknodat()       function it can be guaranteed that the newly created directory,       special file, or regular file is located relative to the desired       directory.

FUTURE DIRECTIONS top

       None.

COPYRIGHT top

       Portions of this text are reprinted and reproduced in electronic       form from IEEE Std 1003.1-2017, Standard for Information       Technology -- Portable Operating System Interface (POSIX), The       Open Group Base Specifications Issue 7, 2018 Edition, Copyright       (C) 2018 by the Institute of Electrical and Electronics Engineers,       Inc and The Open Group.  In the event of any discrepancy between       this version and the original IEEE and The Open Group Standard,       the original IEEE and The Open Group Standard is the referee       document. The original Standard can be obtained online athttp://www.opengroup.org/unix/online.html .       Any typographical or formatting errors that appear in this page       are most likely to have been introduced during the conversion of       the source files to man page format. To report such errors, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group                2017MKNOD(3P)

Pages that refer to this page:sys_stat.h(0p), chmod(3p), creat(3p), exec(3p), fchmod(3p), fstatat(3p), fstatvfs(3p), mkdir(3p), mkfifo(3p), open(3p), umask(3p)