Name

mkstemp, mkostemp — create a unique temporary file

Synopsis

#include <stdlib.h>
int mkstemp( char *template);
 
int mkostemp( char *template,
  int flags);
 
int mkstemps( char *template,
  int suffixlen);
 
int mkostemps( char *template,
  int suffixlen,
  int flags);
 
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
mkstemp():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500
mkostemp():
_GNU_SOURCE
mkstemps():
_BSD_SOURCE || _SVID_SOURCE
mkostemps():
_GNU_SOURCE

DESCRIPTION

The mkstemp() function generates a unique temporary filename from template, creates and opens the file, and returns an open file descriptor for the file.

The last six characters of template must be "XXXXXX" and these are replaced with a string that makes the filename unique. Since it will be modified, template must not be a string constant, but should be declared as a character array.

The file is created with permissions 0600, that is, read plus write for owner only. (In glibc versions 2.06 and earlier, the file is created with permissions 0666, that is, read and write for all users.) The returned file descriptor provides both read and write access to the file. The file is opened with the open(2) O_EXCL flag, guaranteeing that the caller is the process that creates the file.

The mkostemp() function is like mkstemp(), with the difference that flags as for open(2) may be specified in flags (e.g., O_APPEND, O_SYNC).

The mkstemps() function is like mkstemp(), except that the string in template contains a suffix of suffixlen characters. Thus, template is of the form prefixXXXXXXsuffix, and the string XXXXXX is modified as for mkstemp().

The mkostemps() function is to mkstemps() as mkostemp() is to mkstemp().

RETURN VALUE

On success, these functions return the file descriptor of the temporary file. On error, −1 is returned, and errno is set appropriately.

ERRORS

EEXIST

Could not create a unique temporary filename. Now the contents of template are undefined.

EINVAL

For mkstemp() and mkostemp(): The last six characters of template were not XXXXXX; now template is unchanged.

For mkstemps() and mkostemps() template is less than (6 + suffixlen) characters long, or the last 6 characters before the suffix in template were not XXXXXX.

These functions may also fail with any of the errors described for open(2).

VERSIONS

mkostemp() is available since glibc 2.7. mkstemps() and mkostemps() are available since glibc 2.11.

CONFORMING TO

mkstemp(): 4.3BSD, POSIX.1-2001.

mkstemps(): unstandardized, but appears on several other systems.

mkostemp() and mkostemps(): are glibc extensions.

NOTES

The old behavior of creating a file with mode 0666 may be a security risk, especially since other Unix flavors use 0600, and somebody might overlook this detail when porting programs.

More generally, the POSIX specification of mkstemp() does not say anything about file modes, so the application should make sure its file mode creation mask (see umask(2)) is set appropriately before calling mkstemp() (and mkostemp()).

The prototype for mktemp() is in <unistd.h> for libc4, libc5, glibc1; glibc2 follows POSIX.1 and has the prototype in <stdlib.h>

SEE ALSO

mkdtemp(3), mktemp(3), tempnam(3), tmpfile(3), tmpnam(3)

COLOPHON

This page is part of release 3.25 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


  Copyright 1993 David Metcalfe (davidprism.demon.co.uk)
and Copyright (C) 2008, Michael Kerrisk <mtk.manpagesgmail.com>

Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Since the Linux kernel and libraries are constantly changing, this
manual page may be incorrect or out-of-date.  The author(s) assume no
responsibility for errors or omissions, or for damages resulting from
the use of the information contained herein.  The author(s) may not
have taken the same level of care in the production of this manual,
which is licensed free of charge, as they might when working
professionally.

Formatted or processed versions of this manual, if unaccompanied by
the source, must acknowledge the copyright and authors of this work.

References consulted:
    Linux libc source code
    Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
    386BSD man pages
Modified Sat Jul 24 18:48:48 1993 by Rik Faith (faithcs.unc.edu)
Modified 980310, aeb
Modified 990328, aeb
2008-06-19, mtk, Added mkostemp(); various other changes