mkstemps(3) — Linux manual page


MKSTEMP(3)                Linux Programmer's Manual               MKSTEMP(3)

NAME         top

       mkstemp,  mkostemp,  mkstemps,  mkostemps - create a unique temporary

SYNOPSIS         top

       #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);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

           _XOPEN_SOURCE >= 500
               || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
               || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE

       mkostemp(): _GNU_SOURCE
           /* Glibc since 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
       mkostemps(): _GNU_SOURCE

DESCRIPTION         top

       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.  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

       The mkostemp() function is like mkstemp(), with the difference that
       the following bits—with the same meaning as for open(2)—may be
       specified in flags: O_APPEND, O_CLOEXEC, and O_SYNC.  Note that when
       creating the file, mkostemp() includes the values O_RDWR, O_CREAT,
       and O_EXCL in the flags argument given to open(2); including these
       values in the flags argument given to mkostemp() is unnecessary, and
       produces errors on some systems.

       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

RETURN VALUE         top

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

ERRORS         top

       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

VERSIONS         top

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

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface               Attribute     Value   │
       │mkstemp(), mkostemp(),  │ Thread safety │ MT-Safe │
       │mkstemps(), mkostemps() │               │         │

CONFORMING TO         top

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

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

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

NOTES         top

       In glibc versions 2.06 and earlier, the file is created with
       permissions 0666, that is, read and write for all users.  This old
       behavior may be a security risk, especially since other UNIX flavors
       use 0600, and somebody might overlook this detail when porting
       programs.  POSIX.1-2008 adds a requirement that the file be created
       with mode 0600.

       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()).

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.08 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

GNU                              2017-09-15                       MKSTEMP(3)