mkstemp(3) — Linux manual page


mkstemp(3)              Library Functions Manual              mkstemp(3)

NAME         top

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

LIBRARY         top

       Standard C library (libc, -lc)

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

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


           /* glibc >= 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_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 file.

       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 to
       indicate the error.

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 open(2).

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       │ Interface                           Attribute     Value   │
       │ mkstemp(), mkostemp(), mkstemps(),  │ Thread safety │ MT-Safe │
       │ mkostemps()                         │               │         │

STANDARDS         top




HISTORY         top

              4.3BSD, POSIX.1-2001.

              glibc 2.11.  BSD, Mac OS X, Solaris, Tru64.

              glibc 2.7.

              glibc 2.11.

       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

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Linux man-pages 6.9.1          2024-05-02                     mkstemp(3)

Pages that refer to this page: mktemp(1)getpid(2)mkdtemp(3)mktemp(3)pmprintf(3)tempnam(3)tmpfile(3)tmpnam(3)file-hierarchy(7)