mkstemp(3)

NAME

   mkstemp, mkostemp, mkstemps, mkostemps - 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);

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

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

   mkostemp(): _GNU_SOURCE
   mkstemps():
       /* Glibc since 2.19: */ _DEFAULT_SOURCE
           || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_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.  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
   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.

ATTRIBUTES

   For  an  explanation  of  the  terms  used   in   this   section,   see
   attributes(7).

   ┌────────────────────────┬───────────────┬─────────┐
   │Interface               │ Attribute     │ Value   │
   ├────────────────────────┼───────────────┼─────────┤
   │mkstemp(), mkostemp(),  │ Thread safety │ MT-Safe │
   │mkstemps(), mkostemps() │               │         │
   └────────────────────────┴───────────────┴─────────┘

CONFORMING TO

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

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

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

NOTES

   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

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

COLOPHON

   This  page  is  part of release 4.09 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
   https://www.kernel.org/doc/man-pages/.

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