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MKSTEMP(3)                                                              Linux Programmer's Manual                                                             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 <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE

       mkostemp():
           _GNU_SOURCE

       mkstemps():
           /* Glibc since 2.19: */ _DEFAULT_SOURCE
               || /* Glibc <= 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);  in‐
       cluding 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 pre‐
       fixXXXXXXsuffix, 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 to indicate the error.

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(), mkstemps(), mkostemps()                                                                                        │ Thread safety │ MT-Safe │
       └──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

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)

GNU                                                                            2021-03-22                                                                     MKSTEMP(3)