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)):
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
|| /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200112L
mkstemps(): _BSD_SOURCE || _SVID_SOURCE
The mkstemp() function generates a unique temporary filename from tem-
plate, 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
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
The mkostemps() function is to mkstemps() as mkostemp() is to
On success, these functions return the file descriptor of the temporary
These functions may also fail with any of the errors described for
mkostemp() is available since glibc 2.7. mkstemps() and mkostemps()
are available since glibc 2.11.
For an explanation of the terms used in this section, see
|Interface | Attribute | Value |
|mkstemp(), mkostemp(), | Thread safety | MT-Safe |
|mkstemps(), mkostemps() | | |
mkstemp(): 4.3BSD, POSIX.1-2001.
mkstemps(): unstandardized, but appears on several other systems.
mkostemp() and mkostemps(): are glibc extensions.
In glibc versions 2.06 and earlier, the file is created with permis-
sions 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
More generally, the POSIX specification of mkstemp() does not say any-
thing 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()).
mkdtemp(3), mktemp(3), tempnam(3), tmpfile(3), tmpnam(3)
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GNU 2015-03-02 MKSTEMP(3)
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