MKSTEMP(3) Linux Programmer's Manual MKSTEMP(3)
mkstemp, mkostemp, mkstemps, mkostemps - create a unique temporary file
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 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 cre-
ates the file.
The mkostemp() function is like mkstemp(), with the difference that flags as for open(2)
may be specified in flags (e.g., O_APPEND, O_SYNC).
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().
On success, these functions return the file descriptor of the temporary file. On error,
-1 is returned, and errno is set appropriately.
EEXIST Could not create a unique temporary filename. Now the contents of template are
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).
mkostemp() is available since glibc 2.7. mkstemps() and mkostemps() are available since
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 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 pro-
grams. 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()).
The prototype for mktemp() is in <unistd.h> for libc4, libc5, glibc1; glibc2 follows
POSIX.1 and has the prototype in <stdlib.h>.
mkdtemp(3), mktemp(3), tempnam(3), tmpfile(3), tmpnam(3)
This page is part of release 3.55 of the Linux man-pages project. A description of the
project, and information about reporting bugs, can be found at
GNU 2012-12-21 MKSTEMP(3)