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'\" t
.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH mktemp 3 2025-05-17 "Linux man-pages (unreleased)"
.SH NAME
mktemp \- make a unique temporary filename
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.P
.BI "char *mktemp(char *" template );
.fi
.P
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.P
.BR mktemp ():
.nf
Since glibc 2.12:
(_XOPEN_SOURCE >= 500) && ! (_POSIX_C_SOURCE >= 200112L)
|| /* glibc >= 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
Before glibc 2.12:
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500
.\" || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
.fi
.SH DESCRIPTION
.IR "Never use this function" ;
see BUGS.
.P
The
.BR mktemp ()
function generates a unique temporary filename
from
.IR template .
The last six characters of
.I template
must be XXXXXX
and these are replaced with a string that makes the
filename unique.
Since it will be modified,
.I template
must not be a string constant, but should be declared as a character array.
.SH RETURN VALUE
The
.BR mktemp ()
function always returns
.IR template .
If a unique name was created, the last six bytes of
.I template
will have been modified in such a way that the resulting name is unique
(i.e., does not exist already)
If a unique name could not be created,
.I template
is made an empty string, and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EINVAL
The last six characters of
.I template
were not XXXXXX.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface Attribute Value
T{
.na
.nh
.BR mktemp ()
T} Thread safety MT-Safe
.TE
.SH STANDARDS
None.
.SH HISTORY
4.3BSD, POSIX.1-2001.
Removed in POSIX.1-2008.
.\" .SH NOTES
.\" The prototype is in
.\" .I <unistd.h>
.\" for libc4, libc5, glibc1; glibc2 follows the Single UNIX Specification
.\" and has the prototype in
.\" .IR <stdlib.h> .
.SH BUGS
Never use
.BR mktemp ().
Some implementations follow 4.3BSD
and replace XXXXXX by the current process ID and a single letter,
so that at most 26 different names can be returned.
Since on the one hand the names are easy to guess, and on the other
hand there is a race between testing whether the name exists and
opening the file, every use of
.BR mktemp ()
is a security risk.
The race is avoided by
.BR mkstemp (3)
and
.BR mkdtemp (3).
.SH SEE ALSO
.BR mktemp (1),
.BR mkdtemp (3),
.BR mkstemp (3),
.BR tempnam (3),
.BR tmpfile (3),
.BR tmpnam (3)
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