---
name: "mktemp"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/mktemp/3"
---

# mktemp(3)

make a unique temporary filename

## NAME

mktemp - make a unique temporary filename

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <stdlib.h>
```

**char \*mktemp(char \****template***);**

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

**mktemp**():

```
    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
```

## DESCRIPTION

*Never use this function*; see BUGS.

The **mktemp**() function generates a unique temporary filename from *template*. 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.

## RETURN VALUE

The **mktemp**() function always returns *template*. If a unique name was created, the last six bytes of *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, *template* is made an empty string, and *errno* is set to indicate the error.

## ERRORS

- **EINVAL**

  The last six characters of *template* were not XXXXXX.

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **mktemp**() | Thread safety | MT-Safe |

## STANDARDS

None.

## HISTORY

4\.3BSD, POSIX.1-2001. Removed in POSIX.1-2008.

## BUGS

Never use **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 **mktemp**() is a security risk. The race is avoided by [**mkstemp**(3)](/mkstemp/3.md) and [**mkdtemp**(3)](/mkdtemp/3.md).

## SEE ALSO

[**mktemp**(1)](/mktemp/1.md), [**mkdtemp**(3)](/mkdtemp/3.md), [**mkstemp**(3)](/mkstemp/3.md), [**tempnam**(3)](/tempnam/3.md), [**tmpfile**(3)](/tmpfile/3.md), [**tmpnam**(3)](/tmpnam/3.md)