mktemp(3) Library Functions Manual mktemp(3)

mktemp - make a unique temporary filename

Standard C library (libc, -lc)

#include <stdlib.h>
char *mktemp(char *template);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):


    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:

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.

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.

The last six characters of template were not XXXXXX.

For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
mktemp () Thread safety MT-Safe


4.3BSD, POSIX.1-2001. Removed in POSIX.1-2008.

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) and mkdtemp(3).

mktemp(1), mkdtemp(3), mkstemp(3), tempnam(3), tmpfile(3), tmpnam(3)

2024-05-02 Linux man-pages 6.9.1