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This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface
may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface
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NAME
mkdtemp, mkstemp — create a unique directory or file
SYNOPSIS
#include <stdlib.h> char *mkdtemp(char *template); int mkstemp(char *template);
DESCRIPTION
The mkdtemp() function shall create a directory with a unique name derived from template. The
application shall ensure that the string provided in template is a pathname ending with at least six
trailing 'X' characters. The mkdtemp() function shall modify the contents of template by replacing six or
more 'X' characters at the end of the pathname with the same number of characters from the portable
filename character set. The characters shall be chosen such that the resulting pathname does not
duplicate the name of an existing file at the time of the call to mkdtemp(). The mkdtemp() function
shall use the resulting pathname to create the new directory as if by a call to:
mkdir(pathname, S_IRWXU)
The mkstemp() function shall create a regular file with a unique name derived from template and return a
file descriptor for the file open for reading and writing. The application shall ensure that the string
provided in template is a pathname ending with at least six trailing 'X' characters. The mkstemp()
function shall modify the contents of template by replacing six or more 'X' characters at the end of the
pathname with the same number of characters from the portable filename character set. The characters
shall be chosen such that the resulting pathname does not duplicate the name of an existing file at the
time of the call to mkstemp(). The mkstemp() function shall use the resulting pathname to create the
file, and obtain a file descriptor for it, as if by a call to:
open(pathname, O_RDWR|O_CREAT|O_EXCL, S_IRUSR|S_IWUSR)
By behaving as if the O_EXCL flag for open() is set, the function prevents any possible race condition
between testing whether the file exists and opening it for use.
RETURN VALUE
Upon successful completion, the mkdtemp() function shall return the value of template. Otherwise, it
shall return a null pointer and shall set errno to indicate the error.
Upon successful completion, the mkstemp() function shall return an open file descriptor. Otherwise, it
shall return -1 and shall set errno to indicate the error.
ERRORS
The mkdtemp() function shall fail if:
EACCES Search permission is denied on a component of the path prefix, or write permission is denied on
the parent directory of the directory to be created.
EINVAL The string pointed to by template does not end in "XXXXXX".
ELOOP A loop exists in symbolic links encountered during resolution of the path of the directory to be
created.
EMLINK The link count of the parent directory would exceed {LINK_MAX}.
ENAMETOOLONG
The length of a component of a pathname is longer than {NAME_MAX}.
ENOENT A component of the path prefix specified by the template argument does not name an existing
directory.
ENOSPC The file system does not contain enough space to hold the contents of the new directory or to
extend the parent directory of the new directory.
ENOTDIR
A component of the path prefix names an existing file that is neither a directory nor a symbolic
link to a directory.
EROFS The parent directory resides on a read-only file system.
The mkdtemp() function may fail if:
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path of the
directory to be created.
ENAMETOOLONG
The length of a pathname exceeds {PATH_MAX}, or pathname resolution of a symbolic link produced an
intermediate result with a length that exceeds {PATH_MAX}.
The error conditions for the mkstemp() function are defined in open().
The following sections are informative.
EXAMPLES
Generating a Pathname
The following example creates a file with a 10-character name beginning with the characters "file" and
opens the file for reading and writing. The value returned as the value of fd is a file descriptor that
identifies the file.
#include <stdlib.h>
...
char template[] = "/tmp/fileXXXXXX";
int fd;
fd = mkstemp(template);
APPLICATION USAGE
It is possible to run out of letters.
Portable applications should pass exactly six trailing 'X's in the template and no more; implementations
may treat any additional trailing 'X's as either a fixed or replaceable part of the template. To be sure
of only passing six, a fixed string of at least one non-'X' character should precede the six 'X's.
Since 'X' is in the portable filename character set, some of the replacement characters can be 'X's,
leaving part (or even all) of the template effectively unchanged.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
getpid(), mkdir(), open(), tmpfile(), tmpnam()
The Base Definitions volume of POSIX.1‐2017, <stdlib.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original
IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document.
The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page are most likely to have been introduced
during the conversion of the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .