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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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MKDTEMP(3P) POSIX Programmer's Manual MKDTEMP(3P)
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 may not be implemented on Linux.
mkdtemp, mkstemp — create a unique directory or file
#include <stdlib.h>
char *mkdtemp(char *template);
int mkstemp(char *template);
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.
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.
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(3p).
The following sections are informative.
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);
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.
None.
None.
getpid(3p), mkdir(3p), open(3p), tmpfile(3p), tmpnam(3p)
The Base Definitions volume of POSIX.1‐2017, stdlib.h(0p)
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 .
IEEE/The Open Group 2017 MKDTEMP(3P)
Pages that refer to this page: stdlib.h(0p), getpid(3p), mkdir(3p), mkstemp(3p), open(3p), tempnam(3p), tmpfile(3p), tmpnam(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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