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This manual page is part of the POSIX Programmer's Manual. The Linux implementation of
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Linux behavior), or the interface may not be implemented on Linux.
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 .