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Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)mktemp.3 8.1 (Berkeley) 6/4/93 .\" .Dd December 18, 2015 .Dt MKTEMP 3 .Os .Sh NAME .Nm mktemp , .Nm mkstemp , .Nm mkdtemp , .Nm mkdtempat_np , .Nm mkstemps , .Nm mkstempsat_np , .Nm mkostemp , .Nm mkostemps , .Nm mkostempsat_np .Nd make temporary file name (unique) .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In unistd.h .Ft char * .Fo mktemp .Fa "char *template" .Fc .Ft int .Fo mkstemp .Fa "char *template" .Fc .Ft char * .Fo mkdtemp .Fa "char *template" .Fc .Ft char * .Fo mkdtempat_np .Fa "int dfd" .Fa "char *template" .Fc .Ft int .Fo mkstemps .Fa "char *template" .Fa "int suffixlen" .Fc .Ft int .Fo mkstempsat_np .Fa "int dfd" .Fa "char *template" .Fa "int suffixlen" .Fc .Ft int .Fo mkostemp .Fa "char *template" .Fa "int oflags" .Fc .Ft int .Fo mkostemps .Fa "char *template" .Fa "int suffixlen" .Fa "int oflags" .Fc .Ft int .Fo mkostempsat_np .Fa "int dfd" .Fa "char *template" .Fa "int suffixlen" .Fa "int oflags" .Fc .Sh DESCRIPTION The .Fn mktemp function takes the given file name template and overwrites a portion of it to create a file name. This file name is guaranteed not to exist at the time of function invocation and is suitable for use by the application. The template may be any file name with some number of .Ql X Ns s appended to it, for example .Pa /tmp/temp.XXXXXX . The trailing .Ql X Ns s are replaced with a unique alphanumeric combination. The number of unique file names .Fn mktemp can return depends on the number of .Ql X Ns s provided; six .Ql X Ns s will result in .Fn mktemp selecting one of 56800235584 (62 ** 6) possible temporary file names. .Pp The .Fn mkstemp function makes the same replacement to the template and creates the template file, mode 0600, returning a file descriptor opened for reading and writing. This avoids the race between testing for a file's existence and opening it for use. .Pp The .Fn mkdtemp function makes the same replacement to the template as in .Fn mktemp and creates the template directory, mode 0700. .Pp The .Fn mkostemp function is like .Fn mkstemp but allows specifying additional .Xr open 2 flags (defined in .In fcntl.h ) . The permitted flags are .Dv O_APPEND , .Dv O_SHLOCK , .Dv O_EXLOCK and .Dv O_CLOEXEC . .Pp The .Fn mkstemps and .Fn mkostemps functions act the same as .Fn mkstemp and .Fn mkostemp respectively, except they permit a suffix to exist in the template. The template should be of the form .Pa /tmp/tmpXXXXXXsuffix . The .Fn mkstemps and .Fn mkostemps functions are told the length of the suffix string. .Pp The .Fn mkdtempat_np , .Fn mkstempsat_np , and .Fn mkostempsat_np functions act the same as .Fn mkdtemp , .Fn mkstemps , and .Fn mkostemps respectively, except in the case where the .Ar path specifies a relative path. In this case, path is treated as relative to the directory associated with the file descriptor .Ar fd instead of the current working directory. .Sh RETURN VALUES The .Fn mktemp and .Fn mkdtemp functions return a pointer to the template on success and .Dv NULL on failure. The .Fn mkstemp , .Fn mkostemp , .Fn mkstemps and .Fn mkostemps functions return \-1 if no suitable file could be created. If either call fails an error code is placed in the global variable .Va errno . .Sh ERRORS The .Fn mkstemp , .Fn mkostemp , .Fn mkstemps , .Fn mkostemps , and .Fn mkdtemp functions may set .Va errno to one of the following values: .Bl -tag -width Er .It Bq Er ENOTDIR The pathname portion of the template is not an existing directory. .El .Pp The .Fn mkostemp and .Fn mkostemps functions may also set .Va errno to the following value: .Bl -tag -width Er .It Bq Er EINVAL The .Fa oflags argument is invalid. .El .Pp The .Fn mkstemp , .Fn mkostemp , .Fn mkstemps , .Fn mkostemps and .Fn mkdtemp functions may also set .Va errno to any value specified by the .Xr stat 2 function. .Pp The .Fn mkstemp , .Fn mkostemp , .Fn mkstemps and .Fn mkostemps functions may also set .Va errno to any value specified by the .Xr open 2 function. .Pp The .Fn mkdtemp function may also set .Va errno to any value specified by the .Xr mkdir 2 function. .Sh NOTES A common problem that results in a core dump is that the programmer passes in a read-only string to .Fn mktemp , .Fn mkstemp , .Fn mkstemps or .Fn mkdtemp . This is common with programs that were developed before .St -isoC compilers were common. For example, calling .Fn mkstemp with an argument of .Qq /tmp/tempfile.XXXXXX will result in a core dump due to .Fn mkstemp attempting to modify the string constant that was given. .Sh LEGACY SYNOPSIS .Fd #include <unistd.h> .Pp The include file .In unistd.h is necessary and sufficient for all functions. .Sh SEE ALSO .Xr chmod 2 , .Xr getpid 2 , .Xr mkdir 2 , .Xr open 2 , .Xr stat 2 , .Xr compat 5 .Sh STANDARDS The .Fn mkstemp and .Fn mkdtemp functions are expected to conform to .St -p1003.1-2008 . The .Fn mktemp function is expected to conform to .St -p1003.1-2001 and is not specified by .St -p1003.1-2008 . The .Fn mkostemp , .Fn mkstemps and .Fn mkostemps functions do not conform to any standard. .Sh HISTORY A .Fn mktemp function appeared in .At v7 . The .Fn mkstemp function appeared in .Bx 4.4 . The .Fn mkdtemp function first appeared in .Ox 2.2 , and later in .Fx 3.2 . The .Fn mkstemps function first appeared in .Ox 2.4 , and later in .Fx 3.4 . The .Fn mkostemp and .Fn mkostemps functions appeared in OS X 10.12. .Sh BUGS This family of functions produces filenames which can be guessed, though the risk is minimized when large numbers of .Ql X Ns s are used to increase the number of possible temporary filenames. This makes the race in .Fn mktemp , between testing for a file's existence (in the .Fn mktemp function call) and opening it for use (later in the user application) particularly dangerous from a security perspective. Whenever it is possible, .Fn mkstemp or .Fn mkostemp should be used instead, since it does not have the race condition. If .Fn mkstemp cannot be used, the filename created by .Fn mktemp should be created using the .Dv O_EXCL flag to .Xr open 2 and the return status of the call should be tested for failure. This will ensure that the program does not continue blindly in the event that an attacker has already created the file with the intention of manipulating or reading its contents.