diff options
| author | Jacob McDonnell <jacob@jacobmcdonnell.com> | 2026-04-25 19:54:44 -0400 |
|---|---|---|
| committer | Jacob McDonnell <jacob@jacobmcdonnell.com> | 2026-04-25 19:54:44 -0400 |
| commit | a9157ce950dfe2fc30795d43b9d79b9d1bffc48b (patch) | |
| tree | 9df484304b560466d145e662c1c254ff0e9ae0ba /static/openbsd/man3/mktemp.3 | |
| parent | 160aa82b2d39c46ad33723d7d909cb4972efbb03 (diff) | |
docs: Added All OpenBSD Manuals
Diffstat (limited to 'static/openbsd/man3/mktemp.3')
| -rw-r--r-- | static/openbsd/man3/mktemp.3 | 431 |
1 files changed, 431 insertions, 0 deletions
diff --git a/static/openbsd/man3/mktemp.3 b/static/openbsd/man3/mktemp.3 new file mode 100644 index 00000000..a9673581 --- /dev/null +++ b/static/openbsd/man3/mktemp.3 @@ -0,0 +1,431 @@ +.\" $OpenBSD: mktemp.3,v 1.4 2025/08/04 14:11:37 schwarze Exp $ +.\" +.\" Copyright (c) 1989, 1991, 1993 +.\" The Regents of the University of California. All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" 3. 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. +.\" +.Dd $Mdocdate: August 4 2025 $ +.Dt MKTEMP 3 +.Os +.Sh NAME +.Nm mktemp , +.Nm mkstemp , +.Nm mkstemps , +.Nm mkdtemp , +.Nm mkdtemps , +.Nm mkostemp , +.Nm mkostemps +.Nd make temporary file name (unique) +.Sh SYNOPSIS +.In stdlib.h +.Ft char * +.Fn mktemp "char *template" +.Ft int +.Fn mkstemp "char *template" +.Ft int +.Fn mkstemps "char *template" "int suffixlen" +.Ft char * +.Fn mkdtemp "char *template" +.Ft char * +.Fn mkdtemps "char *template" "int suffixlen" +.In stdlib.h +.In fcntl.h +.Ft int +.Fn mkostemp "char *template" "int flags" +.Ft int +.Fn mkostemps "char *template" "int suffixlen" "int flags" +.Sh DESCRIPTION +The +.Fn mktemp +family of functions take the given file name template and overwrite +a portion of it to create a new file name. +This file name is unique and suitable for use by the application. +The template may be any file name with at least six trailing +.Em X Ns s , +for example +.Pa /tmp/temp.XXXXXXXX . +The trailing +.Em X Ns s +are replaced with a unique digit and letter combination. +The number of unique file names that can be returned +depends on the number of +.Em X Ns s +provided; +.Fn mktemp +will try at least 2 ** 31 combinations before giving up. +At least six +.Em X Ns s +must be used, though 10 is much better. +.Pp +The +.Fn mktemp +function generates a temporary file name based on a template as +described above. +Because +.Fn mktemp +does not actually create the temporary file, there is a window of +opportunity during which another process can open the file instead. +Because of this race condition, +.Fn mktemp +should not be used where +.Fn mkstemp +can be used instead. +.Fn mktemp +was marked as a legacy interface in +.St -p1003.1-2001 . +.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 mkostemp +function acts the same as +.Fn mkstemp , +except that the +.Fa flags +argument may contain zero or more of the following flags for the underlying +.Xr open 2 +system call: +.Pp +.Bl -tag -width "O_CLOEXECXX" -offset indent -compact +.It Dv O_APPEND +Append on each write. +.It Dv O_CLOEXEC +Set the close-on-exec flag on the new file descriptor. +.It Dv O_CLOFORK +Set the close-on-fork flag on the new file descriptor. +.It Dv O_SYNC +Perform synchronous I/O operations. +.El +.Pp +The +.Fn mkstemps +and +.Fn mkostemps +functions act the same as +.Fn mkstemp +and +.Fn mkostemp , +except they permit a suffix to exist in the template. +The template should be of the form +.Pa /tmp/tmpXXXXXXXXXXsuffix . +.Fn mkstemps +and +.Fn mkostemps +are told the length of the suffix string, i.e., +.Li strlen("suffix") . +.Pp +The +.Fn mkdtemp +function makes the same replacement to the template as in +.Fn mktemp +and creates the template directory, mode 0700. +The +.Fn mkdtemps +function acts the same as +.Fn mkdtemp , +except that it permits a suffix to exist in the template, +similar to +.Fn mkstemps . +.Sh RETURN VALUES +The +.Fn mktemp , +.Fn mkdtemp , +and +.Fn mkdtemps +functions return a pointer to the template on success and +.Dv NULL +on failure. +The +.Fn mkstemp , +.Fn mkstemps , +.Fn mkostemp , +and +.Fn mkostemps +functions return \-1 if no suitable file could be created. +If any call fails, an error code is placed in the global variable +.Va errno . +.Sh EXAMPLES +Quite often a programmer will want to replace a use of +.Fn mktemp +with +.Fn mkstemp , +usually to avoid the problems described above. +Doing this correctly requires a good understanding of the code in question. +.Pp +For instance, code of this form: +.Bd -literal -offset indent +char sfn[19]; +FILE *sfp; + +strlcpy(sfn, "/tmp/ed.XXXXXXXXXX", sizeof(sfn)); +if (mktemp(sfn) == NULL || (sfp = fopen(sfn, "w+")) == NULL) { + warn("%s", sfn); + return (NULL); +} +return (sfp); +.Ed +.Pp +should be rewritten like this: +.Bd -literal -offset indent +char sfn[19]; +FILE *sfp; +int fd; + +strlcpy(sfn, "/tmp/ed.XXXXXXXXXX", sizeof(sfn)); +if ((fd = mkstemp(sfn)) == -1 || + (sfp = fdopen(fd, "w+")) == NULL) { + if (fd != -1) { + unlink(sfn); + close(fd); + } + warn("%s", sfn); + return (NULL); +} +return (sfp); +.Ed +.Pp +Often one will find code which uses +.Fn mktemp +very early on, perhaps to globally initialize the template nicely, but the +code which calls +.Xr open 2 +or +.Xr fopen 3 +on that file name will occur much later. +(In almost all cases, the use of +.Xr fopen 3 +will mean that the flags +.Dv O_CREAT +| +.Dv O_EXCL +are not given to +.Xr open 2 , +and thus a symbolic link race becomes possible, hence making +necessary the use of +.Xr fdopen 3 +as seen above.) +Furthermore, one must be careful about code which opens, closes, and then +re-opens the file in question. +Finally, one must ensure that upon error the temporary file is +removed correctly. +.Pp +There are also cases where modifying the code to use +.Fn mktemp , +in concert with +.Xr open 2 +using the flags +.Dv O_CREAT +| +.Dv O_EXCL , +is better, as long as the code retries a new template if +.Xr open 2 +fails with an +.Va errno +of +.Er EEXIST . +.Sh ERRORS +The +.Fn mktemp , +.Fn mkstemp , +.Fn mkdtemp , +and +.Fn mkostemp +functions may set +.Va errno +to one of the following values: +.Bl -tag -width Er +.It Bq Er EINVAL +The +.Ar template +argument has fewer than six trailing +.Em X Ns s . +.It Bq Er EEXIST +All file names tried are already in use. +Consider appending more +.Em X Ns s to the +.Ar template . +.El +.Pp +The +.Fn mkstemps +and +.Fn mkostemps +functions may set +.Va errno +to +.Bl -tag -width Er +.It Bq Er EINVAL +The +.Ar template +argument length is less than +.Ar suffixlen +or it has fewer than six +.Em X Ns s +before the suffix. +.It Bq Er EEXIST +All file names tried are already in use. +Consider appending more +.Em X Ns s to the +.Ar template . +.El +.Pp +In addition, the +.Fn mkostemp +and +.Fn mkostemps +functions may also set +.Va errno +to +.Bl -tag -width Er +.It Bq Er EINVAL +.Fa flags +is invalid. +.El +.Pp +The +.Fn mktemp +function may also set +.Va errno +to any value specified by the +.Xr lstat 2 +function. +.Pp +The +.Fn mkstemp , +.Fn mkstemps , +.Fn mkostemp , +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 SEE ALSO +.Xr chmod 2 , +.Xr lstat 2 , +.Xr mkdir 2 , +.Xr open 2 , +.Xr tempnam 3 , +.Xr tmpfile 3 , +.Xr tmpnam 3 +.Sh STANDARDS +The +.Fn mkstemp , +.Fn mkdtemp , +and +.Fn mkostemp +functions conform to the +.St -p1003.1-2024 +specification. +The ability to specify more than six +.Em X Ns s +is an extension to that standard. +.Pp +The +.Fn mktemp +function conforms to +.St -p1003.1-2001 ; +as of +.St -p1003.1-2008 +it is no longer a part of the standard. +.Pp +The +.Fn mkstemps , +.Fn mkdtemps , +and +.Fn mkostemps +functions are non-standard and should not be used if portability is required. +.Sh HISTORY +A +.Fn mktemp +function appeared in +.At v7 . +The +.Fn mkstemp +function appeared in +.Bx 4.3 . +The +.Fn mkdtemp +function appeared in +.Ox 2.2 . +The +.Fn mkstemps +function appeared in +.Ox 2.3 . +The +.Fn mkostemp +and +.Fn mkostemps +functions appeared in +.Ox 5.7 . +The +.Fn mkdtemps +function appeared in +.Ox 7.5 . +.Sh BUGS +For +.Fn mktemp +there is an obvious race between file name selection and file +creation and deletion: the program is typically written to call +.Xr tmpnam 3 , +.Xr tempnam 3 , +or +.Fn mktemp . +Subsequently, the program calls +.Xr open 2 +or +.Xr fopen 3 +and erroneously opens a file (or symbolic link, FIFO or other +device) that the attacker has created in the expected file location. +Hence +.Fn mkstemp +is recommended, since it atomically creates the file. +An attacker can guess the file names produced by +.Fn mktemp . +Whenever it is possible, +.Fn mkstemp +or +.Fn mkdtemp +should be used instead. +.Pp +For this reason, +.Xr ld 1 +will output a warning message whenever it links code that uses +.Fn mktemp . |
