MKDTEMP(3P)

✨ MKDTEMP(3P) ✨ — the POSIX Programmer's Manual page, but make it make sense 💅

okay bestie, this is MKDTEMP(3P) from the POSIX Programmer's Manual, and we're about to have a whole moment about making temp files and dirs that don't collide with anything else. it's giving race-condition-free, it's giving unique names. let's go 🦋

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🎀 PROLOG 🎀

okay so first things first, real talk: this manual page is part of the POSIX Programmer's Manual. the Linux implementation of this interface may differ (so like, go read the corresponding Linux manual page if you need the deets on Linux behavior), or honestly the interface may not be implemented on Linux at all. iykyk. 🙈

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🌸 NAME 🌸

mkdtemp, mkstemp — create a unique directory or file

like. that's the whole vibe. one makes a directory, one makes a file, both make them unique. iconic. 👑

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⭐ SYNOPSIS ⭐

#include <stdlib.h>

char *mkdtemp(char *template);
int mkstemp(char *template);

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🦋 DESCRIPTION 🦋

okay so the mkdtemp() function shall create a directory with a unique name derived from template. and here's the thing — the application shall ensure that the string provided in template is a pathname ending with at least six trailing 'X' characters. that's not optional, bestie, that's the whole mechanism.

then mkdtemp() 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. and 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(). no collisions, periodt.

and then mkdtemp() shall use the resulting pathname to create the new directory as if by a call to:

mkdir(pathname, S_IRWXU)

meanwhile mkstemp() — different function, same energy — 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. same rule applies: the application shall ensure that the string provided in template is a pathname ending with at least six trailing 'X' characters. mkstemp() 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, and those 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().

then mkstemp() 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)

and this part is the main character ✨ — 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. like, nobody can sneak in between your check and your open. she said atomic. 💅

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💖 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. sad girl hours. 😭

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.

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🌈 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. like, you're just not allowed in there bestie.
• EINVAL — the string pointed to by template does not end in "XXXXXX". you had one job 😭
• ELOOP — a loop exists in symbolic links encountered during resolution of the path of the directory to be created. it's giving infinite mirror 🪞
• 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. the disk said no 🍓
• 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. frozen. locked. no notes. 🧊

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}.

heads up bestie: the error conditions for the mkstemp() function are defined in open(). so go peek over there for that one. 👀

and ps — the following sections are informative. (not normative, just vibes. 💜)

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🌸 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);

look at her go. ✨ she's literally just built different.

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💜 APPLICATION USAGE 💜

it is possible to run out of letters. yes, really. that's a real sentence and it's a real warning. the alphabet is finite bestie 😭

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. so to be sure of only passing six, a fixed string of at least one non-'X' character should precede the six 'X's. protect the six. 🫶

and 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. so yeah. the randomness can just... land on X again. it's fine. it's fine!! 💀

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🦋 RATIONALE 🦋

None.

(no thoughts, head empty, the standard simply did not feel like explaining itself today 💅)

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⭐ FUTURE DIRECTIONS ⭐

None.

(nothing coming, nothing planned, no notes. we stay present. 🧘)

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🔥 SEE ALSO 🔥

• getpid()
• mkdir()
• open()
• tmpfile()
• tmpnam()

and also: The Base Definitions volume of POSIX.1‐2017, <stdlib.h> 📚

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👑 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 .

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okay that's the whole page bestie, you ate that 💅✨ this one's IEEE/The Open Group, 2017, and it's still serving <stdlib.h> realness to this very day. go make a temp file, you deserve it 🎀🦋💖