mkstemp(3)

1MKSTEMP(3)                 Linux Programmer's Manual                MKSTEMP(3)
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NAME

6       mkstemp, mkostemp, mkstemps, mkostemps - create a unique temporary file
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SYNOPSIS

9       #include <stdlib.h>
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11       int mkstemp(char *template);
12       int mkostemp(char *template, int flags);
13       int mkstemps(char *template, int suffixlen);
14       int mkostemps(char *template, int suffixlen, int flags);
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16   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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18       mkstemp():
19           _XOPEN_SOURCE >= 500
20               || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
21               || /* Glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
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23       mkostemp():
24           _GNU_SOURCE
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26       mkstemps():
27           /* Glibc since 2.19: */ _DEFAULT_SOURCE
28               || /* Glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
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30       mkostemps():
31           _GNU_SOURCE
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DESCRIPTION

34       The  mkstemp() function generates a unique temporary filename from tem‐
35       plate, creates and opens the file, and returns an open file  descriptor
36       for the file.
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38       The  last six characters of template must be "XXXXXX" and these are re‐
39       placed with a string that makes the filename unique.  Since it will  be
40       modified,  template  must  not  be a string constant, but should be de‐
41       clared as a character array.
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43       The file is created with permissions 0600, that is, read plus write for
44       owner  only.  The returned file descriptor provides both read and write
45       access to the file.  The file is opened with the open(2)  O_EXCL  flag,
46       guaranteeing that the caller is the process that creates the file.
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48       The mkostemp() function is like mkstemp(), with the difference that the
49       following bits—with the same meaning as for open(2)—may be specified in
50       flags:  O_APPEND,  O_CLOEXEC,  and O_SYNC.  Note that when creating the
51       file, mkostemp() includes the values O_RDWR, O_CREAT, and O_EXCL in the
52       flags  argument  given  to open(2); including these values in the flags
53       argument given to mkostemp() is unnecessary,  and  produces  errors  on
54       some systems.
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56       The  mkstemps()  function  is like mkstemp(), except that the string in
57       template contains a suffix of suffixlen characters.  Thus, template  is
58       of  the  form  prefixXXXXXXsuffix, and the string XXXXXX is modified as
59       for mkstemp().
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61       The mkostemps() function is to  mkstemps()  as  mkostemp()  is  to  mk‐
62       stemp().
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RETURN VALUE

65       On success, these functions return the file descriptor of the temporary
66       file.  On error, -1 is returned, and errno is set to indicate  the  er‐
67       ror.
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ERRORS

70       EEXIST Could  not create a unique temporary filename.  Now the contents
71              of template are undefined.
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73       EINVAL For mkstemp() and mkostemp(): The last six  characters  of  tem‐
74              plate were not XXXXXX; now template is unchanged.
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76              For  mkstemps() and mkostemps(): template is less than (6 + suf‐
77              fixlen) characters long, or the last  6  characters  before  the
78              suffix in template were not XXXXXX.
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80       These  functions  may  also  fail  with any of the errors described for
81       open(2).
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VERSIONS

84       mkostemp() is available since glibc 2.7.   mkstemps()  and  mkostemps()
85       are available since glibc 2.11.
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ATTRIBUTES

88       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
89       tributes(7).
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91       ┌────────────────────────────────────────────┬───────────────┬─────────┐
92       │Interface                                   │ Attribute     │ Value   │
93       ├────────────────────────────────────────────┼───────────────┼─────────┤
94       │mkstemp(), mkostemp(), mkstemps(),          │ Thread safety │ MT-Safe │
95       │mkostemps()                                 │               │         │
96       └────────────────────────────────────────────┴───────────────┴─────────┘
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CONFORMING TO

99       mkstemp(): 4.3BSD, POSIX.1-2001.
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101       mkstemps(): unstandardized, but appears on several other systems.
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103       mkostemp() and mkostemps(): are glibc extensions.
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NOTES

106       In  glibc  versions  2.06 and earlier, the file is created with permis‐
107       sions 0666, that is, read and write for all users.  This  old  behavior
108       may  be  a security risk, especially since other UNIX flavors use 0600,
109       and  somebody  might  overlook  this  detail  when  porting   programs.
110       POSIX.1-2008  adds  a  requirement  that  the file be created with mode
111       0600.
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113       More generally, the POSIX specification of mkstemp() does not say  any‐
114       thing  about  file  modes, so the application should make sure its file
115       mode creation mask (see umask(2)) is set appropriately  before  calling
116       mkstemp() (and mkostemp()).
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COLOPHON

122       This  page  is  part of release 5.12 of the Linux man-pages project.  A
123       description of the project, information about reporting bugs,  and  the
124       latest     version     of     this    page,    can    be    found    at
125       https://www.kernel.org/doc/man-pages/.
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129GNU                               2021-03-22                        MKSTEMP(3)