1UMASK(1P) POSIX Programmer's Manual UMASK(1P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
13 umask — get or set the file mode creation mask
14
16 umask [−S] [mask]
17
19 The umask utility shall set the file mode creation mask of the current
20 shell execution environment (see Section 2.12, Shell Execution Environ‐
21 ment) to the value specified by the mask operand. This mask shall
22 affect the initial value of the file permission bits of subsequently
23 created files. If umask is called in a subshell or separate utility
24 execution environment, such as one of the following:
25 (umask 002)
27 nohup umask ...
28 find . −exec umask ... \;
29 it shall not affect the file mode creation mask of the caller's envi‐
31 ronment.
32 If the mask operand is not specified, the umask utility shall write to
34 standard output the value of the file mode creation mask of the invok‐
35 ing process.
36
38 The umask utility shall conform to the Base Definitions volume of
39 POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.
40 The following option shall be supported:
42 −S Produce symbolic output.
44 The default output style is unspecified, but shall be recognized on a
46 subsequent invocation of umask on the same system as a mask operand to
47 restore the previous file mode creation mask.
48
50 The following operand shall be supported:
51 mask A string specifying the new file mode creation mask. The
53 string is treated in the same way as the mode operand
54 described in the EXTENDED DESCRIPTION section for chmod.
55 For a symbolic_mode value, the new value of the file mode
57 creation mask shall be the logical complement of the file
58 permission bits portion of the file mode specified by the
59 symbolic_mode string.
60 In a symbolic_mode value, the permissions op characters '+'
62 and '−' shall be interpreted relative to the current file
63 mode creation mask; '+' shall cause the bits for the indi‐
64 cated permissions to be cleared in the mask; '−' shall cause
65 the bits for the indicated permissions to be set in the mask.
66 The interpretation of mode values that specify file mode bits
68 other than the file permission bits is unspecified.
69 In the octal integer form of mode, the specified bits are set
71 in the file mode creation mask.
72 The file mode creation mask shall be set to the resulting
74 numeric value.
75 The default output of a prior invocation of umask on the same
77 system with no operand also shall be recognized as a mask op‐
78 erand.
79
81 Not used.
82
84 None.
85
87 The following environment variables shall affect the execution of
88 umask:
89 LANG Provide a default value for the internationalization vari‐
91 ables that are unset or null. (See the Base Definitions vol‐
92 ume of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
93 ables for the precedence of internationalization variables
94 used to determine the values of locale categories.)
95 LC_ALL If set to a non-empty string value, override the values of
97 all the other internationalization variables.
98 LC_CTYPE Determine the locale for the interpretation of sequences of
100 bytes of text data as characters (for example, single-byte as
101 opposed to multi-byte characters in arguments).
102 LC_MESSAGES
104 Determine the locale that should be used to affect the format
105 and contents of diagnostic messages written to standard
106 error.
107 NLSPATH Determine the location of message catalogs for the processing
109 of LC_MESSAGES.
110
112 Default.
113
115 When the mask operand is not specified, the umask utility shall write a
116 message to standard output that can later be used as a umask mask oper‐
117 and.
118 If −S is specified, the message shall be in the following format:
120 "u=%s,g=%s,o=%s\n", <owner permissions>, <group permissions>,
122 <other permissions>
123 where the three values shall be combinations of letters from the set
125 {r, w, x}; the presence of a letter shall indicate that the correspond‐
126 ing bit is clear in the file mode creation mask.
127 If a mask operand is specified, there shall be no output written to
129 standard output.
130
132 The standard error shall be used only for diagnostic messages.
133
135 None.
136
138 None.
139
141 The following exit values shall be returned:
142 0 The file mode creation mask was successfully changed, or no mask
144 operand was supplied.
145 >0 An error occurred.
147
149 Default.
150 The following sections are informative.
152
154 Since umask affects the current shell execution environment, it is gen‐
155 erally provided as a shell regular built-in.
156 In contrast to the negative permission logic provided by the file mode
158 creation mask and the octal number form of the mask argument, the sym‐
159 bolic form of the mask argument specifies those permissions that are
160 left alone.
161
163 Either of the commands:
164 umask a=rx,ug+w
166 umask 002
168 sets the mode mask so that subsequently created files have their
170 S_IWOTH bit cleared.
171 After setting the mode mask with either of the above commands, the
173 umask command can be used to write out the current value of the mode
174 mask:
175 $ umask
177 0002
178 (The output format is unspecified, but historical implementations use
180 the octal integer mode format.)
181 $ umask −S
183 u=rwx,g=rwx,o=rx
184 Either of these outputs can be used as the mask operand to a subsequent
186 invocation of the umask utility.
187 Assuming the mode mask is set as above, the command:
189 umask g−w
191 sets the mode mask so that subsequently created files have their
193 S_IWGRP and S_IWOTH bits cleared.
194 The command:
196 umask −− −w
198 sets the mode mask so that subsequently created files have all their
200 write bits cleared. Note that mask operands −r, −w, −x or anything
201 beginning with a <hyphen>, must be preceded by "−−" to keep it from
202 being interpreted as an option.
203
205 Since umask affects the current shell execution environment, it is gen‐
206 erally provided as a shell regular built-in. If it is called in a sub‐
207 shell or separate utility execution environment, such as one of the
208 following:
209 (umask 002)
211 nohup umask ...
212 find . −exec umask ... \;
213 it does not affect the file mode creation mask of the environment of
215 the caller.
216 The description of the historical utility was modified to allow it to
218 use the symbolic modes of chmod. The −s option used in early proposals
219 was changed to −S because −s could be confused with a symbolic_mode
220 form of mask referring to the S_ISUID and S_ISGID bits.
221 The default output style is unspecified to permit implementors to pro‐
223 vide migration to the new symbolic style at the time most appropriate
224 to their users. A −o flag to force octal mode output was omitted
225 because the octal mode may not be sufficient to specify all of the
226 information that may be present in the file mode creation mask when
227 more secure file access permission checks are implemented.
228 It has been suggested that trusted systems developers might appreciate
230 ameliorating the requirement that the mode mask ``affects'' the file
231 access permissions, since it seems access control lists might replace
232 the mode mask to some degree. The wording has been changed to say that
233 it affects the file permission bits, and it leaves the details of the
234 behavior of how they affect the file access permissions to the descrip‐
235 tion in the System Interfaces volume of POSIX.1‐2008.
236
238 None.
239
241 Chapter 2, Shell Command Language, chmod
242 The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
244 Variables, Section 12.2, Utility Syntax Guidelines
245 The System Interfaces volume of POSIX.1‐2008, umask()
247
249 Portions of this text are reprinted and reproduced in electronic form
250 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
251 -- Portable Operating System Interface (POSIX), The Open Group Base
252 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
253 cal and Electronics Engineers, Inc and The Open Group. (This is
254 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
255 event of any discrepancy between this version and the original IEEE and
256 The Open Group Standard, the original IEEE and The Open Group Standard
257 is the referee document. The original Standard can be obtained online
258 at http://www.unix.org/online.html .
259 Any typographical or formatting errors that appear in this page are
261 most likely to have been introduced during the conversion of the source
262 files to man page format. To report such errors, see https://www.ker‐
263 nel.org/doc/man-pages/reporting_bugs.html .
264IEEE/The Open Group 2013 UMASK(1P)