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
12 umask — get or set the file mode creation mask
13
15 umask [-S] [mask]
16
18 The umask utility shall set the file mode creation mask of the current
19 shell execution environment (see Section 2.12, Shell Execution Environ‐
20 ment) to the value specified by the mask operand. This mask shall
21 affect the initial value of the file permission bits of subsequently
22 created files. If umask is called in a subshell or separate utility
23 execution environment, such as one of the following:
24 (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.1‐2017, 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.1‐2017, 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>,
123 <other permissions>
124 where the three values shall be combinations of letters from the set
126 {r, w, x}; the presence of a letter shall indicate that the correspond‐
127 ing bit is clear in the file mode creation mask.
128 If a mask operand is specified, there shall be no output written to
130 standard output.
131
133 The standard error shall be used only for diagnostic messages.
134
136 None.
137
139 None.
140
142 The following exit values shall be returned:
143 0 The file mode creation mask was successfully changed, or no mask
145 operand was supplied.
146 >0 An error occurred.
148
150 Default.
151 The following sections are informative.
153
155 Since umask affects the current shell execution environment, it is gen‐
156 erally provided as a shell regular built-in.
157 In contrast to the negative permission logic provided by the file mode
159 creation mask and the octal number form of the mask argument, the sym‐
160 bolic form of the mask argument specifies those permissions that are
161 left alone.
162
164 Either of the commands:
165 umask a=rx,ug+w
168 umask 002
170 sets the mode mask so that subsequently created files have their
172 S_IWOTH bit cleared.
173 After setting the mode mask with either of the above commands, the
175 umask command can be used to write out the current value of the mode
176 mask:
177 $ umask
180 0002
181 (The output format is unspecified, but historical implementations use
183 the octal integer mode format.)
184 $ umask -S
187 u=rwx,g=rwx,o=rx
188 Either of these outputs can be used as the mask operand to a subsequent
190 invocation of the umask utility.
191 Assuming the mode mask is set as above, the command:
193 umask g-w
196 sets the mode mask so that subsequently created files have their
198 S_IWGRP and S_IWOTH bits cleared.
199 The command:
201 umask -- -w
204 sets the mode mask so that subsequently created files have all their
206 write bits cleared. Note that mask operands -r, -w, -x or anything
207 beginning with a <hyphen-minus>, must be preceded by "--" to keep it
208 from being interpreted as an option.
209
211 Since umask affects the current shell execution environment, it is gen‐
212 erally provided as a shell regular built-in. If it is called in a sub‐
213 shell or separate utility execution environment, such as one of the
214 following:
215 (umask 002)
218 nohup umask ...
219 find . -exec umask ... \;
220 it does not affect the file mode creation mask of the environment of
222 the caller.
223 The description of the historical utility was modified to allow it to
225 use the symbolic modes of chmod. The -s option used in early proposals
226 was changed to -S because -s could be confused with a symbolic_mode
227 form of mask referring to the S_ISUID and S_ISGID bits.
228 The default output style is unspecified to permit implementors to pro‐
230 vide migration to the new symbolic style at the time most appropriate
231 to their users. A -o flag to force octal mode output was omitted
232 because the octal mode may not be sufficient to specify all of the
233 information that may be present in the file mode creation mask when
234 more secure file access permission checks are implemented.
235 It has been suggested that trusted systems developers might appreciate
237 ameliorating the requirement that the mode mask ``affects'' the file
238 access permissions, since it seems access control lists might replace
239 the mode mask to some degree. The wording has been changed to say that
240 it affects the file permission bits, and it leaves the details of the
241 behavior of how they affect the file access permissions to the descrip‐
242 tion in the System Interfaces volume of POSIX.1‐2017.
243
245 None.
246
248 Chapter 2, Shell Command Language, chmod
249 The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment
251 Variables, Section 12.2, Utility Syntax Guidelines
252 The System Interfaces volume of POSIX.1‐2017, umask()
254
256 Portions of this text are reprinted and reproduced in electronic form
257 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
258 table Operating System Interface (POSIX), The Open Group Base Specifi‐
259 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
260 Electrical and Electronics Engineers, Inc and The Open Group. In the
261 event of any discrepancy between this version and the original IEEE and
262 The Open Group Standard, the original IEEE and The Open Group Standard
263 is the referee document. The original Standard can be obtained online
264 at http://www.opengroup.org/unix/online.html .
265 Any typographical or formatting errors that appear in this page are
267 most likely to have been introduced during the conversion of the source
268 files to man page format. To report such errors, see https://www.ker‐
269 nel.org/doc/man-pages/reporting_bugs.html .
270IEEE/The Open Group 2017 UMASK(1P)