1UMASK(P) POSIX Programmer's Manual UMASK(P)
2
6 umask - get or set the file mode creation mask
7
9 umask [-S][mask]
10
12 The umask utility shall set the file mode creation mask of the current
13 shell execution environment (see Shell Execution Environment ) to the
14 value specified by the mask operand. This mask shall affect the initial
15 value of the file permission bits of subsequently created files. If
16 umask is called in a subshell or separate utility execution environ‐
17 ment, such as one of the following:
18 (umask 002)
21 nohup umask ...
22 find . -exec umask ... \;
23 it shall not affect the file mode creation mask of the caller's envi‐
25 ronment.
26 If the mask operand is not specified, the umask utility shall write to
28 standard output the value of the invoking process' file mode creation
29 mask.
30
32 The umask utility shall conform to the Base Definitions volume of
33 IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
34 The following option shall be supported:
36 -S Produce symbolic output.
38 The default output style is unspecified, but shall be recognized on a
41 subsequent invocation of umask on the same system as a mask operand to
42 restore the previous file mode creation mask.
43
45 The following operand shall be supported:
46 mask A string specifying the new file mode creation mask. The string
48 is treated in the same way as the mode operand described in the
49 EXTENDED DESCRIPTION section for chmod.
50 For a symbolic_mode value, the new value of the file mode creation mask
52 shall be the logical complement of the file permission bits portion of
53 the file mode specified by the symbolic_mode string.
54 In a symbolic_mode value, the permissions op characters '+' and '-'
56 shall be interpreted relative to the current file mode creation mask;
57 '+' shall cause the bits for the indicated permissions to be cleared in
58 the mask; '-' shall cause the bits for the indicated permissions to be
59 set in the mask.
60 The interpretation of mode values that specify file mode bits other
62 than the file permission bits is unspecified.
63 In the octal integer form of mode, the specified bits are set in the
65 file mode creation mask.
66 The file mode creation mask shall be set to the resulting numeric
68 value.
69 The default output of a prior invocation of umask on the same system
71 with no operand also shall be recognized as a mask operand.
72
75 Not used.
76
78 None.
79
81 The following environment variables shall affect the execution of
82 umask:
83 LANG Provide a default value for the internationalization variables
85 that are unset or null. (See the Base Definitions volume of
86 IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari‐
87 ables for the precedence of internationalization variables used
88 to determine the values of locale categories.)
89 LC_ALL If set to a non-empty string value, override the values of all
91 the other internationalization variables.
92 LC_CTYPE
94 Determine the locale for the interpretation of sequences of
95 bytes of text data as characters (for example, single-byte as
96 opposed to multi-byte characters in arguments).
97 LC_MESSAGES
99 Determine the locale that should be used to affect the format
100 and contents of diagnostic messages written to standard error.
101 NLSPATH
103 Determine the location of message catalogs for the processing of
104 LC_MESSAGES .
105
108 Default.
109
111 When the mask operand is not specified, the umask utility shall write a
112 message to standard output that can later be used as a umask mask oper‐
113 and.
114 If -S is specified, the message shall be in the following format:
116 "u=%s,g=%s,o=%s\n", <owner permissions>, <group permissions>,
119 <other permissions>
120 where the three values shall be combinations of letters from the set {
122 r, w, x}; the presence of a letter shall indicate that the correspond‐
123 ing bit is clear in the file mode creation mask.
124 If a mask operand is specified, there shall be no output written to
126 standard output.
127
129 The standard error shall be used only for diagnostic messages.
130
132 None.
133
135 None.
136
138 The following exit values shall be returned:
139 0 The file mode creation mask was successfully changed, or no mask
141 operand was supplied.
142 >0 An error occurred.
144
147 Default.
148 The following sections are informative.
150
152 Since umask affects the current shell execution environment, it is gen‐
153 erally provided as a shell regular built-in.
154 In contrast to the negative permission logic provided by the file mode
156 creation mask and the octal number form of the mask argument, the sym‐
157 bolic form of the mask argument specifies those permissions that are
158 left alone.
159
161 Either of the commands:
162 umask a=rx,ug+w
165 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
178 0002
179 (The output format is unspecified, but historical implementations use
181 the octal integer mode format.)
182 $ umask -S
185 u=rwx,g=rwx,o=rx
186 Either of these outputs can be used as the mask operand to a subsequent
188 invocation of the umask utility.
189 Assuming the mode mask is set as above, the command:
191 umask g-w
194 sets the mode mask so that subsequently created files have their
196 S_IWGRP and S_IWOTH bits cleared.
197 The command:
199 umask -- -w
202 sets the mode mask so that subsequently created files have all their
204 write bits cleared. Note that mask operands -r, -w, -x or anything
205 beginning with a hyphen, must be preceded by "--" to keep it from being
206 interpreted as an option.
207
209 Since umask affects the current shell execution environment, it is gen‐
210 erally provided as a shell regular built-in. If it is called in a sub‐
211 shell or separate utility execution environment, such as one of the
212 following:
213 (umask 002)
216 nohup umask ...
217 find . -exec umask ... \;
218 it does not affect the file mode creation mask of the environment of
220 the caller.
221 The description of the historical utility was modified to allow it to
223 use the symbolic modes of chmod. The -s option used in early proposals
224 was changed to -S because -s could be confused with a symbolic_mode
225 form of mask referring to the S_ISUID and S_ISGID bits.
226 The default output style is implementation-defined to permit implemen‐
228 tors to provide migration to the new symbolic style at the time most
229 appropriate to their users. A -o flag to force octal mode output was
230 omitted because the octal mode may not be sufficient to specify all of
231 the information that may be present in the file mode creation mask when
232 more secure file access permission checks are implemented.
233 It has been suggested that trusted systems developers might appreciate
235 ameliorating the requirement that the mode mask "affects" the file
236 access permissions, since it seems access control lists might replace
237 the mode mask to some degree. The wording has been changed to say that
238 it affects the file permission bits, and it leaves the details of the
239 behavior of how they affect the file access permissions to the descrip‐
240 tion in the System Interfaces volume of IEEE Std 1003.1-2001.
241
243 None.
244
246 Shell Command Language , chmod , the System Interfaces volume of
247 IEEE Std 1003.1-2001, umask()
248
250 Portions of this text are reprinted and reproduced in electronic form
251 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
252 -- Portable Operating System Interface (POSIX), The Open Group Base
253 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
254 Electrical and Electronics Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html .
259IEEE/The Open Group 2003 UMASK(P)