1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
|
nice(P) nice(P)
NAME
nice - invoke a utility with an altered nice value
SYNOPSIS
nice [-n increment] utility [argument...]
DESCRIPTION
The nice utility shall invoke a utility, requesting that
it be run with a different nice value (see the Base Def-
initions volume of IEEE Std 1003.1-2001, Section 3.239,
Nice Value). With no options and only if the user has
appropriate privileges, the executed utility shall be
run with a nice value that is some implementation-
defined quantity less than or equal to the nice value of
the current process. If the user lacks appropriate priv-
ileges to affect the nice value in the requested manner,
the nice utility shall not affect the nice value; in
this case, a warning message may be written to standard
error, but this shall not prevent the invocation of
utility or affect the exit status.
OPTIONS
The nice utility shall conform to the Base Definitions
volume of IEEE Std 1003.1-2001, Section 12.2, Utility
Syntax Guidelines.
The following option is supported:
-n increment
A positive or negative decimal integer which
shall have the same effect on the execution of
the utility as if the utility had called the
nice() function with the numeric value of the
increment option-argument.
OPERANDS
The following operands shall be supported:
utility
The name of a utility that is to be invoked. If
the utility operand names any of the special
built-in utilities in Special Built-In Utilities
, the results are undefined.
argument
Any string to be supplied as an argument when
invoking the utility named by the utility oper-
and.
STDIN
Not used.
INPUT FILES
None.
ENVIRONMENT VARIABLES
The following environment variables shall affect the
execution of nice:
LANG Provide a default value for the internationaliza-
tion variables that are unset or null. (See the
Base Definitions volume of IEEE Std 1003.1-2001,
Section 8.2, Internationalization Variables for
the precedence of internationalization variables
used to determine the values of locale cate-
gories.)
LC_ALL If set to a non-empty string value, override the
values of all the other internationalization
variables.
LC_CTYPE
Determine the locale for the interpretation of
sequences of bytes of text data as characters
(for example, single-byte as opposed to multi-
byte characters in arguments).
LC_MESSAGES
Determine the locale that should be used to
affect the format and contents of diagnostic mes-
sages written to standard error.
NLSPATH
Determine the location of message catalogs for
the processing of LC_MESSAGES .
PATH Determine the search path used to locate the
utility to be invoked. See the Base Definitions
volume of IEEE Std 1003.1-2001, Chapter 8, Envi-
ronment Variables.
ASYNCHRONOUS EVENTS
Default.
STDOUT
Not used.
STDERR
The standard error shall be used only for diagnostic
messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
If utility is invoked, the exit status of nice shall be
the exit status of utility; otherwise, the nice utility
shall exit with one of the following values:
1-125 An error occurred in the nice utility.
126 The utility specified by utility was found but
could not be invoked.
127 The utility specified by utility could not be
found.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
The only guaranteed portable uses of this utility are:
nice utility
Run utility with the default lower nice value.
nice -n <positive integer> utility
Run utility with a lower nice value.
On some implementations they have no discernible effect
on the invoked utility and on some others they are
exactly equivalent.
Historical systems have frequently supported the <posi-
tive integer> up to 20. Since there is no error penalty
associated with guessing a number that is too high,
users without access to the system conformance document
(to see what limits are actually in place) could use the
historical 1 to 20 range or attempt to use very large
numbers if the job should be truly low priority.
The nice value of a process can be displayed using the
command:
ps -o nice
The command, env, nice, nohup, time, and xargs utilities
have been specified to use exit code 127 if an error
occurs so that applications can distinguish "failure to
find a utility" from "invoked utility exited with an
error indication". The value 127 was chosen because it
is not commonly used for other meanings; most utilities
use small values for "normal error conditions" and the
values above 128 can be confused with termination due to
receipt of a signal. The value 126 was chosen in a simi-
lar manner to indicate that the utility could be found,
but not invoked. Some scripts produce meaningful error
messages differentiating the 126 and 127 cases. The dis-
tinction between exit codes 126 and 127 is based on
KornShell practice that uses 127 when all attempts to
exec the utility fail with [ENOENT], and uses 126 when
any attempt to exec the utility fails for any other rea-
son.
EXAMPLES
None.
RATIONALE
Due to the text about the limits of the nice value being
implementation-defined, nice is not actually required to
change the nice value of the executed command; the lim-
its could be zero differences from the system default,
although the implementor is required to document this
fact in the conformance document.
The 4.3 BSD version of nice does not check whether
increment is a valid decimal integer. The command nice
-x utility, for example, would be treated the same as
the command nice --1 utility. If the user does not have
appropriate privileges, this results in a "permission
denied" error. This is considered a bug.
When a user without appropriate privileges gives a nega-
tive increment, System V treats it like the command nice
-0 utility, while 4.3 BSD writes a "permission denied"
message and does not run the utility. Neither was con-
sidered clearly superior, so the behavior was left
unspecified.
The C shell has a built-in version of nice that has a
different interface from the one described in this
volume of IEEE Std 1003.1-2001.
The term "utility" is used, rather than "command", to
highlight the fact that shell compound commands, pipe-
lines, and so on, cannot be used. Special built-ins also
cannot be used. However, "utility" includes user appli-
cation programs and shell scripts, not just utilities
defined in this volume of IEEE Std 1003.1-2001.
Historical implementations of nice provide a nice value
range of 40 or 41 discrete steps, with the default nice
value being the midpoint of that range. By default, they
lower the nice value of the executed utility by 10.
Some historical documentation states that the increment
value must be within a fixed range. This is misleading;
the valid increment values on any invocation are deter-
mined by the current process nice value, which is not
always the default.
The definition of nice value is not intended to suggest
that all processes in a system have priorities that are
comparable. Scheduling policy extensions such as the
realtime priorities in the System Interfaces volume of
IEEE Std 1003.1-2001 make the notion of a single under-
lying priority for all scheduling policies problematic.
Some implementations may implement the nice-related fea-
tures to affect all processes on the system, others to
affect just the general time-sharing activities implied
by this volume of IEEE Std 1003.1-2001, and others may
have no effect at all. Because of the use of "implemen-
tation-defined" in nice and renice, a wide range of
implementation strategies are possible.
FUTURE DIRECTIONS
None.
SEE ALSO
Shell Command Language , renice , the System Interfaces
volume of IEEE Std 1003.1-2001, nice()
COPYRIGHT
Portions of this text are reprinted and reproduced in
electronic form from IEEE Std 1003.1, 2003 Edition,
Standard for Information Technology -- Portable Operat-
ing System Interface (POSIX), The Open Group Base Speci-
fications Issue 6, Copyright (C) 2001-2003 by the Insti-
tute 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.open-
group.org/unix/online.html .
POSIX 2003 nice(P)
|
