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NICE(1P) POSIX Programmer's Manual NICE(1P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
nice — invoke a utility with an altered nice value
nice [−n increment] utility [argument...]
The nice utility shall invoke a utility, requesting that it be run
with a different nice value (see the Base Definitions volume of
POSIX.1‐2008, Section 3.240, Nice Value). With no options, the
executed utility shall be run with a nice value that is some
implementation-defined quantity greater than or equal to the nice
value of the current process. If the user lacks appropriate
privileges 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.
The nice utility shall conform to the Base Definitions volume of
POSIX.1‐2008, 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.
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
Section 2.14, 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 operand.
Not used.
None.
The following environment variables shall affect the execution of
nice:
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base Definitions
volume of POSIX.1‐2008, Section 8.2, Internationalization
Variables for the precedence of internationalization
variables used to determine the values of locale
categories.)
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 messages 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 POSIX.1‐2008,
Chapter 8, Environment Variables.
Default.
Not used.
The standard error shall be used only for diagnostic messages.
None.
None.
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.
Default.
The following sections are informative.
The only guaranteed portable uses of this utility are:
nice utility
Run utility with the default higher or equal nice value.
nice −n <positive integer> utility
Run utility with a higher 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 <positive 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 similar 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
distinction 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 reason.
None.
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 negative
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. The standard specifies the System V behavior together with
an optional BSD-style ``permission denied'' message.
The C shell has a built-in version of nice that has a different
interface from the one described in this volume of POSIX.1‐2008.
The term ``utility'' is used, rather than ``command'', to highlight
the fact that shell compound commands, pipelines, and so on, cannot
be used. Special built-ins also cannot be used. However, ``utility''
includes user application programs and shell scripts, not just
utilities defined in this volume of POSIX.1‐2008.
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 raise 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 determined 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 POSIX.1‐2008 make the notion of a single
underlying priority for all scheduling policies problematic. Some
implementations may implement the nice-related features to affect all
processes on the system, others to affect just the general time-
sharing activities implied by this volume of POSIX.1‐2008, and others
may have no effect at all. Because of the use of ``implementation-
defined'' in nice and renice, a wide range of implementation
strategies are possible.
Earlier versions of this standard allowed a −increment option. This
form is no longer specified by POSIX.1‐2008 but may be present in
some implementations.
None.
Chapter 2, Shell Command Language, renice(1p)
The Base Definitions volume of POSIX.1‐2008, Section 3.240, Nice
Value, Chapter 8, Environment Variables, Section 12.2, Utility Syntax
Guidelines
The System Interfaces volume of POSIX.1‐2008, nice(3p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 NICE(1P)
Pages that refer to this page: ps(1p), renice(1p)