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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 Definitions 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 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.
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 operand.
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 internationalization 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
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 IEEE Std 1003.1-2001, Chapter 8, Environment 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 <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.
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 limits 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 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.
Neither was considered 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,
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
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 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 IEEE Std 1003.1-2001 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 IEEE Std 1003.1-2001, 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.
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 Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute 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.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 NICE(P)