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PROGRAM:

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 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.

OPTIONS

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.

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 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.

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 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.

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 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.

EXAMPLES

None.

RATIONALE

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.

FUTURE DIRECTIONS

None.

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