.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "NICE" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" nice 
.SH NAME
nice \- invoke a utility with an altered nice value
.SH SYNOPSIS
.LP
\fBnice\fP \fB[\fP\fB-n\fP \fIincrement\fP\fB]\fP \fIutility\fP
\fB[\fP\fIargument\fP\fB...\fP\fB]\fP\fB\fP
.SH DESCRIPTION
.LP
The \fInice\fP 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 \fInice\fP
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 \fIutility\fP or affect the exit
status.
.SH OPTIONS
.LP
The \fInice\fP utility shall conform to the Base Definitions volume
of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
.LP
The following option is supported:
.TP 7
\fB-n\ \fP \fIincrement\fP
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 \fInice\fP() function with the numeric value of the \fIincrement\fP
option-argument.
.sp
.SH OPERANDS
.LP
The following operands shall be supported:
.TP 7
\fIutility\fP
The name of a utility that is to be invoked. If the \fIutility\fP
operand names any of the special built-in utilities in \fISpecial
Built-In Utilities\fP , the results are undefined.
.TP 7
\fIargument\fP
Any string to be supplied as an argument when invoking the utility
named by the \fIutility\fP operand.
.sp
.SH STDIN
.LP
Not used.
.SH INPUT FILES
.LP
None.
.SH ENVIRONMENT VARIABLES
.LP
The following environment variables shall affect the execution of
\fInice\fP:
.TP 7
\fILANG\fP
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.)
.TP 7
\fILC_ALL\fP
If set to a non-empty string value, override the values of all the
other internationalization variables.
.TP 7
\fILC_CTYPE\fP
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).
.TP 7
\fILC_MESSAGES\fP
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard
error.
.TP 7
\fINLSPATH\fP
Determine the location of message catalogs for the processing of \fILC_MESSAGES
\&.\fP 
.TP 7
\fIPATH\fP
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.
.sp
.SH ASYNCHRONOUS EVENTS
.LP
Default.
.SH STDOUT
.LP
Not used.
.SH STDERR
.LP
The standard error shall be used only for diagnostic messages.
.SH OUTPUT FILES
.LP
None.
.SH EXTENDED DESCRIPTION
.LP
None.
.SH EXIT STATUS
.LP
If \fIutility\fP is invoked, the exit status of \fInice\fP shall be
the exit status of \fIutility\fP; otherwise, the
\fInice\fP utility shall exit with one of the following values:
.TP 7
1-125
An error occurred in the \fInice\fP utility.
.TP 7
\ \ 126
The utility specified by \fIutility\fP was found but could not be
invoked.
.TP 7
\ \ 127
The utility specified by \fIutility\fP could not be found.
.sp
.SH CONSEQUENCES OF ERRORS
.LP
Default.
.LP
\fIThe following sections are informative.\fP
.SH APPLICATION USAGE
.LP
The only guaranteed portable uses of this utility are:
.TP 7
\fInice\ utility\fP
.sp
Run \fIutility\fP with the default lower nice value.
.TP 7
\fInice\ \fP \fB-n\ \fP <\fIpositive\ integer\fP>\fI\ utility\fP
.sp
Run \fIutility\fP with a lower nice value.
.sp
.LP
On some implementations they have no discernible effect on the invoked
utility and on some others they are exactly
equivalent.
.LP
Historical systems have frequently supported the <\fIpositive integer\fP>
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.
.LP
The nice value of a process can be displayed using the command:
.sp
.RS
.nf

\fBps -o nice
\fP
.fi
.RE
.LP
The \fIcommand\fP, \fIenv\fP, \fInice\fP, \fInohup\fP, \fItime\fP,
and \fIxargs\fP 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
\fIexec\fP the utility fail with [ENOENT], and uses 126 when any attempt
to \fIexec\fP the utility fails for any other
reason.
.SH EXAMPLES
.LP
None.
.SH RATIONALE
.LP
Due to the text about the limits of the nice value being implementation-defined,
\fInice\fP 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.
.LP
The 4.3 BSD version of \fInice\fP does not check whether \fIincrement\fP
is a valid decimal integer. The command \fInice\fP
\fB-x\fP \fIutility\fP, for example, would be treated the same as
the command \fInice\fP \fB--1\fP \fIutility\fP. If the user
does not have appropriate privileges, this results in a "permission
denied" error. This is considered a bug.
.LP
When a user without appropriate privileges gives a negative \fIincrement\fP,
System V treats it like the command \fInice\fP
\fB-0\fP \fIutility\fP, 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.
.LP
The C shell has a built-in version of \fInice\fP that has a different
interface from the one described in this volume of
IEEE\ Std\ 1003.1-2001.
.LP
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.
.LP
Historical implementations of \fInice\fP 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.
.LP
Some historical documentation states that the \fIincrement\fP value
must be within a fixed range. This is misleading; the valid
\fIincrement\fP values on any invocation are determined by the current
process nice value, which is not always the default.
.LP
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
\fInice\fP-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 \fInice\fP and \fIrenice\fP, a wide range
of implementation
strategies are possible.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIShell Command Language\fP , \fIrenice\fP , the System
Interfaces volume of IEEE\ Std\ 1003.1-2001, \fInice\fP()
.SH 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 .