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       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.

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.1‐2017, Section 3.244, 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.1‐2017,  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.1‐2017,  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.1‐2017, 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.1‐2017.

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.1‐2017.

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.1‐2017 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.1‐2017,
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.

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1-2017, Standard for Information Technology -- Portable  Operating  System  Interface
       (POSIX),  The  Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       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 .