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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.1‐2008, 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.

COPYRIGHT

       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 .