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NICE(1P)                   POSIX Programmer's Manual                  NICE(1P)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (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 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-argu-
              ment.


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  prece-
              dence 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  exam-
              ple, 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 writ-
              ten 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 num-
       bers 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 dis-
       tinction 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  con-
       sidered 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, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  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 Stan-
       dard,  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(1P)