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 differ (con-
       sult 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  privi-
       leges,  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-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
              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 precedence  of  international-
              ization 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 stan-
              dard 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 equiv-
       alent.

       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  Korn-
       Shell  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 imple-
       mentor 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  util-
       ity,  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.

       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 compara-
       ble.   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 imple-
       mentations may implement the nice-related features to affect all processes on the system, others to affect just the  gen-
       eral  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  possi-
       ble.

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, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                      NICE(1P)