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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 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
       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  incre-
              ment option-argument.

OPERANDS
       The following operands shall be supported:
       utility
              The  name of a utility that is to be invoked. If the utility op-
              erand 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 util-
              ity 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  Vari-
              ables  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
              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 fol-
       lowing 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  num-
       ber  that  is  too high, users without access to the system conformance
       document (to see what limits are actually in place) could use the  his-
       torical  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  val-
       ues  for "normal error conditions" and the values above 128 can be con-
       fused 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 differ-
       entiating 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
       Due to the text about the limits of the nice  value  being  implementa-
       tion-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. Nei-
       ther was considered clearly superior, so the behavior was left unspeci-
       fied.
       The C shell has a built-in version of nice that has a different  inter-
       face 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  utili-
       ties 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 util-
       ity 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 pro-
       cesses in a system have priorities  that  are  comparable.   Scheduling
       policy  extensions such as the realtime priorities in the System Inter-
       faces volume of IEEE Std 1003.1-2001 make the notion of a single under-
       lying  priority for all scheduling policies problematic. Some implemen-
       tations may implement the nice-related features to affect all processes
       on  the  system, others to affect just the general time-sharing activi-
       ties 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  pos-
       sible.
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,  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 .

IEEE/The Open Group                  2003                             NICE(1P)