(coreutils.info.gz) nice invocation

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 23.3 'nice': Run a command with modified niceness
 =================================================
 
 'nice' prints a process's "niceness", or runs a command with modified
 niceness.  "niceness" affects how favorably the process is scheduled in
 the system.  Synopsis:
 
      nice [OPTION]... [COMMAND [ARG]...]
 
    If no arguments are given, 'nice' prints the current niceness.
 Otherwise, 'nice' runs the given COMMAND with its niceness adjusted.  By
 default, its niceness is incremented by 10.
 
    Niceness values range at least from -20 (process has high priority
 and gets more resources, thus slowing down other processes) through 19
 (process has lower priority and runs slowly itself, but has less impact
 on the speed of other running processes).  Some systems may have a wider
 range of niceness values; conversely, other systems may enforce more
 restrictive limits.  An attempt to set the niceness outside the
 supported range is treated as an attempt to use the minimum or maximum
 supported value.
 
    A niceness should not be confused with a scheduling priority, which
 lets applications determine the order in which threads are scheduled to
 run.  Unlike a priority, a niceness is merely advice to the scheduler,
 which the scheduler is free to ignore.  Also, as a point of terminology,
 POSIX defines the behavior of 'nice' in terms of a "nice value", which
 is the nonnegative difference between a niceness and the minimum
 niceness.  Though 'nice' conforms to POSIX, its documentation and
 diagnostics use the term "niceness" for compatibility with historical
 practice.
 
    COMMAND must not be a special built-in utility ( Special
 built-in utilities).
 
    Due to shell aliases and built-in 'nice' functions, using an
 unadorned 'nice' interactively or in a script may get you different
 functionality than that described here.  Invoke it via 'env' (i.e., 'env
 nice ...') to avoid interference from the shell.
 
    Note to change the "niceness" of an existing process, one needs to
 use the 'renice' command.
 
    The program accepts the following option.  Also see  Common
 options.  Options must precede operands.
 
 '-n ADJUSTMENT'
 '--adjustment=ADJUSTMENT'
      Add ADJUSTMENT instead of 10 to the command's niceness.  If
      ADJUSTMENT is negative and you lack appropriate privileges, 'nice'
      issues a warning but otherwise acts as if you specified a zero
      adjustment.
 
      For compatibility 'nice' also supports an obsolete option syntax
      '-ADJUSTMENT'.  New scripts should use '-n ADJUSTMENT' instead.
 
    Exit status:
 
      0   if no COMMAND is specified and the niceness is output
      125 if 'nice' itself fails
      126 if COMMAND is found but cannot be invoked
      127 if COMMAND cannot be found
      the exit status of COMMAND otherwise
 
    It is sometimes useful to run a non-interactive program with reduced
 niceness.
 
      $ nice factor 4611686018427387903
 
    Since 'nice' prints the current niceness, you can invoke it through
 itself to demonstrate how it works.
 
    The default behavior is to increase the niceness by '10':
 
      $ nice
      0
      $ nice nice
      10
      $ nice -n 10 nice
      10
 
    The ADJUSTMENT is relative to the current niceness.  In the next
 example, the first 'nice' invocation runs the second one with niceness
 10, and it in turn runs the final one with a niceness that is 3 more:
 
      $ nice nice -n 3 nice
      13
 
    Specifying a niceness larger than the supported range is the same as
 specifying the maximum supported value:
 
      $ nice -n 10000000000 nice
      19
 
    Only a privileged user may run a process with lower niceness:
 
      $ nice -n -1 nice
      nice: cannot set niceness: Permission denied
      0
      $ sudo nice -n -1 nice
      -1
 
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