nice —
execute a utility with an altered scheduling priority
  
    | nice | [ -nincrement]
      utility [argument ...] | 
nice runs utility at an altered
  scheduling priority. If an increment is given, it is
  used; otherwise an increment of 10 is assumed. The super-user can run
  utilities with priorities higher than normal by using a negative
  increment. The priority can be adjusted over a range of
  -20 (the highest) to 20 (the lowest). A priority of 19 or 20 will prevent a
  process from taking any cycles from others at nice 0 or better.
Available options:
  - -nincrement
- A positive or negative decimal integer used to modify the system
      scheduling priority of utility.
Thenice utility exits with one of the following values:
  - 1-125
- An error occurred in the niceutility.
- 126
- The utility was found but could not be invoked.
- 127
- The utility could not be found.
Otherwise, the exit status of nice will be
    that of utility.
The historic -increment option has
  been deprecated but is still supported in this implementation.
The nice utility conforms to IEEE Std
  1003.2-1992 (“POSIX.2”).
A nice utility appeared in
  Version 6 AT&T UNIX.
nice is built into
  csh(1) with a slightly different
  syntax than described here. The form ‘nice
  +10’ nices to positive nice, and ‘nice
  -10’ can be used by the super-user to give a process more of the
  processor.