shell advanced techniques - change process priority command (nice and renice)

The Shell command is the most common use: nice [-n <Priority>] [execute instructions], wherein the priority range from -20-19, wherein -20 maximum, 19 minimum, only the system administrator can set negative level. `` `???

    #后台执行sleep 100秒，同时在启动时将其nice值置为19
    [root@xieqichao ~]# nice -n 19 sleep 100 &
    [1] 4661
    #后台执行sleep 100秒，同时在启动时将其nice值置为-19
    [root@xieqichao ~]# nice -n -19 sleep 100 &
    [2] 4664
    #关注ps -l输出中用黄色高亮的两行，它们的NI值和我们执行是设置的值一致。
    [root@xieqichao ~]# ps -l
    F S   UID   PID  PPID  C PRI  NI  ADDR  SZ    WCHAN  TTY       TIME        CMD
    4 S     0  2833  2829  0  80   0     -      1739     -         pts/2    00:00:00  bash
    0 S     0  4661  2833  0  99  19    -      1066     -         pts/2    00:00:00  sleep
    4 S     0  4664  2833  0  61 -19    -      1066     -         pts/2    00:00:00  sleep
    4 R     0  4665  2833  1  80   0     -      1231     -         pts/2    00:00:00  ps

renice command is used to reset nice value for the process has been carried out, the order contains several of the following common options:

Options	Explanation
-g	Using the program group name, modify the priority of all programs belonging to the group of programs.
-p	Changing the priority level of the program, this parameter is a preset value.
-u	Specify the user name, all belonging to modify the priority of the user program.

    #切换到stephen用户下执行一个后台进程，这里sleep进程将在后台睡眠1000秒。
    [root@xieqichao ~]# su stephen
    [root@xieqichao ~]# sleep 1000&  
    [1] 4812
    [root@xieqichao ~]# exit   #退回到切换前的root用户
    #查看已经启动的后台sleep进程，其ni值为0，宿主用户为stephen
    [root@xieqichao ~]# ps -eo user,pid,ni,command | grep stephen
    stephen   4812   0 sleep 1000
    root        4821    0 grep  stephen
    #以指定用户的方式修改该用户下所有进程的nice值
    [root@xieqichao ~]# renice -n 5 -u stephen
    500: old priority 0, new priority 5
    #从再次执行ps的输出结果可以看出，该sleep后台进程的nice值已经调成了5
    [root@xieqichao ~]# ps -eo user,pid,ni,command | grep stephen
    stephen   4812   5 sleep 1000
    root         4826   0 grep  stephen
    #以指定进程pid的方式修改该进程的nice值
    [root@xieqichao ~]# renice -n 10 -p 4812
    4812: old priority 5, new priority 10
    #再次执行ps，该sleep后台进程的nice值已经从5变成了10
    [root@xieqichao ~]# ps -eo user,pid,ni,command | grep stephen
    stephen   4812  10 sleep 1000
    root        4829   0 grep  stephen