Wed, Apr 22, 2009
When talking about processes priority is all about managing processor time. The Processor or CPU is like a human juggling multiple tasks at the same time. Sometimes we can have enough room to take on multiple projects. Sometimes we can only focus on one thing at a time. Other times something important pops up and we want to devote all of our energy into solving that problem while putting less important tasks on the back burner.
In Linux we can set guidelines for the CPU to follow when it is looking at all the tasks it has to do. These guidelines are called niceness or nice value. The Linux niceness scale goes from -20 to 19. The lower the number the more priority that task gets. If the niceness value is high number like 19 the task will be set to the lowest priority and the CPU will process it whenever it gets a chance. The default nice value is zero.
By using this scale we can allocate our CPU resources more appropriately. Lower priority programs that are not important can be set to a higher nice value, while high priority programs like daemons and services can be set to receive more of the CPU’s focus. You can even give a specific user a lower nice value for all of his/her processes so you can limit their ability to slow down the computer’s core services.
The easiest way to get a quick picture of what the current niceness priority on a process is to open up the top processes with:
top
top
q
h
1 Fields Management for window 1:Def, whose current sort field is %CPU 2 Navigate with Up/Dn, Right selects for move then <Enter> or Left commits, 3 ‘d‘ or <Space> toggles display, ‘s‘ sets sort. Use ‘q‘ or <Esc> to end! 4 5 * PID = Process Id 6 * USER = Effective User Name 7 * PR = Priority 8 * NI = Nice Value 9 * VIRT = Virtual Image (KiB) 10 * RES = Resident Size (KiB) 11 * SHR = Shared Memory (KiB) 12 * S = Process Status 13 * %CPU = CPU Usage 14 * %MEM = Memory Usage (RES) 15 * TIME+ = CPU Time, hundredths 16 * COMMAND = Command Name/Line 17 PPID = Parent Process pid 18 UID = Effective User Id 19 RUID = Real User Id 20 RUSER = Real User Name 21 SUID = Saved User Id 22 SUSER = Saved User Name 23 GID = Group Id 24 GROUP = Group Name 25 PGRP = Process Group Id 26 TTY = Controlling Tty 27 TPGID = Tty Process Grp Id 28 SID = Session Id 29 nTH = Number of Threads 30 P = Last Used Cpu (SMP) 31 TIME = CPU Time 32 SWAP = Swapped Size (KiB) 33 CODE = Code Size (KiB) 34 DATA = Data+Stack (KiB) 35 nMaj = Major Page Faults 36 nMin = Minor Page Faults 37 nDRT = Dirty Pages Count 38 WCHAN = Sleeping in Function 39 Flags = Task Flags <sched.h> 40 CGROUPS = Control Groups 41 SUPGIDS = Supp Groups IDs 42 SUPGRPS = Supp Groups Names 43 TGID = Thread Group Id 44 ENVIRON = Environment vars 45 vMj = Major Faults delta 46 vMn = Minor Faults delta 47 USED = Res+Swap Size (KiB) 48 nsIPC = IPC namespace Inode 49 nsMNT = MNT namespace Inode 50 nsNET = NET namespace Inode 51 nsPID = PID namespace Inode 52 nsUSER = USER namespace Inode 53 nsUTS = UTS namespace Inode
原文：http://www.cnblogs.com/yuanjiangw/p/6238781.html