{"id":13893,"date":"2019-04-06T13:54:22","date_gmt":"2019-04-06T13:54:22","guid":{"rendered":"http:\/\/www.appservgrid.com\/paw92\/?p=13893"},"modified":"2019-04-06T13:54:22","modified_gmt":"2019-04-06T13:54:22","slug":"how-to-set-linux-process-priority-using-nice-and-renice-commands","status":"publish","type":"post","link":"https:\/\/www.appservgrid.com\/paw92\/index.php\/2019\/04\/06\/how-to-set-linux-process-priority-using-nice-and-renice-commands\/","title":{"rendered":"How to Set Linux Process Priority Using nice and renice Commands"},"content":{"rendered":"

In this article, we\u2019ll briefly explain the\u00a0kernel scheduler<\/strong>\u00a0(also known as the\u00a0process scheduler<\/strong>), and\u00a0process priority<\/strong>, which are topics beyond the scope of this guide. Then we will dive into a little bit of\u00a0Linux process management<\/a>: see how to run a program or command with modified priority and also change the priority of running Linux processes.<\/p>\n

Read Also:<\/strong>\u00a0How to Monitor Linux Processes and Set Process Limits on a Per-User Basis<\/a><\/p>\n

Understanding the Linux Kernel Scheduler<\/h4>\n

The kernel scheduler is a unit of the kernel that determines the most suitable process out of all runnable processes to execute next; it allocates processor time between the runnable processes on a system. A runnable process is one which is waiting only for CPU time, it\u2019s ready to be executed.<\/p>\n

The scheduler forms the core of multitasking in Linux, using a priority-based scheduling algorithm to choose between the runnable processes in the system. It ranks processes based on the most deserving as well as need for CPU time.<\/p>\n

Understanding Process Priority and Nice Value<\/h4>\n

The kernel stores a great deal of information about processes including process priority which is simply the scheduling priority attached to a process. Processes with a higher priority will be executed before those with a lower priority, while processes with the same priority are scheduled one after the next, repeatedly.<\/p>\n

There are a total of\u00a0140<\/strong>\u00a0priorities and two distinct priority ranges implemented in Linux. The first one is nice value (niceness<\/strong>) which ranges from\u00a0-20<\/code>\u00a0(highest priority value) to\u00a019<\/code>\u00a0(lowest priority value) and the default is\u00a00<\/code>, this is what we will uncover in this guide. The other is the real-time priority, which ranges from\u00a01<\/strong>\u00a0to\u00a099<\/strong>\u00a0by default, then\u00a0100<\/strong>\u00a0to\u00a0139<\/strong>\u00a0are meant for user-space.<\/p>\n

One important characteristic of Linux is dynamic priority-based scheduling, which allows nice value of a processes to be changed (increased or decreased) depending on your needs, as we\u2019ll see later on.<\/p>\n

How to Check Nice Value of Linux Processes<\/h3>\n

To see the nice values of processes, we can use utilities such as\u00a0ps<\/a>,\u00a0top<\/a>\u00a0or\u00a0htop<\/a>.<\/p>\n

To view processes nice value with ps command in user-defined format (here the\u00a0NI<\/code>\u00a0column shows niceness of processes).<\/p>\n

$ ps -eo pid,ppid,ni,comm\r\n<\/pre>\n
\n
\"View<\/p>\n
View Linux Processes Nice Values<\/p>\n<\/div>\n
Alternatively, you can use top or htop utilities to view Linux processes nice values as shown.<\/p>\n
$ top\r\n$ htop\r\n<\/pre>\n
\n
\"Check<\/p>\n
Check Linux Process Nice Values using Top Command<\/p>\n<\/div>\n
\n
\"Check<\/p>\n
Check Linux Process Nice Values using Htop Command<\/p>\n<\/div>\n
Difference Between PR or PRI and NI<\/h4>\n
From the\u00a0top<\/strong>\u00a0and\u00a0htop<\/strong>\u00a0outputs above, you\u2019ll notice that there is a column called\u00a0PR<\/code>\u00a0and\u00a0PRI<\/code>\u00a0receptively which show the priority of a process.<\/p>\n
This therefore means that:<\/p>\n