In this article, we’ll briefly explain the kernel scheduler (also known as the process scheduler), and process priority, which are topics beyond the scope of this guide. Then we will dive into a little bit of Linux process management: see how to run a program or command with modified priority and also change the priority of running Linux processes.
In order to view or change the priority of a running program, you must first determine its PID (Process ID). You can do this by opening the Windows Task Manager and clicking on the ' Processes ' tab. You should then see a list of running processes on your.
![Line Line](/uploads/1/2/6/2/126239978/824612544.png)
Read Also:How to Monitor Linux Processes and Set Process Limits on a Per-User Basis
Understanding the Linux Kernel Scheduler
A 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’s ready to be executed.
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 the need for CPU time.
Understanding Process Priority and Nice Value
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.
There are a total of 140 priorities and two distinct priority ranges implemented in Linux. The first one is a nice value (niceness) which ranges from
-20
(highest priority value) to 19
(lowest priority value) and the default is 0
, this is what we will uncover in this guide. The other is the real-time priority, which ranges from 1 to 99 by default, then 100 to 139 are meant for user-space.One important characteristic of Linux is dynamic priority-based scheduling, which allows the nice value of processes to be changed (increased or decreased) depending on your needs, as we’ll see later on.
How to Check Nice Value of Linux Processes
To see the nice values of processes, we can use utilities such as ps, top or htop.
To view processes nice value with ps command in user-defined format (here the
NI
the column shows the niceness of processes).Alternatively, you can use top or htop utilities to view Linux processes nice values as shown.
Check Linux Process Nice Values using Top Command
Check Linux Process Nice Values using Htop Command
Difference Between PR or PRI and NI
From the top and htop outputs above, you’ll notice that there is a column called
PR
and PRI
receptively which shows the priority of a process.This, therefore, means that:
NI
– is the nice value, which is a user-space concept, whilePR
orPRI
– is the process’s actual priority, as seen by the Linux kernel.
How To Calculate PR or PRI Values
Nice value range (NI): -20 to 19
But if you see a
rt
rather than a number as shown in the screenshot below, it basically means the process is running under real-time scheduling priority.How to Run A Command with a Given Nice Value in Linux
Here, we will look at how to prioritize the CPU usage of a program or command. If you have a very CPU-intensive program or task, but you also understand that it might take a long time to complete, you can set it a high or favorable priority using the nice command.
The syntax is as follows:
Important:
- If no value is provided, nice sets a priority of 10 by default.
- A command or program run without nice defaults to a priority of zero.
- Only root can run a command or program with increased or high priority.
- Normal users can only run a command or program with low priority.
For example, instead of starting a program or command with the default priority, you can start it with a specific priority using following nice command.
You can also use the third method which is a little confusing especially for negative niceness values.
Change the Scheduling Priority of a Process in Linux
As we mentioned before, Linux allows dynamic priority-based scheduling. Therefore, if a program is already running, you can change its priority with the renice command in this form:
Change Process Priority
From the sample top output below, the niceness of the teamspe+ with PID 1055 is now
-12
and for all processes owned by user apache is -2
.Still using this output, you can see the formula PR = 20 + NI stands,
Any changes you make with renice command to a user’s processes nice values are only applicable until the next reboot. To set permanent default values, read the next section.
How To Set Default Nice Value Of a Specific User’s Processes
You can set the default nice value of a particular user or group in the /etc/security/limits.conf file. Its primary function is to define the resource limits for the users logged in via PAM.
The syntax for defining a limit for a user is as follows (and the possible values of the various columns are explained in the file):
Now use the syntax below where hard – means enforcing hard links and soft means – enforcing the soft limits.
Alternatively, create a file under /etc/security/limits.d/ which overrides settings in the main file above, and these files are read in alphabetical order.
Start by creating the file /etc/security/limits.d/tecmint-priority.conf for user tecmint:
Then add this configuration in it:
Save and close the file. From now on, any process owned by tecmint will have a nice value of 10 and PR of 30.
For more information, read the man pages of nice and renice:
You might also like to read these following articles about Linux process management.
![Process Process](/uploads/1/2/6/2/126239978/141429060.jpg)
In this article, we briefly explained the kernel scheduler, process priority, looked at how to run a program or command with modified priority and also change the priority of active Linux processes. You can share any thoughts regarding this topic via the feedback form below.
You can start programs with a specific process priority via the Windows command prompt (cmd.exe), with help from the START command!Here are the solutions for Windows 10, 8, 8.1, 7 and Mictosoft's Server 2008 to 2016. Programs with a higher priority will the system preferably treated as programs with lower priority when it comes to the allocation of responsibilities of the system! Content / Solution / Tips: 1.) ... Examples for program starts with process priority. |
LOW | Start application in the IDLE priority class |
ABOVENORMAL | Start application in the ABOVENORMAL priority class |
NORMAL | Start application in the NORMAL priority class |
BELOWNORMAL | Start application in the BELOWNORMAL priority class |
HIGH | Start application in the HIGH priority class |
REALTIME | Start application in the REALTIME priority class |
3.) Help file for START command in Windows command prompt.
FAQ 12: Updated on: 29 July 2018 13:49