What is nice in linux

What does the «nice» value mean in CPU utilization statistics

I am relatively new to Linux and Ubuntu. I have attached the system monitor to the bar (the upper bar of the screen) and opened the preference to configure this gadget. On the processor tab I see that I can mark the choose 5 colors : user, system, nice, IOwait and idle. I can understand all 4 (I think. ) except for «nice». What is this «nice» ? I read this answer and I understand that the superuser can perform tasks with greater priority but , what does it mean if I see it in the system monitor without me running any new nice processes ?

This question is about the CPU’s nice value, not a particular process’ nice value. The Q&A flagged as the duplicate of this only deals with the nice value of a process not whit the nice value of the CPU utilization. Those are of course related but not the same thing. So I think this is not a duplicate of that one.

2 Answers 2

The nice value for the processor is

the time the CPU has spent running users’ processes that have been «niced».

(from man top ) A «niced» process is one with a positive nice value. So if the processor’s nice value is high, that means it is working with some low priority processes. So this indicator is useful when you see high CPU utilization and you are afraid that this high load will have bad effect on your system:

• High CPU utilization with high nice value: Nothing to worry, not so important tasks doing their job, important processes will easily get CPU time if they need. This situation is not a real bottleneck.
• High CPU utilization with low nice value: Something to worry because the CPU is stressed with important processes so these or new processes will have to wait. This situation is a real bottleneck.

I think this nice value is not too important for a simple user, this is more useful in a server environment.

Источник

What does ‘Nice’ mean on the processes tab

‘nice’ refers to the priority the process gets on your CPU. This is a number in the range of -20 (highest priority) to 19 (lowest). You’ll probably find that most applications you’re running are at nice ‘0’, which means that they are running with normal priority and none will get preferential treatment by the scheduler over another.

If you’re running an intensive program, you may wish to launch it from a terminal with nice -n 10 /path/to/program . That way it will impact less on the performance of your system.

Nice is not simply priority multiplied by minus one.

You will find that on unix/linux systems that if a task is hogging the processor, then the system does not grind to a halt. This is because the system will dynamically lower this tasks priority.

The niceness influences the base priority. So while niceness can be thought of as negative priority, it will have less effect than priority would have on a Microsoft NT system, as the Linux scheduler is already doing a good job at keeping things nice.

You must log in to answer this question.

Linked

Related

Hot Network Questions

Subscribe to RSS

To subscribe to this RSS feed, copy and paste this URL into your RSS reader.

Site design / logo © 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA . rev 2023.7.14.43533

Ubuntu and the circle of friends logo are trade marks of Canonical Limited and are used under licence.

By clicking “Accept all cookies”, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy.

Источник

How to Set Linux Process Priority Using nice and renice Commands

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.

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.

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, while
• PR or PRI – is the process’s actual priority, as seen by the Linux kernel.

How To Calculate PR or PRI Values

Total number of priorities = 140 Real time priority range(PR or PRI): 0 to 99 User space priority range: 100 to 139

Nice value range (NI): -20 to 19

PR = 20 + NI PR = 20 + (-20 to + 19) PR = 20 + -20 to 20 + 19 PR = 0 to 39 which is same as 100 to 139.

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.

$ nice -n niceness-value [command args] OR $ nice -niceness-value [command args] #it’s confusing for negative values OR $ nice --adjustment=niceness-value [command args]

• 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.

$ sudo nice -n 5 tar -czf backup.tar.gz ./Documents/* OR $ sudo nice --adjustment=5 tar -czf backup.tar.gz ./Documents/*

You can also use the third method which is a little confusing especially for negative niceness values.

$ sudo nice -5 tar -czf backup.tar.gz ./Documents/*

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:

$ renice -n -12 -p 1055 $ renice -n -2 -u apache

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,

PR for ts3server = 20 + -12 = 8 PR for apache processes = 20 + -2 = 18

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:

# vi /etc/security/limits.d/tecmint-priority.conf

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.

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.

Источник

Команда nice, или вежливые процессы

Когда на компьютере достаточно процессорного времени на исполнение всех процессов, нет необходимости в выставлении приоритетов. Но когда необходимо параллельно запустить несколько процессов, каждый из которых использует всё доступное процессорное время, может очень пригодиться утилита nice.

Команда nice запускает программу с изменённым приоритетом для планироващика задач. Слово «nice» в английском языке обозначает, в частности, «вежливый». По этимологии этой команды процесс с большим значением nice — более вежлив к другим процессам, позволяя им использовать больше процессорного времени, поскольку он сам имеет меньший приоритет (и, следовательно, большее «значение вежливости» — niceness value).

Наибольший приоритет (и наименьшее значение nice) — −20. 19, либо 20 — наименьший приоритет, но это, с другой стороны, самые вежливые процессы.

Чтобы посмотреть идентификатор и значение nice нужного процесса в системе, можно воспользоваться командой ps axl.

Пример использования команды nice — запуск ресурсоёмкой задачи в фоновом режиме, так, чтобы она выполнялась, но освобождала часть процессорного времени для других процессов, как только оно становятся им нужно. Таким образом можно, скажем, запустить кодирование OGG/MP3 с большим значением nice, чтобы оно происходило в фоновом режиме, используя не всё процессорное время, а то, что не используется другими процессами (с меньшим значением nice — то есть с большим приоритетом).

Чтобы запустить команду с определённым приоритетом, слева нужно добавить «nice -n значение_nice», либо «nice —adjustment значение_nice» (adjustment — настройка, регулировка).

То есть: nice -n значение_nice команда.

Если нужно изменить приоритет уже запущенного процесса, можно воспользоваться командой renice.

renice -n значение_nice id_процесса

Команда renice выводит старый и новый приоритет процесса.

Теперь, зная эти команды, можно управлять процессами так, чтобы определённые задачи выполнялись быстрее в случае, когда сразу много процессов используют всё доступное процессорное время.

Источник