Priority Queue

Priority Queue on Linux Servers¶

We can set priorities for Linux commands using nice and renice commands and by setting the processes PR (priority value)

There is a more in depth guide for niceness HERE.

Why?¶

We will sometimes need to update the priority queue for long-running processes that are time sensitive or processes we would prefer to have finish faster.

Nice Values¶

Nice¶

nice is a number range from -20 to +19, the lower the higher priority, that determines a processes' priority. This number is set to 0 by default for new processes and all processes with the same priority are grouped together and run sequentially.

You can run a command while setting the nice command.

nice -n niceness-value command args

e.g.

nice -n -20 bin/magento s:s:d -f -j4 en_US en_GB

This would run the standard magento deploy with the highest nice priority.

Renice¶

We can also adjust niceness value of a pre queued process using the renice command. This can be done using either the process id (PID) or using the user id

Using PID
```
renice -n -20 -p 1000
```
Using UID
```
renice -n -20 -u root
```

Setting default values¶

Default nice values can be set in /etc/security/limits.conf

The syntax is:

#<domain> <type> <item> <value>

For nice purposes the headings can be translated to:

<username> <hard|soft> priority <nice value>

e.g. To enforce top priority for ec user:

ec hard priority -20

Addendum¶

You can get more information on these functions using man.

man nice

man renice

Using HTOP¶

If when checking processes using HTOP you think that a process is running slowly, you can dynamically update the nice value using HTOP.

To increase the priority you can use F7 to minus the nice value.