How to Allow User to Prioritize Process to Negative Niceness

limitnicenot-root-userprocess

I want a user to run a specific process on the system with a negative nice value.
I can't simply fork the process to background as this specific program is a minecraft server and I rely on the command line to control the server.

My current bash script looks like this (the important part):

sleep 10 && \
sudo renice -n $NICENESS $(ps -u $(id -u) -o "%p:%c" | sed -n "s/:java$//p") & \
java -Xmx8G -Xms2G -jar minecraft_server.jar nogui

sleep simply delays execution of renice. renice itself uses ps to check for a java process using the users own ID. There might be other instances of java spawning under different users, but the minecraft server runs under its own user minecraft.

I obviously don't want to enter a password every time I start the server.
from /etc/sudoers:

minecraft ALL = NOPASSWD: /etc/renice

Is there a more elegant way to do this? Simply using nice is not an option, sudo nice bash in combination with the NOPASSWD: option would be a great security issue.

Best Answer

The pam_limits.so module can help you there.

It allows you to set certain limits on specific individual users and groups or wildcards or ranges of users and groups.

The limits you can set are typically ulimit settings but also on the number of concurrent login sessions, processes, CPU time, default priority and maximum priority (renice). Check the limits.conf man page for more.

For example you can configure your mindcraft group to have all their processes started with an increased default priority and you can allow them to use the nice and renice commands to increase the priority of their important jobs manually as well instead of only reducing priority.

# /etc/security/limits.conf
# increase default and max prio for members of the mindcraft group
@mindcraft   hard priority -10
@mindcraft   hard nice     -18

Related Solutions

How to make all the processes start with niceness 5

You can set the priority for a particular user in /etc/security/limits.conf file.

root       hard/soft     priority    10

This way u can set hard or soft limit for any particular user. So all the processes which this root user will start will have 5 as the default priority vale.

According to Wikipedia page:

The exact mathematical effect of setting a particular niceness value for a process depends on the details of how the scheduler is designed on that implementation of Unix.

Here is the snapshot which show the above procedure works:

This image is the screenshot of /etc/security/limits.conf file

This is snapshot of limits.conf file which show a line which i added at last like

root     hard     priority    15

After changing this, I started one ssh session using the command ssh root@localhost

enter image description here

This screenshot show last two lines which shows the nice value of last two processes -bash and sshd: root@pts/3 to be 15.

Edit

Here is the snapshot which shows that u can increase and decrease the niceness of a process enter image description here

Edit 2:

Here is the snapshort which shows that even normal user can change the niceness value.

enter image description here

Linux – Does Linux Change a Process Niceness Automatically

To my knowledge, the Linux kernel does not change the niceness of a process, and I fail to see why it would since it doesn't have to to lower the priority of a process. The niceness is an information given to the kernel, telling it how nice that process is willing to be. The kernel scheduler is free to take this information into account the way it wants in order to change the priority of a process, it doesn't need to change its value.

On the other hand, in user land, there are daemons like AND whose task is to renice processes according to rules set up by the admin. Do you have such a daemon installed on your server?

However, the AND daemon does not renice processes owned by root, and since you set a priority of -1 with setpriority(), I assume this is the case here. Therefore, the only reason I see for that change in niceness is user interaction.

That said, since you are using htop, it is possible that the process has been reniced inadvertently by pressing the ] key or the F8 key.

Best Answer

Related Solutions

How to make all the processes start with niceness 5

Linux – Does Linux Change a Process Niceness Automatically

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