Posts on Artur Meski

Limiting resources on FreeBSD

Fri, 09 Sep 2022 00:00:00 +0000

What is `rctl`

In FreeBSD, in addition to login.conf, we also get a very nice and flexible mechanism for setting resource limits: rctl. I like it in particular for limiting resources allocated to each jail.

Configuration

Here is a short example:

jail:example_jail:vmemoryuse:deny=2G/jail
jail:example_jail:maxproc:deny=200/jail
jail:example_jail:readiops:throttle=500/jail
jail:example_jail:pcpu:deny=70/jail

In the above, for the jail identified by example_jail we allow:

2G of memory,
200 processes,
500 I/O read operations per second,
70% of CPU.

Enabling rctl on boot

Actually, there is no need to enable anything in rc.conf – this is what you can find in /etc/defaults/rc.conf:

Public VMs on OpenBSD

Wed, 28 Jul 2021 00:00:00 +0000

This is a note on how to make a VM running on OpenBSD connect to the host’s network.

Firstly, we need to create a bridge with our external network interface.

# echo "em0" > /etc/hostname.bridge0
# /etc/netstart bridge0

In /etc/vm.conf we need to add a switch on bridge0:

switch "sw" {
    interface bridge0
}

Then, our VM needs to be attached to that switch:

vm "openbsd" {
    memory 8G
    enable
    disk /data/vm/openbsd/main.qcow2
    interface tap {
	switch "sw"
    }
}

My network setup also requires to specify the MAC address of the network interface:

Basic concurrency with fork()

Wed, 23 Jun 2021 00:00:00 +0000

When programming on Linux/Unix, the function fork(2) allows us to create new processes. This is a short and example-driven introduction to the basics of using that function.

First stab

After a brief look at the manual page for fork(2) we can tell that it returns a value of type pid_t and does not take any arguments:

NAME
     fork – create a new process

SYNOPSIS
     #include <unistd.h>

     pid_t
     fork(void);

Let us simply call fork and see what happens and what values does it return.

Quick start: virtual machines on OpenBSD

Sat, 19 Jun 2021 00:00:00 +0000

Since OpenBSD 5.9 it is possible to run virtual machines using a native virtualisation solution.

This is a short note/guide on how to set up a VM on OpenBSD in the simplest way that lets you have a quick play with vmm/vmd.

Preliminaries

First of all, we need to enable vmd on our host and get it running:
```
# rcctl enable vmd
# rcctl start vmd
```
You may also want to make sure you firewall can initially let everything through:

Reading and monitoring files on Linux