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Julia Evans

Lima: a nice way to run Linux VMs on Mac

• tools •

Hello! Here’s a new entry in the “cool software julia likes” section.

A little while ago I started using a Mac, and one of my biggest frustrations with it is that often I need to run Linux-specific software. For example, the nginx playground I posted about the other day only works on Linux because it uses Linux namespaces (via bubblewrap) to sandbox nginx. And I’m working on another playground right now that uses bubblewrap too.

This post is very short, it’s just to say that Lima seems nice and much simpler to get started with than Vagrant.

enter Lima!

I was complaining about this to a friend, and they mentioned Lima, which stands for Linux on Mac. I’d heard of colima (another way to run Linux containers on Mac), but I hadn’t realized that Lima also just lets you run VMs.

It was surprisingly simple to set up. I just had to:

  1. Install Lima (I did nix-env -iA nixpkgs.lima but you can also install it with brew install lima)
  2. Run limactl start default to start the VM
  3. Run lima to get a shell

That’s it! By default it mounts your home directory as read-only inside the VM

There’s a config file in ~/.lima/default/lima.yaml, but I haven’t needed to change it yet.

some nice things about Lima

Some things I appreciate about Lima (as opposed to Vagrant which I’ve used in the past and found kind of frustrating) are:

  1. it provides a default config
  2. it automatically downloads a Ubuntu 22.04 image to use in the VM (which is what I would have probably picked anyway)
  3. it mounts my entire home directory inside the VM, which I really like as a default choice (it feels very seamless)

I think the paradigm of “I have a single chaotic global Linux VM which I use for all my projects” might work better for me than super carefully configured per-project VMs. Though I’m sure that you can have carefully configured per-project VMs with Lima too if you want, I’m just only using the default VM.

problem 1: I don’t know how to mount directories read-write

I wanted to have my entire home directory mounted read-only, but have some subdirectories (like ~/work/nginx-playground) mounted read-write. I did some research and here’s what I found:

Maybe I’ll figure out how to mount directories read-write later, I’m not too bothered by working around it for now.

problem 2: networking

I’m trying to set up some weird networking stuff (this tun/tap setup) in Lima and while it appeared to work at first, actually the tun network device seems to be unreliable in a weird way for reasons I don’t understand.

Another weird Lima networking thing: here’s what gets printed out when I ping a machine:

$ ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
ping: Warning: time of day goes back (-7148662230695168869us), taking countermeasures
ping: Warning: time of day goes back (-7148662230695168680us), taking countermeasures
64 bytes from 8.8.8.8: icmp_seq=0 ttl=255 time=0.000 ms
wrong data byte #16 should be 0x10 but was 0x0
#16	0 6 0 1 6c 55 ad 64 0 0 0 0 72 95 9 0 0 0 0 0 10 11 12 13 14 15 16 17 18 19 1a 1b
#48	1c 1d 1e 1f 20 21 22 23
ping: Warning: time of day goes back (-6518721232815721329us), taking countermeasures
64 bytes from 8.8.8.8: icmp_seq=0 ttl=255 time=0.000 ms (DUP!)
wrong data byte #16 should be 0x10 but was 0x0
#16	0 6 0 2 6d 55 ad 64 0 0 0 0 2f 9d 9 0 0 0 0 0 10 11 12 13 14 15 16 17 18 19 1a 1b
#48	1c 1d 1e 1f 20 21 22 23
ping: Warning: time of day goes back (-4844789546316441458us), taking countermeasures
64 bytes from 8.8.8.8: icmp_seq=0 ttl=255 time=0.000 ms (DUP!)
wrong data byte #16 should be 0x10 but was 0x0
#16	0 6 0 3 6e 55 ad 64 0 0 0 0 69 b3 9 0 0 0 0 0 10 11 12 13 14 15 16 17 18 19 1a 1b
#48	1c 1d 1e 1f 20 21 22 23
ping: Warning: time of day goes back (-3834857329877608539us), taking countermeasures
64 bytes from 8.8.8.8: icmp_seq=0 ttl=255 time=0.000 ms (DUP!)
wrong data byte #16 should be 0x10 but was 0x0
#16	0 6 0 4 6f 55 ad 64 0 0 0 0 6c c0 9 0 0 0 0 0 10 11 12 13 14 15 16 17 18 19 1a 1b
#48	1c 1d 1e 1f 20 21 22 23
ping: Warning: time of day goes back (-2395394298978302982us), taking countermeasures
64 bytes from 8.8.8.8: icmp_seq=0 ttl=255 time=0.000 ms (DUP!)
wrong data byte #16 should be 0x10 but was 0x0
#16	0 6 0 5 70 55 ad 64 0 0 0 0 65 d3 9 0 0 0 0 0 10 11 12 13 14 15 16 17 18 19 1a 1b
#48	1c 1d 1e 1f 20 21 22 23

This seems to be a known issue with ICMP.

why not use containers?

I wanted a VM and not a Linux container because:

  1. the playground runs on a VM in production, not in a container, and generally it’s easier to develop in a similar environment to production
  2. all of my playgrounds use Linux namespaces, and I don’t know how to create a namespace inside a container. Probably you can but I don’t feel like figuring it out and it seems like an unnecessary distraction.
  3. on Mac you need to run containers inside a Linux VM anyway, so I’d rather use a VM directly and not introduce another unnecessary layer

OrbStack seems nice too

After I wrote this, a bunch of people commented to say that OrbStack is great. I was struggling with the networking in Lima (like I mentioned above) so I tried out OrbStack and the network does seem to be better.

ping acts normally, unlike in Lima:

$ ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_seq=1 ttl=113 time=19.8 ms
64 bytes from 8.8.8.8: icmp_seq=2 ttl=113 time=15.9 ms
64 bytes from 8.8.8.8: icmp_seq=3 ttl=113 time=23.1 ms
64 bytes from 8.8.8.8: icmp_seq=4 ttl=113 time=22.7 ms

The setup steps for OrbStack are:

  1. Download OrbStack from the website
  2. In the GUI, create a VM
  3. Run orb
  4. That’s it

So it seems equally simple to set up.

that’s all!

Some other notes:

  • It looks like Lima works on Linux too
  • a bunch of people on Mastodon also said colima (built on top of Lima) is a nice Docker alternative on Mac for running Linux containers

Open sourcing the nginx playground Why is DNS still hard to learn?