Schroot cheatsheet

I don’t always install software whose idea of installation instructions is curl ... | sudo, but when I do, I jail it. In this case, I’m setting up a chroot for Nodejs:

sudo apt install schroot debootstrap
sudo mkdir /srv/npm-chroot
sudo debootstrap stable /srv/npm-chroot
sudo mkdir -p /srv/npm-chroot/home/joe/projects
sudo chown -R joe:joe /srv/npm-chroot/home/joe/

In these examples, “joe” is my username.

The “s” in “schroot” stands for “securely,” but it might as well be “simple” because “schroot” handles fiddly bookkeeping tasks for setting up your environment, based on its config file.

Edit /etc/schroot/schroot.conf:

[npm]
description=npm projects
type=directory
directory=/srv/npm-chroot
root-users=joe
setup.fstab=joe-projects/fstab

Normally, schroot mounts /home from the host as /home in the chroot. I don’t want programs in jail to muck about with my home on the host though, so I edit the setup.fstab option. Its default lives in /etc/schroot/default/fstab.

For my purposes, the schroot’s default configuration is a good start, so:

sudo mkdir /etc/schroot/joe-projects
sudo cp /etc/schroot/default/fstab /etc/schroot/joe-projects/

Edit /etc/schroot/joe-projects/fstab, removing the /home line and adding instead:

/home/joe/projects /home/joe/projects none rw,bind 0 0

Finally, enter the chroot, as root.

schroot -c npm -u root

I like to install sudo so it feels like a normal Ubuntu:

# now in the schroot
apt update
apt install sudo
exit

Then log in as my normal user:

# in the host
schroot -c npm

From here I can install npm in relative isolation; this is not sufficient for isolating malicious software, but it’s a nice way to avoid inconsiderate programs from pooping all over your system.