Joys of schroot

Schroot is good! Try schroot. You have LVM set up and some free extents in a vg? Try this:

# Create a new logical volume for a sid chroot
lvcreate -n schroot-sid -L1G YOUR-VG-NAME
mke2fs -j /dev/YOUR-VG-NAME/schroot-sid

# Debootstrap sid into it
mount /dev/YOUR-VG-NAME/schroot-sid /mnt
debootstrap --keyring=/etc/apt/trusted.gpg sid /mnt http://ftp.uk.debian.org/debian
umount /mnt

Then apt-get install schroot and put this in your /etc/schroot/schroot.conf:

[sid]
type=lvm-snapshot
device=/dev/YOUR-VG-NAME/schroot-sid
description=Debian sid
priority=5
users=YOUR-USER-NAME
root-users=YOUR-USER-NAME
source-root-users=root
aliases=unstable
lvm-snapshot-options=--size 2G

Now, schroot -c sid will make a LVM snapshot of /dev/YOUR-VG-NAME/schroot-sid, mount it, set it up as a nice working system, and chroot into it running a shell. Have a look around: resolv.conf is set up, your home directory is bind mounted, /proc and /sys are mounted.

When you exit the chroot, the LVM snapshot disappears, and /dev/YOUR-VG-NAME/schroot-sid is unchanged.

If you want to modify /dev/YOUR-VG-NAME/schroot-sid, you just schroot -c sid-source.

In my laptop, I did this:

# schroot -c sid-source
(sid)# echo APT::Install-Recommends "false";' > /etc/apt/apt.conf.d/50enrico
(sid)# apt-get install build-essential, pbuilder, devscripts, fakeroot
(sid)# apt-get clean

At this point, to build a debian package like if I were using pbuilder, I do this:

pkgdir$ schroot -c sid
(sid)pkgdir$ su -c /usr/lib/pbuilder/pbuilder-satisfydepends
(sid)pkgdir$ debuild -us -uc

You can repeat this whole process with lenny and etch, for example, and if you are on an amd64 system, you can also do sid32, lenny32 and etch32.

If you don't want to redownload packages all the time, install approx and configure the -source chroots to use it. This also allows you to easily switch all systems from one mirror to another if, for example, you are traveling abroad.

If you want to do the same as pbuilder update, you can do this:

# schroot -c sid-source
(sid)# apt-get update
(sid)# apt-get dist-upgrade
(sid)# apt-get autoremove
(sid)# apt-get clean

You can use schroot -c sid-source for all sorts of permanent maintenance works.

You can also create persistent named snapshots:

$ schroot -b -c sid -n playground

This will only disappear when you do:

$ schroot -c playground -e

And you can enter the schroot as many time as you want with:

$ schroot -r -c playground

You can also enter a temporary snapshot as many times as you want, by using the random name that schroot generated for it (you can see it, for example, when running df or mount).

You fear that lvm snapshots are a little fragile and a little slow at the moment? It's not a problem: your home is bind-mounted inside the chroot, so you can do all the work in your normal home filesystem, without stressing the snapshot.

This is good not only to build packages. For example, now that svk is broken in sid and lenny, I just did schroot -b -c etch -n svk, installed svk on it, and then every time I need svk, I can do schroot -r -c svk and have it ready.

Added links: * using sbuild as a Debian maintainer * a similar article about schroot