For a little while now I've wanted to be able to chroot both SFTP and SHH accounts on one of my multi-user VPSs.
SFTP on its own is not so difficult. OpenSSH 4.9p1 and above includes the ChrootDirectory directive. And an SFTP chroot is a little more forgiving in so far as it doesn't actually require any supporting system or userpsace services (a shell, ls, cp, etc.), which is why you often see ChrootDirectory accompanied with ForceCommand internal-sftp which will prevent SSH access altogether.
What I'd like to do is create a restricted environment for both SSH and SFTP.
I spent a little while looking at a very interesting project from Olivier Sessink called Jailkit. Jailkit has most of what I was looking for but, it has quite a few moving parts, including the need to replace a users shell with a special Jailkit shim that hands over to Jailkit. This is okay but it means changes to passwd are required, and editing your /etc/ssh/sshd_config to use Subsystem sftp /usr/lib/openssh/sftp-server and not Subsystem sftp internal-sftp if you want to chroot and jail both SFTP and SHH logins.
It turns out that OpenSSH gets us most of the way there with the ChrootDirectory directive.
And so here are the steps required to create a minimal chroot jail on Ubuntu 12.04 LTS.
Bash is fun. I mean it's a little weird, but it's fun. I've been reading the Linux Command Line and Shell Scripting Bible which I highly recommend. I also wanted a script I could use to update the multiple WordPress installations I'm now hosting.
I found Liz Quilty's handy WordPress mass update script 3.4.1, but wanted to refactor the script to use functions, curl, and tar (as well as remove support for WordPress MU)
And so here it is, one of a handful of Bash script exercises I've completed to-date. Enjoy, and thanks Liz for the head start.
First, a machine specific configuration file (read the warning in the comments section of the script below). Place the config file next to the script file; that is, place wp-upgrade.conf in the same directory as wp-upgrade.sh.