Chrooted SSH/SFTP Tutorial (Debian Etch) Page 2

By admin on May 13, 2010 with Comments 0

This tutorial describes two ways how to give users chrooted SSH
access. With this setup, you can give your users shell access without
having to fear that they can see your whole system. Your users will be
jailed in a specific directory which they will not be able to break out
of. The users will also be able to use SFTP in their chroot jails.

3 Second Method (Per Script)

There’s a script called make_chroot_jail.sh on http://www.fuschlberger.net/programs/ssh-scp-sftp-chroot-jail/ that automates setting up SSH/SFTP chroot jails. It works flawlessly on Debian Etch.

3.1 Get The Script

First, we need to install some prerequisites:

apt-get install sudo debianutils coreutils

Then we download make_chroot_jail.sh to /usr/local/sbin and make it executable for the root user:

cd /usr/local/sbin
wget http://www.fuschlberger.net/programs/ssh-scp-sftp-chroot-jail/make_chroot_jail.sh
chmod 700 /usr/local/sbin/make_chroot_jail.sh

3.2 Use make_chroot_jail.sh

Now we can already use the script. Usage is as follows:

make_chroot_jail.sh username [/path/to/chroot-shell [/path/to/chroot]]

It doesn’t matter if the user is already existing or not. If he’s existing, he will be updated; if not, he will be created. If you don’t specify the path to chroot-shell and the path to the chroot jail, the default values /bin/chroot-shell and /home/jail will be used, e.g.:

make_chroot_jail.sh testuser

I want to use /home/chroot as the chroot jail, therefore I have to specify the path to chroot-shell as well:

make_chroot_jail.sh testuser /bin/chroot-shell /home/chroot

This will create/update the user testuser with the chroot jail /home/chroot.

To update all files/libraries in the chroot jail, run

make_chroot_jail.sh update

or

make_chroot_jail.sh update/bin/chroot-shell /home/chroot

depending on how you created your users.

3.3 ProFTPd

If you use ProFTPd, you should read this:

As mentioned on http://www.fuschlberger.net/programs/ssh-scp-sftp-chroot-jail/, you shouldnot add /bin/chroot-shell to /etc/shells because that would allow users to break out of the chroot jail. This is a problem for ProFTPd, because in ProFTPd’s standard configuration, only users with a shell listed in /etc/shells can use ProFTPd. This means, that users that use /bin/chroot-shell cannot use ProFTPd.

To change this, open /etc/proftpd/proftpd.conf and add:

vi /etc/proftpd/proftpd.conf

[...]
RequireValidShell off
[...]

Then restart ProFTPd:

/etc/init.d/proftpd restart

Now all users can use ProFTPd, regardless of what shell they have, which again might not be something you want. But the best solution would be to simply use SFTP and drop normal FTP.