A proper way to create a chrooted chroot SSH on CentOS 7

linux - A proper way to create a chrooted SSH on CentOS 7 - Server Fault
linux - A proper way to create a chrooted SSH on CentOS 7 - Server Fault

Luckily, I was able to come up with a way to do that.

Step 1: Add a group for chrooted users

groupadd chrootusers

Step 2: Configure SSH

nano /etc/ssh/sshd_config

Replace

Subsystem     sftp    /usr/libexec/openssh/sftp-server

With

Subsystem     sftp    internal-sftp

Paste at the End

Match Group chrootusers
  ChrootDirectory /home/%u

Run

systemctl restart sshd
systemctl status sshd

Step 3: Add a user

Change peter to your desired user name.

export NEW_USER_NAME=peter

useradd ${NEW_USER_NAME}
usermod -G chrootusers -d / ${NEW_USER_NAME}
passwd ${NEW_USER_NAME}

Step 4: Install packages and create the necessary directory structure

yum --installroot=/home/${NEW_USER_NAME} --releasever=7 --nogpg --disablerepo='*' --enablerepo=base install centos-release openssh-clients wget vi nano zip unzip tar mariadb findutils iputils bind-utils rsync

Step 5: Mount proc and dev

echo "none /home/${NEW_USER_NAME}/proc proc defaults 0 0" >> /etc/fstab
echo "/dev /home/${NEW_USER_NAME}/dev none bind 0 0" >> /etc/fstab

Run

mount -a

Step 6: Configure the DNS servers

echo "nameserver 8.8.8.8" >> /home/${NEW_USER_NAME}/etc/resolv.conf
echo "nameserver 8.8.4.4" >> /home/${NEW_USER_NAME}/etc/resolv.conf

That's all.

Keep in mind that $NEW_USER_NAME is bound to the current session!

Start from Step 3 when adding another user.

To install more packages later use the same command as in Step 4.

---

When logging in using SSH you will get messages like cannot find name for user ID x. They are safe to ignore, but if you'd like to get rid of them, you will need to duplicate the user in chroot:

export NEW_USER_ID=$(id -u ${NEW_USER_NAME})
export NEW_USER_GROUP_ID=$(id -g ${NEW_USER_NAME})

chroot /home/${NEW_USER_NAME} /bin/bash -c 'useradd -u ${NEW_USER_ID} ${NEW_USER_NAME}'
chroot /home/${NEW_USER_NAME} /bin/bash -c 'groupadd -g ${NEW_USER_GROUP_ID} chrootusers'