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Question

Giving access to a block storage directory to a chroot user

My web users are jailed in their home folder by chroot. I need to give them rw sftp access to a directory on a block storage volume (mounted at /mnt/vol_01, thus outside of their home directory). All permissions are recursively set rw for user:www-data and I also set the same ACL permissions. For testing, I already tried to mount --bind the directory on the BSV inside the home folder of a user. Though the sftp user can read the files on the BSV, the uploads fail, with a sftp protocol error -31, even so, a file is created, but he gets a zero byte size. On the other hand, sftp account logged as root user will work with no issue.

How to fix the issue and give read/write access to the BSV directory to the chroot users? Thanks in advance for any clue :)

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Bobby Iliev
Site Moderator
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• March 14, 2025

Hey Ralph 👋

If I recall correctly OpenSSH requires the chroot base dir to be owned by root and to be not writable. So try to keep /home/user as root:root with chmod 755, then create a subdir like /home/user/uploads and bind-mount your volume there:

mkdir /home/user/uploads
mount --bind /mnt/vol_01 /home/user/uploads

Make sure the mounted dir has the right permissions (user:www-data, chmod 775). In sshd_config use something like this:

Match User your_sftp_user
  ChrootDirectory /home/your_sftp_user
  ForceCommand internal-sftp

Restart SSH with systemctl restart sshd, and give it another try.

- Bobby

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