My apologies: having sent the first version of this request I realise it will be much easier for people to help me if I include the file contents that I refer to in-line:
I have set up an sftp/scp only shell for a jailed user (guest, pwd guest) under Raspbian Stretch and following very precisely the steps in the jailkit howto instructions for that scenario, except for the change in user name.
On sftp address@hidden the connection closes immediately after entering the password. Here are the relevant lines in auth.log.
Dec 14 09:47:29 raspberrypi sshd[7725]: Accepted password for guest from ::1 port 44498 ssh2
Dec 14 09:47:29 raspberrypi sshd[7725]: pam_unix(sshd:session): session opened for user guest by (uid=0)
Dec 14 09:47:29 raspberrypi systemd-logind[294]: New session c119 of user guest.
Dec 14 09:47:29 raspberrypi systemd: pam_unix(systemd-user:session): session opened for user guest by (uid=0)
Dec 14 09:47:29 raspberrypi jk_chrootsh[7742]: now entering jail /srv/sftpjail for user guest (1002) with arguments -c /usr/lib/openssh/sftp-server
Dec 14 09:47:29 raspberrypi jk_lsh[7742]: jk_lsh version 2.20, started
Dec 14 09:47:29 raspberrypi jk_lsh[7742]: cannot find user info for USER guest: Success
Dec 14 09:47:29 raspberrypi sshd[7740]: Received disconnect from ::1 port 44498:11: disconnected by user
Dec 14 09:47:29 raspberrypi sshd[7740]: Disconnected from ::1 port 44498
Dec 14 09:47:29 raspberrypi sshd[7725]: pam_unix(sshd:session): session closed for user guest
Dec 14 09:47:29 raspberrypi systemd-logind[294]: Removed session c119.
Dec 14 09:47:29 raspberrypi systemd: pam_unix(systemd-user:session): session closed for user guest
The key issue appears to be that jk_lsh cannot find info for guest at line 7; this is followed by a disconnect from "me", i.e. user pi, ::1.
The two passwd files appear to be in order: /etc/passwd
root:x:0:0:root:/root:/bin/bash
guest:x:1002:1002:,,,:/srv/sftpjail/./home/guest:/usr/sbin/jk_chrootsh
/srv/sftpjail/etc/passwd.
root:x:0:0:root:/root:/bin/bash
guest:x:1002:1002:,,,:/home/guest:/usr/sbin/jk_lsh
This is driving me a bit frantic so any help much appreciated!
Thanks, John