If you happen to work on OSX with MacPorts and GPGTools using SmartCard for SSH then installing OpenSC (0.16.0 in my case) will break your smart card access for GPG/SSH. If you remove OpenSC with an uninstall utility things get back to normal.
There are situations when you have a nice server out there, and you want/need someone to upload important files, but you only want to give them a minimal access to the system. You can use SSHD with sFTP and /sbin/nologin shell for that in chroot environment (dedicated limited userspace). Note that SCP in fact requires a working shell, so you need to use sFTP in this case..
Create a new user account with existing ftp group and /sbin/nologin shell:
# adduser
Alternatively you can modify an existing account to share:
# pw groupmod ftp -m username # pw usermod username -s /sbin/nologin
You need to set correct permissions to the user home directory and public directory inside for upload:
# chown root:wheel /home/username # mkdir /home/username/public # chown username:ftp /home/username/public
Now modify the SSHD server configuration file /etc/ssh/sshd_config and append:
Match Group ftp ChrootDirectory /home/%u ForceCommand internal-sftp AllowTcpForwarding no PermitTunnel no X11Forwarding no
Remember to restart the SSHD in order to apply new configuration:
# service sshd restart
Once the account is not necessary anymore remember to remove it:
# pw userdel username