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Thursday, 15 December 2016

Preventing user from logging in via SSH although allowing SCP operations (scponly)

I have come across numerous scenarios where scripts and programs will require SCP to work properly - although do not require SSH access.

By default on CentOS there is not a shell that allows you to restrict SSH but allow SCP - so instead we have to install the 'scponly' shell from EPEL:

yum install scponly

Once installed it should be added to: /etc/shells

/bin/sh
...
/usr/bin/scponly
/bin/scponly

proceed by creating a group for it:

sudo groupadd scponly

Create directory you wish to serve e.g.:

/var/secure/uploads

and ensure the appropriate ownership information is applied (I only want the script to read the files):

sudo chown root:scponly

and permissions e.g.:

sudo chmod 770 /var/secure/uploads

sudo chmod 640 /var/secure/uploads/*

and create a new user and ensure they are part of the 'scponly' group and the appropriate shell is assigned to them:

sudo useradd -m -d /home/script -s "/usr/bin/scponly" -c "script" -G scponly script




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