Sending email notifications of SSH logins on a system

There are some setups where it's beneficial to get a notice of user logins on a system. Here's one way to do it.

Create /usr/local/sbin/

if [ "$PAM_TYPE" != "open_session" ]
  exit 0
    echo "User: $PAM_USER"
    echo "Remote host: $PAM_RHOST"
    echo "Service: $PAM_SERVICE"
    echo "TTY: $PAM_TTY"
    echo "Date: `date`"
    echo "Server: `uname -a`"
  } | mail -s "$PAM_SERVICE login on `hostname -s` for account $PAM_USER" root
exit 0
# chmod 500 /usr/local/sbin/

Append the execution trigger to certain files, e.g. /etc/pam.d/[sshd|su|sudo]:

session    optional /usr/local/sbin/

For example the following triggers the notification from SSH logins, and successful su's and sudo's:

echo "session    optional /usr/local/sbin/" >> /etc/pam.d/sshd 
echo "session    optional /usr/local/sbin/" >> /etc/pam.d/su
echo "session    optional /usr/local/sbin/" >> /etc/pam.d/sudo

Check that mail exists; if not, it's in the package mailx:

# yum install mailx

Check the root account mail has been sensibly forwarded (e.g. /etc/aliases). Ensure there's a local MTA installed.

SSH: Allow only certain users to login with password

I got tired of the SSH failed login spam most public servers get. Allowing password login only for the users who really need it is an easy way to reduce login spam and also shrink the server's attack surface somewhat.

Create the specified user group and add users to it:

# groupadd -r password
# usermod -G password <user>

Append to /etc/ssh/sshd_config:

# Can't login with a password if not a member of the group "password"
PasswordAuthentication no
Match group password
    PasswordAuthentication yes

Also check that there are no other PasswordAuthentication directives effective in the file. Restart sshd. Test the login before killing existing connections.

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