FreeBSD India

This sounds strange, what? Ok, let me tell you for what you would need that…I have a user which works with my MySQL-database by Windows-ODBC. The usual communication between client and server runs unencrypted. So I decided to tunnel the communication through an ssh-tunnel.

• Problem 1: User has shell-access and the user has the opportunity to log into my system and do things I don’t like.
  Solution 1: Don’t give him shell-access, but a program which runs forever and the user gets some output on his terminal to get no timeout.
• Problem 2: User could port-forward not only mysql-protocol but also SMTP, POP3… whatever. But I don’t want that.
  Restrict him to forward only special ports.

Create a file ~user/.ssh/authorized_keys like this

#  -> command=”…”
#     this command simply prints something to prevent a timeout while
#     the ssh-session is running. quoting-character like double quotes
#     in this command must be quoted with backslash
#  -> permitopen=”127.0.0.1:3306″
#     restrict the person using this key to only portforwarding
#     3306 to localhost
#  -> from=…
#     only allow connections from this host (not needed but sometimes useful)
# the rest is the public key
command=”/usr/bin/perl -e ‘$|=1;while (1) { print scalar localtime() . ”n”;sleep 30}’”,
permitopen=”127.0.0.1:3308″,
from=”box1.freebsd.org.in”
ssh-dss AAAAB3NzaC1kc3MAAACBAJ4vXg== some@comment_for_key

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You can use the wall command to send a message to every user on a system. General syntax of wall command is as follows:
wall
Message
Message
…
….
..
When the message is complete, press Control-D.1) To display message “Disk failure system will be down for 30 minute” to all users use wall as follows:
# wall
Disk failure system will be down for 30 minute
--UNIX Admin
--MyCorp.com


When the message is complete, press Control-D (CTRL+D) to send message to all user.

2) To display message “Web server under DOS attack, come to IDC # 3″ to all WHEEL group member use wall command with –g option as follows:
# wall –g wheel
Web server under DOS attack, come to IDC # 3 to investigate matter further.
-- IT HEAD

When the message is complete, press Control-D (CTRL+D) to send message to all user.

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