If users have access to the files on your server, but you don’t want they to be able to execute commands, you can limit access to  sftp only.

Add a user to your system as normal with a password and then run the following command:

usermod -s /usr/lib/sftp-server username

Then change add the following to /etc/shells to make it a valid shell:

echo '/usr/lib/sftp-server' >> /etc/shells

Now this user can only run the sftp server as shell



Just use the following command:

iptables -A INPUT -p tcp --syn --dport 22 -m connlimit --connlimit-above 5 -j REJECT

In this example our connections are limited to 5.

OpenSSH 5.6 released

Valic —  August 30, 2010 — Leave a comment

OpenSSH 5.6 has just been released. It will be available from the mirrors listed at http://www.openssh.com/ shortly.


* Added a ControlPersist option to ssh_config(5) that automatically starts a background ssh(1) multiplex master when connecting. This connection can stay alive indefinitely, or can be set to automatically close after a user-specified duration of inactivity.

* Hostbased authentication may now use certificate host keys. CA keys must be specified in a known_hosts file using the @cert-authority marker as described in sshd(8).

* ssh-keygen(1) now supports signing certificate using a CA key that has been stored in a PKCS#11 token.

* ssh(1) will now log the hostname and address that we connected to at LogLevel=verbose after authentication is successful to mitigate “phishing” attacks by servers with trusted keys that accept authentication silently and automatically before presenting fake password/passphrase prompts.

Note that, for such an attack to be successful, the user must have disabled StrictHostKeyChecking (enabled by default) or an attacker must have access to a trusted host key for the destination server.

* Expand %h to the hostname in ssh_config Hostname options. While this sounds useless, it is actually handy for working with unqualified

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The following steps can be used to ssh from one system to another without specifying a password.

Step 1. On the client run the following commands:

ssh-keygen -t rsa

The output will look like this:

[email protected]:~# ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
cd:1c:6b:4e:01:1d:8c:02:40:24:24:95:02:dc:12:7f [email protected]

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