Slow ssh login

Originally, I thought it was the sshd DNS configuration (i.e. UseDNS) which is already set to no. It turns out that the first domain server in /etc/resolv.conf on the server is slow. After switching the order of the servers, ssh become fast again... This is related to the entries I added to hosts.deny.

tcpwrapper: hosts.allow / hosts.deny

hosts.allow will overide hosts.deny.
Below is a configuration I use for my home computer that can not be connected directly from outside:

hosts.allow:
sshd: 192.168.0.0/255.255.255.224 except 192.168.0.1
hosts.deny:
sshd: ALL

The Below is a machine that can be connected from outside:

hosts.allow:
sshd: 192.168.0.0/255.255.255.224 except 192.168.0.1
hosts.deny:
sshd: PARANOID,UNKNOWN
sshd: *.com.mx,*.com.ar,*.it, *.ro

ssh session stuck

press ~ tehn . to send a break/recover.

Tunnel VNC over ssh

This will be faster than using VNC over X over ssh (i.e., ssh -X). Let us say we want to tunnel vnc from remote to local and the vncserver on remote is started on port 2 (5092).

local$ ssh -C -L 5902:127.0.0.1:5902  uid@remote

Then on remote start vncserver if it is not started

remote$ vncserver :2

Now on start vncviewer on local to connect to remote vnc server:

local$ vncviewer locathost:2

X over ssh

Use either -X or -Y option with ssh.

localhost$ ssh -X remotehost
remotehost$ xterm     # this remotehost xterm will show on your local machine

Ssh Read from remote host remote.com: Connection reset by peer

My hosting company firewall seems to drop idle connections. When I do a who on the server, there are many ssh sessions that are already dropped on the client side. I add the following to the /etc/ssh/sshd_config, then restarted the sshd. Connection reset does not happen anymore. Had to adjust ClientAliveInterval a few times to half of the firewall's timeout value.

TCPKeepAlive yes
ClientAliveInterval 240

Also you can change this in the kernel:

# cat /proc/sys/net/ipv4/tcp_keepalive_time
7200
# echo 240 > /proc/sys/net/ipv4/tcp_keepalive_time

And make changes to /etc/sysctl.conf permanently.

net.ipv4.tcp_keepalive_time = 180