SSH

How to email admins automatically after a Linux server starts?

Managing a cluster of servers, I would like to notified when a server is started. How to make the Linux servers email me or other admins automatically after they are started? I did this by adding a crontab entry on each servers like @reboot date | mailx -S smtp=smtp://smtp.example.com -s “`hostname` started” -r zma@example.com zma@example.com…

How to log connections hitting certain rules in iptables on Linux?

How to log connections hitting certain rules in iptables on Linux? Like the one that are dropped because of too frequently creating SSH connections. You can create a new chain named LOGNDROP that log the connections and drop them, then pass the connection to be redirected to the LOGNDROP chain. $tables -N LOGNDROP # Connections…

How to use iptables to limit rates new SSH incoming connections from each IP on Linux?

How to use iptables to limit rates new SSH incoming connections from each IP on Linux? For example, at most 6 SSH connection attempts every 60 seconds. You may use these rules (skip the first one, if you have set the basic rules): for tables in iptables ip6tables ; do # Allow established inbound connections…

Fixing “Remote Host Identification Has Changed” Error When SSH to a Server

If you encounter an error message like the one below when attempting to SSH to a server: @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! Someone could be eavesdropping on you right now (man-in-the-middle attack)! It is also possible that a host key has…

Setting up a VPN over SSH

SSH tunnel and port forwarding is great and convenient to use. But is it possible to set up a VPN like connection over SSH? If you are on Linux or Mac, you can use sshuttle: https://github.com/apenwarr/sshuttle If you are on Windows, you can use ProxyCap: http://www.proxycap.com/index.html Both are great software.

Git branching tutorial

Good tutorials on git branching. The “Git Branching” chapter of Pro Git book is the best one that I ever seen: http://git-scm.com/book/en/Git-Branching It deserve the time to study the whole chapter. If you are working with a git server, this chapter is especially useful: http://git-scm.com/book/en/Git-Branching-Remote-Branches

Direct multi-hop ssh connection

How to use multi-hop ssh connection without needs to ssh multiple times? As a example, you are connecting to server.example.com through proxy.example.com from laptop.example.com as follows: laptop —-> proxy —-> server 2 possible methods: Method 1: Use the similar method as in Directly SSH to hosts using internal IPs through the gateway. Add this to…

How to use different keys for different git servers?

I have access to different git servers. I have several keys for these servers. How to use different keys for different git servers? Use the .ssh/config file to specify different configuration for different SSH servers used by git: For example: Host git.example.org Port 22111 IdentityFile ~/.ssh/id_rsa.git.example.org Host code.example.org Port 22 IdentityFile ~/.ssh/id_rsa.code.example.org which specifies the…

Shared hosting services with SSH enabled

Which shared hosting services have SSH enabled? SSH is a great tool for management and development. Lots shared hosting services support SSH. Here is a non-complete list: Dreamhost SSH on dreamhost: http://wiki.dreamhost.com/Enabling_Shell_Access BlueHost SSH on BlueHost: http://my.bluehost.com/cgi/help/180 GoDaddy SSH on GoDaddy: http://support.godaddy.com/help/article/4942 HostGator SSH on HostGator: http://support.hostgator.com/articles/hosting-guide/lets-get-started/how-do-i-get-and-use-ssh-access HostMonster SSH on HostMonster: http://my.hostmonster.com/cgi/help/180 ServerGrove SSH on…

Force Linux to reboot

How to force Linux to reboot when the reboot command does not work. Enable the use of the magic SysRq option: # echo 1 > /proc/sys/kernel/sysrq Reboot the machine: # echo b > /proc/sysrq-trigger Even if you could not log on the system but sshd is working, you can force the Linux to reboot by:…