As a Linux user, we use ssh command to log in to remote machines. The more you use ssh command, the more time you are wasting in typing some significant commands. We can use either alias defined in your .bashrc file or functions to minimize the time you spend on CLI. But this is not a better solution. The better solution is to use SSH-alias in ssh config file.
A couple of examples where we can better the ssh commands we use.
Connecting to ssh to AWS instance is a pain. Just to type below command, every time is complete waste your time as well.
ssh -p 3000 -i /home/surendra/mysshkey.pem ec2-user@ec2-54-20-184-202.us-west-2.compute.amazonaws.comto
ssh aws1
Connecting to a system when debugging.
ssh -vvv the_good_user@red1.taggle.abc.com.au
to
ssh xyz
In this post, we will see how to achieve shorting of your ssh commands without using bash alias or functions. The main advantage of ssh alias is that all your ssh command shortcuts are stored in a single file and easy to maintain. The other advantage is we can use same alias for both SSH and SCP commands alike.
Before we jump into actual configurations, we should know difference between /etc/ssh/ssh_config, /etc/ssh/sshd_config, and ~/.ssh/config files. Below is the explanation for these files.
Difference between /etc/ssh/ssh_config and ~/.ssh/config
System-level SSH configurations are stored in /etc/ssh/ssh_config. Whereas user-level ssh configurations are stored in ~/.ssh/config file.
Difference between /etc/ssh/ssh_config and /etc/ssh/sshd_config
System-level SSH configurations are stored in /etc/ssh/ssh_config. Whereas system level SSH server configurations are stored in /etc/ssh/sshd_config file.
Syntax for configuration in ~/.ssh/config file
Syntax for ~/.ssh/config file content.
config val config val1 val2
Example1: Create SSH alias for a host(www.linuxnix.com)
Edit file ~/.ssh/config with following content
Host tlj User root HostName 18.197.176.13 port 22
Save the file
The above ssh alias uses
- tlj as an alias name
- root as a user who will log in
- 18.197.176.13 as hostname IP address
- 22 as a port to access SSH service.
Output:
sanne@Surendras-MacBook-Pro:~ > ssh tlj Welcome to Ubuntu 16.04.3 LTS (GNU/Linux 4.4.0-93-generic x86_64) * Documentation: https://help.ubuntu.com * Management: https://landscape.canonical.com * Support: https://ubuntu.com/advantage Get cloud support with Ubuntu Advantage Cloud Guest: http://www.ubuntu.com/business/services/cloud Last login: Sat Oct 14 01:00:43 2017 from 20.244.25.231 root@linuxnix:~# exit logout Connection to 18.197.176.13 closed.
Example2: Using ssh key to login to the system without using password using IdentityFile.
Example:
Host aws User ec2-users HostName ec2-54-200-184-202.us-west-2.compute.amazonaws.com IdentityFile ~/Downloads/surendra.pem port 22
Example3: Use a different alias for the same host. In below example, we use tlj, linuxnix, linuxnix.com for same IP/hostname 18.197.176.13.
~/.ssh/config file content
Host tlj linuxnix linuxnix.com User root HostName 18.197.176.13 port 22
Output:
sanne@Surendras-MacBook-Pro:~ > ssh tlj Welcome to Ubuntu 16.04.3 LTS (GNU/Linux 4.4.0-93-generic x86_64) * Documentation: https://help.ubuntu.com * Management: https://landscape.canonical.com * Support: https://ubuntu.com/advantage Get cloud support with Ubuntu Advantage Cloud Guest: http://www.ubuntu.com/business/services/cloud Last login: Sat Oct 14 01:00:43 2017 from 220.244.205.231 root@linuxnix:~# exit logout Connection to 18.197.176.13 closed. sanne@Surendras-MacBook-Pro:~ > ssh linuxnix.com Welcome to Ubuntu 16.04.3 LTS (GNU/Linux 4.4.0-93-generic x86_64) * Documentation: https://help.ubuntu.com * Management: https://landscape.canonical.com * Support: https://ubuntu.com/advantage
Get cloud support with Ubuntu Advantage Cloud Guest: http://www.ubuntu.com/business/services/cloud Last login: Sun Oct 15 20:31:08 2017 from 1.129.110.13 root@linuxnix:~# exit logout Connection to 138.197.176.103 closed. [6571] sanne@Surendras-MacBook-Pro:~ > ssh linuxnix Welcome to Ubuntu 16.04.3 LTS (GNU/Linux 4.4.0-93-generic x86_64) * Documentation: https://help.ubuntu.com * Management: https://landscape.canonical.com * Support: https://ubuntu.com/advantage Get cloud support with Ubuntu Advantage Cloud Guest: http://www.ubuntu.com/business/services/cloud Last login: Sun Oct 15 20:31:20 2017 from 1.129.110.13 root@linuxnix:~# exit logout Connection to 18.197.176.13 closed.
Example4: Copy a file to remote system using same SSH alias
Syntax:
scp <filename> <ssh_alias>:<location>
Example:
sanne@Surendras-MacBook-Pro:~ > scp abc.txt tlj:/tmp abc.txt 100% 12KB 11.7KB/s 00:01 sanne@Surendras-MacBook-Pro:~ >
As we already set ssh host as an alias, using SCP is a breeze as both ssh and SCP use almost same syntax and options.
To do scp a file from local machine to remote one use below.
Examaple5: Resolve SSH timeout issues in Linux. By default, your ssh logins are timed out if you don’t activily use the terminial.
SSH timeouts are one more pain where you have to re-login to a remote machine after a certain time. We can set SSH time out right in side your ~/.ssh/config file to make your session active for whatever time you want. To achieve this we will use two SSH options for keeping the session alive. One ServerAliveInterval keeps your session live for number of seconds and ServerAliveCountMax will initial session after session for a given number.
ServerAliveInterval A ServerAliveCountMax B
Example:
Host tlj linuxnix linuxnix.com User root HostName 18.197.176.13 port 22 ServerAliveInterval 60 ServerAliveCountMax 30
We will see some other exiting howto in our next post. Keep visiting linuxnix.com.
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