Rich SSH host aliases

Going to talk about shells, yep. Photo by Sahra Peterson on Unsplash.

Bad title, but nice little trick: you can use ssh configuration file to define rich shell commands to be executed on a remote host. And here is an example.

Imagine you have a remote host with MySQL server on it, and sometimes you need to go there and execute a statement or two. You could wind up some visual DB admin tool like phpMyAdmin or DataGrip, but maybe it’s just some quick query like select count(*) from users, and simple utility like mysql would do just fine. So, you probably do something like this (assuming you already have your key-base authentication configured):

$ ssh my.dev.server.com
Last login: Mon Jul 27 02:15:13 2020 from 1.2.3.4
user@my.dev.server.com $ mysql -u username -p
Enter password: ****
mysql> select count(*) from users;
+----------+
| count(*) |
+----------+
|        5 |
+----------+
1 row in set (0.00 sec)
mysql>

Probably opening up DB admin tool would be quicker and less tedious, but let’s try to optimize our console-only approach via ~/.ssh/config.

First, we can configure ssh to execute our command right away:

Host my.dev.server.com
    RemoteCommand mysql -u username -p
    RequestTTY yes

This saves us from typing one command — mysql -u username -p — and also prevents us from using ssh to establish usual session. Let’s fix that like this:

Host dev mysql.dev
    Hostname my.dev.server.com
Host mysql.dev
    RemoteCommand mysql -u username -p
    RequestTTY yes

This adds two aliases to real (long and clumsy) hostname, and by choosing specific alias you can either open normal ssh connection:

$ ssh dev
Last login: Mon Jul 27 02:35:07 2020 from 1.2.3.4
user@my.dev.server.com $

Or immediately run mysql:

$ ssh mysql.dev
Enter password: ****
mysql>

To avoid entering password every time you can use ~/my.cnf on the remote server:

[client]
user=username
password=sEcrEt

Or maybe you have some application running on the server which happens to have .env file with username/password/database in it, and in this case RemoteCommand in ~/.ssh/config can be modified like this:

Host dev mysql.dev
    Hostname my.dev.server.com
Host mysql.dev
    RemoteCommand sh -c '. /path/to/app/.env; mysql -u $DBUSER -p$DBPASS -D $DBNAME'
    RequestTTY yes

With this config you can access mysql utility instantly:

$ ssh mysql.dev
mysql>

In a similar fashion other commands can be aliased, e.g.:

• top.dev: top -o %MEM -d 1 (or whatever other defaults you choose)
• stats.dev: docker stats
• logs.dev: tail -f /var/log/syslog
• etc.