This post is part of a series about using SSH more effectively. SSH is one of those programs that a lot of developers interact with but few seem to take full advantage of. This series highlights some of the very powerful features that have saved me a lot of time over the years.
Passing Commands To SSH
You can run a quick command on a remote system without needing to open a whole persistent terminal session. When the command is finished running the SSH tunnel will be closed. There are two ways to do this, because SSH is open source software and why not.
Here’s how to quickly check what version of Java is running on a remote system:
ssh username@serveraddress “java -version”
ssh username@serveraddress -C “java -version”
Note the capital C, lowercase c changes the cipher, which isn’t any kind of move you want to do.
Personally I like to use the
-C variant because just tacking the command at the end without any kind of flag feels dirty; but
you know, you gotta be yourself. Both styles are correct and do the exact same thing.
If the command you’re running requires elevated privileges (thus requiring a password prompt), or otherwise requires interaction, like editing
files or browsing them with
less, you’ll need to also pass
-t to force a tty session (which is just a fancy way to say a session where one is interacting with a machine).
Some examples of how you can use
-C and cases where you’ll also need
Bouncing a service
ssh -t username@serveraddress -C "sudo service restart nginx"
Grepping a root owned log file
ssh -t username@serveraddress -C "sudo grep NOAUTH /var/log/nginx/error.log"
Grepping some random file you own
ssh username@serveraddress -C "grep PATH ~/.bashrc"
Reading a log
ssh -t username@serveraddress -C "sudo less /var/log/nginx/error.log"
Monitoring resource consumption
ssh -t username@serveraddress -C "top"
Editing a config file in place
Please don’t do this, consider using configuration management and templating
ssh -t username@serveraddress -C "vim ~/.bashrc"
While it’s true that my favorite kind of infrastructure is the kind that no one is allowed to SSH into that’s not a reality for most people. Every now and then we need to login to a remote system and make things happen. Hopefully that’s been made a little easier for you after reading this post.