Mastering SSH: Run Remote Commands, Scripts, and Interactive Sessions

SSH is the fundamental tool for remote connections on Linux, and beyond simple logins it can automate a wide range of remote operations.

Remote Command Execution

You can run a command on a remote host without logging in, for example to check disk usage: ssh [email protected] "df -h" Multiple commands can be chained with a semicolon: ssh [email protected] "pwd; cat hello.txt" The first command returns the home directory ( /home/nick), and the second displays the contents of hello.txt. When using multiple commands, always enclose them in quotes to ensure they run remotely.

Executing Interactive Commands

Commands that require a TTY, such as sudo ls /root or top, fail without a pseudo‑terminal. Adding the -t option forces TTY allocation, keeping the session alive until the interactive command exits.

ssh -t [email protected] "sudo ls /root"

ssh -t [email protected] "top"

The official description of -t is: "Force pseudo‑terminal allocation. This can be used to execute arbitrary screen‑based programs on a remote machine…" Multiple -t options can be used for extra assurance.

Executing Multi‑Line Commands

Multi‑line commands can be sent by opening a single‑ or double‑quoted block and writing several lines before closing the quote. When the command itself contains quotes, mix single and double quotes to avoid conflicts.

Remote Script Execution

Running a Local Script on a Remote Host

Create a local script test.sh (e.g., containing ls and pwd) and pipe it to SSH: ssh [email protected] < test.sh To pass arguments, use bash -s on the remote side:

ssh [email protected] 'bash -s' < test.sh helloworld

The script receives bash as $0 and helloworld as $1.

Running a Script Stored on the Remote Server

If test.sh resides in the remote user's home directory, execute it by specifying the absolute path: ssh [email protected] "/home/nick/test.sh" Arguments can be passed similarly:

ssh [email protected] /home/nick/test.sh helloworld

The script outputs the script name as $0 and helloworld as $1.