How To Run / Execute Command Using SSH

The ssh client will login to a server called server1, using user name called user1 and run a command call command1.

Examples: run commands over ssh

Get remote server date and time:

ssh user1@server1 date

Find out remote server disk space usage:

ssh user1@server1 'df -H'

Find out remote server kernel version and Linux distro names:

ssh root@nas01 uname -mrs

OR

ssh root@nas01 lsb_release -a

Sample session:

Animated gif 01: Running commands using ssh client

Run a script called /scripts/backup.sh:

ssh operator@oracle1  '/scripts/backup.sh'

Run sudo or su command using the following syntax:

## sudo syntax ##
ssh -t user@hostname sudo command
ssh -t user@hostname 'sudo command1 arg1 arg2'
 
 
## su syntax ##
ssh user@nas01 su -c "/path/to/command1 arg1 arg2"
 
# RHEL/CentOS specific #
ssh user@nas01 su --session-command="/path/to/command1 arg1 arg2"
ssh vivek@nixcraft.home.server su --session-command="/sbin/service httpd restart"

Without the -t option you will get an error that read as “sudo: Sorry, you must have a tty to run sudo on a Linux and Unix“.

Running and executing multiple ssh command

Create a new file named commands.txt using the cat command:
cat > commands.txt
Append command you wish to run:

date
uptime
df -H

Next execute commands remotely using ssh command from local file called commands.txt:

ssh server_name < commands.txt
ssh user@server_name < commands.txt
ssh admin@ls.backup < commands.txt

How to run multiple ssh command when using shell scripts

The multi-line command syntax is as follows and need to take help of Here document feature provided by bash:

#!/bin/bash
_remote="ls.backup"
_user="vivek"
 
echo "Local system name: $HOSTNAME"
echo "Local date and time: $(date)"
 
echo
echo "*** Running commands on remote host named $_remote ***"
echo
ssh -T $_remote <<'EOL'
	now="$(date)"
	name="$HOSTNAME"
	up="$(uptime)"
	echo "Server name is $name"
	echo "Server date and time is $now"
	echo "Server uptime: $up"
	echo "Bye"
EOL

Run the script:

Multi-line command executing using Heredoc feature of bash

Summing up

Please note that when you pass the -T to ssh when you wish to disable pseudo-terminal allocation. On the other hand, we can force pseudo-terminal allocation bypassing the -t option to ssh to execute arbitrary screen-based programs on a remote machine, which can be very useful. For instance, when implementing menu services. Multiple -t options force tty allocation, even if ssh has no local tty. See ssh man page online or read it locally by typing the man command:
man ssh