In client PC

Generate ssh key if you don't have one

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$ ssh-keygen -t rsa -b 4096 -C "your_email@example.com"

Then copy (to clipboard) the public key (with the extension .pub), e.g.

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$ pbcopy < ~/.ssh/id_rsa.pub

In server

Add the public key to ~/.ssh/authorized_keys

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$ vim ~/.ssh/authorized_keys

Then paste the public key to next line of this file, save it

Test it

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$ ssh -i ~/.ssh/id_rsa user@xxx.xxx.xxx.xxx

You should be able to login without prompt you to input password

References: