OpenSSH : Use SSH-Agent

	Use SSH-Agent to automate inputting passphrase on key-pair authentication. Using SSH-Agent is valid for users who set SSH Key Pair with Passphrase.
[1]	It's necessarry to set key-pair with Passphrase first.
[2]	This is how to use SSH-Agent.

# start SSH-Agent debian@node01:~$  eval $(ssh-agent) Agent pid 1452 # add Identity debian@node01:~$  ssh-add Enter passphrase for /home/debian/.ssh/id_ed25519: Identity added: /home/debian/.ssh/id_ed25519 (debian@dlp.srv.world) # confirm debian@node01:~$  ssh-add -l 256 SHA256:DgSUdzX8e5T2xKy6YV9juS610Z8YtltX2Hw6XFJcgUQ debian@dlp.srv.world (ED25519) # try to connect with SSH without passphrase debian@node01:~$  ssh dlp.srv.world hostname dlp.srv.world # exit from SSH-Agent debian@node01:~$  eval $(ssh-agent -k) Agent pid 1452 killed