Add user ssh-agent as daemon to Ubuntu 18.04LTS server.

README.md

Add user ssh-agent as daemon to Ubuntu 18.04LTS server

Create a new systemd user unit, which starts ssh-agent upon login to server. Will remain resident until the final session for the user has logged out.

Steps

• Create /etc/systemd/user/ssh-agent.service.

• Run the following commands (under your user account, not root) to install the systemd unit and start:

   $ systemctl --user enable ssh-agent.service
   $ systemctl --user start ssh-agent.service

• Add the following to ~/.bashrc:

   export SSH_AUTH_SOCK="$XDG_RUNTIME_DIR/ssh-agent.socket"

• Logout then login, confirm ssh-agent is running:

   $ systemctl --user status ssh-agent.service
   $ ssh-add -L

• Done.

Reference

• https://www.freebsd.org/cgi/man.cgi?query=ssh-agent&sektion=1&manpath=OpenBSD+3.4
• https://wiki.archlinux.org/title/Systemd/User

ssh-agent.service

[Unit]
Description=SSH authentication agent

[Service]
ExecStart=/usr/bin/ssh-agent -a %t/ssh-agent.socket -D
Type=simple

[Install]
WantedBy=default.target

Thank you for tip.
Your file do not works for me. (ubuntu20.22)
I fixed it like below,

[Unit]
Description=SSH key agent

[Service]
Type=simple
Environment=SSH_AUTH_SOCK=%t/ssh-agent.socket
ExecStart=/usr/bin/ssh-agent -D -a $SSH_AUTH_SOCK

[Install]
WantedBy=default.target

and works.