Copy an SSH Key to Remote Servers (Linux and Windows)

14 May 2026

Generate the key pair (if you don't have one)

ssh-keygen -t ed25519 -C "identifying_comment"
# Creates ~/.ssh/id_ed25519 (private) and ~/.ssh/id_ed25519.pub (public)

Only the public key (.pub) goes to the server. Never share the private one.

From Linux / macOS

ssh-copy-id (recommended):

ssh-copy-id -i ~/.ssh/id_ed25519.pub user@server

Manual:

cat ~/.ssh/id_ed25519.pub | ssh user@server \
  "mkdir -p ~/.ssh && chmod 700 ~/.ssh && cat >> ~/.ssh/authorized_keys && chmod 600 ~/.ssh/authorized_keys"

From Windows (PowerShell)

$pubKey = Get-Content "$env:USERPROFILE\.ssh\id_ed25519.pub"
ssh user@server "mkdir -p ~/.ssh && chmod 700 ~/.ssh && echo '$pubKey' >> ~/.ssh/authorized_keys && chmod 600 ~/.ssh/authorized_keys"

With Git Bash or WSL you can use ssh-copy-id like on Linux.

Test: ssh -i ~/.ssh/id_ed25519 user@server should log in without a password.

Many servers at once

#!/bin/bash
# deploy_key.sh - copy the public key to several servers
KEY="$HOME/.ssh/id_ed25519.pub"
USER_NAME="admin"
SERVERS=(
  "192.168.1.10"
  "192.168.1.11"
  "srv-web01.domain.local"
)

for HOST in "${SERVERS[@]}"; do
  echo "-> Copying to $HOST..."
  ssh-copy-id -i "$KEY" "$USER_NAME@$HOST" && echo "OK" || echo "FAILED: $HOST"
done

chmod +x deploy_key.sh && ./deploy_key.sh

Permissions on the server

Wrong permissions are the most common reason SSH ignores authorized_keys:

chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys
chown -R $USER:$USER ~/.ssh

Quick troubleshooting

Symptom	Likely cause
Still asks for a password	Wrong permissions on `~/.ssh` or `authorized_keys`
`Permission denied (publickey)`	Key not copied or wrong user
Works with `-i` but not without	Key not in `~/.ssh/config` or not loaded in the agent

Debug with:

ssh -vvv user@server 2>&1 | grep -E "key|auth|permission"

Bonus: ~/.ssh/config

Host srv-web
    HostName 192.168.1.10
    User admin
    IdentityFile ~/.ssh/id_ed25519

Host srv-db
    HostName 192.168.1.11
    User dbadmin
    IdentityFile ~/.ssh/id_ed25519

Then just ssh srv-web.

Related: SSH key-only login on Ubuntu.