SSH key login 설정법

A. 주사용처

서버 백업

서버간 데이터 동기화시 rsync 이용시

kt cloud / AWS cloud 로그인시

B. 설정 방법

1. 클라이언트 서버에서 ssh-keygen

root@control:/home/user# ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:gzcO5QMV6N1NVHZKaxXLXd0z6SzNXeV/V3JoLipAs98 root@control
The key"s randomart image is:
+---[RSA 2048]----+
| .o. ...+.@|
| .. .o.@B|
| .+... o %oX|
| ..B. . .= B+|
| = S . o +|
| * = . . o|
| + E |
| . |
| |
+----[SHA256]-----+

2. key 확인

root@control:/home/user# ll /root/.ssh/
total 20
drwx------ 2 root root 4096 Jul 16 20:41 ./
drwx------ 4 root root 4096 Jul 13 04:05 ../
-rw------- 1 root root 1675 Jul 16 20:41 id_rsa
-rw-r--r-- 1 root root 394 Jul 16 20:41 id_rsa.pub
-rw-r--r-- 1 root root 222 Jul 3 03:13 known_hosts

3. 원격 서버로 key 복사

root@control:/home/user# scp $HOME/.ssh/id_rsa.pub user@com1:id_rsa.pub
assword:
id_rsa.pub

# 키 파일 내용 복사

# authorized_keys 파일은 /etc/ssh/sshd_config 에서 확인 필요. authorized_keys2 인 경우도 있음.

root@com1:/home/user# cat $HOME/id_rsa.pub >> $HOME/.ssh/authorized_keys

root@com1:/home/user# chmod 600 $HOME/.ssh/authorized_keys

4. 원격 서버 로그인

root@control:/home/user# ssh root@com1
Welcome to Ubuntu 16.04.4 LTS (GNU/Linux 4.4.0-31-generic x86_64)

* Documentation: https://help.ubuntu.com
* Management: https://landscape.canonical.com
* Support: https://ubuntu.com/advantage

20 packages can be updated.
4 updates are security updates.

*** System restart required ***

C. 체크 사항

1. centos 7 : authorized_keys2

2. ubuntu 16.04 : authorized_keys

3.authorized_keys(2) 파일의 권한이 600이 아니거나, 사용자가 틀릴경우 로그인 안됨.