SSH/ko

SSH(Secure SHell)은 유닉스 같은 운영체제의 전통 텔넷 도구를 대체하는 암호화 터미널 프로그램입니다.

In addition to remote terminal access provided by the main binary, the SSH suite of programs has grown to include other tools such as  (Secure Copy Program) and  (Secure File Transfer Protocol).

원래 SSH는 free가 아니었습니다(여기서 free는 무료인지 자유인지 정확하지 않아 free로 표기했습니다. 역자 주). 그러나 오늘날 젠투에 미리 설치되어 나오는 OpenBSD의 OpenSSH는 가장 인기있는 프로그램이면서 SSH 구현체의 사실상 표준으로 자리잡았습니다.

Check install
Most deployments of Gentoo Linux will already have OpenSSH installed on the system. This can be checked by running the command. If it is installed a usage statement should be printed:

If no usage statement is printed is either corrupted or not installed. It is also possible that a user is simply rebuilding OpenSSH to include a new USE configuration. Whatever the case, proceed on to view possible USE settings.

Emerge
After changing the necessary USE flags, do not forget to install (or rebuild) OpenSSH:

Create keys
In order to provide a secure shell, cryptographic keys are used to manage the encryption, decryption, and hashing functionalities offered by SSH.

On the first start of the SSH service, system keys will be generated. Keys can be (re)generated using the command.

To generate the key used for SSH protocol version 1 (which usually is not enabled anymore; it has been deprecated in favor of protocol version 2) use:

SSH 프로토콜 버전 2의 키를 만들려면(DSA와 RSA 알고리즘):

서버 설정
설정 파일의 위치 변경을 포함하는 OpenRC의 에서 더 많은 설정을 할 수 있지만,  SSH 서버는 보통  파일에서 설정합니다. 서버 설정하는 방법에 대한 자세한 내용은 sshd_config man page를 보십시오.

Users should study Sven's OpenSSH guide for a security focused configuration.

클라이언트 설정
The client and related programs (,, etc.) can be configured using the following files:



For more information read the manual:

무 암호 인증
git 서버 관리를 위한 간단한 방법입니다.

클라이언트
클라이언트에서 다음 명령을 실행하십시오:

서버
Make sure an account for the user exists on the server, and then place the clients' file into the server's  file in the user's home directory.

Single machine testing
위 절차를 지역 머신에서 시험할 수 있습니다:

Intrusion prevention
SSH is a commonly attacked service. Tools such as sshguard and fail2ban monitor logs and black list remote users who have repeatedly attempted, yet failed to login. Utilize them as needed to secure a frequently attacked system.

OpenRC
Add the OpenSSH daemon to the default runlevel:

Start the sshd daemon with:

The OpenSSH server can be controlled like any other OpenRC-managed service:

Systemd
To have the OpenSSH daemon start when the system starts:

To start the OpenSSH daemon now:

To check if the service has started:

Troubleshooting
There are 3 different levels of debug modes that can help troubleshooting issues. With the  option SSH prints debugging messages about its progress. This is helpful in debugging connection, authentication, and configuration problems. Multiple  options increase the verbosity. Maximum verbosity is three levels deep.

Death of long-lived connections
Many internet access devices perform Network Address Translation (NAT), a process that enables devices on a private network such as that typically found in a home or business place to access foreign networks, such as the internet, despite only having a single IP address on that network. Unfortunately, not all NAT devices are created equal, and some of them incorrectly close long-lived, occasional-use TCP connections such as those used by SSH. This is generally observable as a sudden inability to interact with the remote server, even though the client program has not exited.

In order to resolve the issue, OpenSSH clients and servers can be configured to send a 'keep alive', or invisible message aimed at maintaining and confirming the live status of the link:


 * To enable keep alive for all clients connecting to your local server, set  (or some other value, in seconds) within the  file.
 * To enable keep alive for all servers connected to by your local client, set  (or some other value, in seconds) within the  file.

X11 forwarding, not forwarding, or tunneling
Problem: After having made the necessary changes to the configuration files for permitting X11 forwarding, it is discovered X applications are executing on the server and are not being forwarded to the client.

Solution: What is likely occurring during SSH login into the remote server or host, the DISPLAY variable is either being unset or is being set after the SSH session sets it.

Test for this scenario perform the following after logging in remotely:

The output should be something similar to  or   using server side   setting. If the usual  is not displayed, check to make sure the DISPLAY variable within  is not being unset or re-initializing. If it is, remove or comment out any custom initialization of the DISPLAY variable to prevent the code in from executing during a SSH login:

Be sure to substitute  in the command above with the proper username.

A trick that works to complete this task would be to define an alias within the users' file.

External resources

 * Securing OpenSSH - Gentoo developer documentation.
 * OpenSSH Key Management Part1 - Gentoo documentation, have a look at all 3 parts.