SSH/ru

SSH (Secure SHell) это программа терминала, использующая шифрование, которая заменяет классическую программу telnet на Unix и подобных ей операционных системах.

In addition to remote terminal access provided by the main ssh binary, the SSH suite of programs has grown to include other tools such as scp (secure copy) and sftp (secure file transfer protocol).

Originally, SSH was not free. However, today the most popular and de-facto standard implementation of SSH is OpenBSD's OpenSSH, which comes pre-installed on Gentoo.

Installation
Most deployments will already have OpenSSH installed (through the package). This package uses the following USE flags:

After changing USE flags, don't forget to rebuild OpenSSH:

Server
Add openssh to the default runlevel if this hasn't been done already.

Start sshd daemon with:

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

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 as it has been deprecated in favor of protocol version 2):

To generate the keys for SSH protocol version 2 (DSA and RSA algorithms):

Server configuration
The SSH server is usually configured in the file, though it is also possible to perform further configuration in OpenRC's, including changing the location of the configuration file. For detailed information on how to configure the server see the sshd_config man page.

Вы также можете изучить этот гайд для конфигурации, ориентированной на безопасность.

Client configuration
The ssh client and related programs (scp, sftp, etc.) can be configured in following files:

For more information read the  manual:

Passwordless Authentication
Handy for git server management

Client
On the client run the following command:

Server
Make sure an account for the user exists on the server, and then place the clients' file into the  file.

Single Machine Testing
The above procedure can be tested out locally:

Troubleshooting
There are 3 different levels of debug modes that can help troubleshooting issues. With -v ssh prints debugging messages about its progress. This is helpful in debugging connection, authentication, and configuration problems. Multiple -v options increase the verbosity. The maximum is 3.

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, though the ssh client program has not exited.

Чтобы решить данную проблему, клиенты и сервера OpenSSH могут быть сконфигурированы посылать специальные невидимые сообщения 'keep alive', нацеленные на поддержку и подтверждение использования соединения.
 * Для разрешения keep alive для всех клиентов, подсоединенных к вашему локальному серверу, установите ClientAliveInterval 30 (или некоторое другое значение, в секундах) в файле.
 * Для разрешения keep alive для всех серверов, подсоединенных к вашему локальному клиенту, установите ServerAliveInterval 30 (или некоторое другое значение, в секундах) в файле.

X11 Forwarding Not Forwarding or Tunneling!
Problem: After you have made the necessary changes to the configuration files for permitting X11 Forwarding, you find 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  variable is either being unset or is being set after the SSH session sets it.

Test for this scenario as follows after logging in remotely:

You should get something similar to "localhost:10.0" or "localhost2.local:10.0" using server side  setting. If you're getting the usual ":0.0", check to make sure you are not unsetting or initializing the  variable within. If so, remove or comment your custom initialization of  or prevent  from executing during SSH login:

A trick would be to alias this within.

Смотри также

 * Securing OpenSSH - Документация Gentoo-разработчика
 * OpenSSH Key Management Part1 - Документация Gentoo, просмотрите все 3 части.
 * Гайд по авторизации по ключам Gentoo Linux
 * autossh - Определяет, когда соединение SSH обрывается, и заново подсоединяется.