78 lines
1.8 KiB
Markdown
78 lines
1.8 KiB
Markdown
|
---
|
||
|
|
tags: [encryption, shell, server-management]
|
||
|
|
created: Tuesday, March 04, 2025
|
||
|
|
---
|
||
|
|
|
||
|
|
# SSH
|
||
|
|
|
||
|
|
SSH is the de facto standard for remote access to a Unix machine.
|
||
|
|
|
||
|
|
`ssh` is the client which you use to connect to another machine.
|
||
|
|
|
||
|
|
`sshd` is the server that manages incoming client requests for access.
|
||
|
|
|
||
|
|
## sshd
|
||
|
|
|
||
|
|
Typically the SSH server will be turned off.
|
||
|
|
|
||
|
|
To run at boot:
|
||
|
|
|
||
|
|
```sh
|
||
|
|
sudo systemctl enable sshd
|
||
|
|
```
|
||
|
|
|
||
|
|
To start immediately:
|
||
|
|
|
||
|
|
```sh
|
||
|
|
sudo systemctl start sshd
|
||
|
|
```
|
||
|
|
|
||
|
|
The `sshd` configuration is found in the directory `/etc/ssh`.
|
||
|
|
|
||
|
|
The config file is `/etc/ssh/sshd_config`.
|
||
|
|
|
||
|
|
Mostly you can leave this alone but the following is a useful property to set:
|
||
|
|
|
||
|
|
```
|
||
|
|
PermitRootLogin no
|
||
|
|
```
|
||
|
|
|
||
|
|
See [Disable non-root ssh access](Disable_non-root_ssh_access.md) for more.
|
||
|
|
|
||
|
|
## Known hosts
|
||
|
|
|
||
|
|
Within your home directory at `./ssh/known_hosts` you will find a record of all
|
||
|
|
the public keys of the servers you have connected. This file exists for both
|
||
|
|
servers and clients, e.g:
|
||
|
|
|
||
|
|
```sh
|
||
|
|
cat ./ssh/known_hosts
|
||
|
|
# systemsobscure.net ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIKn6vyv9b+Nk5r
|
||
|
|
# YVSAk5KvsTiC24K6uSpzCHzgLNoqt2
|
||
|
|
```
|
||
|
|
|
||
|
|
This shows the public key of my server at `systemsobscure.net` along with
|
||
|
|
others.
|
||
|
|
|
||
|
|
## Authorized keys
|
||
|
|
|
||
|
|
On servers only, there is also an `authorized_keys` file which shows the
|
||
|
|
server's own public keys that it presents to clients.
|
||
|
|
|
||
|
|
If I go to my server I see that this key matches the one I have on my client
|
||
|
|
computer `known_hosts`:
|
||
|
|
|
||
|
|
```sh
|
||
|
|
sudo cat /etc/ssh/ssh_host_ed25519_key.pub
|
||
|
|
# ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIKn6vyv9b+Nk5rYVSAk5KvsTiC24K6uSpzCHzgLNoqt2 root@self-host-server
|
||
|
|
|
||
|
|
```
|
||
|
|
|
||
|
|
Each user on a server will also have a `~/.ssh` directory also containing an
|
||
|
|
`authorized_keys` file. This contains the public keys of clients who are allowed
|
||
|
|
to connect to that user account.
|
||
|
|
|
||
|
|
Hence I see the same public key of my desktop client machine in both places.
|
||
|
|
|
||
|
|
## How the tunnel is created
|