# Referensi Cepat SSH

*Koneksi, key, konfigurasi, tunnel, SCP, SFTP*

> Source: OpenSSH Documentation (openssh.com) · MIT

## Koneksi

### Koneksi Dasar

```
ssh user@host                   # connect to host
ssh -p 2222 user@host           # custom port
ssh user@host command            # run remote command
ssh -t user@host "top"          # force TTY allocation
```

### Flag Koneksi

| Command | Description |
|---------|-------------|
| `-p port` | Koneksi ke port tertentu |
| `-i key` | Gunakan identity (private key) tertentu |
| `-t` | Paksa alokasi pseudo-terminal |
| `-v / -vv / -vvv` | Verbose debugging (semakin detail) |
| `-q` | Mode senyap (sembunyikan peringatan) |
| `-N` | Tanpa perintah remote (untuk tunnel) |
| `-f` | Jalankan di background sebelum perintah |
| `-J jump` | Jump host (ProxyJump) |

## Manajemen Key

### Buat Key

```
ssh-keygen -t ed25519 -C "you@example.com"
ssh-keygen -t rsa -b 4096 -C "you@example.com"
ssh-keygen -t ed25519 -f ~/.ssh/mykey
ssh-keygen -p -f ~/.ssh/id_ed25519  # change passphrase
```

### Deploy Public Key

```
ssh-copy-id user@host
ssh-copy-id -i ~/.ssh/mykey.pub user@host
# Manual: append .pub to remote authorized_keys
cat ~/.ssh/id_ed25519.pub | ssh user@host \
  "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"
```

### File Key

| Command | Description |
|---------|-------------|
| `~/.ssh/id_ed25519` | Private key (jaga kerahasiaannya) |
| `~/.ssh/id_ed25519.pub` | Public key (boleh dibagikan) |
| `~/.ssh/authorized_keys` | Remote: public key yang diterima |
| `~/.ssh/known_hosts` | Fingerprint host yang dikenal |

## File Konfigurasi

### Dasar ~/.ssh/config

```
Host myserver
  HostName 192.168.1.100
  User deploy
  Port 2222
  IdentityFile ~/.ssh/deploy_key

# Then connect with just:
# ssh myserver
```

### Opsi Konfigurasi Berguna

```
Host *
  ServerAliveInterval 60
  ServerAliveCountMax 3
  AddKeysToAgent yes
  IdentitiesOnly yes

Host bastion
  HostName bastion.example.com
  User admin
```

### Direktif Konfigurasi

| Command | Description |
|---------|-------------|
| `Host` | Pola alias untuk entri |
| `HostName` | Hostname atau IP sebenarnya |
| `User` | Nama pengguna login |
| `Port` | Port remote (default 22) |
| `IdentityFile` | Path ke private key |
| `ProxyJump` | Lewati host lain sebagai perantara |
| `ServerAliveInterval` | Interval keep-alive (detik) |
| `IdentitiesOnly` | Hanya gunakan key yang ditentukan |

## Port Forwarding

### Local Forwarding (-L)

```
# Access remote port 5432 via local port 5432
ssh -L 5432:localhost:5432 user@host
# Access remote-db:3306 through ssh host
ssh -L 3306:remote-db:3306 user@host
# Bind to all interfaces
ssh -L 0.0.0.0:8080:localhost:80 user@host
```

### Remote Forwarding (-R)

```
# Expose local port 3000 on remote port 8080
ssh -R 8080:localhost:3000 user@host
# Allow remote connections from any interface
ssh -R 0.0.0.0:8080:localhost:3000 user@host
```

### Dynamic Forwarding (-D)

```
# SOCKS5 proxy on local port 1080
ssh -D 1080 user@host
# Background SOCKS proxy
ssh -D 1080 -fN user@host
```

## SCP & SFTP

### SCP (Salinan Aman)

```
scp file.txt user@host:/remote/path/
scp user@host:/remote/file.txt ./local/
scp -r dir/ user@host:/remote/path/
scp -P 2222 file.txt user@host:/path/
```

### SFTP (Transfer Interaktif)

```
sftp user@host
# Inside sftp session:
# put local.txt    — upload file
# get remote.txt   — download file
# ls / lcd / cd    — list / change directory
```

### Flag Transfer

| Command | Description |
|---------|-------------|
| `-r` | Rekursif (salin direktori) |
| `-P port` | Tentukan port (SCP pakai -P, bukan -p) |
| `-C` | Aktifkan kompresi |
| `-l limit` | Batas bandwidth dalam Kbit/s |
| `-i key` | Gunakan identity file tertentu |

## Agent Forwarding

### SSH Agent

```
eval "$(ssh-agent -s)"          # start agent
ssh-add ~/.ssh/id_ed25519       # add key to agent
ssh-add -l                      # list loaded keys
ssh-add -D                      # remove all keys
```

### Meneruskan Agent

```
ssh -A user@host                # forward agent
# Or in ~/.ssh/config:
# Host myserver
#   ForwardAgent yes
```

### Catatan Agent

> Agent forwarding memungkinkan host remote menggunakan key
lokal tanpa menyalinnya. Gunakan hanya pada host yang
tepercaya. Lebih baik gunakan ProxyJump daripada agent
forwarding bila memungkinkan.

## Tunnel

### Tunnel Persisten

```
# Background tunnel that stays open
ssh -fNT -L 5432:localhost:5432 user@host
# Auto-reconnecting tunnel (with autossh)
autossh -M 0 -fNT -L 5432:localhost:5432 user@host
```

### Jump Host / Bastion

```
ssh -J bastion user@internal-host
ssh -J user1@hop1,user2@hop2 user@target
# Config equivalent:
# Host internal
#   HostName 10.0.0.5
#   ProxyJump bastion
```

### Manajemen Tunnel

| Command | Description |
|---------|-------------|
| `-f` | Jalankan di background setelah autentikasi |
| `-N` | Tanpa perintah remote |
| `-T` | Nonaktifkan pseudo-terminal |
| `~.` | Matikan sesi SSH yang macet (escape) |
| `~C` | Buka command line untuk forwarding |
| `~#` | Tampilkan daftar koneksi yang diteruskan |

## Troubleshooting

### Debug Koneksi

```
ssh -vvv user@host              # max verbosity
ssh -G user@host                # dump config (dry run)
ssh-keyscan host                # fetch host keys
ssh-keygen -R host              # remove from known_hosts
```

### Masalah Umum

| Command | Description |
|---------|-------------|
| `Permission denied` | Key, user, atau izin ~/.ssh salah (700/600) |
| `Host key changed` | Jalankan ssh-keygen -R host, lalu sambungkan kembali |
| `Connection timed out` | Periksa firewall, port, dan keterjangkauan host |
| `Too many auth failures` | Gunakan -i untuk menentukan key atau IdentitiesOnly |
| `Broken pipe` | Tambahkan ServerAliveInterval ke konfigurasi |

### Izin File

```
chmod 700 ~/.ssh
chmod 600 ~/.ssh/id_ed25519     # private key
chmod 644 ~/.ssh/id_ed25519.pub # public key
chmod 600 ~/.ssh/authorized_keys
chmod 644 ~/.ssh/known_hosts
```

## Praktik Keamanan Terbaik

### Hardening Server

| Command | Description |
|---------|-------------|
| `PasswordAuthentication no` | Nonaktifkan login dengan password |
| `PermitRootLogin no` | Nonaktifkan akses SSH sebagai root |
| `AllowUsers deploy` | Whitelist pengguna yang diizinkan |
| `Port 2222` | Gunakan port non-default (hindari scanner) |
| `MaxAuthTries 3` | Batasi percobaan autentikasi |

### Praktik Key

> Utamakan key Ed25519 (lebih kecil, lebih cepat, lebih aman).
Selalu atur passphrase pada private key.
Gunakan ssh-agent agar tidak perlu mengetik passphrase berulang.
Ganti key secara berkala; cabut key yang tidak digunakan.
Gunakan IdentitiesOnly untuk mengontrol key yang ditawarkan.

## Multiplexing

### Berbagi Koneksi

```
# In ~/.ssh/config
Host *
  ControlMaster auto
  ControlPath ~/.ssh/sockets/%r@%h-%p
  ControlPersist 600

# Create socket directory
mkdir -p ~/.ssh/sockets
```

### Keuntungan Multiplexing

> Menggunakan ulang satu koneksi TCP untuk beberapa sesi SSH
ke host yang sama. Menghilangkan handshake berulang —
koneksi lebih cepat dan overhead lebih rendah.
ControlPersist menjaga master tetap aktif (dalam detik).

## Escape Sequence

### Perintah Escape SSH

| Command | Description |
|---------|-------------|
| `~.` | Akhiri koneksi (matikan sesi yang macet) |
| `~^Z` | Suspensi sesi SSH |
| `~C` | Buka command line (tambah forwarding) |
| `~#` | Tampilkan daftar koneksi yang diteruskan |
| `~&` | Jalankan SSH di background (menunggu koneksi) |
| `~?` | Tampilkan bantuan escape |
| `~~` | Kirim tilde literal |