57_Wolve
60433e4c8d
On a fresh AlmaLinux 9.8 box, install_bruteforce_protection ran unguarded under 'set -euo pipefail'. When sshguard (from EPEL) wasn't installable at that moment, the single failed dnf aborted the ENTIRE harden run before it wrote sshd_config or installed the pam_exec login notifier -- leaving a stock, unhardened box and a silently-missing ntfy hook. - oslib: install the iptables backend best-effort first, then sshguard, and return sshguard's status so callers can treat it as non-fatal. - harden-ssh/harden-jumphost: install_openssh now dies with a clear message on failure; sshguard is '|| warn' so sshd hardening and the notifier still apply. - install_login_notifier verifies the script + pam hook landed and logs 'Login notifier ACTIVE' (or a loud warning) instead of failing silently. - ntfy-ssh-login.sh: NTFY_DEBUG=1 logs delivery attempts + curl errors to /var/log/ssh-notify.log so the next silent failure leaves a trace. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
396 lines
16 KiB
Bash
396 lines
16 KiB
Bash
#!/usr/bin/env bash
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#
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# harden-ssh.sh
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#
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# SSH hardening for Alpine, Debian, and Alma Linux. Run on a fresh box (and,
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# for the simplex relay, BEFORE deploy-simplex.sh).
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#
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# All distro-specific operations go through scripts/oslib.sh. The OS-specific
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# surface for this script is: package install, the sshd service name, the
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# external sftp-server path, host-key keygen suppression (Alpine only), the
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# sshguard log source + firewall backend, and the boot hook that installs the
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# iptables jump. Each is clearly marked.
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#
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# What this does:
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# 1. Generates fresh Ed25519 host keys; removes RSA/ECDSA/DSA host keys
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# 2. Generates an Ed25519 root keypair, installs the public key into
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# /root/.ssh/authorized_keys, and PRINTS the private key to stdout once.
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# 3. Forces post-quantum hybrid KEX only (mlkem768x25519, sntrup761x25519).
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# 4. Modern ciphers and MACs only.
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# 5. Disables everything but an interactive terminal + SFTP (no forwarding,
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# tunneling, X11, agent, password auth).
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# 6. Optional non-default port (SSH_PORT).
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# 7. Installs sshguard for brute-force protection.
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# 8. Validates with `sshd -t` and prompts before reloading (so you don't
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# lock yourself out).
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#
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# A note on "quantum-safe": stock OpenSSH gives PQ KEY EXCHANGE (protects the
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# session key against store-now-decrypt-later) but classical Ed25519 AUTH
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# keys -- the strongest practical posture available without breaking client
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# compatibility.
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#
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# Usage:
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# bash harden-ssh.sh # port stays 22
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# SSH_PORT=2222 bash harden-ssh.sh # change port
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# ALLOWED_IP=1.2.3.4 bash harden-ssh.sh # whitelist your client IP
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# FORCE=1 bash harden-ssh.sh # skip the confirm prompt
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set -euo pipefail
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# Load the OS abstraction layer (sits next to this script).
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SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
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# shellcheck source=scripts/oslib.sh
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. "$SCRIPT_DIR/oslib.sh"
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# ============================================================================
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# CONFIG
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# ============================================================================
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: "${SSH_PORT:=22}"
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: "${ALLOWED_IP:=}" # optional: your client IP, sshguard-whitelisted
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: "${KEY_COMMENT:=root@$(hostname)-$(date +%Y%m%d)}"
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: "${FORCE:=0}"
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# log()/warn()/die() come from oslib (_log/_warn/_die); alias for readability.
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log() { _log "$@"; }
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warn() { _warn "$@"; }
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die() { _die "$@"; }
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[[ $EUID -eq 0 ]] || die "Run as root."
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os_detect
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log "Detected OS: ${OS_ID} (family ${OS_FAMILY}, init ${INIT_SYSTEM})"
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# ----------------------------------------------------------------------------
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# 1. Pre-flight: ensure an ssh client exists before probing its version
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# ----------------------------------------------------------------------------
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if ! command -v ssh >/dev/null 2>&1; then
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log "ssh not found; installing openssh..."
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install_openssh || die "Could not install OpenSSH; cannot harden. Fix the package error above, then re-run."
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fi
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log "Checking OpenSSH version supports PQ KEX..."
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SSH_VER=$(ssh -V 2>&1 | grep -oE 'OpenSSH_[0-9]+\.[0-9]+' | head -1 | sed 's/OpenSSH_//')
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SSH_MAJOR=${SSH_VER%%.*}
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SSH_MINOR=${SSH_VER##*.}
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# OpenSSH 9.0+ has sntrup761x25519-sha512; 9.9+ adds mlkem768x25519-sha256.
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HAS_MLKEM=0
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HAS_SNTRUP=0
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[[ $SSH_MAJOR -gt 9 || ( $SSH_MAJOR -eq 9 && $SSH_MINOR -ge 0 ) ]] && HAS_SNTRUP=1
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[[ $SSH_MAJOR -gt 9 || ( $SSH_MAJOR -eq 9 && $SSH_MINOR -ge 9 ) ]] && HAS_MLKEM=1
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[[ $HAS_SNTRUP -eq 1 || $HAS_MLKEM -eq 1 ]] \
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|| die "OpenSSH ${SSH_VER} has no PQ KEX. Need >= 9.0. Upgrade the base OS first."
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log "OpenSSH ${SSH_VER}: ML-KEM=${HAS_MLKEM} sntrup761=${HAS_SNTRUP}"
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KEX_LIST=""
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[[ $HAS_MLKEM -eq 1 ]] && KEX_LIST="mlkem768x25519-sha256"
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[[ $HAS_SNTRUP -eq 1 ]] && KEX_LIST="${KEX_LIST:+$KEX_LIST,}sntrup761x25519-sha512"
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# ----------------------------------------------------------------------------
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# 2. Install packages (OS-gated inside oslib)
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# ----------------------------------------------------------------------------
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log "Installing OpenSSH server + sshguard + iptables..."
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install_openssh || die "OpenSSH packages failed to install; cannot harden SSH. Fix the package error above, then re-run."
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# sshguard is best-effort: a host where it can't install right now (e.g. EPEL
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# momentarily unreachable) must still get the sshd_config hardening AND the login
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# notifier -- not a silently half-configured box. Warn and press on.
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install_bruteforce_protection \
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|| warn "sshguard not installed; brute-force protection is OFF. Add it later with: dnf install -y epel-release sshguard. Continuing with the rest of the hardening."
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# The external SFTP subsystem binary path differs per distro.
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SFTP_PATH="$(sftp_server_path)"
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[[ -x "$SFTP_PATH" ]] || warn "sftp-server not found at expected path ($SFTP_PATH); SFTP may not work until installed."
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# ----------------------------------------------------------------------------
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# 3. Host keys -- regenerate with Ed25519 only
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# ----------------------------------------------------------------------------
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log "Regenerating host keys (Ed25519 only)..."
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rm -f /etc/ssh/ssh_host_rsa_key* \
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/etc/ssh/ssh_host_ecdsa_key* \
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/etc/ssh/ssh_host_dsa_key*
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if [[ ! -f /etc/ssh/ssh_host_ed25519_key ]]; then
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ssh-keygen -q -t ed25519 -f /etc/ssh/ssh_host_ed25519_key -N "" \
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-C "host@$(hostname)-$(date +%Y%m%d)"
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fi
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chmod 600 /etc/ssh/ssh_host_ed25519_key
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chmod 644 /etc/ssh/ssh_host_ed25519_key.pub
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log "Host key fingerprint (verify on first connect):"
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ssh-keygen -l -f /etc/ssh/ssh_host_ed25519_key.pub | sed 's/^/ /'
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# Alpine's OpenRC sshd init regenerates RSA/ECDSA keys on each start; pin off.
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# No-op on systemd distros.
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sshd_disable_keygen
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# ----------------------------------------------------------------------------
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# 4. Root user keypair
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# ----------------------------------------------------------------------------
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log "Generating Ed25519 keypair for root..."
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mkdir -p /root/.ssh
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chmod 700 /root/.ssh
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touch /root/.ssh/authorized_keys
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chmod 600 /root/.ssh/authorized_keys
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TMP_KEY=$(mktemp -u /tmp/root_ed25519.XXXXXX)
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ssh-keygen -q -t ed25519 -f "$TMP_KEY" -N "" -C "$KEY_COMMENT"
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ROOT_PUB=$(cat "${TMP_KEY}.pub")
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ROOT_PRIV=$(cat "$TMP_KEY")
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# Idempotency: don't add the same pubkey twice.
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grep -qxF "$ROOT_PUB" /root/.ssh/authorized_keys || echo "$ROOT_PUB" >> /root/.ssh/authorized_keys
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# Seed root's authorized_keys with the shared admin keys from globals/ so the
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# box has a known, secure default login (SSH_KEYS_URL first, else
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# globals/authorized_keys). Best-effort: needs the repo's lib.sh present.
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if [[ "${SEED_KEYS:-1}" == "1" && -f "$SCRIPT_DIR/lib.sh" ]]; then
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# shellcheck source=scripts/lib.sh
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. "$SCRIPT_DIR/lib.sh"
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load_globals
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if declare -f resolve_ssh_keys >/dev/null 2>&1; then
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SEEDED=0
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while IFS= read -r k; do
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[[ -n "$k" ]] || continue
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grep -qxF "$k" /root/.ssh/authorized_keys || { echo "$k" >> /root/.ssh/authorized_keys; SEEDED=$((SEEDED+1)); }
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done <<< "$(resolve_ssh_keys 2>/dev/null || true)"
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[[ "$SEEDED" -gt 0 ]] && log "Seeded ${SEEDED} admin key(s) into /root/.ssh/authorized_keys from globals."
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fi
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fi
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# ----------------------------------------------------------------------------
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# 5. sshd_config
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# ----------------------------------------------------------------------------
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log "Writing /etc/ssh/sshd_config..."
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[[ -f /etc/ssh/sshd_config.orig ]] || cp /etc/ssh/sshd_config /etc/ssh/sshd_config.orig
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cat > /etc/ssh/sshd_config <<EOF
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# Generated by harden-ssh.sh on ${OS_ID} -- $(date -u +%FT%TZ)
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# Original config preserved at /etc/ssh/sshd_config.orig
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Port ${SSH_PORT}
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AddressFamily any
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ListenAddress 0.0.0.0
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ListenAddress ::
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PidFile /run/sshd.pid
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# --- Host key: Ed25519 only ---
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HostKey /etc/ssh/ssh_host_ed25519_key
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# --- Post-quantum hybrid KEX only ---
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# Anything not in this list (every classical-only KEX) is rejected, which is
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# what protects the session key against "store now, decrypt later".
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KexAlgorithms ${KEX_LIST}
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# --- Modern ciphers and MACs ---
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Ciphers chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes128-gcm@openssh.com
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MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128-etm@openssh.com
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# --- Host key signature algorithms ---
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HostKeyAlgorithms ssh-ed25519,ssh-ed25519-cert-v01@openssh.com
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# --- Public key algorithms accepted from clients ---
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# Ed25519 + RSA-4096 (RSA kept for older YubiKey PIV firmware pre-5.7).
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PubkeyAcceptedAlgorithms ssh-ed25519,ssh-ed25519-cert-v01@openssh.com,sk-ssh-ed25519@openssh.com,sk-ssh-ed25519-cert-v01@openssh.com,rsa-sha2-512,rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256,rsa-sha2-256-cert-v01@openssh.com
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RequiredRSASize 4096
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# --- Authentication ---
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PermitRootLogin prohibit-password
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PubkeyAuthentication yes
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PasswordAuthentication no
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PermitEmptyPasswords no
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ChallengeResponseAuthentication no
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KbdInteractiveAuthentication no
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UsePAM yes
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AuthenticationMethods publickey
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MaxAuthTries 3
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MaxSessions 4
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LoginGraceTime 30s
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# Expose the authenticated key to the session (file at \$SSH_USER_AUTH) so the
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# pam_exec login notifier can report which key was used.
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ExposeAuthInfo yes
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# --- Session restrictions: terminal + SFTP only, no forwarding/tunneling ---
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X11Forwarding no
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X11UseLocalhost yes
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AllowAgentForwarding no
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AllowTcpForwarding no
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AllowStreamLocalForwarding no
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DisableForwarding yes # belt-and-braces: kills *all* forwarding types
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GatewayPorts no
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PermitTunnel no
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PermitUserRC no
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PermitListen none
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PermitOpen none
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PrintMotd no
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TCPKeepAlive no
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ClientAliveInterval 300
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ClientAliveCountMax 2
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# --- Misc ---
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StrictModes yes
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IgnoreRhosts yes
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HostbasedAuthentication no
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Compression no
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Banner none
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# SFTP subsystem: external sftp-server binary (path is per-distro, resolved
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# by oslib's sftp_server_path). Enabled for backup retrieval, with logging to
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# AUTHPRIV at INFO so file transfers are auditable.
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Subsystem sftp ${SFTP_PATH} -f AUTHPRIV -l INFO
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# Restrict who can SSH in. Add other users here if you create them.
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AllowUsers root
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EOF
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# ----------------------------------------------------------------------------
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# 6. Validate config
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# ----------------------------------------------------------------------------
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log "Validating sshd config..."
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if ! sshd -t 2>/tmp/sshd-test.err; then
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cat /tmp/sshd-test.err >&2
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cp /etc/ssh/sshd_config.orig /etc/ssh/sshd_config
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die "sshd config invalid; restored original. NOT reloading."
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fi
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rm -f /tmp/sshd-test.err
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# ----------------------------------------------------------------------------
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# 7. sshguard (brute-force protection)
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# ----------------------------------------------------------------------------
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log "Configuring sshguard (backend + log source are OS-gated in oslib)..."
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mkdir -p /etc/sshguard
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WHITELIST=/etc/sshguard/whitelist
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{
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echo "127.0.0.1"
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echo "::1"
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[[ -n "$ALLOWED_IP" ]] && echo "$ALLOWED_IP"
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} > "$WHITELIST"
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SSHGUARD_BACKEND="$(sshguard_backend)"
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SSHGUARD_LOGREADER="$(sshguard_logreader)"
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[[ -x "${SSHGUARD_BACKEND}" ]] || warn "sshguard backend not found at ${SSHGUARD_BACKEND}; brute-force blocking may be inactive."
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cat > /etc/sshguard/sshguard.conf <<EOF
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BACKEND="${SSHGUARD_BACKEND}"
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${SSHGUARD_LOGREADER:+LOGREADER="${SSHGUARD_LOGREADER}"}
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THRESHOLD=30
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BLOCK_TIME=300
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DETECTION_TIME=1800
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PID_FILE=/run/sshguard.pid
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WHITELIST_FILE=${WHITELIST}
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EOF
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# INPUT -> sshguard jump. When the host firewall (harden-firewall.sh) is enabled
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# it owns the whole INPUT chain -- including this jump -- and persists it via the
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# distro's native iptables package, so we install the firewall and skip the
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# standalone boot hook. Otherwise fall back to the minimal init-agnostic boot
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# hook that just (re)inserts the jump at every boot.
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: "${ENABLE_FIREWALL:=1}"
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if [[ "$ENABLE_FIREWALL" == "1" && -f "$SCRIPT_DIR/harden-firewall.sh" ]]; then
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log "Installing host firewall (deny-by-default INPUT; carries the sshguard jump)..."
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SSH_PORT="$SSH_PORT" OPEN_PORTS="${OPEN_PORTS:-}" \
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FW_SSH_SOURCE="${FW_SSH_SOURCE:-}" FW_ALLOW_PING="${FW_ALLOW_PING:-1}" \
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FORCE=1 bash "$SCRIPT_DIR/harden-firewall.sh" apply \
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|| warn "harden-firewall.sh failed; INPUT left unfiltered. Re-run it manually."
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else
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HOOK=$(mktemp)
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cat > "$HOOK" <<'EOF'
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#!/bin/sh
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# Ensure sshguard chain exists and INPUT jumps to it for the SSH port.
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SSH_PORT=$(awk '/^Port / {print $2; exit}' /etc/ssh/sshd_config)
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SSH_PORT=${SSH_PORT:-22}
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for ipt in iptables ip6tables; do
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command -v "$ipt" >/dev/null 2>&1 || continue
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$ipt -N sshguard 2>/dev/null || true
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$ipt -C INPUT -p tcp --dport "$SSH_PORT" -j sshguard 2>/dev/null \
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|| $ipt -I INPUT -p tcp --dport "$SSH_PORT" -j sshguard
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done
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EOF
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install_boot_hook sshguard-iptables "$HOOK"
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rm -f "$HOOK"
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fi
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svc_enable_start sshguard || warn "Could not start sshguard; check 'sshguard.conf' on this distro."
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# ----------------------------------------------------------------------------
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# 7b. Optional: SSH login notifier (pam_exec -> ntfy)
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# ----------------------------------------------------------------------------
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# Enabled when NTFY_URL is provided. Reports user + source IP + the key used,
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# filtered by NOTIFY_GROUPS (empty here = every login on this host).
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if [[ -n "${NTFY_URL:-}" ]]; then
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: "${NTFY_REGION:=$(host_region)}"
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log "Installing SSH login notifier (ntfy)..."
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install_login_notifier "$SCRIPT_DIR/ntfy-ssh-login.sh" || warn "Notifier install had issues."
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fi
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# ----------------------------------------------------------------------------
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# 7c. Optional: daily unattended updates (set AUTO_UPDATE=1). New OS branches
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# are reported, not auto-applied.
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# ----------------------------------------------------------------------------
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if [[ "${AUTO_UPDATE:-0}" == "1" && -f "$SCRIPT_DIR/auto-update.sh" ]]; then
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log "Scheduling daily auto-update..."
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AUTO_REBOOT="${AUTO_REBOOT:-0}" \
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ALLOW_RELEASE_UPGRADE="${ALLOW_RELEASE_UPGRADE:-0}" \
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NOTIFY="${NOTIFY:-1}" \
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bash "$SCRIPT_DIR/auto-update.sh" install || warn "Could not schedule auto-update."
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fi
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# ----------------------------------------------------------------------------
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# 8. Enable sshd & reload (with safety prompt)
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# ----------------------------------------------------------------------------
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SSHD_SVC="$(sshd_service)"
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log "Enabling ${SSHD_SVC} at boot..."
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svc_enable "$SSHD_SVC"
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# Print the private key BEFORE reloading sshd so a bad reload still leaves you
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# with what you need to get back in via console.
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cat <<EOF
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================================================================
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COPY THIS PRIVATE KEY TO YOUR CLIENT *NOW*
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Save it as e.g. ~/.ssh/id_ed25519_host on your local machine,
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chmod 600, and connect with:
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ssh -i ~/.ssh/id_ed25519_host -p ${SSH_PORT} root@<host>
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----- BEGIN ROOT PRIVATE KEY (Ed25519) -----
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${ROOT_PRIV}
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----- END ROOT PRIVATE KEY -----
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Public key (already in /root/.ssh/authorized_keys):
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${ROOT_PUB}
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Host fingerprint (verify on first connect):
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$(ssh-keygen -l -f /etc/ssh/ssh_host_ed25519_key.pub)
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================================================================
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EOF
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shred -u "$TMP_KEY" "${TMP_KEY}.pub" 2>/dev/null || rm -f "$TMP_KEY" "${TMP_KEY}.pub"
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if [[ "$FORCE" != "1" ]]; then
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cat <<EOF
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sshd config has passed validation. Ready to reload sshd.
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If you are connected via SSH RIGHT NOW, open a SECOND session in another
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terminal -- before answering yes -- to verify the new keys, port, and PQ
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KEX work. If something is wrong, this reload will end your current session.
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Test in another terminal first:
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ssh -i ~/.ssh/<your saved key> -p ${SSH_PORT} \\
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-o KexAlgorithms=${KEX_LIST} root@<host>
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Reload sshd now? [y/N]
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EOF
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read -r ans
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if [[ "${ans,,}" != "y" && "${ans,,}" != "yes" ]]; then
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warn "Skipping reload. Run 'svc reload of ${SSHD_SVC}' manually when ready."
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exit 0
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fi
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fi
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log "Reloading ${SSHD_SVC}..."
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svc_reload "$SSHD_SVC"
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log "Done. Your session, if any, should remain alive (reload preserves connections)."
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log "Test from another machine before closing this session."
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