311 lines
11 KiB
Nix
311 lines
11 KiB
Nix
# Global configuration for the SSH client.
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{ config, lib, pkgs, ... }:
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with lib;
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let
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cfg = config.programs.ssh;
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askPassword = cfg.askPassword;
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askPasswordWrapper = pkgs.writeScript "ssh-askpass-wrapper"
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''
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#! ${pkgs.runtimeShell} -e
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export DISPLAY="$(systemctl --user show-environment | ${pkgs.gnused}/bin/sed 's/^DISPLAY=\(.*\)/\1/; t; d')"
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exec ${askPassword} "$@"
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'';
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knownHosts = map (h: getAttr h cfg.knownHosts) (attrNames cfg.knownHosts);
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knownHostsText = (flip (concatMapStringsSep "\n") knownHosts
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(h: assert h.hostNames != [];
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optionalString h.certAuthority "@cert-authority " + concatStringsSep "," h.hostNames + " "
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+ (if h.publicKey != null then h.publicKey else readFile h.publicKeyFile)
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)) + "\n";
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in
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{
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###### interface
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options = {
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programs.ssh = {
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enableAskPassword = mkOption {
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type = types.bool;
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default = config.services.xserver.enable;
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defaultText = literalExpression "config.services.xserver.enable";
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description = "Whether to configure SSH_ASKPASS in the environment.";
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};
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askPassword = mkOption {
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type = types.str;
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default = "${pkgs.x11_ssh_askpass}/libexec/x11-ssh-askpass";
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defaultText = literalExpression ''"''${pkgs.x11_ssh_askpass}/libexec/x11-ssh-askpass"'';
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description = "Program used by SSH to ask for passwords.";
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};
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forwardX11 = mkOption {
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type = types.bool;
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default = false;
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description = ''
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Whether to request X11 forwarding on outgoing connections by default.
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This is useful for running graphical programs on the remote machine and have them display to your local X11 server.
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Historically, this value has depended on the value used by the local sshd daemon, but there really isn't a relation between the two.
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Note: there are some security risks to forwarding an X11 connection.
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NixOS's X server is built with the SECURITY extension, which prevents some obvious attacks.
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To enable or disable forwarding on a per-connection basis, see the -X and -x options to ssh.
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The -Y option to ssh enables trusted forwarding, which bypasses the SECURITY extension.
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'';
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};
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setXAuthLocation = mkOption {
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type = types.bool;
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description = ''
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Whether to set the path to <command>xauth</command> for X11-forwarded connections.
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This causes a dependency on X11 packages.
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'';
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};
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pubkeyAcceptedKeyTypes = mkOption {
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type = types.listOf types.str;
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default = [];
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example = [ "ssh-ed25519" "ssh-rsa" ];
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description = ''
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Specifies the key types that will be used for public key authentication.
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'';
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};
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hostKeyAlgorithms = mkOption {
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type = types.listOf types.str;
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default = [];
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example = [ "ssh-ed25519" "ssh-rsa" ];
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description = ''
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Specifies the host key algorithms that the client wants to use in order of preference.
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'';
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};
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extraConfig = mkOption {
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type = types.lines;
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default = "";
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description = ''
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Extra configuration text prepended to <filename>ssh_config</filename>. Other generated
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options will be added after a <code>Host *</code> pattern.
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See <citerefentry><refentrytitle>ssh_config</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for help.
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'';
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};
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startAgent = mkOption {
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type = types.bool;
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default = false;
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description = ''
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Whether to start the OpenSSH agent when you log in. The OpenSSH agent
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remembers private keys for you so that you don't have to type in
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passphrases every time you make an SSH connection. Use
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<command>ssh-add</command> to add a key to the agent.
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'';
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};
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agentTimeout = mkOption {
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type = types.nullOr types.str;
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default = null;
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example = "1h";
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description = ''
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How long to keep the private keys in memory. Use null to keep them forever.
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'';
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};
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agentPKCS11Whitelist = mkOption {
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type = types.nullOr types.str;
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default = null;
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example = literalExpression ''"''${pkgs.opensc}/lib/opensc-pkcs11.so"'';
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description = ''
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A pattern-list of acceptable paths for PKCS#11 shared libraries
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that may be used with the -s option to ssh-add.
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'';
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};
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package = mkOption {
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type = types.package;
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default = pkgs.openssh;
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defaultText = literalExpression "pkgs.openssh";
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description = ''
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The package used for the openssh client and daemon.
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'';
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};
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knownHosts = mkOption {
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default = {};
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type = types.attrsOf (types.submodule ({ name, ... }: {
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options = {
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certAuthority = mkOption {
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type = types.bool;
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default = false;
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description = ''
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This public key is an SSH certificate authority, rather than an
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individual host's key.
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'';
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};
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hostNames = mkOption {
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type = types.listOf types.str;
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default = [];
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description = ''
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A list of host names and/or IP numbers used for accessing
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the host's ssh service.
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'';
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};
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publicKey = mkOption {
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default = null;
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type = types.nullOr types.str;
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example = "ecdsa-sha2-nistp521 AAAAE2VjZHN...UEPg==";
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description = ''
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The public key data for the host. You can fetch a public key
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from a running SSH server with the <command>ssh-keyscan</command>
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command. The public key should not include any host names, only
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the key type and the key itself.
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'';
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};
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publicKeyFile = mkOption {
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default = null;
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type = types.nullOr types.path;
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description = ''
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The path to the public key file for the host. The public
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key file is read at build time and saved in the Nix store.
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You can fetch a public key file from a running SSH server
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with the <command>ssh-keyscan</command> command. The content
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of the file should follow the same format as described for
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the <literal>publicKey</literal> option.
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'';
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};
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};
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config = {
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hostNames = mkDefault [ name ];
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};
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}));
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description = ''
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The set of system-wide known SSH hosts.
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'';
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example = literalExpression ''
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{
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myhost = {
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hostNames = [ "myhost" "myhost.mydomain.com" "10.10.1.4" ];
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publicKeyFile = ./pubkeys/myhost_ssh_host_dsa_key.pub;
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};
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myhost2 = {
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hostNames = [ "myhost2" ];
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publicKeyFile = ./pubkeys/myhost2_ssh_host_dsa_key.pub;
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};
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}
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'';
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};
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kexAlgorithms = mkOption {
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type = types.nullOr (types.listOf types.str);
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default = null;
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example = [ "curve25519-sha256@libssh.org" "diffie-hellman-group-exchange-sha256" ];
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description = ''
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Specifies the available KEX (Key Exchange) algorithms.
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'';
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};
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ciphers = mkOption {
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type = types.nullOr (types.listOf types.str);
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default = null;
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example = [ "chacha20-poly1305@openssh.com" "aes256-gcm@openssh.com" ];
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description = ''
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Specifies the ciphers allowed and their order of preference.
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'';
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};
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macs = mkOption {
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type = types.nullOr (types.listOf types.str);
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default = null;
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example = [ "hmac-sha2-512-etm@openssh.com" "hmac-sha1" ];
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description = ''
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Specifies the MAC (message authentication code) algorithms in order of preference. The MAC algorithm is used
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for data integrity protection.
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'';
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};
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};
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};
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config = {
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programs.ssh.setXAuthLocation =
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mkDefault (config.services.xserver.enable || config.programs.ssh.forwardX11 || config.services.openssh.forwardX11);
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assertions =
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[ { assertion = cfg.forwardX11 -> cfg.setXAuthLocation;
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message = "cannot enable X11 forwarding without setting XAuth location";
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}
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] ++ flip mapAttrsToList cfg.knownHosts (name: data: {
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assertion = (data.publicKey == null && data.publicKeyFile != null) ||
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(data.publicKey != null && data.publicKeyFile == null);
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message = "knownHost ${name} must contain either a publicKey or publicKeyFile";
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});
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# SSH configuration. Slight duplication of the sshd_config
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# generation in the sshd service.
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environment.etc."ssh/ssh_config".text =
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''
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# Custom options from `extraConfig`, to override generated options
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${cfg.extraConfig}
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# Generated options from other settings
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Host *
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AddressFamily ${if config.networking.enableIPv6 then "any" else "inet"}
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${optionalString cfg.setXAuthLocation ''
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XAuthLocation ${pkgs.xorg.xauth}/bin/xauth
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''}
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ForwardX11 ${if cfg.forwardX11 then "yes" else "no"}
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${optionalString (cfg.pubkeyAcceptedKeyTypes != []) "PubkeyAcceptedKeyTypes ${concatStringsSep "," cfg.pubkeyAcceptedKeyTypes}"}
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${optionalString (cfg.hostKeyAlgorithms != []) "HostKeyAlgorithms ${concatStringsSep "," cfg.hostKeyAlgorithms}"}
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${optionalString (cfg.kexAlgorithms != null) "KexAlgorithms ${concatStringsSep "," cfg.kexAlgorithms}"}
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${optionalString (cfg.ciphers != null) "Ciphers ${concatStringsSep "," cfg.ciphers}"}
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${optionalString (cfg.macs != null) "MACs ${concatStringsSep "," cfg.macs}"}
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'';
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environment.etc."ssh/ssh_known_hosts".text = knownHostsText;
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# FIXME: this should really be socket-activated for über-awesomeness.
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systemd.user.services.ssh-agent = mkIf cfg.startAgent
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{ description = "SSH Agent";
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wantedBy = [ "default.target" ];
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unitConfig.ConditionUser = "!@system";
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serviceConfig =
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{ ExecStartPre = "${pkgs.coreutils}/bin/rm -f %t/ssh-agent";
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ExecStart =
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"${cfg.package}/bin/ssh-agent " +
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optionalString (cfg.agentTimeout != null) ("-t ${cfg.agentTimeout} ") +
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optionalString (cfg.agentPKCS11Whitelist != null) ("-P ${cfg.agentPKCS11Whitelist} ") +
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"-a %t/ssh-agent";
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StandardOutput = "null";
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Type = "forking";
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Restart = "on-failure";
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SuccessExitStatus = "0 2";
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};
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# Allow ssh-agent to ask for confirmation. This requires the
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# unit to know about the user's $DISPLAY (via ‘systemctl
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# import-environment’).
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environment.SSH_ASKPASS = optionalString cfg.enableAskPassword askPasswordWrapper;
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environment.DISPLAY = "fake"; # required to make ssh-agent start $SSH_ASKPASS
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};
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environment.extraInit = optionalString cfg.startAgent
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''
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if [ -z "$SSH_AUTH_SOCK" -a -n "$XDG_RUNTIME_DIR" ]; then
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export SSH_AUTH_SOCK="$XDG_RUNTIME_DIR/ssh-agent"
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fi
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'';
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environment.variables.SSH_ASKPASS = optionalString cfg.enableAskPassword askPassword;
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};
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}
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