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diff --git a/sshd_config.0 b/sshd_config.0 new file mode 100644 index 0000000..8132c3f --- /dev/null +++ b/sshd_config.0 @@ -0,0 +1,1153 @@ +SSHD_CONFIG(5) File Formats Manual SSHD_CONFIG(5) + +NAME + sshd_config M-bM-^@M-^S OpenSSH daemon configuration file + +DESCRIPTION + sshd(8) reads configuration data from /etc/ssh/sshd_config (or the file + specified with -f on the command line). The file contains keyword- + argument pairs, one per line. For each keyword, the first obtained value + will be used. Lines starting with M-bM-^@M-^X#M-bM-^@M-^Y and empty lines are interpreted as + comments. Arguments may optionally be enclosed in double quotes (") in + order to represent arguments containing spaces. + + The possible keywords and their meanings are as follows (note that + keywords are case-insensitive and arguments are case-sensitive): + + AcceptEnv + Specifies what environment variables sent by the client will be + copied into the session's environ(7). See SendEnv and SetEnv in + ssh_config(5) for how to configure the client. The TERM + environment variable is always accepted whenever the client + requests a pseudo-terminal as it is required by the protocol. + Variables are specified by name, which may contain the wildcard + characters M-bM-^@M-^X*M-bM-^@M-^Y and M-bM-^@M-^X?M-bM-^@M-^Y. Multiple environment variables may be + separated by whitespace or spread across multiple AcceptEnv + directives. Be warned that some environment variables could be + used to bypass restricted user environments. For this reason, + care should be taken in the use of this directive. The default + is not to accept any environment variables. + + AddressFamily + Specifies which address family should be used by sshd(8). Valid + arguments are any (the default), inet (use IPv4 only), or inet6 + (use IPv6 only). + + AllowAgentForwarding + Specifies whether ssh-agent(1) forwarding is permitted. The + default is yes. Note that disabling agent forwarding does not + improve security unless users are also denied shell access, as + they can always install their own forwarders. + + AllowGroups + This keyword can be followed by a list of group name patterns, + separated by spaces. If specified, login is allowed only for + users whose primary group or supplementary group list matches one + of the patterns. Only group names are valid; a numerical group + ID is not recognized. By default, login is allowed for all + groups. The allow/deny groups directives are processed in the + following order: DenyGroups, AllowGroups. + + See PATTERNS in ssh_config(5) for more information on patterns. + + AllowStreamLocalForwarding + Specifies whether StreamLocal (Unix-domain socket) forwarding is + permitted. The available options are yes (the default) or all to + allow StreamLocal forwarding, no to prevent all StreamLocal + forwarding, local to allow local (from the perspective of ssh(1)) + forwarding only or remote to allow remote forwarding only. Note + that disabling StreamLocal forwarding does not improve security + unless users are also denied shell access, as they can always + install their own forwarders. + + AllowTcpForwarding + Specifies whether TCP forwarding is permitted. The available + options are yes (the default) or all to allow TCP forwarding, no + to prevent all TCP forwarding, local to allow local (from the + perspective of ssh(1)) forwarding only or remote to allow remote + forwarding only. Note that disabling TCP forwarding does not + improve security unless users are also denied shell access, as + they can always install their own forwarders. + + AllowUsers + This keyword can be followed by a list of user name patterns, + separated by spaces. If specified, login is allowed only for + user names that match one of the patterns. Only user names are + valid; a numerical user ID is not recognized. By default, login + is allowed for all users. If the pattern takes the form + USER@HOST then USER and HOST are separately checked, restricting + logins to particular users from particular hosts. HOST criteria + may additionally contain addresses to match in CIDR + address/masklen format. The allow/deny users directives are + processed in the following order: DenyUsers, AllowUsers. + + See PATTERNS in ssh_config(5) for more information on patterns. + + AuthenticationMethods + Specifies the authentication methods that must be successfully + completed for a user to be granted access. This option must be + followed by one or more lists of comma-separated authentication + method names, or by the single string any to indicate the default + behaviour of accepting any single authentication method. If the + default is overridden, then successful authentication requires + completion of every method in at least one of these lists. + + For example, "publickey,password publickey,keyboard-interactive" + would require the user to complete public key authentication, + followed by either password or keyboard interactive + authentication. Only methods that are next in one or more lists + are offered at each stage, so for this example it would not be + possible to attempt password or keyboard-interactive + authentication before public key. + + For keyboard interactive authentication it is also possible to + restrict authentication to a specific device by appending a colon + followed by the device identifier bsdauth or pam. depending on + the server configuration. For example, + "keyboard-interactive:bsdauth" would restrict keyboard + interactive authentication to the bsdauth device. + + If the publickey method is listed more than once, sshd(8) + verifies that keys that have been used successfully are not + reused for subsequent authentications. For example, + "publickey,publickey" requires successful authentication using + two different public keys. + + Note that each authentication method listed should also be + explicitly enabled in the configuration. + + The available authentication methods are: "gssapi-with-mic", + "hostbased", "keyboard-interactive", "none" (used for access to + password-less accounts when PermitEmptyPasswords is enabled), + "password" and "publickey". + + AuthorizedKeysCommand + Specifies a program to be used to look up the user's public keys. + The program must be owned by root, not writable by group or + others and specified by an absolute path. Arguments to + AuthorizedKeysCommand accept the tokens described in the TOKENS + section. If no arguments are specified then the username of the + target user is used. + + The program should produce on standard output zero or more lines + of authorized_keys output (see AUTHORIZED_KEYS in sshd(8)). + AuthorizedKeysCommand is tried after the usual AuthorizedKeysFile + files and will not be executed if a matching key is found there. + By default, no AuthorizedKeysCommand is run. + + AuthorizedKeysCommandUser + Specifies the user under whose account the AuthorizedKeysCommand + is run. It is recommended to use a dedicated user that has no + other role on the host than running authorized keys commands. If + AuthorizedKeysCommand is specified but AuthorizedKeysCommandUser + is not, then sshd(8) will refuse to start. + + AuthorizedKeysFile + Specifies the file that contains the public keys used for user + authentication. The format is described in the AUTHORIZED_KEYS + FILE FORMAT section of sshd(8). Arguments to AuthorizedKeysFile + accept the tokens described in the TOKENS section. After + expansion, AuthorizedKeysFile is taken to be an absolute path or + one relative to the user's home directory. Multiple files may be + listed, separated by whitespace. Alternately this option may be + set to none to skip checking for user keys in files. The default + is ".ssh/authorized_keys .ssh/authorized_keys2". + + AuthorizedPrincipalsCommand + Specifies a program to be used to generate the list of allowed + certificate principals as per AuthorizedPrincipalsFile. The + program must be owned by root, not writable by group or others + and specified by an absolute path. Arguments to + AuthorizedPrincipalsCommand accept the tokens described in the + TOKENS section. If no arguments are specified then the username + of the target user is used. + + The program should produce on standard output zero or more lines + of AuthorizedPrincipalsFile output. If either + AuthorizedPrincipalsCommand or AuthorizedPrincipalsFile is + specified, then certificates offered by the client for + authentication must contain a principal that is listed. By + default, no AuthorizedPrincipalsCommand is run. + + AuthorizedPrincipalsCommandUser + Specifies the user under whose account the + AuthorizedPrincipalsCommand is run. It is recommended to use a + dedicated user that has no other role on the host than running + authorized principals commands. If AuthorizedPrincipalsCommand + is specified but AuthorizedPrincipalsCommandUser is not, then + sshd(8) will refuse to start. + + AuthorizedPrincipalsFile + Specifies a file that lists principal names that are accepted for + certificate authentication. When using certificates signed by a + key listed in TrustedUserCAKeys, this file lists names, one of + which must appear in the certificate for it to be accepted for + authentication. Names are listed one per line preceded by key + options (as described in AUTHORIZED_KEYS FILE FORMAT in sshd(8)). + Empty lines and comments starting with M-bM-^@M-^X#M-bM-^@M-^Y are ignored. + + Arguments to AuthorizedPrincipalsFile accept the tokens described + in the TOKENS section. After expansion, AuthorizedPrincipalsFile + is taken to be an absolute path or one relative to the user's + home directory. The default is none, i.e. not to use a + principals file M-bM-^@M-^S in this case, the username of the user must + appear in a certificate's principals list for it to be accepted. + + Note that AuthorizedPrincipalsFile is only used when + authentication proceeds using a CA listed in TrustedUserCAKeys + and is not consulted for certification authorities trusted via + ~/.ssh/authorized_keys, though the principals= key option offers + a similar facility (see sshd(8) for details). + + Banner The contents of the specified file are sent to the remote user + before authentication is allowed. If the argument is none then + no banner is displayed. By default, no banner is displayed. + + CASignatureAlgorithms + Specifies which algorithms are allowed for signing of + certificates by certificate authorities (CAs). The default is: + + ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521, + ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa + + Certificates signed using other algorithms will not be accepted + for public key or host-based authentication. + + ChallengeResponseAuthentication + Specifies whether challenge-response authentication is allowed + (e.g. via PAM or through authentication styles supported in + login.conf(5)) The default is yes. + + ChrootDirectory + Specifies the pathname of a directory to chroot(2) to after + authentication. At session startup sshd(8) checks that all + components of the pathname are root-owned directories which are + not writable by any other user or group. After the chroot, + sshd(8) changes the working directory to the user's home + directory. Arguments to ChrootDirectory accept the tokens + described in the TOKENS section. + + The ChrootDirectory must contain the necessary files and + directories to support the user's session. For an interactive + session this requires at least a shell, typically sh(1), and + basic /dev nodes such as null(4), zero(4), stdin(4), stdout(4), + stderr(4), and tty(4) devices. For file transfer sessions using + SFTP no additional configuration of the environment is necessary + if the in-process sftp-server is used, though sessions which use + logging may require /dev/log inside the chroot directory on some + operating systems (see sftp-server(8) for details). + + For safety, it is very important that the directory hierarchy be + prevented from modification by other processes on the system + (especially those outside the jail). Misconfiguration can lead + to unsafe environments which sshd(8) cannot detect. + + The default is none, indicating not to chroot(2). + + Ciphers + Specifies the ciphers allowed. Multiple ciphers must be comma- + separated. If the specified list begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, + then the specified ciphers will be appended to the default set + instead of replacing them. If the specified list begins with a + M-bM-^@M-^X-M-bM-^@M-^Y character, then the specified ciphers (including wildcards) + will be removed from the default set instead of replacing them. + If the specified list begins with a M-bM-^@M-^X^M-bM-^@M-^Y character, then the + specified ciphers will be placed at the head of the default set. + + The supported ciphers are: + + 3des-cbc + aes128-cbc + aes192-cbc + aes256-cbc + aes128-ctr + aes192-ctr + aes256-ctr + aes128-gcm@openssh.com + aes256-gcm@openssh.com + chacha20-poly1305@openssh.com + + The default is: + + chacha20-poly1305@openssh.com, + aes128-ctr,aes192-ctr,aes256-ctr, + aes128-gcm@openssh.com,aes256-gcm@openssh.com + + The list of available ciphers may also be obtained using "ssh -Q + cipher". + + ClientAliveCountMax + Sets the number of client alive messages which may be sent + without sshd(8) receiving any messages back from the client. If + this threshold is reached while client alive messages are being + sent, sshd will disconnect the client, terminating the session. + It is important to note that the use of client alive messages is + very different from TCPKeepAlive. The client alive messages are + sent through the encrypted channel and therefore will not be + spoofable. The TCP keepalive option enabled by TCPKeepAlive is + spoofable. The client alive mechanism is valuable when the + client or server depend on knowing when a connection has become + unresponsive. + + The default value is 3. If ClientAliveInterval is set to 15, and + ClientAliveCountMax is left at the default, unresponsive SSH + clients will be disconnected after approximately 45 seconds. + Setting a zero ClientAliveCountMax disables connection + termination. + + ClientAliveInterval + Sets a timeout interval in seconds after which if no data has + been received from the client, sshd(8) will send a message + through the encrypted channel to request a response from the + client. The default is 0, indicating that these messages will + not be sent to the client. + + Compression + Specifies whether compression is enabled after the user has + authenticated successfully. The argument must be yes, delayed (a + legacy synonym for yes) or no. The default is yes. + + DenyGroups + This keyword can be followed by a list of group name patterns, + separated by spaces. Login is disallowed for users whose primary + group or supplementary group list matches one of the patterns. + Only group names are valid; a numerical group ID is not + recognized. By default, login is allowed for all groups. The + allow/deny groups directives are processed in the following + order: DenyGroups, AllowGroups. + + See PATTERNS in ssh_config(5) for more information on patterns. + + DenyUsers + This keyword can be followed by a list of user name patterns, + separated by spaces. Login is disallowed for user names that + match one of the patterns. Only user names are valid; a + numerical user ID is not recognized. By default, login is + allowed for all users. If the pattern takes the form USER@HOST + then USER and HOST are separately checked, restricting logins to + particular users from particular hosts. HOST criteria may + additionally contain addresses to match in CIDR address/masklen + format. The allow/deny users directives are processed in the + following order: DenyUsers, AllowUsers. + + See PATTERNS in ssh_config(5) for more information on patterns. + + DisableForwarding + Disables all forwarding features, including X11, ssh-agent(1), + TCP and StreamLocal. This option overrides all other forwarding- + related options and may simplify restricted configurations. + + ExposeAuthInfo + Writes a temporary file containing a list of authentication + methods and public credentials (e.g. keys) used to authenticate + the user. The location of the file is exposed to the user + session through the SSH_USER_AUTH environment variable. The + default is no. + + FingerprintHash + Specifies the hash algorithm used when logging key fingerprints. + Valid options are: md5 and sha256. The default is sha256. + + ForceCommand + Forces the execution of the command specified by ForceCommand, + ignoring any command supplied by the client and ~/.ssh/rc if + present. The command is invoked by using the user's login shell + with the -c option. This applies to shell, command, or subsystem + execution. It is most useful inside a Match block. The command + originally supplied by the client is available in the + SSH_ORIGINAL_COMMAND environment variable. Specifying a command + of internal-sftp will force the use of an in-process SFTP server + that requires no support files when used with ChrootDirectory. + The default is none. + + GatewayPorts + Specifies whether remote hosts are allowed to connect to ports + forwarded for the client. By default, sshd(8) binds remote port + forwardings to the loopback address. This prevents other remote + hosts from connecting to forwarded ports. GatewayPorts can be + used to specify that sshd should allow remote port forwardings to + bind to non-loopback addresses, thus allowing other hosts to + connect. The argument may be no to force remote port forwardings + to be available to the local host only, yes to force remote port + forwardings to bind to the wildcard address, or clientspecified + to allow the client to select the address to which the forwarding + is bound. The default is no. + + GSSAPIAuthentication + Specifies whether user authentication based on GSSAPI is allowed. + The default is no. + + GSSAPICleanupCredentials + Specifies whether to automatically destroy the user's credentials + cache on logout. The default is yes. + + GSSAPIStrictAcceptorCheck + Determines whether to be strict about the identity of the GSSAPI + acceptor a client authenticates against. If set to yes then the + client must authenticate against the host service on the current + hostname. If set to no then the client may authenticate against + any service key stored in the machine's default store. This + facility is provided to assist with operation on multi homed + machines. The default is yes. + + HostbasedAcceptedKeyTypes + Specifies the key types that will be accepted for hostbased + authentication as a list of comma-separated patterns. + Alternately if the specified list begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, + then the specified key types will be appended to the default set + instead of replacing them. If the specified list begins with a + M-bM-^@M-^X-M-bM-^@M-^Y character, then the specified key types (including wildcards) + will be removed from the default set instead of replacing them. + If the specified list begins with a M-bM-^@M-^X^M-bM-^@M-^Y character, then the + specified key types will be placed at the head of the default + set. The default for this option is: + + ecdsa-sha2-nistp256-cert-v01@openssh.com, + ecdsa-sha2-nistp384-cert-v01@openssh.com, + ecdsa-sha2-nistp521-cert-v01@openssh.com, + sk-ecdsa-sha2-nistp256-cert-v01@openssh.com, + ssh-ed25519-cert-v01@openssh.com, + sk-ssh-ed25519-cert-v01@openssh.com, + rsa-sha2-512-cert-v01@openssh.com, + rsa-sha2-256-cert-v01@openssh.com, + ssh-rsa-cert-v01@openssh.com, + ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521, + sk-ecdsa-sha2-nistp256@openssh.com, + ssh-ed25519,sk-ssh-ed25519@openssh.com, + rsa-sha2-512,rsa-sha2-256,ssh-rsa + + The list of available key types may also be obtained using "ssh + -Q HostbasedAcceptedKeyTypes". + + HostbasedAuthentication + Specifies whether rhosts or /etc/hosts.equiv authentication + together with successful public key client host authentication is + allowed (host-based authentication). The default is no. + + HostbasedUsesNameFromPacketOnly + Specifies whether or not the server will attempt to perform a + reverse name lookup when matching the name in the ~/.shosts, + ~/.rhosts, and /etc/hosts.equiv files during + HostbasedAuthentication. A setting of yes means that sshd(8) + uses the name supplied by the client rather than attempting to + resolve the name from the TCP connection itself. The default is + no. + + HostCertificate + Specifies a file containing a public host certificate. The + certificate's public key must match a private host key already + specified by HostKey. The default behaviour of sshd(8) is not to + load any certificates. + + HostKey + Specifies a file containing a private host key used by SSH. The + defaults are /etc/ssh/ssh_host_ecdsa_key, + /etc/ssh/ssh_host_ed25519_key and /etc/ssh/ssh_host_rsa_key. + + Note that sshd(8) will refuse to use a file if it is group/world- + accessible and that the HostKeyAlgorithms option restricts which + of the keys are actually used by sshd(8). + + It is possible to have multiple host key files. It is also + possible to specify public host key files instead. In this case + operations on the private key will be delegated to an + ssh-agent(1). + + HostKeyAgent + Identifies the UNIX-domain socket used to communicate with an + agent that has access to the private host keys. If the string + "SSH_AUTH_SOCK" is specified, the location of the socket will be + read from the SSH_AUTH_SOCK environment variable. + + HostKeyAlgorithms + Specifies the host key algorithms that the server offers. The + default for this option is: + + ecdsa-sha2-nistp256-cert-v01@openssh.com, + ecdsa-sha2-nistp384-cert-v01@openssh.com, + ecdsa-sha2-nistp521-cert-v01@openssh.com, + sk-ecdsa-sha2-nistp256-cert-v01@openssh.com, + ssh-ed25519-cert-v01@openssh.com, + sk-ssh-ed25519-cert-v01@openssh.com, + rsa-sha2-512-cert-v01@openssh.com, + rsa-sha2-256-cert-v01@openssh.com, + ssh-rsa-cert-v01@openssh.com, + ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521, + sk-ecdsa-sha2-nistp256@openssh.com, + ssh-ed25519,sk-ssh-ed25519@openssh.com, + rsa-sha2-512,rsa-sha2-256,ssh-rsa + + The list of available key types may also be obtained using "ssh + -Q HostKeyAlgorithms". + + IgnoreRhosts + Specifies whether to ignore per-user .rhosts and .shosts files + during HostbasedAuthentication. The system-wide /etc/hosts.equiv + and /etc/shosts.equiv are still used regardless of this setting. + + Accepted values are yes (the default) to ignore all per-user + files, shosts-only to allow the use of .shosts but to ignore + .rhosts or no to allow both .shosts and rhosts. + + IgnoreUserKnownHosts + Specifies whether sshd(8) should ignore the user's + ~/.ssh/known_hosts during HostbasedAuthentication and use only + the system-wide known hosts file /etc/ssh/known_hosts. The + default is M-bM-^@M-^\noM-bM-^@M-^]. + + Include + Include the specified configuration file(s). Multiple pathnames + may be specified and each pathname may contain glob(7) wildcards + that will be expanded and processed in lexical order. Files + without absolute paths are assumed to be in /etc/ssh. An Include + directive may appear inside a Match block to perform conditional + inclusion. + + IPQoS Specifies the IPv4 type-of-service or DSCP class for the + connection. Accepted values are af11, af12, af13, af21, af22, + af23, af31, af32, af33, af41, af42, af43, cs0, cs1, cs2, cs3, + cs4, cs5, cs6, cs7, ef, le, lowdelay, throughput, reliability, a + numeric value, or none to use the operating system default. This + option may take one or two arguments, separated by whitespace. + If one argument is specified, it is used as the packet class + unconditionally. If two values are specified, the first is + automatically selected for interactive sessions and the second + for non-interactive sessions. The default is af21 (Low-Latency + Data) for interactive sessions and cs1 (Lower Effort) for non- + interactive sessions. + + KbdInteractiveAuthentication + Specifies whether to allow keyboard-interactive authentication. + The argument to this keyword must be yes or no. The default is + to use whatever value ChallengeResponseAuthentication is set to + (by default yes). + + KerberosAuthentication + Specifies whether the password provided by the user for + PasswordAuthentication will be validated through the Kerberos + KDC. To use this option, the server needs a Kerberos servtab + which allows the verification of the KDC's identity. The default + is no. + + KerberosGetAFSToken + If AFS is active and the user has a Kerberos 5 TGT, attempt to + acquire an AFS token before accessing the user's home directory. + The default is no. + + KerberosOrLocalPasswd + If password authentication through Kerberos fails then the + password will be validated via any additional local mechanism + such as /etc/passwd. The default is yes. + + KerberosTicketCleanup + Specifies whether to automatically destroy the user's ticket + cache file on logout. The default is yes. + + KexAlgorithms + Specifies the available KEX (Key Exchange) algorithms. Multiple + algorithms must be comma-separated. Alternately if the specified + list begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the specified methods will + be appended to the default set instead of replacing them. If the + specified list begins with a M-bM-^@M-^X-M-bM-^@M-^Y character, then the specified + methods (including wildcards) will be removed from the default + set instead of replacing them. If the specified list begins with + a M-bM-^@M-^X^M-bM-^@M-^Y character, then the specified methods will be placed at the + head of the default set. The supported algorithms are: + + curve25519-sha256 + curve25519-sha256@libssh.org + diffie-hellman-group1-sha1 + diffie-hellman-group14-sha1 + diffie-hellman-group14-sha256 + diffie-hellman-group16-sha512 + diffie-hellman-group18-sha512 + diffie-hellman-group-exchange-sha1 + diffie-hellman-group-exchange-sha256 + ecdh-sha2-nistp256 + ecdh-sha2-nistp384 + ecdh-sha2-nistp521 + sntrup4591761x25519-sha512@tinyssh.org + + The default is: + + curve25519-sha256,curve25519-sha256@libssh.org, + ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521, + diffie-hellman-group-exchange-sha256, + diffie-hellman-group16-sha512,diffie-hellman-group18-sha512, + diffie-hellman-group14-sha256 + + The list of available key exchange algorithms may also be + obtained using "ssh -Q KexAlgorithms". + + ListenAddress + Specifies the local addresses sshd(8) should listen on. The + following forms may be used: + + ListenAddress hostname|address [rdomain domain] + ListenAddress hostname:port [rdomain domain] + ListenAddress IPv4_address:port [rdomain domain] + ListenAddress [hostname|address]:port [rdomain domain] + + The optional rdomain qualifier requests sshd(8) listen in an + explicit routing domain. If port is not specified, sshd will + listen on the address and all Port options specified. The + default is to listen on all local addresses on the current + default routing domain. Multiple ListenAddress options are + permitted. For more information on routing domains, see + rdomain(4). + + LoginGraceTime + The server disconnects after this time if the user has not + successfully logged in. If the value is 0, there is no time + limit. The default is 120 seconds. + + LogLevel + Gives the verbosity level that is used when logging messages from + sshd(8). The possible values are: QUIET, FATAL, ERROR, INFO, + VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO. + DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify + higher levels of debugging output. Logging with a DEBUG level + violates the privacy of users and is not recommended. + + MACs Specifies the available MAC (message authentication code) + algorithms. The MAC algorithm is used for data integrity + protection. Multiple algorithms must be comma-separated. If the + specified list begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the specified + algorithms will be appended to the default set instead of + replacing them. If the specified list begins with a M-bM-^@M-^X-M-bM-^@M-^Y + character, then the specified algorithms (including wildcards) + will be removed from the default set instead of replacing them. + If the specified list begins with a M-bM-^@M-^X^M-bM-^@M-^Y character, then the + specified algorithms will be placed at the head of the default + set. + + The algorithms that contain "-etm" calculate the MAC after + encryption (encrypt-then-mac). These are considered safer and + their use recommended. The supported MACs are: + + hmac-md5 + hmac-md5-96 + hmac-sha1 + hmac-sha1-96 + hmac-sha2-256 + hmac-sha2-512 + umac-64@openssh.com + umac-128@openssh.com + hmac-md5-etm@openssh.com + hmac-md5-96-etm@openssh.com + hmac-sha1-etm@openssh.com + hmac-sha1-96-etm@openssh.com + hmac-sha2-256-etm@openssh.com + hmac-sha2-512-etm@openssh.com + umac-64-etm@openssh.com + umac-128-etm@openssh.com + + The default is: + + umac-64-etm@openssh.com,umac-128-etm@openssh.com, + hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com, + hmac-sha1-etm@openssh.com, + umac-64@openssh.com,umac-128@openssh.com, + hmac-sha2-256,hmac-sha2-512,hmac-sha1 + + The list of available MAC algorithms may also be obtained using + "ssh -Q mac". + + Match Introduces a conditional block. If all of the criteria on the + Match line are satisfied, the keywords on the following lines + override those set in the global section of the config file, + until either another Match line or the end of the file. If a + keyword appears in multiple Match blocks that are satisfied, only + the first instance of the keyword is applied. + + The arguments to Match are one or more criteria-pattern pairs or + the single token All which matches all criteria. The available + criteria are User, Group, Host, LocalAddress, LocalPort, RDomain, + and Address (with RDomain representing the rdomain(4) on which + the connection was received). + + The match patterns may consist of single entries or comma- + separated lists and may use the wildcard and negation operators + described in the PATTERNS section of ssh_config(5). + + The patterns in an Address criteria may additionally contain + addresses to match in CIDR address/masklen format, such as + 192.0.2.0/24 or 2001:db8::/32. Note that the mask length + provided must be consistent with the address - it is an error to + specify a mask length that is too long for the address or one + with bits set in this host portion of the address. For example, + 192.0.2.0/33 and 192.0.2.0/8, respectively. + + Only a subset of keywords may be used on the lines following a + Match keyword. Available keywords are AcceptEnv, + AllowAgentForwarding, AllowGroups, AllowStreamLocalForwarding, + AllowTcpForwarding, AllowUsers, AuthenticationMethods, + AuthorizedKeysCommand, AuthorizedKeysCommandUser, + AuthorizedKeysFile, AuthorizedPrincipalsCommand, + AuthorizedPrincipalsCommandUser, AuthorizedPrincipalsFile, + Banner, ChrootDirectory, ClientAliveCountMax, + ClientAliveInterval, DenyGroups, DenyUsers, ForceCommand, + GatewayPorts, GSSAPIAuthentication, HostbasedAcceptedKeyTypes, + HostbasedAuthentication, HostbasedUsesNameFromPacketOnly, + IgnoreRhosts, Include, IPQoS, KbdInteractiveAuthentication, + KerberosAuthentication, LogLevel, MaxAuthTries, MaxSessions, + PasswordAuthentication, PermitEmptyPasswords, PermitListen, + PermitOpen, PermitRootLogin, PermitTTY, PermitTunnel, + PermitUserRC, PubkeyAcceptedKeyTypes, PubkeyAuthentication, + RekeyLimit, RevokedKeys, RDomain, SetEnv, StreamLocalBindMask, + StreamLocalBindUnlink, TrustedUserCAKeys, X11DisplayOffset, + X11Forwarding and X11UseLocalhost. + + MaxAuthTries + Specifies the maximum number of authentication attempts permitted + per connection. Once the number of failures reaches half this + value, additional failures are logged. The default is 6. + + MaxSessions + Specifies the maximum number of open shell, login or subsystem + (e.g. sftp) sessions permitted per network connection. Multiple + sessions may be established by clients that support connection + multiplexing. Setting MaxSessions to 1 will effectively disable + session multiplexing, whereas setting it to 0 will prevent all + shell, login and subsystem sessions while still permitting + forwarding. The default is 10. + + MaxStartups + Specifies the maximum number of concurrent unauthenticated + connections to the SSH daemon. Additional connections will be + dropped until authentication succeeds or the LoginGraceTime + expires for a connection. The default is 10:30:100. + + Alternatively, random early drop can be enabled by specifying the + three colon separated values start:rate:full (e.g. "10:30:60"). + sshd(8) will refuse connection attempts with a probability of + rate/100 (30%) if there are currently start (10) unauthenticated + connections. The probability increases linearly and all + connection attempts are refused if the number of unauthenticated + connections reaches full (60). + + PasswordAuthentication + Specifies whether password authentication is allowed. The + default is yes. + + PermitEmptyPasswords + When password authentication is allowed, it specifies whether the + server allows login to accounts with empty password strings. The + default is no. + + PermitListen + Specifies the addresses/ports on which a remote TCP port + forwarding may listen. The listen specification must be one of + the following forms: + + PermitListen port + PermitListen host:port + + Multiple permissions may be specified by separating them with + whitespace. An argument of any can be used to remove all + restrictions and permit any listen requests. An argument of none + can be used to prohibit all listen requests. The host name may + contain wildcards as described in the PATTERNS section in + ssh_config(5). The wildcard M-bM-^@M-^X*M-bM-^@M-^Y can also be used in place of a + port number to allow all ports. By default all port forwarding + listen requests are permitted. Note that the GatewayPorts option + may further restrict which addresses may be listened on. Note + also that ssh(1) will request a listen host of M-bM-^@M-^\localhostM-bM-^@M-^] if no + listen host was specifically requested, and this name is treated + differently to explicit localhost addresses of M-bM-^@M-^\127.0.0.1M-bM-^@M-^] and + M-bM-^@M-^\::1M-bM-^@M-^]. + + PermitOpen + Specifies the destinations to which TCP port forwarding is + permitted. The forwarding specification must be one of the + following forms: + + PermitOpen host:port + PermitOpen IPv4_addr:port + PermitOpen [IPv6_addr]:port + + Multiple forwards may be specified by separating them with + whitespace. An argument of any can be used to remove all + restrictions and permit any forwarding requests. An argument of + none can be used to prohibit all forwarding requests. The + wildcard M-bM-^@M-^X*M-bM-^@M-^Y can be used for host or port to allow all hosts or + ports respectively. Otherwise, no pattern matching or address + lookups are performed on supplied names. By default all port + forwarding requests are permitted. + + PermitRootLogin + Specifies whether root can log in using ssh(1). The argument + must be yes, prohibit-password, forced-commands-only, or no. The + default is prohibit-password. + + If this option is set to prohibit-password (or its deprecated + alias, without-password), password and keyboard-interactive + authentication are disabled for root. + + If this option is set to forced-commands-only, root login with + public key authentication will be allowed, but only if the + command option has been specified (which may be useful for taking + remote backups even if root login is normally not allowed). All + other authentication methods are disabled for root. + + If this option is set to no, root is not allowed to log in. + + PermitTTY + Specifies whether pty(4) allocation is permitted. The default is + yes. + + PermitTunnel + Specifies whether tun(4) device forwarding is allowed. The + argument must be yes, point-to-point (layer 3), ethernet (layer + 2), or no. Specifying yes permits both point-to-point and + ethernet. The default is no. + + Independent of this setting, the permissions of the selected + tun(4) device must allow access to the user. + + PermitUserEnvironment + Specifies whether ~/.ssh/environment and environment= options in + ~/.ssh/authorized_keys are processed by sshd(8). Valid options + are yes, no or a pattern-list specifying which environment + variable names to accept (for example "LANG,LC_*"). The default + is no. Enabling environment processing may enable users to + bypass access restrictions in some configurations using + mechanisms such as LD_PRELOAD. + + PermitUserRC + Specifies whether any ~/.ssh/rc file is executed. The default is + yes. + + PidFile + Specifies the file that contains the process ID of the SSH + daemon, or none to not write one. The default is + /var/run/sshd.pid. + + Port Specifies the port number that sshd(8) listens on. The default + is 22. Multiple options of this type are permitted. See also + ListenAddress. + + PrintLastLog + Specifies whether sshd(8) should print the date and time of the + last user login when a user logs in interactively. The default + is yes. + + PrintMotd + Specifies whether sshd(8) should print /etc/motd when a user logs + in interactively. (On some systems it is also printed by the + shell, /etc/profile, or equivalent.) The default is yes. + + PubkeyAcceptedKeyTypes + Specifies the key types that will be accepted for public key + authentication as a list of comma-separated patterns. + Alternately if the specified list begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, + then the specified key types will be appended to the default set + instead of replacing them. If the specified list begins with a + M-bM-^@M-^X-M-bM-^@M-^Y character, then the specified key types (including wildcards) + will be removed from the default set instead of replacing them. + If the specified list begins with a M-bM-^@M-^X^M-bM-^@M-^Y character, then the + specified key types will be placed at the head of the default + set. The default for this option is: + + ecdsa-sha2-nistp256-cert-v01@openssh.com, + ecdsa-sha2-nistp384-cert-v01@openssh.com, + ecdsa-sha2-nistp521-cert-v01@openssh.com, + sk-ecdsa-sha2-nistp256-cert-v01@openssh.com, + ssh-ed25519-cert-v01@openssh.com, + sk-ssh-ed25519-cert-v01@openssh.com, + rsa-sha2-512-cert-v01@openssh.com, + rsa-sha2-256-cert-v01@openssh.com, + ssh-rsa-cert-v01@openssh.com, + ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521, + sk-ecdsa-sha2-nistp256@openssh.com, + ssh-ed25519,sk-ssh-ed25519@openssh.com, + rsa-sha2-512,rsa-sha2-256,ssh-rsa + + The list of available key types may also be obtained using "ssh + -Q PubkeyAcceptedKeyTypes". + + PubkeyAuthOptions + Sets one or more public key authentication options. The + supported keywords are: none (the default; indicating no + additional options are enabled), touch-required and + verify-required. + + The touch-required option causes public key authentication using + a FIDO authenticator algorithm (i.e. ecdsa-sk or ed25519-sk) to + always require the signature to attest that a physically present + user explicitly confirmed the authentication (usually by touching + the authenticator). By default, sshd(8) requires user presence + unless overridden with an authorized_keys option. The + touch-required flag disables this override. + + The verify-required option requires a FIDO key signature attest + that the user was verified, e.g. via a PIN. + + Neither the touch-required or verify-required options have any + effect for other, non-FIDO, public key types. + + PubkeyAuthentication + Specifies whether public key authentication is allowed. The + default is yes. + + RekeyLimit + Specifies the maximum amount of data that may be transmitted + before the session key is renegotiated, optionally followed a + maximum amount of time that may pass before the session key is + renegotiated. The first argument is specified in bytes and may + have a suffix of M-bM-^@M-^XKM-bM-^@M-^Y, M-bM-^@M-^XMM-bM-^@M-^Y, or M-bM-^@M-^XGM-bM-^@M-^Y to indicate Kilobytes, + Megabytes, or Gigabytes, respectively. The default is between + M-bM-^@M-^X1GM-bM-^@M-^Y and M-bM-^@M-^X4GM-bM-^@M-^Y, depending on the cipher. The optional second + value is specified in seconds and may use any of the units + documented in the TIME FORMATS section. The default value for + RekeyLimit is default none, which means that rekeying is + performed after the cipher's default amount of data has been sent + or received and no time based rekeying is done. + + RevokedKeys + Specifies revoked public keys file, or none to not use one. Keys + listed in this file will be refused for public key + authentication. Note that if this file is not readable, then + public key authentication will be refused for all users. Keys + may be specified as a text file, listing one public key per line, + or as an OpenSSH Key Revocation List (KRL) as generated by + ssh-keygen(1). For more information on KRLs, see the KEY + REVOCATION LISTS section in ssh-keygen(1). + + RDomain + Specifies an explicit routing domain that is applied after + authentication has completed. The user session, as well and any + forwarded or listening IP sockets, will be bound to this + rdomain(4). If the routing domain is set to %D, then the domain + in which the incoming connection was received will be applied. + + SecurityKeyProvider + Specifies a path to a library that will be used when loading FIDO + authenticator-hosted keys, overriding the default of using the + built-in USB HID support. + + SetEnv Specifies one or more environment variables to set in child + sessions started by sshd(8) as M-bM-^@M-^\NAME=VALUEM-bM-^@M-^]. The environment + value may be quoted (e.g. if it contains whitespace characters). + Environment variables set by SetEnv override the default + environment and any variables specified by the user via AcceptEnv + or PermitUserEnvironment. + + StreamLocalBindMask + Sets the octal file creation mode mask (umask) used when creating + a Unix-domain socket file for local or remote port forwarding. + This option is only used for port forwarding to a Unix-domain + socket file. + + The default value is 0177, which creates a Unix-domain socket + file that is readable and writable only by the owner. Note that + not all operating systems honor the file mode on Unix-domain + socket files. + + StreamLocalBindUnlink + Specifies whether to remove an existing Unix-domain socket file + for local or remote port forwarding before creating a new one. + If the socket file already exists and StreamLocalBindUnlink is + not enabled, sshd will be unable to forward the port to the Unix- + domain socket file. This option is only used for port forwarding + to a Unix-domain socket file. + + The argument must be yes or no. The default is no. + + StrictModes + Specifies whether sshd(8) should check file modes and ownership + of the user's files and home directory before accepting login. + This is normally desirable because novices sometimes accidentally + leave their directory or files world-writable. The default is + yes. Note that this does not apply to ChrootDirectory, whose + permissions and ownership are checked unconditionally. + + Subsystem + Configures an external subsystem (e.g. file transfer daemon). + Arguments should be a subsystem name and a command (with optional + arguments) to execute upon subsystem request. + + The command sftp-server implements the SFTP file transfer + subsystem. + + Alternately the name internal-sftp implements an in-process SFTP + server. This may simplify configurations using ChrootDirectory + to force a different filesystem root on clients. + + By default no subsystems are defined. + + SyslogFacility + Gives the facility code that is used when logging messages from + sshd(8). The possible values are: DAEMON, USER, AUTH, LOCAL0, + LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The + default is AUTH. + + TCPKeepAlive + Specifies whether the system should send TCP keepalive messages + to the other side. If they are sent, death of the connection or + crash of one of the machines will be properly noticed. However, + this means that connections will die if the route is down + temporarily, and some people find it annoying. On the other + hand, if TCP keepalives are not sent, sessions may hang + indefinitely on the server, leaving "ghost" users and consuming + server resources. + + The default is yes (to send TCP keepalive messages), and the + server will notice if the network goes down or the client host + crashes. This avoids infinitely hanging sessions. + + To disable TCP keepalive messages, the value should be set to no. + + TrustedUserCAKeys + Specifies a file containing public keys of certificate + authorities that are trusted to sign user certificates for + authentication, or none to not use one. Keys are listed one per + line; empty lines and comments starting with M-bM-^@M-^X#M-bM-^@M-^Y are allowed. If + a certificate is presented for authentication and has its signing + CA key listed in this file, then it may be used for + authentication for any user listed in the certificate's + principals list. Note that certificates that lack a list of + principals will not be permitted for authentication using + TrustedUserCAKeys. For more details on certificates, see the + CERTIFICATES section in ssh-keygen(1). + + UseDNS Specifies whether sshd(8) should look up the remote host name, + and to check that the resolved host name for the remote IP + address maps back to the very same IP address. + + If this option is set to no (the default) then only addresses and + not host names may be used in ~/.ssh/authorized_keys from and + sshd_config Match Host directives. + + UsePAM Enables the Pluggable Authentication Module interface. If set to + yes this will enable PAM authentication using + ChallengeResponseAuthentication and PasswordAuthentication in + addition to PAM account and session module processing for all + authentication types. + + Because PAM challenge-response authentication usually serves an + equivalent role to password authentication, you should disable + either PasswordAuthentication or ChallengeResponseAuthentication. + + If UsePAM is enabled, you will not be able to run sshd(8) as a + non-root user. The default is no. + + VersionAddendum + Optionally specifies additional text to append to the SSH + protocol banner sent by the server upon connection. The default + is none. + + X11DisplayOffset + Specifies the first display number available for sshd(8)'s X11 + forwarding. This prevents sshd from interfering with real X11 + servers. The default is 10. + + X11Forwarding + Specifies whether X11 forwarding is permitted. The argument must + be yes or no. The default is no. + + When X11 forwarding is enabled, there may be additional exposure + to the server and to client displays if the sshd(8) proxy display + is configured to listen on the wildcard address (see + X11UseLocalhost), though this is not the default. Additionally, + the authentication spoofing and authentication data verification + and substitution occur on the client side. The security risk of + using X11 forwarding is that the client's X11 display server may + be exposed to attack when the SSH client requests forwarding (see + the warnings for ForwardX11 in ssh_config(5)). A system + administrator may have a stance in which they want to protect + clients that may expose themselves to attack by unwittingly + requesting X11 forwarding, which can warrant a no setting. + + Note that disabling X11 forwarding does not prevent users from + forwarding X11 traffic, as users can always install their own + forwarders. + + X11UseLocalhost + Specifies whether sshd(8) should bind the X11 forwarding server + to the loopback address or to the wildcard address. By default, + sshd binds the forwarding server to the loopback address and sets + the hostname part of the DISPLAY environment variable to + localhost. This prevents remote hosts from connecting to the + proxy display. However, some older X11 clients may not function + with this configuration. X11UseLocalhost may be set to no to + specify that the forwarding server should be bound to the + wildcard address. The argument must be yes or no. The default + is yes. + + XAuthLocation + Specifies the full pathname of the xauth(1) program, or none to + not use one. The default is /usr/X11R6/bin/xauth. + +TIME FORMATS + sshd(8) command-line arguments and configuration file options that + specify time may be expressed using a sequence of the form: + time[qualifier], where time is a positive integer value and qualifier is + one of the following: + + M-bM-^_M-(noneM-bM-^_M-) seconds + s | S seconds + m | M minutes + h | H hours + d | D days + w | W weeks + + Each member of the sequence is added together to calculate the total time + value. + + Time format examples: + + 600 600 seconds (10 minutes) + 10m 10 minutes + 1h30m 1 hour 30 minutes (90 minutes) + +TOKENS + Arguments to some keywords can make use of tokens, which are expanded at + runtime: + + %% A literal M-bM-^@M-^X%M-bM-^@M-^Y. + %D The routing domain in which the incoming connection was + received. + %F The fingerprint of the CA key. + %f The fingerprint of the key or certificate. + %h The home directory of the user. + %i The key ID in the certificate. + %K The base64-encoded CA key. + %k The base64-encoded key or certificate for authentication. + %s The serial number of the certificate. + %T The type of the CA key. + %t The key or certificate type. + %U The numeric user ID of the target user. + %u The username. + + AuthorizedKeysCommand accepts the tokens %%, %f, %h, %k, %t, %U, and %u. + + AuthorizedKeysFile accepts the tokens %%, %h, %U, and %u. + + AuthorizedPrincipalsCommand accepts the tokens %%, %F, %f, %h, %i, %K, + %k, %s, %T, %t, %U, and %u. + + AuthorizedPrincipalsFile accepts the tokens %%, %h, %U, and %u. + + ChrootDirectory accepts the tokens %%, %h, %U, and %u. + + RoutingDomain accepts the token %D. + +FILES + /etc/ssh/sshd_config + Contains configuration data for sshd(8). This file should be + writable by root only, but it is recommended (though not + necessary) that it be world-readable. + +SEE ALSO + sftp-server(8), sshd(8) + +AUTHORS + OpenSSH is a derivative of the original and free ssh 1.2.12 release by + Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo + de Raadt and Dug Song removed many bugs, re-added newer features and + created OpenSSH. Markus Friedl contributed the support for SSH protocol + versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support + for privilege separation. + +OpenBSD 6.8 August 27, 2020 OpenBSD 6.8 |