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diff --git a/sshd_config.0 b/sshd_config.0 new file mode 100644 index 0000000..c9a09a4 --- /dev/null +++ b/sshd_config.0 @@ -0,0 +1,573 @@ +SSHD_CONFIG(5) OpenBSD Programmer's Manual SSHD_CONFIG(5) + +NAME + sshd_config - OpenSSH SSH daemon configuration file + +SYNOPSIS + /etc/ssh/sshd_config + +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-argu- + ment pairs, one per line. Lines starting with `#' 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 key- + words 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 in + ssh_config(5) for how to configure the client. Note that envi- + ronment passing is only supported for protocol 2. Variables are + specified by name, which may contain the wildcard characters `*' + and `?'. 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'', ``inet'' (use IPv4 only), or ``inet6'' + (use IPv6 only). The default is ``any''. + + 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 directives are processed in the following + order: DenyUsers, AllowUsers, DenyGroups, and finally + AllowGroups. + + See PATTERNS in ssh_config(5) for more information on patterns. + + AllowTcpForwarding + Specifies whether TCP forwarding is permitted. The default is + ``yes''. Note that disabling TCP forwarding does not improve se- + curity unless users are also denied shell access, as they can al- + ways 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 us- + er 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 US- + ER@HOST then USER and HOST are separately checked, restricting + logins to particular users from particular hosts. The allow/deny + directives are processed in the following order: DenyUsers, + AllowUsers, DenyGroups, and finally AllowGroups. + + See PATTERNS in ssh_config(5) for more information on patterns. + + AuthorizedKeysFile + Specifies the file that contains the public keys that can be used + for user authentication. AuthorizedKeysFile may contain tokens + of the form %T which are substituted during connection setup. + The following tokens are defined: %% is replaced by a literal + '%', %h is replaced by the home directory of the user being au- + thenticated, and %u is replaced by the username of that user. + After expansion, AuthorizedKeysFile is taken to be an absolute + path or one relative to the user's home directory. The default + is ``.ssh/authorized_keys''. + + Banner In some jurisdictions, sending a warning message before authenti- + cation may be relevant for getting legal protection. The con- + tents of the specified file are sent to the remote user before + authentication is allowed. This option is only available for + protocol version 2. By default, no banner is displayed. + + ChallengeResponseAuthentication + Specifies whether challenge-response authentication is allowed. + All authentication styles from login.conf(5) are supported. The + default is ``yes''. + + Ciphers + Specifies the ciphers allowed for protocol version 2. Multiple + ciphers must be comma-separated. The supported ciphers are + ``3des-cbc'', ``aes128-cbc'', ``aes192-cbc'', ``aes256-cbc'', + ``aes128-ctr'', ``aes192-ctr'', ``aes256-ctr'', ``arcfour128'', + ``arcfour256'', ``arcfour'', ``blowfish-cbc'', and + ``cast128-cbc''. The default is: + + aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128, + arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr, + aes192-ctr,aes256-ctr + + ClientAliveCountMax + Sets the number of client alive messages (see below) which may be + sent without sshd(8) receiving any messages back from the client. + If this threshold is reached while client alive messages are be- + ing sent, sshd will disconnect the client, terminating the ses- + sion. It is important to note that the use of client alive mes- + sages is very different from TCPKeepAlive (below). The client + alive messages are sent through the encrypted channel and there- + fore will not be spoofable. The TCP keepalive option enabled by + TCPKeepAlive is spoofable. The client alive mechanism is valu- + able when the client or server depend on knowing when a connec- + tion has become inactive. + + The default value is 3. If ClientAliveInterval (see below) is + set to 15, and ClientAliveCountMax is left at the default, unre- + sponsive SSH clients will be disconnected after approximately 45 + seconds. This option applies to protocol version 2 only. + + 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. This option applies to protocol ver- + sion 2 only. + + Compression + Specifies whether compression is allowed, or delayed until the + user has authenticated successfully. The argument must be + ``yes'', ``delayed'', or ``no''. The default is ``delayed''. + + 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 recog- + nized. By default, login is allowed for all groups. The al- + low/deny directives are processed in the following order: + DenyUsers, AllowUsers, DenyGroups, and finally 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 numeri- + cal 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. The allow/deny directives are pro- + cessed in the following order: DenyUsers, AllowUsers, DenyGroups, + and finally AllowGroups. + + See PATTERNS in ssh_config(5) for more information on patterns. + + ForceCommand + Forces the execution of the command specified by ForceCommand, + ignoring any command supplied by the client. The command is in- + voked 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. + + 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 con- + nect. The argument may be ``no'' to force remote port forward- + ings to be available to the local host only, ``yes'' to force re- + mote 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''. Note that this option applies to protocol + version 2 only. + + GSSAPICleanupCredentials + Specifies whether to automatically destroy the user's credentials + cache on logout. The default is ``yes''. Note that this option + applies to protocol version 2 only. + + HostbasedAuthentication + Specifies whether rhosts or /etc/hosts.equiv authentication to- + gether with successful public key client host authentication is + allowed (host-based authentication). This option is similar to + RhostsRSAAuthentication and applies to protocol version 2 only. + The default is ``no''. + + HostbasedUsesNameFromPacketOnly + Specifies whether or not the server will attempt to perform a re- + verse 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''. + + HostKey + Specifies a file containing a private host key used by SSH. The + default is /etc/ssh/ssh_host_key for protocol version 1, and + /etc/ssh/ssh_host_rsa_key and /etc/ssh/ssh_host_dsa_key for pro- + tocol version 2. Note that sshd(8) will refuse to use a file if + it is group/world-accessible. It is possible to have multiple + host key files. ``rsa1'' keys are used for version 1 and ``dsa'' + or ``rsa'' are used for version 2 of the SSH protocol. + + IgnoreRhosts + Specifies that .rhosts and .shosts files will not be used in + RhostsRSAAuthentication or HostbasedAuthentication. + + /etc/hosts.equiv and /etc/shosts.equiv are still used. The de- + fault is ``yes''. + + IgnoreUserKnownHosts + Specifies whether sshd(8) should ignore the user's + ~/.ssh/known_hosts during RhostsRSAAuthentication or + HostbasedAuthentication. The default is ``no''. + + 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 pass- + word 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''. + + KeyRegenerationInterval + In protocol version 1, the ephemeral server key is automatically + regenerated after this many seconds (if it has been used). The + purpose of regeneration is to prevent decrypting captured ses- + sions by later breaking into the machine and stealing the keys. + The key is never stored anywhere. If the value is 0, the key is + never regenerated. The default is 3600 (seconds). + + ListenAddress + Specifies the local addresses sshd(8) should listen on. The fol- + lowing forms may be used: + + ListenAddress host|IPv4_addr|IPv6_addr + ListenAddress host|IPv4_addr:port + ListenAddress [host|IPv6_addr]:port + + If port is not specified, sshd will listen on the address and all + prior Port options specified. The default is to listen on all + local addresses. Multiple ListenAddress options are permitted. + Additionally, any Port options must precede this option for non- + port qualified addresses. + + LoginGraceTime + The server disconnects after this time if the user has not suc- + cessfully 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) algo- + rithms. The MAC algorithm is used in protocol version 2 for data + integrity protection. Multiple algorithms must be comma-separat- + ed. The default is: ``hmac-md5,hmac-sha1,hmac-ripemd160,hmac- + sha1-96,hmac-md5-96''. + + 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, un- + til either another Match line or the end of the file. The argu- + ments to Match are one or more criteria-pattern pairs. The + available criteria are User, Group, Host, and Address. Only a + subset of keywords may be used on the lines following a Match + keyword. Available keywords are AllowTcpForwarding, Banner, + ForceCommand, GatewayPorts, GSSApiAuthentication, + KbdInteractiveAuthentication, KerberosAuthentication, + PasswordAuthentication, PermitOpen, RhostsRSAAuthentication, + RSAAuthentication, 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. + + MaxStartups + Specifies the maximum number of concurrent unauthenticated con- + nections to the SSH daemon. Additional connections will be + dropped until authentication succeeds or the LoginGraceTime ex- + pires for a connection. The default is 10. + + 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 in- + creases linearly and all connection attempts are refused if the + number of unauthenticated connections reaches ``full'' (60). + + PasswordAuthentication + Specifies whether password authentication is allowed. The de- + fault 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''. + + PermitOpen + Specifies the destinations to which TCP port forwarding is per- + mitted. The forwarding specification must be one of the follow- + ing 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 re- + strictions and permit any forwarding requests. By default all + port forwarding requests are permitted. + + PermitRootLogin + Specifies whether root can log in using ssh(1). The argument + must be ``yes'', ``without-password'', ``forced-commands-only'', + or ``no''. The default is ``yes''. + + If this option is set to ``without-password'', password authenti- + cation is 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. + + PermitTunnel + Specifies whether tun(4) device forwarding is allowed. The argu- + ment 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''. + + PermitUserEnvironment + Specifies whether ~/.ssh/environment and environment= options in + ~/.ssh/authorized_keys are processed by sshd(8). The default is + ``no''. Enabling environment processing may enable users to by- + pass access restrictions in some configurations using mechanisms + such as LD_PRELOAD. + + PidFile + Specifies the file that contains the process ID of the SSH dae- + mon. 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''. + + Protocol + Specifies the protocol versions sshd(8) supports. The possible + values are `1' and `2'. Multiple versions must be comma-separat- + ed. The default is ``2,1''. Note that the order of the protocol + list does not indicate preference, because the client selects + among multiple protocol versions offered by the server. Specify- + ing ``2,1'' is identical to ``1,2''. + + PubkeyAuthentication + Specifies whether public key authentication is allowed. The de- + fault is ``yes''. Note that this option applies to protocol ver- + sion 2 only. + + RhostsRSAAuthentication + Specifies whether rhosts or /etc/hosts.equiv authentication to- + gether with successful RSA host authentication is allowed. The + default is ``no''. This option applies to protocol version 1 on- + ly. + + RSAAuthentication + Specifies whether pure RSA authentication is allowed. The de- + fault is ``yes''. This option applies to protocol version 1 on- + ly. + + ServerKeyBits + Defines the number of bits in the ephemeral protocol version 1 + server key. The minimum value is 512, and the default is 768. + + 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''. + + 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(8) implements the ``sftp'' file transfer subsystem. + By default no subsystems are defined. Note that this option ap- + plies to protocol version 2 only. + + 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 de- + fault 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 tem- + porarily, 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 re- + sources. + + 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''. + + UseDNS Specifies whether sshd(8) should look up the remote host name and + check that the resolved host name for the remote IP address maps + back to the very same IP address. The default is ``yes''. + + UseLogin + Specifies whether login(1) is used for interactive login ses- + sions. The default is ``no''. Note that login(1) is never used + for remote command execution. Note also, that if this is en- + abled, X11Forwarding will be disabled because login(1) does not + know how to handle xauth(1) cookies. If UsePrivilegeSeparation + is specified, it will be disabled after authentication. + + UsePAM Enables the Pluggable Authentication Module interface. If set to + ``yes'' this will enable PAM authentication using + ChallengeResponseAuthentication and PasswordAuthentication in ad- + dition to PAM account and session module processing for all au- + thentication 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''. + + UsePrivilegeSeparation + Specifies whether sshd(8) separates privileges by creating an un- + privileged child process to deal with incoming network traffic. + After successful authentication, another process will be created + that has the privilege of the authenticated user. The goal of + privilege separation is to prevent privilege escalation by con- + taining any corruption within the unprivileged processes. The + default is ``yes''. + + 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 below), though this is not the default. Addi- + tionally, the authentication spoofing and authentication data + verification and substitution occur on the client side. The se- + curity risk of using X11 forwarding is that the client's X11 dis- + play 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 pro- + tect 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. X11 forwarding is automatically disabled if UseLogin + is enabled. + + 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 wild- + card address. The argument must be ``yes'' or ``no''. The de- + fault is ``yes''. + + XAuthLocation + Specifies the full pathname of the xauth(1) program. The default + is /usr/X11R6/bin/xauth. + +TIME FORMATS + sshd(8) command-line arguments and configuration file options that speci- + fy 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 fol- + lowing: + + <none> 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) + +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 neces- + sary) that it be world-readable. + +SEE ALSO + 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 cre- + ated 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 4.1 September 25, 1999 9 |
