714 lines
37 KiB
Plaintext
714 lines
37 KiB
Plaintext
SSHD_CONFIG(5) OpenBSD Programmer's Manual SSHD_CONFIG(5)
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NAME
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sshd_config - OpenSSH SSH daemon configuration file
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SYNOPSIS
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/etc/ssh/sshd_config
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DESCRIPTION
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sshd(8) reads configuration data from /etc/ssh/sshd_config (or the file
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specified with -f on the command line). The file contains keyword-
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argument pairs, one per line. Lines starting with `#' and empty lines
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are interpreted as comments. Arguments may optionally be enclosed in
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double quotes (") in order to represent arguments containing spaces.
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The possible keywords and their meanings are as follows (note that
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keywords are case-insensitive and arguments are case-sensitive):
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AcceptEnv
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Specifies what environment variables sent by the client will be
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copied into the session's environ(7). See SendEnv in
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ssh_config(5) for how to configure the client. Note that
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environment passing is only supported for protocol 2. Variables
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are specified by name, which may contain the wildcard characters
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`*' and `?'. Multiple environment variables may be separated by
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whitespace or spread across multiple AcceptEnv directives. Be
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warned that some environment variables could be used to bypass
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restricted user environments. For this reason, care should be
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taken in the use of this directive. The default is not to accept
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any environment variables.
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AddressFamily
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Specifies which address family should be used by sshd(8). Valid
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arguments are ``any'', ``inet'' (use IPv4 only), or ``inet6''
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(use IPv6 only). The default is ``any''.
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AllowAgentForwarding
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Specifies whether ssh-agent(1) forwarding is permitted. The
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default is ``yes''. Note that disabling agent forwarding does
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not improve security unless users are also denied shell access,
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as they can always install their own forwarders.
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AllowGroups
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This keyword can be followed by a list of group name patterns,
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separated by spaces. If specified, login is allowed only for
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users whose primary group or supplementary group list matches one
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of the patterns. Only group names are valid; a numerical group
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ID is not recognized. By default, login is allowed for all
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groups. The allow/deny directives are processed in the following
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order: DenyUsers, AllowUsers, DenyGroups, and finally
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AllowGroups.
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See PATTERNS in ssh_config(5) for more information on patterns.
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AllowTcpForwarding
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Specifies whether TCP forwarding is permitted. The default is
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``yes''. Note that disabling TCP forwarding does not improve
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security unless users are also denied shell access, as they can
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always install their own forwarders.
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AllowUsers
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This keyword can be followed by a list of user name patterns,
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separated by spaces. If specified, login is allowed only for
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user names that match one of the patterns. Only user names are
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valid; a numerical user ID is not recognized. By default, login
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is allowed for all users. If the pattern takes the form
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USER@HOST then USER and HOST are separately checked, restricting
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logins to particular users from particular hosts. The allow/deny
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directives are processed in the following order: DenyUsers,
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AllowUsers, DenyGroups, and finally AllowGroups.
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See PATTERNS in ssh_config(5) for more information on patterns.
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AuthorizedKeysFile
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Specifies the file that contains the public keys that can be used
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for user authentication. The format is described in the
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AUTHORIZED_KEYS FILE FORMAT section of sshd(8).
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AuthorizedKeysFile may contain tokens of the form %T which are
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substituted during connection setup. The following tokens are
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defined: %% is replaced by a literal '%', %h is replaced by the
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home directory of the user being authenticated, and %u is
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replaced by the username of that user. After expansion,
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AuthorizedKeysFile is taken to be an absolute path or one
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relative to the user's home directory. The default is
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``.ssh/authorized_keys''.
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AuthorizedPrincipalsFile
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Specifies a file that lists principal names that are accepted for
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certificate authentication. When using certificates signed by a
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key listed in TrustedUserCAKeys, this file lists names, one of
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which must appear in the certificate for it to be accepted for
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authentication. Names are listed one per line preceded by key
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options (as described in AUTHORIZED_KEYS FILE FORMAT in sshd(8)).
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Empty lines and comments starting with `#' are ignored.
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AuthorizedPrincipalsFile may contain tokens of the form %T which
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are substituted during connection setup. The following tokens
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are defined: %% is replaced by a literal '%', %h is replaced by
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the home directory of the user being authenticated, and %u is
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replaced by the username of that user. After expansion,
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AuthorizedPrincipalsFile is taken to be an absolute path or one
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relative to the user's home directory.
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The default is not to use a principals file - in this case, the
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username of the user must appear in a certificate's principals
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list for it to be accepted. Note that AuthorizedPrincipalsFile
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is only used when authentication proceeds using a CA listed in
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TrustedUserCAKeys and is not consulted for certification
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authorities trusted via ~/.ssh/authorized_keys, though the
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principals= key option offers a similar facility (see sshd(8) for
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details).
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Banner The contents of the specified file are sent to the remote user
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before authentication is allowed. If the argument is ``none''
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then no banner is displayed. This option is only available for
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protocol version 2. By default, no banner is displayed.
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ChallengeResponseAuthentication
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Specifies whether challenge-response authentication is allowed
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(e.g. via PAM or though authentication styles supported in
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login.conf(5)) The default is ``yes''.
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ChrootDirectory
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Specifies the pathname of a directory to chroot(2) to after
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authentication. All components of the pathname must be root-
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owned directories that are not writable by any other user or
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group. After the chroot, sshd(8) changes the working directory
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to the user's home directory.
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The pathname may contain the following tokens that are expanded
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at runtime once the connecting user has been authenticated: %% is
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replaced by a literal '%', %h is replaced by the home directory
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of the user being authenticated, and %u is replaced by the
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username of that user.
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The ChrootDirectory must contain the necessary files and
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directories to support the user's session. For an interactive
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session this requires at least a shell, typically sh(1), and
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basic /dev nodes such as null(4), zero(4), stdin(4), stdout(4),
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stderr(4), arandom(4) and tty(4) devices. For file transfer
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sessions using ``sftp'', no additional configuration of the
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environment is necessary if the in-process sftp server is used,
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though sessions which use logging do require /dev/log inside the
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chroot directory (see sftp-server(8) for details).
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The default is not to chroot(2).
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Ciphers
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Specifies the ciphers allowed for protocol version 2. Multiple
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ciphers must be comma-separated. The supported ciphers are
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``3des-cbc'', ``aes128-cbc'', ``aes192-cbc'', ``aes256-cbc'',
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``aes128-ctr'', ``aes192-ctr'', ``aes256-ctr'', ``arcfour128'',
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``arcfour256'', ``arcfour'', ``blowfish-cbc'', and
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``cast128-cbc''. The default is:
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aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
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aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
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aes256-cbc,arcfour
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ClientAliveCountMax
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Sets the number of client alive messages (see below) which may be
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sent without sshd(8) receiving any messages back from the client.
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If this threshold is reached while client alive messages are
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being sent, sshd will disconnect the client, terminating the
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session. It is important to note that the use of client alive
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messages is very different from TCPKeepAlive (below). The client
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alive messages are sent through the encrypted channel and
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therefore will not be spoofable. The TCP keepalive option
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enabled by TCPKeepAlive is spoofable. The client alive mechanism
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is valuable when the client or server depend on knowing when a
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connection has become inactive.
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The default value is 3. If ClientAliveInterval (see below) is
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set to 15, and ClientAliveCountMax is left at the default,
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unresponsive SSH clients will be disconnected after approximately
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45 seconds. This option applies to protocol version 2 only.
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ClientAliveInterval
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Sets a timeout interval in seconds after which if no data has
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been received from the client, sshd(8) will send a message
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through the encrypted channel to request a response from the
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client. The default is 0, indicating that these messages will
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not be sent to the client. This option applies to protocol
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version 2 only.
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Compression
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Specifies whether compression is allowed, or delayed until the
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user has authenticated successfully. The argument must be
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``yes'', ``delayed'', or ``no''. The default is ``delayed''.
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DenyGroups
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This keyword can be followed by a list of group name patterns,
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separated by spaces. Login is disallowed for users whose primary
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group or supplementary group list matches one of the patterns.
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Only group names are valid; a numerical group ID is not
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recognized. By default, login is allowed for all groups. The
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allow/deny directives are processed in the following order:
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DenyUsers, AllowUsers, DenyGroups, and finally AllowGroups.
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See PATTERNS in ssh_config(5) for more information on patterns.
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DenyUsers
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This keyword can be followed by a list of user name patterns,
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separated by spaces. Login is disallowed for user names that
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match one of the patterns. Only user names are valid; a
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numerical user ID is not recognized. By default, login is
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allowed for all users. If the pattern takes the form USER@HOST
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then USER and HOST are separately checked, restricting logins to
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particular users from particular hosts. The allow/deny
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directives are processed in the following order: DenyUsers,
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AllowUsers, DenyGroups, and finally AllowGroups.
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See PATTERNS in ssh_config(5) for more information on patterns.
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ForceCommand
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Forces the execution of the command specified by ForceCommand,
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ignoring any command supplied by the client and ~/.ssh/rc if
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present. The command is invoked by using the user's login shell
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with the -c option. This applies to shell, command, or subsystem
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execution. It is most useful inside a Match block. The command
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originally supplied by the client is available in the
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SSH_ORIGINAL_COMMAND environment variable. Specifying a command
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of ``internal-sftp'' will force the use of an in-process sftp
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server that requires no support files when used with
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ChrootDirectory.
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GatewayPorts
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Specifies whether remote hosts are allowed to connect to ports
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forwarded for the client. By default, sshd(8) binds remote port
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forwardings to the loopback address. This prevents other remote
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hosts from connecting to forwarded ports. GatewayPorts can be
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used to specify that sshd should allow remote port forwardings to
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bind to non-loopback addresses, thus allowing other hosts to
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connect. The argument may be ``no'' to force remote port
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forwardings to be available to the local host only, ``yes'' to
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force remote port forwardings to bind to the wildcard address, or
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``clientspecified'' to allow the client to select the address to
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which the forwarding is bound. The default is ``no''.
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GSSAPIAuthentication
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Specifies whether user authentication based on GSSAPI is allowed.
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The default is ``no''. Note that this option applies to protocol
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version 2 only.
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GSSAPICleanupCredentials
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Specifies whether to automatically destroy the user's credentials
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cache on logout. The default is ``yes''. Note that this option
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applies to protocol version 2 only.
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HostbasedAuthentication
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Specifies whether rhosts or /etc/hosts.equiv authentication
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together with successful public key client host authentication is
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allowed (host-based authentication). This option is similar to
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RhostsRSAAuthentication and applies to protocol version 2 only.
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The default is ``no''.
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HostbasedUsesNameFromPacketOnly
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Specifies whether or not the server will attempt to perform a
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reverse name lookup when matching the name in the ~/.shosts,
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~/.rhosts, and /etc/hosts.equiv files during
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HostbasedAuthentication. A setting of ``yes'' means that sshd(8)
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uses the name supplied by the client rather than attempting to
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resolve the name from the TCP connection itself. The default is
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``no''.
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HostCertificate
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Specifies a file containing a public host certificate. The
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certificate's public key must match a private host key already
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specified by HostKey. The default behaviour of sshd(8) is not to
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load any certificates.
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HostKey
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Specifies a file containing a private host key used by SSH. The
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default is /etc/ssh/ssh_host_key for protocol version 1, and
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/etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_ecdsa_key and
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/etc/ssh/ssh_host_rsa_key for protocol version 2. Note that
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sshd(8) will refuse to use a file if it is group/world-
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accessible. It is possible to have multiple host key files.
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``rsa1'' keys are used for version 1 and ``dsa'', ``ecdsa'' or
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``rsa'' are used for version 2 of the SSH protocol.
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IgnoreRhosts
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Specifies that .rhosts and .shosts files will not be used in
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RhostsRSAAuthentication or HostbasedAuthentication.
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/etc/hosts.equiv and /etc/shosts.equiv are still used. The
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default is ``yes''.
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IgnoreUserKnownHosts
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Specifies whether sshd(8) should ignore the user's
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~/.ssh/known_hosts during RhostsRSAAuthentication or
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HostbasedAuthentication. The default is ``no''.
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IPQoS Specifies the IPv4 type-of-service or DSCP class for the
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connection. Accepted values are ``af11'', ``af12'', ``af13'',
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``af14'', ``af22'', ``af23'', ``af31'', ``af32'', ``af33'',
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``af41'', ``af42'', ``af43'', ``cs0'', ``cs1'', ``cs2'', ``cs3'',
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``cs4'', ``cs5'', ``cs6'', ``cs7'', ``ef'', ``lowdelay'',
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``throughput'', ``reliability'', or a numeric value. This option
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may take one or two arguments, separated by whitespace. If one
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argument is specified, it is used as the packet class
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unconditionally. If two values are specified, the first is
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automatically selected for interactive sessions and the second
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for non-interactive sessions. The default is ``lowdelay'' for
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interactive sessions and ``throughput'' for non-interactive
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sessions.
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KerberosAuthentication
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Specifies whether the password provided by the user for
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PasswordAuthentication will be validated through the Kerberos
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KDC. To use this option, the server needs a Kerberos servtab
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which allows the verification of the KDC's identity. The default
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is ``no''.
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KerberosGetAFSToken
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If AFS is active and the user has a Kerberos 5 TGT, attempt to
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acquire an AFS token before accessing the user's home directory.
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The default is ``no''.
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KerberosOrLocalPasswd
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If password authentication through Kerberos fails then the
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password will be validated via any additional local mechanism
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such as /etc/passwd. The default is ``yes''.
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KerberosTicketCleanup
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Specifies whether to automatically destroy the user's ticket
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cache file on logout. The default is ``yes''.
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KexAlgorithms
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Specifies the available KEX (Key Exchange) algorithms. Multiple
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algorithms must be comma-separated. The default is
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``ecdh-sha2-nistp256'', ``ecdh-sha2-nistp384'',
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``ecdh-sha2-nistp521'', ``diffie-hellman-group-exchange-sha256'',
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``diffie-hellman-group-exchange-sha1'',
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``diffie-hellman-group14-sha1'', ``diffie-hellman-group1-sha1''.
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KeyRegenerationInterval
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In protocol version 1, the ephemeral server key is automatically
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regenerated after this many seconds (if it has been used). The
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purpose of regeneration is to prevent decrypting captured
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sessions by later breaking into the machine and stealing the
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keys. The key is never stored anywhere. If the value is 0, the
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key is never regenerated. The default is 3600 (seconds).
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ListenAddress
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Specifies the local addresses sshd(8) should listen on. The
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following forms may be used:
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ListenAddress host|IPv4_addr|IPv6_addr
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ListenAddress host|IPv4_addr:port
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ListenAddress [host|IPv6_addr]:port
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If port is not specified, sshd will listen on the address and all
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prior Port options specified. The default is to listen on all
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local addresses. Multiple ListenAddress options are permitted.
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Additionally, any Port options must precede this option for non-
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port qualified addresses.
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LoginGraceTime
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The server disconnects after this time if the user has not
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successfully logged in. If the value is 0, there is no time
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limit. The default is 120 seconds.
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LogLevel
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Gives the verbosity level that is used when logging messages from
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sshd(8). The possible values are: QUIET, FATAL, ERROR, INFO,
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VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO.
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DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
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higher levels of debugging output. Logging with a DEBUG level
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violates the privacy of users and is not recommended.
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MACs Specifies the available MAC (message authentication code)
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algorithms. The MAC algorithm is used in protocol version 2 for
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data integrity protection. Multiple algorithms must be comma-
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separated. The default is:
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hmac-md5,hmac-sha1,umac-64@openssh.com,
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hmac-ripemd160,hmac-sha1-96,hmac-md5-96
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Match Introduces a conditional block. If all of the criteria on the
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Match line are satisfied, the keywords on the following lines
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override those set in the global section of the config file,
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until either another Match line or the end of the file.
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The arguments to Match are one or more criteria-pattern pairs.
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The available criteria are User, Group, Host, and Address. The
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match patterns may consist of single entries or comma-separated
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lists and may use the wildcard and negation operators described
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in the PATTERNS section of ssh_config(5).
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The patterns in an Address criteria may additionally contain
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addresses to match in CIDR address/masklen format, e.g.
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``192.0.2.0/24'' or ``3ffe:ffff::/32''. Note that the mask
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length provided must be consistent with the address - it is an
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error to specify a mask length that is too long for the address
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or one with bits set in this host portion of the address. For
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example, ``192.0.2.0/33'' and ``192.0.2.0/8'' respectively.
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Only a subset of keywords may be used on the lines following a
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Match keyword. Available keywords are AllowAgentForwarding,
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AllowTcpForwarding, AuthorizedKeysFile, AuthorizedPrincipalsFile,
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Banner, ChrootDirectory, ForceCommand, GatewayPorts,
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GSSAPIAuthentication, HostbasedAuthentication,
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HostbasedUsesNameFromPacketOnly, KbdInteractiveAuthentication,
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KerberosAuthentication, MaxAuthTries, MaxSessions,
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PasswordAuthentication, PermitEmptyPasswords, PermitOpen,
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PermitRootLogin, PermitTunnel, PubkeyAuthentication,
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RhostsRSAAuthentication, RSAAuthentication, X11DisplayOffset,
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X11Forwarding and X11UseLocalHost.
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MaxAuthTries
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Specifies the maximum number of authentication attempts permitted
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per connection. Once the number of failures reaches half this
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value, additional failures are logged. The default is 6.
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MaxSessions
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Specifies the maximum number of open sessions permitted per
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network connection. The default is 10.
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MaxStartups
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Specifies the maximum number of concurrent unauthenticated
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connections to the SSH daemon. Additional connections will be
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dropped until authentication succeeds or the LoginGraceTime
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expires for a connection. The default is 10.
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Alternatively, random early drop can be enabled by specifying the
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three colon separated values ``start:rate:full'' (e.g.
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"10:30:60"). sshd(8) will refuse connection attempts with a
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probability of ``rate/100'' (30%) if there are currently
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``start'' (10) unauthenticated connections. The probability
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increases linearly and all connection attempts are refused if the
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number of unauthenticated connections reaches ``full'' (60).
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PasswordAuthentication
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Specifies whether password authentication is allowed. The
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default is ``yes''.
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PermitEmptyPasswords
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When password authentication is allowed, it specifies whether the
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server allows login to accounts with empty password strings. The
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default is ``no''.
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PermitOpen
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Specifies the destinations to which TCP port forwarding is
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permitted. The forwarding specification must be one of the
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following forms:
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PermitOpen host:port
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PermitOpen IPv4_addr:port
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PermitOpen [IPv6_addr]:port
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Multiple forwards may be specified by separating them with
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whitespace. An argument of ``any'' can be used to remove all
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restrictions 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
|
|
authentication 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
|
|
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''.
|
|
|
|
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
|
|
bypass access restrictions in some configurations using
|
|
mechanisms such as LD_PRELOAD.
|
|
|
|
PidFile
|
|
Specifies the file that contains the process ID of the SSH
|
|
daemon. 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-
|
|
separated. The default is `2'. Note that the order of the
|
|
protocol list does not indicate preference, because the client
|
|
selects among multiple protocol versions offered by the server.
|
|
Specifying ``2,1'' is identical to ``1,2''.
|
|
|
|
PubkeyAuthentication
|
|
Specifies whether public key authentication is allowed. The
|
|
default is ``yes''. Note that this option applies to protocol
|
|
version 2 only.
|
|
|
|
RevokedKeys
|
|
Specifies a list of revoked public keys. 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.
|
|
|
|
RhostsRSAAuthentication
|
|
Specifies whether rhosts or /etc/hosts.equiv authentication
|
|
together with successful RSA host authentication is allowed. The
|
|
default is ``no''. This option applies to protocol version 1
|
|
only.
|
|
|
|
RSAAuthentication
|
|
Specifies whether pure RSA authentication is allowed. The
|
|
default is ``yes''. This option applies to protocol version 1
|
|
only.
|
|
|
|
ServerKeyBits
|
|
Defines the number of bits in the ephemeral protocol version 1
|
|
server key. The minimum value is 512, and the default is 1024.
|
|
|
|
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(8) 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. Note that this option
|
|
applies 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
|
|
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. Keys are listed one per line; empty lines and
|
|
comments starting with `#' 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
|
|
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
|
|
sessions. The default is ``no''. Note that login(1) is never
|
|
used for remote command execution. Note also, that if this is
|
|
enabled, 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
|
|
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''.
|
|
|
|
UsePrivilegeSeparation
|
|
Specifies whether sshd(8) separates privileges by creating an
|
|
unprivileged 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
|
|
containing 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.
|
|
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. 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
|
|
wildcard address. The argument must be ``yes'' or ``no''. The
|
|
default 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
|
|
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:
|
|
|
|
<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
|
|
necessary) 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
|
|
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 4.8 December 8, 2010 OpenBSD 4.8
|