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.\" ========================================================================
.\"
.IX Title "Config::Model::models::Sshd 3pm"
.TH Config::Model::models::Sshd 3pm "2021-01-17" "perl v5.32.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Config::Model::models::Sshd \- Configuration class Sshd
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Configuration classes used by Config::Model
.PP
This configuration class was generated from sshd_system documentation.
by parse\-man.pl <https://github.com/dod38fr/config-model-openssh/contrib/parse-man.pl>
.SH "Elements"
.IX Header "Elements"
.SS "AcceptEnv"
.IX Subsection "AcceptEnv"
Specifies what environment
variables sent by the client will be copied into the
session's \fBenviron\fR\|(7). See \fBSendEnv\fR and
\&\fBSetEnv\fR in \fBssh_config\fR\|(5) for how to configure the
client. The \s-1TERM\s0 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 '*'
and '?'. Multiple environment variables may be
separated by whitespace or spread across multiple
\&\fBAcceptEnv\fR 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. \fI Optional. Type list of uniline.  \fR
.SS "AllowAgentForwarding"
.IX Subsection "AllowAgentForwarding"
Specifies whether \fBssh\-agent\fR\|(1)
forwarding is permitted. The default is \fByes\fR. Note
that disabling agent forwarding does not improve security
unless users are also denied shell access, as they can
always install their own forwarders. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "AllowGroups"
.IX Subsection "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 \s-1ID\s0
is not recognized. By default, login is allowed for all
groups. The allow/deny groups directives are processed in
the following order: \fBDenyGroups\fR,
\&\fBAllowGroups\fR.
.PP
See \s-1PATTERNS\s0 in
\&\fBssh_config\fR\|(5) for more information on patterns. \fI Optional. Type list of uniline.  \fR
.SS "AllowStreamLocalForwarding"
.IX Subsection "AllowStreamLocalForwarding"
Specifies whether StreamLocal
(Unix-domain socket) forwarding is permitted. The available
options are \fByes\fR (the default) or \fBall\fR to allow
StreamLocal forwarding, \fBno\fR to prevent all StreamLocal
forwarding, \fBlocal\fR to allow local (from the
perspective of \fBssh\fR\|(1)) forwarding only or \fBremote\fR 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. \fI Optional. Type enum. choice: 'yes', 'all', 'no', 'local', 'remote'.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "AllowTcpForwarding"
.IX Subsection "AllowTcpForwarding"
Specifies whether \s-1TCP\s0
forwarding is permitted. The available options are
\&\fByes\fR (the default) or \fBall\fR to allow \s-1TCP\s0
forwarding, \fBno\fR to prevent all \s-1TCP\s0 forwarding,
\&\fBlocal\fR to allow local (from the perspective of \fBssh\fR\|(1))
forwarding only or \fBremote\fR to allow remote forwarding
only. Note that disabling \s-1TCP\s0 forwarding does not improve
security unless users are also denied shell access, as they
can always install their own forwarders. \fI Optional. Type enum. choice: 'yes', 'all', 'no', 'local', 'remote'.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "AllowUsers"
.IX Subsection "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 \s-1ID\s0 is not recognized. By default, login is allowed for
all users. If the pattern takes the form USER@HOST then \s-1USER\s0
and \s-1HOST\s0 are separately checked, restricting logins to
particular users from particular hosts. \s-1HOST\s0 criteria may
additionally contain addresses to match in \s-1CIDR\s0
address/masklen format. The allow/deny users directives are
processed in the following order: \fBDenyUsers\fR,
\&\fBAllowUsers\fR.
.PP
See \s-1PATTERNS\s0 in
\&\fBssh_config\fR\|(5) for more information on patterns. \fI Optional. Type list of uniline.  \fR
.SS "AuthenticationMethods"
.IX Subsection "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 \fBany\fR 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.
.PP
For example,
\&\*(L"publickey,password
publickey,keyboard\-interactive\*(R" 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.
.PP
For keyboard
interactive authentication it is also possible to restrict
authentication to a specific device by appending a colon
followed by the device identifier \fBbsdauth\fR or
\&\fBpam\fR. depending on the server configuration. For
example, \*(L"keyboard\-interactive:bsdauth\*(R" would
restrict keyboard interactive authentication to the
\&\fBbsdauth\fR device.
.PP
If the
publickey method is listed more than once, \fBsshd\fR\|(8) verifies
that keys that have been used successfully are not reused
for subsequent authentications. For example,
\&\*(L"publickey,publickey\*(R" requires successful
authentication using two different public keys.
.PP
Note that each
authentication method listed should also be explicitly
enabled in the configuration.
.PP
The available
authentication methods are: \*(L"gssapi-with-mic\*(R",
\&\*(L"hostbased\*(R", \*(L"keyboard-interactive\*(R",
\&\*(L"none\*(R" (used for access to password-less accounts
when \fBPermitEmptyPasswords\fR is enabled),
\&\*(L"password\*(R" and \*(L"publickey\*(R". \fI Optional. Type uniline.  \fR
.SS "AuthorizedKeysCommand"
.IX Subsection "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
\&\fBAuthorizedKeysCommand\fR accept the tokens described in
the \fI\s-1TOKENS\s0\fR section. If no arguments are specified
then the username of the target user is used.
.PP
The program
should produce on standard output zero or more lines of
authorized_keys output (see \fI\s-1AUTHORIZED_KEYS\s0\fR in
\&\fBsshd\fR\|(8)). \fBAuthorizedKeysCommand\fR is tried after the
usual \fBAuthorizedKeysFile\fR files and will not be
executed if a matching key is found there. By default, no
\&\fBAuthorizedKeysCommand\fR is run. \fI Optional. Type uniline.  \fR
.SS "AuthorizedKeysCommandUser"
.IX Subsection "AuthorizedKeysCommandUser"
Specifies the user under whose
account the \fBAuthorizedKeysCommand\fR is run. It is
recommended to use a dedicated user that has no other role
on the host than running authorized keys commands. If
\&\fBAuthorizedKeysCommand\fR is specified but
\&\fBAuthorizedKeysCommandUser\fR is not, then \fBsshd\fR\|(8) will
refuse to start. \fI Optional. Type uniline.  \fR
.SS "AuthorizedKeysFile"
.IX Subsection "AuthorizedKeysFile"
Specifies the file that
contains the public keys used for user authentication. The
format is described in the \s-1AUTHORIZED_KEYS FILE FORMAT\s0
section of \fBsshd\fR\|(8). Arguments to \fBAuthorizedKeysFile\fR
accept the tokens described in the \fI\s-1TOKENS\s0\fR section.
After expansion, \fBAuthorizedKeysFile\fR 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
\&\fBnone\fR to skip checking for user keys in files. The
default is \*(L".ssh/authorized_keys
\&.ssh/authorized_keys2\*(R". \fI Optional. Type list of uniline.  \fR
.PP
Note: AuthorizedKeysFile values are migrated from '\- AuthorizedKeysFile2'
.SS "AuthorizedPrincipalsCommand"
.IX Subsection "AuthorizedPrincipalsCommand"
Specifies a program to be used
to generate the list of allowed certificate principals as
per \fBAuthorizedPrincipalsFile\fR. The program must be
owned by root, not writable by group or others and specified
by an absolute path. Arguments to
\&\fBAuthorizedPrincipalsCommand\fR accept the tokens
described in the \fI\s-1TOKENS\s0\fR section. If no arguments are
specified then the username of the target user is used.
.PP
The program
should produce on standard output zero or more lines of
\&\fBAuthorizedPrincipalsFile\fR output. If either
\&\fBAuthorizedPrincipalsCommand\fR or
\&\fBAuthorizedPrincipalsFile\fR is specified, then
certificates offered by the client for authentication must
contain a principal that is listed. By default, no
\&\fBAuthorizedPrincipalsCommand\fR is run. \fI Optional. Type uniline.  \fR
.SS "AuthorizedPrincipalsCommandUser"
.IX Subsection "AuthorizedPrincipalsCommandUser"
Specifies the user under whose
account the \fBAuthorizedPrincipalsCommand\fR is run. It is
recommended to use a dedicated user that has no other role
on the host than running authorized principals commands. If
\&\fBAuthorizedPrincipalsCommand\fR is specified but
\&\fBAuthorizedPrincipalsCommandUser\fR is not, then \fBsshd\fR\|(8)
will refuse to start. \fI Optional. Type uniline.  \fR
.SS "AuthorizedPrincipalsFile"
.IX Subsection "AuthorizedPrincipalsFile"
Specifies a file that lists
principal names that are accepted for certificate
authentication. When using certificates signed by a key
listed in \fBTrustedUserCAKeys\fR, 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 \fI\s-1AUTHORIZED_KEYS
FILE FORMAT\s0\fR in \fBsshd\fR\|(8)). Empty lines and comments
starting with '#' are ignored.
.PP
Arguments to
\&\fBAuthorizedPrincipalsFile\fR accept the tokens described
in the \fI\s-1TOKENS\s0\fR section. After expansion,
\&\fBAuthorizedPrincipalsFile\fR is taken to be an absolute
path or one relative to the user's home directory. The
default is \fBnone\fR, i.e. not to use a principals file
X in this case, the username of the user must appear
in a certificate's principals list for it to be
accepted.
.PP
Note that
\&\fBAuthorizedPrincipalsFile\fR is only used when
authentication proceeds using a \s-1CA\s0 listed in
\&\fBTrustedUserCAKeys\fR and is not consulted for
certification authorities trusted via
\&\fI~/.ssh/authorized_keys\fR, though the \fBprincipals=\fR
key option offers a similar facility (see \fBsshd\fR\|(8) for
details). \fI Optional. Type uniline.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
none
.SS "Banner"
.IX Subsection "Banner"
The contents of
the specified file are sent to the remote user before
authentication is allowed. If the argument is \fBnone\fR
then no banner is displayed. By default, no banner is
displayed. \fI Optional. Type uniline.  \fR
.SS "ChrootDirectory"
.IX Subsection "ChrootDirectory"
Specifies the pathname of a
directory to \fBchroot\fR\|(2) to after authentication. At session
startup \fBsshd\fR\|(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, \fBsshd\fR\|(8) changes the
working directory to the user's home directory.
Arguments to \fBChrootDirectory\fR accept the tokens
described in the \fI\s-1TOKENS\s0\fR section.
.PP
The
\&\fBChrootDirectory\fR must contain the necessary files and
directories to support the user's session. For an
interactive session this requires at least a shell,
typically \fBsh\fR\|(1), and basic \fI/dev\fR nodes such as
\&\fBnull\fR\|(4), \fBzero\fR\|(4), \fBstdin\fR\|(4), \fBstdout\fR\|(4), \fBstderr\fR\|(4), and \fBtty\fR\|(4)
devices. For file transfer sessions using \s-1SFTP\s0 no additional
configuration of the environment is necessary if the
in-process sftp-server is used, though sessions which use
logging may require \fI/dev/log\fR inside the chroot
directory on some operating systems (see \fBsftp\-server\fR\|(8) for
details).
.PP
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 \fBsshd\fR\|(8) cannot detect.
.PP
The default is
\&\fBnone\fR, indicating not to \fBchroot\fR\|(2). \fI Optional. Type uniline.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
none
.SS "ClientAliveCountMax"
.IX Subsection "ClientAliveCountMax"
Sets the number of client alive
messages which may be sent without \fBsshd\fR\|(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 \fBTCPKeepAlive\fR. The client alive
messages are sent through the encrypted channel and
therefore will not be spoofable. The \s-1TCP\s0 keepalive option
enabled by \fBTCPKeepAlive\fR is spoofable. The client
alive mechanism is valuable when the client or server depend
on knowing when a connection has become unresponsive.
.PP
The default
value is 3. If \fBClientAliveInterval\fR is set to 15, and
\&\fBClientAliveCountMax\fR is left at the default,
unresponsive \s-1SSH\s0 clients will be disconnected after
approximately 45 seconds. Setting a zero
\&\fBClientAliveCountMax\fR disables connection
termination. \fI Optional. Type integer.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
3
.SS "ClientAliveInterval"
.IX Subsection "ClientAliveInterval"
Sets a timeout interval in
seconds after which if no data has been received from the
client, \fBsshd\fR\|(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. \fI Optional. Type integer.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
0
.SS "DenyGroups"
.IX Subsection "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 \s-1ID\s0 is not recognized. By default,
login is allowed for all groups. The allow/deny groups
directives are processed in the following order:
\&\fBDenyGroups\fR, \fBAllowGroups\fR.
.PP
See \s-1PATTERNS\s0 in
\&\fBssh_config\fR\|(5) for more information on patterns. \fI Optional. Type list of uniline.  \fR
.SS "DenyUsers"
.IX Subsection "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 \s-1ID\s0 is not
recognized. By default, login is allowed for all users. If
the pattern takes the form USER@HOST then \s-1USER\s0 and \s-1HOST\s0 are
separately checked, restricting logins to particular users
from particular hosts. \s-1HOST\s0 criteria may additionally
contain addresses to match in \s-1CIDR\s0 address/masklen format.
The allow/deny users directives are processed in the
following order: \fBDenyUsers\fR, \fBAllowUsers\fR.
.PP
See \s-1PATTERNS\s0 in
\&\fBssh_config\fR\|(5) for more information on patterns. \fI Optional. Type list of uniline.  \fR
.SS "ForceCommand"
.IX Subsection "ForceCommand"
Forces the execution of the
command specified by \fBForceCommand\fR, ignoring any
command supplied by the client and \fI~/.ssh/rc\fR 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
\&\fBMatch\fR block. The command originally supplied by the
client is available in the \s-1SSH_ORIGINAL_COMMAND\s0 environment
variable. Specifying a command of \fBinternal-sftp\fR will
force the use of an in-process \s-1SFTP\s0 server that requires no
support files when used with \fBChrootDirectory\fR. The
default is \fBnone\fR. \fI Optional. Type uniline.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
none
.SS "GatewayPorts"
.IX Subsection "GatewayPorts"
Specifies whether remote hosts
are allowed to connect to ports forwarded for the client. By
default, \fBsshd\fR\|(8) binds remote port forwardings to the
loopback address. This prevents other remote hosts from
connecting to forwarded ports. \fBGatewayPorts\fR 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 \fBno\fR to
force remote port forwardings to be available to the local
host only, \fByes\fR to force remote port forwardings to
bind to the wildcard address, or \fBclientspecified\fR to
allow the client to select the address to which the
forwarding is bound. The default is \fBno\fR. \fI Optional. Type enum. choice: 'no', 'yes', 'clientspecified'.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
no
.SS "GSSAPIAuthentication"
.IX Subsection "GSSAPIAuthentication"
Specifies whether user
authentication based on \s-1GSSAPI\s0 is allowed. The default is
\&\fBno\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
no
.SS "HostbasedAcceptedKeyTypes"
.IX Subsection "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 '+' character, then the specified
key types will be appended to the default set instead of
replacing them. If the specified list begins with a
\&'\-' 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 '^' character, then the specified key types
will be placed at the head of the default set. The default
for this option is:
.PP
ecdsa\-sha2\-nistp256\-cert\-v01@openssh.com,
.PP
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,
.PP
ecdsa\-sha2\-nistp256,ecdsa\-sha2\-nistp384,ecdsa\-sha2\-nistp521,
.PP
sk\-ecdsa\-sha2\-nistp256@openssh.com, 
ssh\-ed25519,sk\-ssh\-ed25519@openssh.com, 
rsa\-sha2\-512,rsa\-sha2\-256,ssh\-rsa
.PP
The list of
available key types may also be obtained using \*(L"ssh \-Q
HostbasedAcceptedKeyTypes\*(R". \fI Optional. Type uniline.  \fR
.SS "HostbasedAuthentication"
.IX Subsection "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 \fBno\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
no
.SS "HostbasedUsesNameFromPacketOnly"
.IX Subsection "HostbasedUsesNameFromPacketOnly"
Specifies whether or not the
server will attempt to perform a reverse name lookup when
matching the name in the \fI~/.shosts\fR, \fI~/.rhosts\fR,
and \fI/etc/hosts.equiv\fR files during
\&\fBHostbasedAuthentication\fR. A setting of \fByes\fR
means that \fBsshd\fR\|(8) uses the name supplied by the client
rather than attempting to resolve the name from the \s-1TCP\s0
connection itself. The default is \fBno\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
no
.SS "IgnoreRhosts"
.IX Subsection "IgnoreRhosts"
Specifies whether to ignore
per-user \fI.rhosts\fR and \fI.shosts\fR files during
\&\fBHostbasedAuthentication\fR. The system-wide
\&\fI/etc/hosts.equiv\fR and \fI/etc/ssh/shosts.equiv\fR are
still used regardless of this setting.
.PP
Accepted values
are \fByes\fR (the default) to ignore all per-user files,
\&\fBshosts-only\fR to allow the use of \fI.shosts\fR but to
ignore \fI.rhosts\fR or \fBno\fR to allow both
\&\fI.shosts\fR and \fIrhosts\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "Include"
.IX Subsection "Include"
Include the specified
configuration file(s). Multiple pathnames may be specified
and each pathname may contain \fBglob\fR\|(7) wildcards that will be
expanded and processed in lexical order. Files without
absolute paths are assumed to be in \fI/etc/ssh\fR. An
\&\fBInclude\fR directive may appear inside a \fBMatch\fR
block to perform conditional inclusion. \fI Optional. Type list of uniline.  \fR
.SS "IPQoS"
.IX Subsection "IPQoS"
Specifies the
IPv4 type-of-service or \s-1DSCP\s0 class for the connection.
Accepted values are \fBaf11\fR, \fBaf12\fR, \fBaf13\fR,
\&\fBaf21\fR, \fBaf22\fR, \fBaf23\fR, \fBaf31\fR,
\&\fBaf32\fR, \fBaf33\fR, \fBaf41\fR, \fBaf42\fR,
\&\fBaf43\fR, \fBcs0\fR, \fBcs1\fR, \fBcs2\fR, \fBcs3\fR,
\&\fBcs4\fR, \fBcs5\fR, \fBcs6\fR, \fBcs7\fR, \fBef\fR,
\&\fBle\fR, \fBlowdelay\fR, \fBthroughput\fR,
\&\fBreliability\fR, a numeric value, or \fBnone\fR 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 \fBlowdelay\fR for
interactive sessions and \fBthroughput\fR for
non-interactive sessions. \fI Optional. Type uniline.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
af21 cs1
.SS "KbdInteractiveAuthentication"
.IX Subsection "KbdInteractiveAuthentication"
Specifies whether to allow
keyboard-interactive authentication. The argument to this
keyword must be \fByes\fR or \fBno\fR. The default is to
use whatever value \fBChallengeResponseAuthentication\fR is
set to (by default \fByes\fR). \fI Optional. Type boolean.  \fR
.SS "KerberosAuthentication"
.IX Subsection "KerberosAuthentication"
Specifies whether the password
provided by the user for \fBPasswordAuthentication\fR will
be validated through the Kerberos \s-1KDC.\s0 To use this option,
the server needs a Kerberos servtab which allows the
verification of the \s-1KDC\s0's identity. The default is
\&\fBno\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
no
.SS "LogLevel"
.IX Subsection "LogLevel"
Gives the verbosity level that
is used when logging messages from \fBsshd\fR\|(8). The possible
values are: \s-1QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG,
DEBUG1, DEBUG2,\s0 and \s-1DEBUG3.\s0 The default is \s-1INFO. DEBUG\s0 and
\&\s-1DEBUG1\s0 are equivalent. \s-1DEBUG2\s0 and \s-1DEBUG3\s0 each specify higher
levels of debugging output. Logging with a \s-1DEBUG\s0 level
violates the privacy of users and is not recommended. \fI Optional. Type enum. choice: '\s-1QUIET\s0', '\s-1FATAL\s0', '\s-1ERROR\s0', '\s-1INFO\s0', '\s-1VERBOSE\s0', '\s-1DEBUG\s0', '\s-1DEBUG1\s0', '\s-1DEBUG2\s0', '\s-1DEBUG3\s0'.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
\&\s-1INFO\s0
.SS "MaxAuthTries"
.IX Subsection "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. \fI Optional. Type integer.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
6
.SS "MaxSessions"
.IX Subsection "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 \fBMaxSessions\fR 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. \fI Optional. Type integer.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
10
.SS "PasswordAuthentication"
.IX Subsection "PasswordAuthentication"
Specifies whether password
authentication is allowed. The default is \fByes\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "PermitEmptyPasswords"
.IX Subsection "PermitEmptyPasswords"
When password authentication is
allowed, it specifies whether the server allows login to
accounts with empty password strings. The default is
\&\fBno\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
no
.SS "PermitListen"
.IX Subsection "PermitListen"
Specifies the addresses/ports
on which a remote \s-1TCP\s0 port forwarding may listen. The listen
specification must be one of the following forms:
.PP
\&\fBPermitListen\fR\fIport\fR \fB
PermitListen\fR \fIhost\fR:\fIport\fR
.PP
Multiple
permissions may be specified by separating them with
whitespace. An argument of \fBany\fR can be used to remove
all restrictions and permit any listen requests. An argument
of \fBnone\fR can be used to prohibit all listen requests.
The host name may contain wildcards as described in the
\&\s-1PATTERNS\s0 section in \fBssh_config\fR\|(5). The wildcard
\&'*' 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 \fBGatewayPorts\fR
option may further restrict which addresses may be listened
on. Note also that \fBssh\fR\|(1) will request a listen host of
\&\fBlocalhost\fR if no listen host was specifically
requested, and this name is treated differently to explicit
localhost addresses of X127.0.0.1X and
X::1X. \fI Optional. Type list of uniline.  \fR
.SS "PermitOpen"
.IX Subsection "PermitOpen"
Specifies the destinations to
which \s-1TCP\s0 port forwarding is permitted. The forwarding
specification must be one of the following forms:
.PP
\&\fBPermitOpen\fR\fIhost\fR:\fIport\fR \fB
PermitOpen\fR \fIIPv4_addr\fR:\fIport\fR \fB
PermitOpen\fR \fI[IPv6_addr]\fR:\fIport\fR
.PP
Multiple
forwards may be specified by separating them with
whitespace. An argument of \fBany\fR can be used to remove
all restrictions and permit any forwarding requests. An
argument of \fBnone\fR can be used to prohibit all
forwarding requests. The wildcard '*' 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. \fI Optional. Type list of uniline.  \fR
.SS "PermitRootLogin"
.IX Subsection "PermitRootLogin"
Specifies whether root can log
in using \fBssh\fR\|(1). The argument must be \fByes\fR,
\&\fBprohibit-password\fR, \fBforced-commands-only\fR, or
\&\fBno\fR. The default is \fBprohibit-password\fR.
.PP
If this option
is set to \fBprohibit-password\fR (or its deprecated alias,
\&\fBwithout-password\fR), password and keyboard-interactive
authentication are disabled for root.
.PP
If this option
is set to \fBforced-commands-only\fR, root login with
public key authentication will be allowed, but only if the
\&\fIcommand\fR 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.
.PP
If this option
is set to \fBno\fR, root is not allowed to log in. \fI Optional. Type enum. choice: 'yes', 'prohibit\-password', 'forced\-commands\-only', 'no'.  \fR
.SS "PermitTTY"
.IX Subsection "PermitTTY"
Specifies whether \fBpty\fR\|(4)
allocation is permitted. The default is \fByes\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "PermitTunnel"
.IX Subsection "PermitTunnel"
Specifies whether \fBtun\fR\|(4) device
forwarding is allowed. The argument must be \fByes\fR,
\&\fBpoint-to-point\fR (layer 3), \fBethernet\fR (layer 2),
or \fBno\fR. Specifying \fByes\fR permits both
\&\fBpoint-to-point\fR and \fBethernet\fR. The default is
\&\fBno\fR.
.PP
Independent of
this setting, the permissions of the selected \fBtun\fR\|(4) device
must allow access to the user. \fI Optional. Type enum. choice: 'yes', 'point\-to\-point', 'ethernet', 'no'.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
no
.SS "PermitUserRC"
.IX Subsection "PermitUserRC"
Specifies whether any
\&\fI~/.ssh/rc\fR file is executed. The default is
\&\fByes\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "PubkeyAcceptedKeyTypes"
.IX Subsection "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 '+' character, then the specified
key types will be appended to the default set instead of
replacing them. If the specified list begins with a
\&'\-' 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 '^' character, then the specified key types
will be placed at the head of the default set. The default
for this option is:
.PP
ecdsa\-sha2\-nistp256\-cert\-v01@openssh.com,
.PP
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,
.PP
ecdsa\-sha2\-nistp256,ecdsa\-sha2\-nistp384,ecdsa\-sha2\-nistp521,
.PP
sk\-ecdsa\-sha2\-nistp256@openssh.com, 
ssh\-ed25519,sk\-ssh\-ed25519@openssh.com, 
rsa\-sha2\-512,rsa\-sha2\-256,ssh\-rsa
.PP
The list of
available key types may also be obtained using \*(L"ssh \-Q
PubkeyAcceptedKeyTypes\*(R". \fI Optional. Type uniline.  \fR
.SS "PubkeyAuthentication"
.IX Subsection "PubkeyAuthentication"
Specifies whether public key
authentication is allowed. The default is \fByes\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "RekeyLimit"
.IX Subsection "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 'K', 'M', or 'G' to
indicate Kilobytes, Megabytes, or Gigabytes, respectively.
The default is between '1G' and
\&'4G', depending on the cipher. The optional
second value is specified in seconds and may use any of the
units documented in the \fI\s-1TIME FORMATS\s0\fR section. The
default value for \fBRekeyLimit\fR is \fBdefault none\fR,
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. \fI Optional. Type uniline.  \fR
.SS "RevokedKeys"
.IX Subsection "RevokedKeys"
Specifies revoked public keys
file, or \fBnone\fR 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 (\s-1KRL\s0) as generated by
\&\fBssh\-keygen\fR\|(1). For more information on KRLs, see the \s-1KEY
REVOCATION LISTS\s0 section in \fBssh\-keygen\fR\|(1). \fI Optional. Type uniline.  \fR
.SS "RDomain"
.IX Subsection "RDomain"
Specifies an explicit routing
domain that is applied after authentication has completed.
The user session, as well and any forwarded or listening \s-1IP\s0
sockets, will be bound to this \fBrdomain\fR\|(4). If the routing
domain is set to \fB\f(CB%D\fB\fR, then the domain in which the
incoming connection was received will be applied. \fI Optional. Type uniline.  \fR
.SS "SetEnv"
.IX Subsection "SetEnv"
Specifies one
or more environment variables to set in child sessions
started by \fBsshd\fR\|(8) as XNAME=VALUEX. The
environment value may be quoted (e.g. if it contains
whitespace characters). Environment variables set by
\&\fBSetEnv\fR override the default environment and any
variables specified by the user via \fBAcceptEnv\fR or
\&\fBPermitUserEnvironment\fR. \fI Optional. Type uniline.  \fR
.SS "StreamLocalBindMask"
.IX Subsection "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.
.PP
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. \fI Optional. Type uniline.  \fR
.SS "StreamLocalBindUnlink"
.IX Subsection "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 \fBStreamLocalBindUnlink\fR is not
enabled, \fBsshd\fR 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.
.PP
The argument
must be \fByes\fR or \fBno\fR. The default is
\&\fBno\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
no
.SS "TrustedUserCAKeys"
.IX Subsection "TrustedUserCAKeys"
Specifies a file containing
public keys of certificate authorities that are trusted to
sign user certificates for authentication, or \fBnone\fR to
not use one. 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 \s-1CA\s0 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 \fBTrustedUserCAKeys\fR. For more
details on certificates, see the \s-1CERTIFICATES\s0 section in
\&\fBssh\-keygen\fR\|(1). \fI Optional. Type uniline.  \fR
.SS "X11DisplayOffset"
.IX Subsection "X11DisplayOffset"
Specifies the first display
number available for \fBsshd\fR\|(8)'s X11 forwarding. This
prevents sshd from interfering with real X11 servers. The
default is 10. \fI Optional. Type uniline.  \fR
.SS "X11Forwarding"
.IX Subsection "X11Forwarding"
Specifies whether X11
forwarding is permitted. The argument must be \fByes\fR or
\&\fBno\fR. The default is \fBno\fR.
.PP
When X11
forwarding is enabled, there may be additional exposure to
the server and to client displays if the \fBsshd\fR\|(8) proxy
display is configured to listen on the wildcard address (see
\&\fBX11UseLocalhost\fR), 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 \s-1SSH\s0 client requests forwarding (see the warnings
for \fBForwardX11\fR in \fBssh_config\fR\|(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
\&\fBno\fR setting.
.PP
Note that
disabling X11 forwarding does not prevent users from
forwarding X11 traffic, as users can always install their
own forwarders. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
no
.SS "X11UseLocalhost"
.IX Subsection "X11UseLocalhost"
Specifies whether \fBsshd\fR\|(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 \s-1DISPLAY\s0 environment variable to
\&\fBlocalhost\fR. This prevents remote hosts from connecting
to the proxy display. However, some older X11 clients may
not function with this configuration. \fBX11UseLocalhost\fR
may be set to \fBno\fR to specify that the forwarding
server should be bound to the wildcard address. The argument
must be \fByes\fR or \fBno\fR. The default is
\&\fByes\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "AuthorizedKeysFile2"
.IX Subsection "AuthorizedKeysFile2"
This parameter is now ignored by Ssh. \fBDeprecated\fR \fI Optional. Type list of uniline.  \fR
.SS "Protocol"
.IX Subsection "Protocol"
\&\fBDeprecated\fR \fI Optional. Type uniline.  \fR
.SS "RSAAuthentication"
.IX Subsection "RSAAuthentication"
\&\fBDeprecated\fR \fI Optional. Type uniline.  \fR
.SS "RhostsRSAAuthentication"
.IX Subsection "RhostsRSAAuthentication"
\&\fBDeprecated\fR \fI Optional. Type uniline.  \fR
.SS "UsePrivilegeSeparation"
.IX Subsection "UsePrivilegeSeparation"
\&\fBDeprecated\fR \fI Optional. Type uniline.  \fR
.SS "KeyRegenerationInterval"
.IX Subsection "KeyRegenerationInterval"
\&\fBDeprecated\fR \fI Optional. Type uniline.  \fR
.SS "AddressFamily"
.IX Subsection "AddressFamily"
Specifies which address family
should be used by \fBsshd\fR\|(8). Valid arguments are \fBany\fR
(the default), \fBinet\fR (use IPv4 only), or \fBinet6\fR
(use IPv6 only). \fI Optional. Type enum. choice: 'any', 'inet', 'inet6'.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
any
.SS "CASignatureAlgorithms"
.IX Subsection "CASignatureAlgorithms"
Specifies which algorithms are
allowed for signing of certificates by certificate
authorities (CAs). The default is:
.PP
ecdsa\-sha2\-nistp256,ecdsa\-sha2\-nistp384,ecdsa\-sha2\-nistp521,
.PP
ssh\-ed25519,rsa\-sha2\-512,rsa\-sha2\-256,ssh\-rsa
.PP
Certificates
signed using other algorithms will not be accepted for
public key or host-based authentication. \fI Optional. Type uniline.  \fR
.SS "ChallengeResponseAuthentication"
.IX Subsection "ChallengeResponseAuthentication"
Specifies whether
challenge-response authentication is allowed (e.g. via \s-1PAM\s0).
The default is \fByes\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "Ciphers"
.IX Subsection "Ciphers"
Specifies the ciphers allowed.
Multiple ciphers must be comma-separated. If the specified
list begins with a '+' character, then the
specified ciphers will be appended to the default set
instead of replacing them. If the specified list begins with
a '\-' 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 '^' character, then the specified ciphers will
be placed at the head of the default set.
.PP
The supported
ciphers are:
.PP
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
.PP
The default
is:
.PP
chacha20\-poly1305@openssh.com,
.PP
aes128\-ctr,aes192\-ctr,aes256\-ctr, 
aes128\-gcm@openssh.com,aes256\-gcm@openssh.com
.PP
The list of
available ciphers may also be obtained using \*(L"ssh \-Q
cipher\*(R". \fI Optional. Type uniline.  \fR
.SS "Compression"
.IX Subsection "Compression"
Specifies whether compression
is enabled after the user has authenticated successfully.
The argument must be \fByes\fR, \fBdelayed\fR (a legacy
synonym for \fByes\fR) or \fBno\fR. The default is
\&\fByes\fR. \fI Optional. Type enum. choice: 'yes', 'delayed', 'no'.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "DebianBanner"
.IX Subsection "DebianBanner"
Specifies whether the
distribution-specified extra version suffix is included
during initial protocol handshake. The default is
\&\fByes\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "DisableForwarding"
.IX Subsection "DisableForwarding"
Disables all forwarding
features, including X11, \fBssh\-agent\fR\|(1), \s-1TCP\s0 and StreamLocal.
This option overrides all other forwarding-related options
and may simplify restricted configurations. \fI Optional. Type uniline.  \fR
.SS "ExposeAuthInfo"
.IX Subsection "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 \s-1SSH_USER_AUTH\s0 environment variable. The default is
\&\fBno\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
no
.SS "FingerprintHash"
.IX Subsection "FingerprintHash"
Specifies the hash algorithm
used when logging key fingerprints. Valid options are:
\&\fBmd5\fR and \fBsha256\fR. The default is
\&\fBsha256\fR. \fI Optional. Type enum. choice: 'md5', 'sha256'.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
sha256
.SS "GSSAPICleanupCredentials"
.IX Subsection "GSSAPICleanupCredentials"
Specifies whether to
automatically destroy the user's credentials cache on
logout. The default is \fByes\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "GSSAPIKeyExchange"
.IX Subsection "GSSAPIKeyExchange"
Specifies whether key exchange
based on \s-1GSSAPI\s0 is allowed. \s-1GSSAPI\s0 key exchange
doesn't rely on ssh keys to verify host identity. The
default is \fBno\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
no
.SS "GSSAPIStrictAcceptorCheck"
.IX Subsection "GSSAPIStrictAcceptorCheck"
Determines whether to be strict
about the identity of the \s-1GSSAPI\s0 acceptor a client
authenticates against. If set to \fByes\fR then the client
must authenticate against the host service on the current
hostname. If set to \fBno\fR 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 \fByes\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "GSSAPIStoreCredentialsOnRekey"
.IX Subsection "GSSAPIStoreCredentialsOnRekey"
Controls whether the
user's \s-1GSSAPI\s0 credentials should be updated following
a successful connection rekeying. This option can be used to
accepted renewed or updated credentials from a compatible
client. The default is \fBno\fR.
.PP
For this to
work \fBGSSAPIKeyExchange\fR needs to be enabled in the
server and also used by the client. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
no
.SS "GSSAPIKexAlgorithms"
.IX Subsection "GSSAPIKexAlgorithms"
The list of key exchange
algorithms that are accepted by \s-1GSSAPI\s0 key exchange.
Possible values are
.PP
gss\-gex\-sha1\-,
.PP
gss\-group1\-sha1\-, 
gss\-group14\-sha1\-, 
gss\-group14\-sha256\-, 
gss\-group16\-sha512\-, 
gss\-nistp256\-sha256\-, 
gss\-curve25519\-sha256\-
.PP
The default is
Xgss\-group14\-sha256\-,gss\-group16\-sha512\-,gss\-nistp256\-sha256\-,gss\-curve25519\-sha256\-,gss\-gex\-sha1\-,gss\-group14\-sha1\-X.
This option only applies to connections using \s-1GSSAPI.\s0 \fI Optional. Type uniline.  \fR
.SS "HostCertificate"
.IX Subsection "HostCertificate"
Specifies a file containing a
public host certificate. The certificate's public key
must match a private host key already specified by
\&\fBHostKey\fR. The default behaviour of \fBsshd\fR\|(8) is not to
load any certificates. \fI Optional. Type uniline.  \fR
.SS "HostKey"
.IX Subsection "HostKey"
Specifies a file containing a
private host key used by \s-1SSH.\s0 The defaults are
\&\fI/etc/ssh/ssh_host_ecdsa_key\fR,
\&\fI/etc/ssh/ssh_host_ed25519_key\fR and
\&\fI/etc/ssh/ssh_host_rsa_key\fR.
.PP
Note that
\&\fBsshd\fR\|(8) will refuse to use a file if it is
group/world\-accessible and that the \fBHostKeyAlgorithms\fR
option restricts which of the keys are actually used by
\&\fBsshd\fR\|(8).
.PP
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
\&\fBssh\-agent\fR\|(1). \fI Optional. Type uniline.  \fR
.SS "HostKeyAgent"
.IX Subsection "HostKeyAgent"
Identifies the UNIX-domain
socket used to communicate with an agent that has access to
the private host keys. If the string
\&\*(L"\s-1SSH_AUTH_SOCK\*(R"\s0 is specified, the location of the
socket will be read from the \s-1SSH_AUTH_SOCK\s0 environment
variable. \fI Optional. Type uniline.  \fR
.SS "HostKeyAlgorithms"
.IX Subsection "HostKeyAlgorithms"
Specifies the host key
algorithms that the server offers. The default for this
option is:
.PP
ecdsa\-sha2\-nistp256\-cert\-v01@openssh.com,
.PP
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,
.PP
ecdsa\-sha2\-nistp256,ecdsa\-sha2\-nistp384,ecdsa\-sha2\-nistp521,
.PP
sk\-ecdsa\-sha2\-nistp256@openssh.com, 
ssh\-ed25519,sk\-ssh\-ed25519@openssh.com, 
rsa\-sha2\-512,rsa\-sha2\-256,ssh\-rsa
.PP
The list of
available key types may also be obtained using \*(L"ssh \-Q
HostKeyAlgorithms\*(R". \fI Optional. Type uniline.  \fR
.SS "IgnoreUserKnownHosts"
.IX Subsection "IgnoreUserKnownHosts"
Specifies whether \fBsshd\fR\|(8)
should ignore the user's \fI~/.ssh/known_hosts\fR
during \fBHostbasedAuthentication\fR and use only the
system-wide known hosts file \fI/etc/ssh/known_hosts\fR.
The default is \fBno\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
no
.SS "KerberosGetAFSToken"
.IX Subsection "KerberosGetAFSToken"
If \s-1AFS\s0 is active and the user
has a Kerberos 5 \s-1TGT,\s0 attempt to acquire an \s-1AFS\s0 token before
accessing the user's home directory. The default is
\&\fBno\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
no
.SS "KerberosOrLocalPasswd"
.IX Subsection "KerberosOrLocalPasswd"
If password authentication
through Kerberos fails then the password will be validated
via any additional local mechanism such as
\&\fI/etc/passwd\fR. The default is \fByes\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "KerberosTicketCleanup"
.IX Subsection "KerberosTicketCleanup"
Specifies whether to
automatically destroy the user's ticket cache file on
logout. The default is \fByes\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "KexAlgorithms"
.IX Subsection "KexAlgorithms"
Specifies the available \s-1KEX\s0
(Key Exchange) algorithms. Multiple algorithms must be
comma-separated. Alternately if the specified list begins
with a '+' character, then the specified methods
will be appended to the default set instead of replacing
them. If the specified list begins with a '\-'
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 '^'
character, then the specified methods will be placed at the
head of the default set. The supported algorithms are:
.PP
curve25519\-sha256
.PP
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
.PP
The default
is:
.PP
curve25519\-sha256,curve25519\-sha256@libssh.org,
.PP
ecdh\-sha2\-nistp256,ecdh\-sha2\-nistp384,ecdh\-sha2\-nistp521,
.PP
diffie\-hellman\-group\-exchange\-sha256,
.PP
diffie\-hellman\-group16\-sha512,diffie\-hellman\-group18\-sha512,
.PP
diffie\-hellman\-group14\-sha256
.PP
The list of
available key exchange algorithms may also be obtained using
\&\*(L"ssh \-Q KexAlgorithms\*(R". \fI Optional. Type uniline.  \fR
.SS "ListenAddress"
.IX Subsection "ListenAddress"
Specifies the local addresses
\&\fBsshd\fR\|(8) should listen on. The following forms may be
used:
.PP
\&\fBListenAddress\fR\fIhostname\fR|\fIaddress\fR [\fBrdomain\fR\fIdomain\fR] \fB
ListenAddress\fR \fIhostname\fR:\fIport\fR
[\fBrdomain\fR \fIdomain\fR] \fB
ListenAddress\fR \fIIPv4_address\fR:\fIport\fR
[\fBrdomain\fR \fIdomain\fR] \fB
ListenAddress\fR [
.PP
\&\fIhostname\fR|\fIaddress\fR ]:\fIport\fR
[\fBrdomain\fR \fIdomain\fR]
.PP
The optional
\&\fBrdomain\fR qualifier requests \fBsshd\fR\|(8) listen in an
explicit routing domain. If \fIport\fR is not specified,
sshd will listen on the address and all \fBPort\fR options
specified. The default is to listen on all local addresses
on the current default routing domain. Multiple
\&\fBListenAddress\fR options are permitted. For more
information on routing domains, see \fBrdomain\fR\|(4). \fI Optional. Type uniline.  \fR
.SS "LoginGraceTime"
.IX Subsection "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. \fI Optional. Type uniline.  \fR
.SS "MACs"
.IX Subsection "MACs"
Specifies the
available \s-1MAC\s0 (message authentication code) algorithms. The
\&\s-1MAC\s0 algorithm is used for data integrity protection.
Multiple algorithms must be comma-separated. If the
specified list begins with a '+' character, then
the specified algorithms will be appended to the default set
instead of replacing them. If the specified list begins with
a '\-' 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 '^' character, then the specified algorithms
will be placed at the head of the default set.
.PP
The algorithms
that contain \*(L"\-etm\*(R" calculate the \s-1MAC\s0 after
encryption (encrypt-then-mac). These are considered safer
and their use recommended. The supported MACs are:
.PP
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
.PP
The default
is:
.PP
umac\-64\-etm@openssh.com,umac\-128\-etm@openssh.com,
.PP
hmac\-sha2\-256\-etm@openssh.com,hmac\-sha2\-512\-etm@openssh.com,
.PP
hmac\-sha1\-etm@openssh.com, 
umac\-64@openssh.com,umac\-128@openssh.com, 
hmac\-sha2\-256,hmac\-sha2\-512,hmac\-sha1
.PP
The list of
available \s-1MAC\s0 algorithms may also be obtained using
\&\*(L"ssh \-Q mac\*(R". \fI Optional. Type uniline.  \fR
.SS "Match"
.IX Subsection "Match"
Introduces a
conditional block. If all of the criteria on the
\&\fBMatch\fR line are satisfied, the keywords on the
following lines override those set in the global section of
the config file, until either another \fBMatch\fR line or
the end of the file. If a keyword appears in multiple
\&\fBMatch\fR blocks that are satisfied, only the first
instance of the keyword is applied.
.PP
The arguments
to \fBMatch\fR are one or more criteria-pattern pairs or
the single token \fBAll\fR which matches all criteria. The
available criteria are \fBUser\fR, \fBGroup\fR,
\&\fBHost\fR, \fBLocalAddress\fR, \fBLocalPort\fR,
\&\fBRDomain\fR, and \fBAddress\fR (with \fBRDomain\fR
representing the \fBrdomain\fR\|(4) on which the connection was
received).
.PP
The match
patterns may consist of single entries or comma-separated
lists and may use the wildcard and negation operators
described in the \fI\s-1PATTERNS\s0\fR section of
\&\fBssh_config\fR\|(5).
.PP
The patterns in
an \fBAddress\fR criteria may additionally contain
addresses to match in \s-1CIDR\s0 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.
.PP
Only a subset
of keywords may be used on the lines following a
\&\fBMatch\fR keyword. Available keywords are
\&\fBAcceptEnv\fR, \fBAllowAgentForwarding\fR,
\&\fBAllowGroups\fR, \fBAllowStreamLocalForwarding\fR,
\&\fBAllowTcpForwarding\fR, \fBAllowUsers\fR,
\&\fBAuthenticationMethods\fR, \fBAuthorizedKeysCommand\fR,
\&\fBAuthorizedKeysCommandUser\fR, \fBAuthorizedKeysFile\fR,
\&\fBAuthorizedPrincipalsCommand\fR,
\&\fBAuthorizedPrincipalsCommandUser\fR,
\&\fBAuthorizedPrincipalsFile\fR, \fBBanner\fR,
\&\fBChrootDirectory\fR, \fBClientAliveCountMax\fR,
\&\fBClientAliveInterval\fR, \fBDenyGroups\fR,
\&\fBDenyUsers\fR, \fBForceCommand\fR, \fBGatewayPorts\fR,
\&\fBGSSAPIAuthentication\fR,
\&\fBHostbasedAcceptedKeyTypes\fR,
\&\fBHostbasedAuthentication\fR,
\&\fBHostbasedUsesNameFromPacketOnly\fR, \fBIgnoreRhosts\fR,
\&\fBInclude\fR, \fBIPQoS\fR,
\&\fBKbdInteractiveAuthentication\fR,
\&\fBKerberosAuthentication\fR, \fBLogLevel\fR,
\&\fBMaxAuthTries\fR, \fBMaxSessions\fR,
\&\fBPasswordAuthentication\fR, \fBPermitEmptyPasswords\fR,
\&\fBPermitListen\fR, \fBPermitOpen\fR,
\&\fBPermitRootLogin\fR, \fBPermitTTY\fR,
\&\fBPermitTunnel\fR, \fBPermitUserRC\fR,
\&\fBPubkeyAcceptedKeyTypes\fR, \fBPubkeyAuthentication\fR,
\&\fBRekeyLimit\fR, \fBRevokedKeys\fR, \fBRDomain\fR,
\&\fBSetEnv\fR, \fBStreamLocalBindMask\fR,
\&\fBStreamLocalBindUnlink\fR, \fBTrustedUserCAKeys\fR,
\&\fBX11DisplayOffset\fR, \fBX11Forwarding\fR and
\&\fBX11UseLocalhost\fR. \fI Optional. Type list of node of class Sshd::MatchBlock .  \fR
.SS "MaxStartups"
.IX Subsection "MaxStartups"
Specifies the maximum number of
concurrent unauthenticated connections to the \s-1SSH\s0 daemon.
Additional connections will be dropped until authentication
succeeds or the \fBLoginGraceTime\fR expires for a
connection. The default is 10:30:100.
.PP
Alternatively,
random early drop can be enabled by specifying the three
colon separated values start:rate:full (e.g.
\&\*(L"10:30:60\*(R"). \fBsshd\fR\|(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). \fI Optional. Type uniline.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
10
.SS "PermitUserEnvironment"
.IX Subsection "PermitUserEnvironment"
Specifies whether
\&\fI~/.ssh/environment\fR and \fBenvironment=\fR options in
\&\fI~/.ssh/authorized_keys\fR are processed by \fBsshd\fR\|(8).
Valid options are \fByes\fR, \fBno\fR or a pattern-list
specifying which environment variable names to accept (for
example \*(L"\s-1LANG\s0,LC_*\*(R"). The default is \fBno\fR.
Enabling environment processing may enable users to bypass
access restrictions in some configurations using mechanisms
such as \s-1LD_PRELOAD.\s0 \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
no
.SS "PidFile"
.IX Subsection "PidFile"
Specifies the file that
contains the process \s-1ID\s0 of the \s-1SSH\s0 daemon, or \fBnone\fR to
not write one. The default is \fI/run/sshd.pid\fR. \fI Optional. Type uniline.  \fR
.SS "Port"
.IX Subsection "Port"
Specifies the
port number that \fBsshd\fR\|(8) listens on. The default is 22.
Multiple options of this type are permitted. See also
\&\fBListenAddress\fR. \fI Optional. Type uniline.  \fR
.SS "PrintLastLog"
.IX Subsection "PrintLastLog"
Specifies whether \fBsshd\fR\|(8)
should print the date and time of the last user login when a
user logs in interactively. The default is \fByes\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "PrintMotd"
.IX Subsection "PrintMotd"
Specifies whether \fBsshd\fR\|(8)
should print \fI/etc/motd\fR when a user logs in
interactively. (On some systems it is also printed by the
shell, \fI/etc/profile\fR, or equivalent.) The default is
\&\fByes\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "PubkeyAuthOptions"
.IX Subsection "PubkeyAuthOptions"
Sets one or more public key
authentication options. The supported keywords are:
\&\fBnone\fR (the default; indicating no additional options
are enabled), \fBtouch-required\fR and
\&\fBverify-required\fR.
.PP
The
\&\fBtouch-required\fR option causes public key
authentication using a \s-1FIDO\s0 authenticator algorithm (i.e.
\&\fBecdsa-sk\fR or \fBed25519\-sk\fR) to always require the
signature to attest that a physically present user
explicitly confirmed the authentication (usually by touching
the authenticator). By default, \fBsshd\fR\|(8) requires user
presence unless overridden with an authorized_keys option.
The \fBtouch-required\fR flag disables this override.
.PP
The
\&\fBverify-required\fR option requires a \s-1FIDO\s0 key signature
attest that the user was verified, e.g. via a \s-1PIN.\s0
.PP
Neither the
\&\fBtouch-required\fR or \fBverify-required\fR options have
any effect for other, non-FIDO, public key types. \fI Optional. Type enum. choice: 'touch\-required', 'verify\-required'.  \fR
.SS "SecurityKeyProvider"
.IX Subsection "SecurityKeyProvider"
Specifies a path to a library
that will be used when loading \s-1FIDO\s0 authenticator-hosted
keys, overriding the default of using the built-in \s-1USB HID\s0
support. \fI Optional. Type uniline.  \fR
.SS "StrictModes"
.IX Subsection "StrictModes"
Specifies whether \fBsshd\fR\|(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 \fByes\fR. Note that this does not apply to
\&\fBChrootDirectory\fR, whose permissions and ownership are
checked unconditionally. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "Subsystem"
.IX Subsection "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.
.PP
The command
\&\fBsftp-server\fR implements the \s-1SFTP\s0 file transfer
subsystem.
.PP
Alternately the
name \fBinternal-sftp\fR implements an in-process \s-1SFTP\s0
server. This may simplify configurations using
\&\fBChrootDirectory\fR to force a different filesystem root
on clients.
.PP
By default no
subsystems are defined. \fI Optional. Type hash of uniline.  \fR
.SS "SyslogFacility"
.IX Subsection "SyslogFacility"
Gives the facility code that is
used when logging messages from \fBsshd\fR\|(8). The possible values
are: \s-1DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, LOCAL3,
LOCAL4, LOCAL5, LOCAL6, LOCAL7.\s0 The default is \s-1AUTH.\s0 \fI Optional. Type enum. choice: '\s-1DAEMON\s0', '\s-1USER\s0', '\s-1AUTH\s0', '\s-1LOCAL0\s0', '\s-1LOCAL1\s0', '\s-1LOCAL2\s0', '\s-1LOCAL3\s0', '\s-1LOCAL4\s0', '\s-1LOCAL5\s0', '\s-1LOCAL6\s0', '\s-1LOCAL7\s0'.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
\&\s-1AUTH\s0
.SS "TCPKeepAlive"
.IX Subsection "TCPKeepAlive"
Specifies whether the system
should send \s-1TCP\s0 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 \s-1TCP\s0
keepalives are not sent, sessions may hang indefinitely on
the server, leaving \*(L"ghost\*(R" users and consuming
server resources.
.PP
The default is
\&\fByes\fR (to send \s-1TCP\s0 keepalive messages), and the server
will notice if the network goes down or the client host
crashes. This avoids infinitely hanging sessions.
.PP
To disable \s-1TCP\s0
keepalive messages, the value should be set to
\&\fBno\fR.
.PP
This option was
formerly called \fBKeepAlive\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
yes
.SS "UseDNS"
.IX Subsection "UseDNS"
Specifies
whether \fBsshd\fR\|(8) should look up the remote host name, and to
check that the resolved host name for the remote \s-1IP\s0 address
maps back to the very same \s-1IP\s0 address.
.PP
If this option
is set to \fBno\fR (the default) then only addresses and
not host names may be used in \fI~/.ssh/authorized_keys\fR\fBfrom\fR and \fBsshd_config Match Host\fR
directives. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
no
.SS "UsePAM"
.IX Subsection "UsePAM"
Enables the
Pluggable Authentication Module interface. If set to
\&\fByes\fR this will enable \s-1PAM\s0 authentication using
\&\fBChallengeResponseAuthentication\fR and
\&\fBPasswordAuthentication\fR in addition to \s-1PAM\s0 account and
session module processing for all authentication types.
.PP
Because \s-1PAM\s0
challenge-response authentication usually serves an
equivalent role to password authentication, you should
disable either \fBPasswordAuthentication\fR or
\&\fBChallengeResponseAuthentication.\fR
.PP
If
\&\fBUsePAM\fR is enabled, you will not be able to run
\&\fBsshd\fR\|(8) as a non-root user. The default is \fBno\fR. \fI Optional. Type boolean.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
no
.SS "VersionAddendum"
.IX Subsection "VersionAddendum"
Optionally specifies additional
text to append to the \s-1SSH\s0 protocol banner sent by the server
upon connection. The default is \fBnone\fR. \fI Optional. Type uniline.  \fR
.SS "XAuthLocation"
.IX Subsection "XAuthLocation"
Specifies the full pathname of
the \fBxauth\fR\|(1) program, or \fBnone\fR to not use one. The
default is \fI/usr/bin/xauth\fR. \fI Optional. Type uniline.  \fR
.IP "upstream_default value :" 4
.IX Item "upstream_default value :"
/usr/bin/xauth
.SH "SEE ALSO"
.IX Header "SEE ALSO"
.IP "\(bu" 4
cme
.IP "\(bu" 4
Config::Model::models::Sshd::MatchBlock
.SH "LICENSE"
.IX Header "LICENSE"
.IP "\s-1LGPL2\s0" 4
.IX Item "LGPL2"