jammy (3) Config::Model::models::Sshd.3pm.gz
NAME
Config::Model::models::Sshd - Configuration class Sshd
DESCRIPTION
Configuration classes used by Config::Model
This configuration class was generated from sshd_system documentation. by parse-man.pl
<https://github.com/dod38fr/config-model-openssh/contrib/parse-man.pl>
Elements
AcceptEnv
Specifies what environment variables sent by the client will be copied into the session's environ(7). See
SendEnv and SetEnv in ssh_config(5) for how to configure the client. The TERM environment variable is
always accepted whenever the client requests a pseudo-terminal as it is required by the protocol.
Variables are specified by name, which may contain the wildcard characters '*' and '?'. Multiple
environment variables may be separated by whitespace or spread across multiple AcceptEnv directives. Be
warned that some environment variables could be used to bypass restricted user environments. For this
reason, care should be taken in the use of this directive. The default is not to accept any environment
variables. Optional. Type list of uniline.
AllowAgentForwarding
Specifies whether ssh-agent(1) forwarding is permitted. The default is yes. Note that disabling agent
forwarding does not improve security unless users are also denied shell access, as they can always
install their own forwarders. Optional. Type boolean.
upstream_default value :
yes
AllowGroups
This keyword can be followed by a list of group name patterns, separated by spaces. If specified, login
is allowed only for users whose primary group or supplementary group list matches one of the patterns.
Only group names are valid; a numerical group ID is not recognized. By default, login is allowed for all
groups. The allow/deny groups directives are processed in the following order: DenyGroups, AllowGroups.
See PATTERNS in ssh_config(5) for more information on patterns. Optional. Type list of uniline.
AllowStreamLocalForwarding
Specifies whether StreamLocal (Unix-domain socket) forwarding is permitted. The available options are yes
(the default) or all to allow StreamLocal forwarding, no to prevent all StreamLocal forwarding, local to
allow local (from the perspective of ssh(1)) forwarding only or remote to allow remote forwarding only.
Note that disabling StreamLocal forwarding does not improve security unless users are also denied shell
access, as they can always install their own forwarders. Optional. Type enum. choice: 'yes', 'all',
'no', 'local', 'remote'.
upstream_default value :
yes
AllowTcpForwarding
Specifies whether TCP forwarding is permitted. The available options are yes (the default) or all to
allow TCP forwarding, no to prevent all TCP forwarding, local to allow local (from the perspective of
ssh(1)) forwarding only or remote to allow remote forwarding only. Note that disabling TCP forwarding
does not improve security unless users are also denied shell access, as they can always install their own
forwarders. Optional. Type enum. choice: 'yes', 'all', 'no', 'local', 'remote'.
upstream_default value :
yes
AllowUsers
This keyword can be followed by a list of user name patterns, separated by spaces. If specified, login is
allowed only for user names that match one of the patterns. Only user names are valid; a numerical user
ID is not recognized. By default, login is allowed for all users. If the pattern takes the form USER@HOST
then USER and HOST are separately checked, restricting logins to particular users from particular hosts.
HOST criteria may additionally contain addresses to match in CIDR address/masklen format. The allow/deny
users directives are processed in the following order: DenyUsers, AllowUsers.
See PATTERNS in ssh_config(5) for more information on patterns. Optional. Type list of uniline.
AuthenticationMethods
Specifies the authentication methods that must be successfully completed for a user to be granted access.
This option must be followed by one or more lists of comma-separated authentication method names, or by
the single string any to indicate the default behaviour of accepting any single authentication method. If
the default is overridden, then successful authentication requires completion of every method in at least
one of these lists.
For example, "publickey, password publickey, keyboard-interactive" would require the user to complete
public key authentication, followed by either password or keyboard interactive authentication. Only
methods that are next in one or more lists are offered at each stage, so for this example it would not be
possible to attempt password or keyboard-interactive authentication before public key.
For keyboard interactive authentication it is also possible to restrict authentication to a specific
device by appending a colon followed by the device identifier bsdauth or pam. depending on the server
configuration. For example, "keyboard-interactive:bsdauth" would restrict keyboard interactive
authentication to the bsdauth device.
If the publickey method is listed more than once, sshd(8) verifies that keys that have been used
successfully are not reused for subsequent authentications. For example, "publickey, publickey" requires
successful authentication using two different public keys.
Note that each authentication method listed should also be explicitly enabled in the configuration.
The available authentication methods are: "gssapi-with-mic", "hostbased", "keyboard-interactive", "none"
(used for access to password-less accounts when PermitEmptyPasswords is enabled), "password" and
"publickey". Optional. Type uniline.
AuthorizedKeysCommand
Specifies a program to be used to look up the user's public keys. The program must be owned by root, not
writable by group or others and specified by an absolute path. Arguments to AuthorizedKeysCommand accept
the tokens described in the TOKENS section. If no arguments are specified then the username of the target
user is used.
The program should produce on standard output zero or more lines of authorized_keys output (see
AUTHORIZED_KEYS in sshd(8)). AuthorizedKeysCommand is tried after the usual AuthorizedKeysFile files and
will not be executed if a matching key is found there. By default, no AuthorizedKeysCommand is run.
Optional. Type uniline.
AuthorizedKeysCommandUser
Specifies the user under whose account the AuthorizedKeysCommand is run. It is recommended to use a
dedicated user that has no other role on the host than running authorized keys commands. If
AuthorizedKeysCommand is specified but AuthorizedKeysCommandUser is not, then sshd(8) will refuse to
start. Optional. Type uniline.
AuthorizedKeysFile
Specifies the file that contains the public keys used for user authentication. The format is described in
the AUTHORIZED_KEYS FILE FORMAT section of sshd(8). Arguments to AuthorizedKeysFile accept the tokens
described in the TOKENS section. After expansion, AuthorizedKeysFile is taken to be an absolute path or
one relative to the user's home directory. Multiple files may be listed, separated by whitespace.
Alternately this option may be set to none to skip checking for user keys in files. The default is
".ssh/authorized_keys .ssh/authorized_keys2". Optional. Type list of uniline.
Note: AuthorizedKeysFile values are migrated from '- AuthorizedKeysFile2'
AuthorizedPrincipalsCommand
Specifies a program to be used to generate the list of allowed certificate principals as per
AuthorizedPrincipalsFile. The program must be owned by root, not writable by group or others and
specified by an absolute path. Arguments to AuthorizedPrincipalsCommand accept the tokens described in
the TOKENS section. If no arguments are specified then the username of the target user is used.
The program should produce on standard output zero or more lines of AuthorizedPrincipalsFile output. If
either AuthorizedPrincipalsCommand or AuthorizedPrincipalsFile is specified, then certificates offered by
the client for authentication must contain a principal that is listed. By default, no
AuthorizedPrincipalsCommand is run. Optional. Type uniline.
AuthorizedPrincipalsCommandUser
Specifies the user under whose account the AuthorizedPrincipalsCommand is run. It is recommended to use a
dedicated user that has no other role on the host than running authorized principals commands. If
AuthorizedPrincipalsCommand is specified but AuthorizedPrincipalsCommandUser is not, then sshd(8) will
refuse to start. Optional. Type uniline.
AuthorizedPrincipalsFile
Specifies a file that lists principal names that are accepted for certificate authentication. When using
certificates signed by a key listed in TrustedUserCAKeys, this file lists names, one of which must appear
in the certificate for it to be accepted for authentication. Names are listed one per line preceded by
key options (as described in AUTHORIZED_KEYS FILE FORMAT in sshd(8)). Empty lines and comments starting
with '#' are ignored.
Arguments to AuthorizedPrincipalsFile accept the tokens described in the TOKENS section. After expansion,
AuthorizedPrincipalsFile is taken to be an absolute path or one relative to the user's home directory.
The default is none, i.e. not to use a principals file X in this case, the username of the user must
appear in a certificate's principals list for it to be accepted.
Note that AuthorizedPrincipalsFile is only used when authentication proceeds using a CA listed in
TrustedUserCAKeys and is not consulted for certification authorities trusted via ~/.ssh/authorized_keys,
though the principals= key option offers a similar facility (see sshd(8) for details). Optional. Type
uniline.
upstream_default value :
none
Banner
The contents of the specified file are sent to the remote user before authentication is allowed. If the
argument is none then no banner is displayed. By default, no banner is displayed. Optional. Type
uniline.
ChrootDirectory
Specifies the pathname of a directory to chroot(2) to after authentication. At session startup sshd(8)
checks that all components of the pathname are root-owned directories which are not writable by any other
user or group. After the chroot, sshd(8) changes the working directory to the user's home directory.
Arguments to ChrootDirectory accept the tokens described in the TOKENS section.
The ChrootDirectory must contain the necessary files and directories to support the user's session. For
an interactive session this requires at least a shell, typically sh(1), and basic /dev nodes such as
null(4), zero(4), stdin(4), stdout(4), stderr(4), and tty(4) devices. For file transfer sessions using
SFTP no additional configuration of the environment is necessary if the in-process sftp-server is used,
though sessions which use logging may require /dev/log inside the chroot directory on some operating
systems (see sftp-server(8) for details).
For safety, it is very important that the directory hierarchy be prevented from modification by other
processes on the system (especially those outside the jail). Misconfiguration can lead to unsafe
environments which sshd(8) cannot detect.
The default is none, indicating not to chroot(2). Optional. Type uniline.
upstream_default value :
none
ClientAliveCountMax
Sets the number of client alive messages which may be sent without sshd(8) receiving any messages back
from the client. If this threshold is reached while client alive messages are being sent, sshd will
disconnect the client, terminating the session. It is important to note that the use of client alive
messages is very different from TCPKeepAlive. The client alive messages are sent through the encrypted
channel and therefore will not be spoofable. The TCP keepalive option enabled by TCPKeepAlive is
spoofable. The client alive mechanism is valuable when the client or server depend on knowing when a
connection has become unresponsive.
The default value is 3. If ClientAliveInterval is set to 15, and ClientAliveCountMax is left at the
default, unresponsive SSH clients will be disconnected after approximately 45 seconds. Setting a zero
ClientAliveCountMax disables connection termination. Optional. Type integer.
upstream_default value :
3
ClientAliveInterval
Sets a timeout interval in seconds after which if no data has been received from the client, sshd(8) will
send a message through the encrypted channel to request a response from the client. The default is 0,
indicating that these messages will not be sent to the client. Optional. Type integer.
upstream_default value :
0
DenyGroups
This keyword can be followed by a list of group name patterns, separated by spaces. Login is disallowed
for users whose primary group or supplementary group list matches one of the patterns. Only group names
are valid; a numerical group ID is not recognized. By default, login is allowed for all groups. The
allow/deny groups directives are processed in the following order: DenyGroups, AllowGroups.
See PATTERNS in ssh_config(5) for more information on patterns. Optional. Type list of uniline.
DenyUsers
This keyword can be followed by a list of user name patterns, separated by spaces. Login is disallowed
for user names that match one of the patterns. Only user names are valid; a numerical user ID is not
recognized. By default, login is allowed for all users. If the pattern takes the form USER@HOST then USER
and HOST are separately checked, restricting logins to particular users from particular hosts. HOST
criteria may additionally contain addresses to match in CIDR address/masklen format. The allow/deny
users directives are processed in the following order: DenyUsers, AllowUsers.
See PATTERNS in ssh_config(5) for more information on patterns. Optional. Type list of uniline.
DisableForwarding
Disables all forwarding features, including X11, ssh-agent(1), TCP and StreamLocal. This option
overrides all other forwarding-related options and may simplify restricted configurations. Optional.
Type uniline.
ForceCommand
Forces the execution of the command specified by ForceCommand, ignoring any command supplied by the
client and ~/.ssh/rc if present. The command is invoked by using the user's login shell with the -c
option. This applies to shell, command, or subsystem execution. It is most useful inside a Match block.
The command originally supplied by the client is available in the SSH_ORIGINAL_COMMAND environment
variable. Specifying a command of internal-sftp will force the use of an in-process SFTP server that
requires no support files when used with ChrootDirectory. The default is none. Optional. Type uniline.
upstream_default value :
none
GatewayPorts
Specifies whether remote hosts are allowed to connect to ports forwarded for the client. By default,
sshd(8) binds remote port forwardings to the loopback address. This prevents other remote hosts from
connecting to forwarded ports. GatewayPorts can be used to specify that sshd should allow remote port
forwardings to bind to non-loopback addresses, thus allowing other hosts to connect. The argument may be
no to force remote port forwardings to be available to the local host only, yes to force remote port
forwardings to bind to the wildcard address, or clientspecified to allow the client to select the address
to which the forwarding is bound. The default is no. Optional. Type enum. choice: 'no', 'yes',
'clientspecified'.
upstream_default value :
no
GSSAPIAuthentication
Specifies whether user authentication based on GSSAPI is allowed. The default is no. Optional. Type
boolean.
upstream_default value :
no
HostbasedAcceptedAlgorithms
Specifies the signature algorithms 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
signature algorithms will be appended to the default set instead of replacing them. If the specified list
begins with a '-' character, then the specified signature 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 signature algorithms will be placed at the head of the default set. The
default for this option is:
ssh-ed25519-cert-v01@openssh.com, ecdsa-sha2-nistp256-cert-v01@openssh.com,
ecdsa-sha2-nistp384-cert-v01@openssh.com, ecdsa-sha2-nistp521-cert-v01@openssh.com,
sk-ssh-ed25519-cert-v01@openssh.com, sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
rsa-sha2-512-cert-v01@openssh.com, rsa-sha2-256-cert-v01@openssh.com, ssh-rsa-cert-v01@openssh.com,
ssh-ed25519, ecdsa-sha2-nistp256, ecdsa-sha2-nistp384, ecdsa-sha2-nistp521, sk-ssh-ed25519@openssh.com,
sk-ecdsa-sha2-nistp256@openssh.com, rsa-sha2-512, rsa-sha2-256, ssh-rsa
The list of available signature algorithms may also be obtained using "ssh -Q
HostbasedAcceptedAlgorithms". This was formerly named HostbasedAcceptedKeyTypes. Optional. Type uniline.
HostbasedAuthentication
Specifies whether rhosts or /etc/hosts.equiv authentication together with successful public key client
host authentication is allowed (host-based authentication). The default is no. Optional. Type boolean.
upstream_default value :
no
HostbasedUsesNameFromPacketOnly
Specifies whether or not the server will attempt to perform a reverse name lookup when matching the name
in the ~/.shosts, ~/.rhosts, and /etc/hosts.equiv files during HostbasedAuthentication. A setting of yes
means that sshd(8) uses the name supplied by the client rather than attempting to resolve the name from
the TCP connection itself. The default is no. Optional. Type boolean.
upstream_default value :
no
IgnoreRhosts
Specifies whether to ignore per-user .rhosts and .shosts files during HostbasedAuthentication. The
system-wide /etc/hosts.equiv and /etc/ssh/shosts.equiv are still used regardless of this setting.
Accepted values are yes (the default) to ignore all per-user files, shosts-only to allow the use of
.shosts but to ignore .rhosts or no to allow both .shosts and rhosts. Optional. Type boolean.
upstream_default value :
yes
Include
Include the specified configuration file(s). Multiple pathnames may be specified and each pathname may
contain glob(7) wildcards that will be expanded and processed in lexical order. Files without absolute
paths are assumed to be in /etc/ssh. An Include directive may appear inside a Match block to perform
conditional inclusion. Optional. Type list of uniline.
IPQoS
Specifies the IPv4 type-of-service or DSCP class for the connection. Accepted values are af11, af12,
af13, af21, af22, af23, af31, af32, af33, af41, af42, af43, cs0, cs1, cs2, cs3, cs4, cs5, cs6, cs7, ef,
le, lowdelay, throughput, reliability, a numeric value, or none to use the operating system default. This
option may take one or two arguments, separated by whitespace. If one argument is specified, it is used
as the packet class unconditionally. If two values are specified, the first is automatically selected
for interactive sessions and the second for non-interactive sessions. The default is lowdelay for
interactive sessions and throughput for non-interactive sessions. Optional. Type uniline.
upstream_default value :
af21 cs1
KbdInteractiveAuthentication
Specifies whether to allow keyboard-interactive authentication. The default is yes. The argument to this
keyword must be yes or no. ChallengeResponseAuthentication is a deprecated alias for this. Optional.
Type boolean.
upstream_default value :
yes
Note: KbdInteractiveAuthentication is migrated with '$old' and with:
• $old => "- ChallengeResponseAuthentication"
KerberosAuthentication
Specifies whether the password provided by the user for PasswordAuthentication will be validated through
the Kerberos KDC. To use this option, the server needs a Kerberos servtab which allows the verification
of the KDC's identity. The default is no. Optional. Type boolean.
upstream_default value :
no
LogLevel
Gives the verbosity level that is used when logging messages from sshd(8). The possible values are:
QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO. DEBUG and
DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify higher levels of debugging output. Logging with a
DEBUG level violates the privacy of users and is not recommended. Optional. Type enum. choice: 'QUIET',
'FATAL', 'ERROR', 'INFO', 'VERBOSE', 'DEBUG', 'DEBUG1', 'DEBUG2', 'DEBUG3'.
upstream_default value :
INFO
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. Optional. Type
integer.
upstream_default value :
6
MaxSessions
Specifies the maximum number of open shell, login or subsystem (e.g. sftp) sessions permitted per network
connection. Multiple sessions may be established by clients that support connection multiplexing.
Setting MaxSessions to 1 will effectively disable session multiplexing, whereas setting it to 0 will
prevent all shell, login and subsystem sessions while still permitting forwarding. The default is 10.
Optional. Type integer.
upstream_default value :
10
PasswordAuthentication
Specifies whether password authentication is allowed. The default is yes. Optional. Type boolean.
upstream_default value :
yes
PermitEmptyPasswords
When password authentication is allowed, it specifies whether the server allows login to accounts with
empty password strings. The default is no. Optional. Type boolean.
upstream_default value :
no
PermitListen
Specifies the addresses/ports on which a remote TCP port forwarding may listen. The listen specification
must be one of the following forms:
PermitListenport PermitListen host:port
Multiple permissions may be specified by separating them with whitespace. An argument of any can be used
to remove all restrictions and permit any listen requests. An argument of none can be used to prohibit
all listen requests. The host name may contain wildcards as described in the PATTERNS section in
ssh_config(5). The wildcard '*' can also be used in place of a port number to allow all ports. By default
all port forwarding listen requests are permitted. Note that the GatewayPorts option may further restrict
which addresses may be listened on. Note also that ssh(1) will request a listen host of localhost 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. Optional. Type list of uniline.
PermitOpen
Specifies the destinations to which TCP port forwarding is permitted. The forwarding specification must
be one of the following forms:
PermitOpenhost:port PermitOpen IPv4_addr:port PermitOpen [IPv6_addr]:port
Multiple forwards may be specified by separating them with whitespace. An argument of any can be used to
remove all restrictions and permit any forwarding requests. An argument of none can be used to prohibit
all forwarding requests. The wildcard '*' 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. Optional. Type list of uniline.
PermitRootLogin
Specifies whether root can log in using ssh(1). The argument must be yes, prohibit-password, forced-
commands-only, or no. The default is prohibit-password.
If this option is set to prohibit-password (or its deprecated alias, without-password), password and
keyboard-interactive authentication are disabled for root.
If this option is set to forced-commands-only, root login with public key authentication will be allowed,
but only if the command option has been specified (which may be useful for taking remote backups even if
root login is normally not allowed). All other authentication methods are disabled for root.
If this option is set to no, root is not allowed to log in. Optional. Type enum. choice: 'yes',
'prohibit-password', 'forced-commands-only', 'no'.
PermitTTY
Specifies whether pty(4) allocation is permitted. The default is yes. Optional. Type boolean.
upstream_default value :
yes
PermitTunnel
Specifies whether tun(4) device forwarding is allowed. The argument must be yes, point-to-point (layer
3), ethernet (layer 2), or no. Specifying yes permits both point-to-point and ethernet. The default is
no.
Independent of this setting, the permissions of the selected tun(4) device must allow access to the user.
Optional. Type enum. choice: 'yes', 'point-to-point', 'ethernet', 'no'.
upstream_default value :
no
PermitUserRC
Specifies whether any ~/.ssh/rc file is executed. The default is yes. Optional. Type boolean.
upstream_default value :
yes
PubkeyAcceptedAlgorithms
Specifies the signature algorithms 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 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. The default for this option is:
ssh-ed25519-cert-v01@openssh.com, ecdsa-sha2-nistp256-cert-v01@openssh.com,
ecdsa-sha2-nistp384-cert-v01@openssh.com, ecdsa-sha2-nistp521-cert-v01@openssh.com,
sk-ssh-ed25519-cert-v01@openssh.com, sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
rsa-sha2-512-cert-v01@openssh.com, rsa-sha2-256-cert-v01@openssh.com, ssh-rsa-cert-v01@openssh.com,
ssh-ed25519, ecdsa-sha2-nistp256, ecdsa-sha2-nistp384, ecdsa-sha2-nistp521, sk-ssh-ed25519@openssh.com,
sk-ecdsa-sha2-nistp256@openssh.com, rsa-sha2-512, rsa-sha2-256, ssh-rsa
The list of available signature algorithms may also be obtained using "ssh -Q PubkeyAcceptedAlgorithms".
Optional. Type uniline.
PubkeyAuthentication
Specifies whether public key authentication is allowed. The default is yes. Optional. Type boolean.
upstream_default value :
yes
RekeyLimit
Specifies the maximum amount of data that may be transmitted before the session key is renegotiated,
optionally followed by 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 TIME FORMATS
section. The default value for RekeyLimit is default none, which means that rekeying is performed after
the cipher's default amount of data has been sent or received and no time based rekeying is done.
Optional. Type uniline.
RevokedKeys
Specifies revoked public keys file, or none to not use one. Keys listed in this file will be refused for
public key authentication. Note that if this file is not readable, then public key authentication will be
refused for all users. Keys may be specified as a text file, listing one public key per line, or as an
OpenSSH Key Revocation List (KRL) as generated by ssh-keygen(1). For more information on KRLs, see the
KEY REVOCATION LISTS section in ssh-keygen(1). Optional. Type uniline.
SetEnv
Specifies one or more environment variables to set in child sessions started by sshd(8) as XNAME=VALUEX.
The environment value may be quoted (e.g. if it contains whitespace characters). Environment variables
set by SetEnv override the default environment and any variables specified by the user via AcceptEnv or
PermitUserEnvironment. Optional. Type uniline.
StreamLocalBindMask
Sets the octal file creation mode mask (umask) used when creating a Unix-domain socket file for local or
remote port forwarding. This option is only used for port forwarding to a Unix-domain socket file.
The default value is 0177, which creates a Unix-domain socket file that is readable and writable only by
the owner. Note that not all operating systems honor the file mode on Unix-domain socket files.
Optional. Type uniline.
StreamLocalBindUnlink
Specifies whether to remove an existing Unix-domain socket file for local or remote port forwarding
before creating a new one. If the socket file already exists and StreamLocalBindUnlink is not enabled,
sshd will be unable to forward the port to the Unix-domain socket file. This option is only used for port
forwarding to a Unix-domain socket file.
The argument must be yes or no. The default is no. Optional. Type boolean.
upstream_default value :
no
TrustedUserCAKeys
Specifies a file containing public keys of certificate authorities that are trusted to sign user
certificates for authentication, or none to not use one. Keys are listed one per line; empty lines and
comments starting with '#' 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). Optional. Type uniline.
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. Optional. Type uniline.
X11Forwarding
Specifies whether X11 forwarding is permitted. The argument must be yes or no. The default is no.
When X11 forwarding is enabled, there may be additional exposure to the server and to client displays if
the sshd(8) proxy display is configured to listen on the wildcard address (see X11UseLocalhost), though
this is not the default. Additionally, the authentication spoofing and authentication data verification
and substitution occur on the client side. The security risk of using X11 forwarding is that the
client's X11 display server may be exposed to attack when the SSH client requests forwarding (see the
warnings for ForwardX11 in ssh_config(5)). A system administrator may have a stance in which they want to
protect clients that may expose themselves to attack by unwittingly requesting X11 forwarding, which can
warrant a no setting.
Note that disabling X11 forwarding does not prevent users from forwarding X11 traffic, as users can
always install their own forwarders. Optional. Type boolean.
upstream_default value :
no
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. Optional. Type boolean.
upstream_default value :
yes
AuthorizedKeysFile2
This parameter is now ignored by Ssh. Deprecated Optional. Type list of uniline.
ChallengeResponseAuthentication
Deprecated Optional. Type boolean.
KeyRegenerationInterval
Deprecated Optional. Type uniline.
Protocol
Deprecated Optional. Type uniline.
RDomain
Deprecated Optional. Type uniline.
RSAAuthentication
Deprecated Optional. Type uniline.
RhostsRSAAuthentication
Deprecated Optional. Type uniline.
UsePrivilegeSeparation
Deprecated Optional. Type uniline.
AddressFamily
Specifies which address family should be used by sshd(8). Valid arguments are any (the default), inet
(use IPv4 only), or inet6 (use IPv6 only). Optional. Type enum. choice: 'any', 'inet', 'inet6'.
upstream_default value :
any
CASignatureAlgorithms
Specifies which algorithms are allowed for signing of certificates by certificate authorities (CAs). The
default is:
ssh-ed25519, ecdsa-sha2-nistp256, ecdsa-sha2-nistp384, ecdsa-sha2-nistp521, sk-ssh-ed25519@openssh.com,
sk-ecdsa-sha2-nistp256@openssh.com, rsa-sha2-512, rsa-sha2-256
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.
Certificates signed using other algorithms will not be accepted for public key or host-based
authentication. Optional. Type uniline.
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.
The supported ciphers are:
3des-cbc aes128-cbc aes192-cbc aes256-cbc aes128-ctr aes192-ctr aes256-ctr aes128-gcm@openssh.com
aes256-gcm@openssh.com chacha20-poly1305@openssh.com
The default is:
chacha20-poly1305@openssh.com, aes128-ctr, aes192-ctr, aes256-ctr, aes128-gcm@openssh.com,
aes256-gcm@openssh.com
The list of available ciphers may also be obtained using "ssh -Q cipher". Optional. Type uniline.
Compression
Specifies whether compression is enabled after the user has authenticated successfully. The argument
must be yes, delayed (a legacy synonym for yes) or no. The default is yes. Optional. Type enum. choice:
'yes', 'delayed', 'no'.
upstream_default value :
yes
DebianBanner
Specifies whether the distribution-specified extra version suffix is included during initial protocol
handshake. The default is yes. Optional. Type boolean.
upstream_default value :
yes
ExposeAuthInfo
Writes a temporary file containing a list of authentication methods and public credentials (e.g. keys)
used to authenticate the user. The location of the file is exposed to the user session through the
SSH_USER_AUTH environment variable. The default is no. Optional. Type boolean.
upstream_default value :
no
FingerprintHash
Specifies the hash algorithm used when logging key fingerprints. Valid options are: md5 and sha256. The
default is sha256. Optional. Type enum. choice: 'md5', 'sha256'.
upstream_default value :
sha256
GSSAPICleanupCredentials
Specifies whether to automatically destroy the user's credentials cache on logout. The default is yes.
Optional. Type boolean.
upstream_default value :
yes
GSSAPIKeyExchange
Specifies whether key exchange based on GSSAPI is allowed. GSSAPI key exchange doesn't rely on ssh keys
to verify host identity. The default is no. Optional. Type boolean.
upstream_default value :
no
GSSAPIStrictAcceptorCheck
Determines whether to be strict about the identity of the GSSAPI acceptor a client authenticates against.
If set to yes then the client must authenticate against the host service on the current hostname. If set
to no then the client may authenticate against any service key stored in the machine's default store.
This facility is provided to assist with operation on multi homed machines. The default is yes.
Optional. Type boolean.
upstream_default value :
yes
GSSAPIStoreCredentialsOnRekey
Controls whether the user's GSSAPI 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 no.
For this to work GSSAPIKeyExchange needs to be enabled in the server and also used by the client.
Optional. Type boolean.
upstream_default value :
no
GSSAPIKexAlgorithms
The list of key exchange algorithms that are accepted by GSSAPI key exchange. Possible values are
gss-gex-sha1-, gss-group1-sha1-, gss-group14-sha1-, gss-group14-sha256-, gss-group16-sha512-,
gss-nistp256-sha256-, gss-curve25519-sha256-
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 GSSAPI. Optional. Type
uniline.
HostCertificate
Specifies a file containing a public host certificate. The certificate's public key must match a private
host key already specified by HostKey. The default behaviour of sshd(8) is not to load any certificates.
Optional. Type uniline.
HostKey
Specifies a file containing a private host key used by SSH. The defaults are /etc/ssh/ssh_host_ecdsa_key,
/etc/ssh/ssh_host_ed25519_key and /etc/ssh/ssh_host_rsa_key.
Note that sshd(8) will refuse to use a file if it is group/world-accessible and that the
HostKeyAlgorithms option restricts which of the keys are actually used by sshd(8).
It is possible to have multiple host key files. It is also possible to specify public host key files
instead. In this case operations on the private key will be delegated to an ssh-agent(1). Optional. Type
uniline.
HostKeyAgent
Identifies the UNIX-domain socket used to communicate with an agent that has access to the private host
keys. If the string "SSH_AUTH_SOCK" is specified, the location of the socket will be read from the
SSH_AUTH_SOCK environment variable. Optional. Type uniline.
HostKeyAlgorithms
Specifies the host key signature algorithms that the server offers. The default for this option is:
ssh-ed25519-cert-v01@openssh.com, ecdsa-sha2-nistp256-cert-v01@openssh.com,
ecdsa-sha2-nistp384-cert-v01@openssh.com, ecdsa-sha2-nistp521-cert-v01@openssh.com,
sk-ssh-ed25519-cert-v01@openssh.com, sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
rsa-sha2-512-cert-v01@openssh.com, rsa-sha2-256-cert-v01@openssh.com, ssh-rsa-cert-v01@openssh.com,
ssh-ed25519, ecdsa-sha2-nistp256, ecdsa-sha2-nistp384, ecdsa-sha2-nistp521, sk-ssh-ed25519@openssh.com,
sk-ecdsa-sha2-nistp256@openssh.com, rsa-sha2-512, rsa-sha2-256, ssh-rsa
The list of available signature algorithms may also be obtained using "ssh -Q HostKeyAlgorithms".
Optional. Type uniline.
IgnoreUserKnownHosts
Specifies whether sshd(8) should ignore the user's ~/.ssh/known_hosts during HostbasedAuthentication and
use only the system-wide known hosts file /etc/ssh/known_hosts. The default is no. Optional. Type
boolean.
upstream_default value :
no
KerberosGetAFSToken
If AFS is active and the user has a Kerberos 5 TGT, attempt to acquire an AFS token before accessing the
user's home directory. The default is no. Optional. Type boolean.
upstream_default value :
no
KerberosOrLocalPasswd
If password authentication through Kerberos fails then the password will be validated via any additional
local mechanism such as /etc/passwd. The default is yes. Optional. Type boolean.
upstream_default value :
yes
KerberosTicketCleanup
Specifies whether to automatically destroy the user's ticket cache file on logout. The default is yes.
Optional. Type boolean.
upstream_default value :
yes
KexAlgorithms
Specifies the available KEX (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:
curve25519-sha256 curve25519-sha256@libssh.org diffie-hellman-group1-sha1 diffie-hellman-group14-sha1
diffie-hellman-group14-sha256 diffie-hellman-group16-sha512 diffie-hellman-group18-sha512
diffie-hellman-group-exchange-sha1 diffie-hellman-group-exchange-sha256 ecdh-sha2-nistp256
ecdh-sha2-nistp384 ecdh-sha2-nistp521 sntrup761x25519-sha512@openssh.com
The default is:
curve25519-sha256, curve25519-sha256@libssh.org, ecdh-sha2-nistp256, ecdh-sha2-nistp384,
ecdh-sha2-nistp521, diffie-hellman-group-exchange-sha256, diffie-hellman-group16-sha512,
diffie-hellman-group18-sha512, diffie-hellman-group14-sha256
The list of available key exchange algorithms may also be obtained using "ssh -Q KexAlgorithms".
Optional. Type uniline.
ListenAddress
Specifies the local addresses sshd(8) should listen on. The following forms may be used:
ListenAddresshostname|address ListenAddress hostname:port ListenAddress IPv4_address:port ListenAddress [
hostname|address ]:port
If port is not specified, sshd will listen on the address and all Port options specified. The default is
to listen on all local addresses. Multiple ListenAddress options are permitted. Optional. Type uniline.
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. Optional. Type uniline.
LogVerbose
Specify one or more overrides to LogLevel. An override consists of a pattern lists that matches the
source file, function and line number to force detailed logging for. For example, an override pattern of:
kex.c:*:1000,*:kex_exchange_identification():*, packet.c:*
would enable detailed logging for line 1000 of kex.c, everything in the kex_exchange_identification()
function, and all code in the packet.c file. This option is intended for debugging and no overrides are
enabled by default. Optional. Type uniline.
MACs
Specifies the available MAC (message authentication code) algorithms. The MAC algorithm is used for data
integrity protection. Multiple algorithms must be comma-separated. If the specified list begins with a
'+' 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.
The algorithms that contain "-etm" calculate the MAC after encryption (encrypt-then-mac). These are
considered safer and their use recommended. The supported MACs are:
hmac-md5 hmac-md5-96 hmac-sha1 hmac-sha1-96 hmac-sha2-256 hmac-sha2-512 umac-64@openssh.com
umac-128@openssh.com hmac-md5-etm@openssh.com hmac-md5-96-etm@openssh.com hmac-sha1-etm@openssh.com
hmac-sha1-96-etm@openssh.com hmac-sha2-256-etm@openssh.com hmac-sha2-512-etm@openssh.com
umac-64-etm@openssh.com umac-128-etm@openssh.com
The default is:
umac-64-etm@openssh.com, umac-128-etm@openssh.com, hmac-sha2-256-etm@openssh.com,
hmac-sha2-512-etm@openssh.com, hmac-sha1-etm@openssh.com, umac-64@openssh.com, umac-128@openssh.com,
hmac-sha2-256, hmac-sha2-512, hmac-sha1
The list of available MAC algorithms may also be obtained using "ssh -Q mac". Optional. Type uniline.
Match
Introduces a conditional block. If all of the criteria on the Match line are satisfied, the keywords on
the following lines override those set in the global section of the config file, until either another
Match line or the end of the file. If a keyword appears in multiple Match blocks that are satisfied, only
the first instance of the keyword is applied.
The arguments to Match are one or more criteria-pattern pairs or the single token All which matches all
criteria. The available criteria are User, Group, Host, LocalAddress, LocalPort, and Address.
The match patterns may consist of single entries or comma-separated lists and may use the wildcard and
negation operators described in the PATTERNS section of ssh_config(5).
The patterns in an Address criteria may additionally contain addresses to match in CIDR address/masklen
format, such as 192.0.2.0/24 or 2001:db8::/32. Note that the mask length provided must be consistent with
the address - it is an error to specify a mask length that is too long for the address or one with bits
set in this host portion of the address. For example, 192.0.2.0/33 and 192.0.2.0/8, respectively.
Only a subset of keywords may be used on the lines following a Match keyword. Available keywords are
AcceptEnv, AllowAgentForwarding, AllowGroups, AllowStreamLocalForwarding, AllowTcpForwarding, AllowUsers,
AuthenticationMethods, AuthorizedKeysCommand, AuthorizedKeysCommandUser, AuthorizedKeysFile,
AuthorizedPrincipalsCommand, AuthorizedPrincipalsCommandUser, AuthorizedPrincipalsFile, Banner,
ChrootDirectory, ClientAliveCountMax, ClientAliveInterval, DenyGroups, DenyUsers, DisableForwarding,
ForceCommand, GatewayPorts, GSSAPIAuthentication, HostbasedAcceptedAlgorithms, HostbasedAuthentication,
HostbasedUsesNameFromPacketOnly, IgnoreRhosts, Include, IPQoS, KbdInteractiveAuthentication,
KerberosAuthentication, LogLevel, MaxAuthTries, MaxSessions, PasswordAuthentication,
PermitEmptyPasswords, PermitListen, PermitOpen, PermitRootLogin, PermitTTY, PermitTunnel, PermitUserRC,
PubkeyAcceptedAlgorithms, PubkeyAuthentication, RekeyLimit, RevokedKeys, SetEnv, StreamLocalBindMask,
StreamLocalBindUnlink, TrustedUserCAKeys, X11DisplayOffset, X11Forwarding and X11UseLocalhost. Optional.
Type list of node of class Sshd::MatchBlock .
MaxStartups
Specifies the maximum number of concurrent unauthenticated connections to the SSH daemon. Additional
connections will be dropped until authentication succeeds or the LoginGraceTime expires for a connection.
The default is 10:30:100.
Alternatively, random early drop can be enabled by specifying the three colon separated values
start:rate:full (e.g. "10:30:60"). sshd(8) will refuse connection attempts with a probability of
rate/100 (30%) if there are currently start (10) unauthenticated connections. The probability increases
linearly and all connection attempts are refused if the number of unauthenticated connections reaches
full (60). Optional. Type uniline.
upstream_default value :
10
ModuliFile
Specifies the moduli(5) file that contains the Diffie-Hellman groups used for the
Xdiffie-hellman-group-exchange-sha1X and Xdiffie-hellman-group-exchange-sha256X key exchange methods. The
default is /etc/ssh/moduli. Optional. Type uniline.
upstream_default value :
/etc/ssh/moduli
PermitUserEnvironment
Specifies whether ~/.ssh/environment and environment= options in ~/.ssh/authorized_keys are processed by
sshd(8). Valid options are yes, no or a pattern-list specifying which environment variable names to
accept (for example "LANG, LC_*"). The default is no. Enabling environment processing may enable users
to bypass access restrictions in some configurations using mechanisms such as LD_PRELOAD. Optional. Type
boolean.
upstream_default value :
no
PerSourceMaxStartups
Specifies the number of unauthenticated connections allowed from a given source address, or none if there
is no limit. This limit is applied in addition to MaxStartups, whichever is lower. The default is none.
Optional. Type uniline.
upstream_default value :
none
PerSourceNetBlockSize
Specifies the number of bits of source address that are grouped together for the purposes of applying
PerSourceMaxStartups limits. Values for IPv4 and optionally IPv6 may be specified, separated by a colon.
The default is 32:128, which means each address is considered individually. Optional. Type uniline.
upstream_default value :
32:128
PidFile
Specifies the file that contains the process ID of the SSH daemon, or none to not write one. The default
is /run/sshd.pid. Optional. Type uniline.
Port
Specifies the port number that sshd(8) listens on. The default is 22. Multiple options of this type are
permitted. See also ListenAddress. Optional. Type uniline.
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. Optional. Type boolean.
upstream_default value :
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. Optional. Type boolean.
upstream_default value :
yes
PubkeyAuthOptions
Sets one or more public key authentication options. The supported keywords are: none (the default;
indicating no additional options are enabled), touch-required and verify-required.
The touch-required option causes public key authentication using a FIDO authenticator algorithm (i.e.
ecdsa-sk or ed25519-sk) to always require the signature to attest that a physically present user
explicitly confirmed the authentication (usually by touching the authenticator). By default, sshd(8)
requires user presence unless overridden with an authorized_keys option. The touch-required flag
disables this override.
The verify-required option requires a FIDO key signature attest that the user was verified, e.g. via a
PIN.
Neither the touch-required or verify-required options have any effect for other, non-FIDO, public key
types. Optional. Type enum. choice: 'none', 'touch-required', 'verify-required'.
SecurityKeyProvider
Specifies a path to a library that will be used when loading FIDO authenticator-hosted keys, overriding
the default of using the built-in USB HID support. Optional. Type uniline.
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. Optional. Type boolean.
upstream_default value :
yes
Subsystem
Configures an external subsystem (e.g. file transfer daemon). Arguments should be a subsystem name and a
command (with optional arguments) to execute upon subsystem request.
The command sftp-server 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. Optional. Type hash of uniline.
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.
Optional. Type enum. choice: 'DAEMON', 'USER', 'AUTH', 'LOCAL0', 'LOCAL1', 'LOCAL2', 'LOCAL3', 'LOCAL4',
'LOCAL5', 'LOCAL6', 'LOCAL7'.
upstream_default value :
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.
This option was formerly called KeepAlive. Optional. Type boolean.
upstream_default value :
yes
UseDNS
Specifies whether sshd(8) should look up the remote host name, and to check that the resolved host name
for the remote IP address maps back to the very same IP address.
If this option is set to no (the default) then only addresses and not host names may be used in
~/.ssh/authorized_keysfrom and sshd_config Match Host directives. Optional. Type boolean.
upstream_default value :
no
UsePAM
Enables the Pluggable Authentication Module interface. If set to yes this will enable PAM authentication
using KbdInteractiveAuthentication and PasswordAuthentication in addition to PAM account and session
module processing for all authentication types.
Because PAM keyboard-interactive authentication usually serves an equivalent role to password
authentication, you should disable either PasswordAuthentication or KbdInteractiveAuthentication.
If UsePAM is enabled, you will not be able to run sshd(8) as a non-root user. The default is no.
Optional. Type boolean.
upstream_default value :
no
VersionAddendum
Optionally specifies additional text to append to the SSH protocol banner sent by the server upon
connection. The default is none. Optional. Type uniline.
XAuthLocation
Specifies the full pathname of the xauth(1) program, or none to not use one. The default is
/usr/bin/xauth. Optional. Type uniline.
upstream_default value :
/usr/bin/xauth
SEE ALSO
• cme
• Config::Model::models::Sshd::MatchBlock
LICENSE
LGPL2