===================================================================
RCS file: /cvsrepo/anoncvs/cvs/src/usr.bin/ssh/sshd.8,v
retrieving revision 1.176
retrieving revision 1.176.2.6
diff -u -r1.176 -r1.176.2.6
--- src/usr.bin/ssh/sshd.8	2002/04/05 20:56:21	1.176
+++ src/usr.bin/ssh/sshd.8	2003/04/03 22:35:18	1.176.2.6
@@ -34,7 +34,7 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.\" $OpenBSD: sshd.8,v 1.176 2002/04/05 20:56:21 stevesk Exp $
+.\" $OpenBSD: sshd.8,v 1.176.2.6 2003/04/03 22:35:18 miod Exp $
 .Dd September 25, 1999
 .Dt SSHD 8
 .Os
@@ -43,6 +43,7 @@
 .Nd OpenSSH SSH daemon
 .Sh SYNOPSIS
 .Nm sshd
+.Bk -words
 .Op Fl deiqtD46
 .Op Fl b Ar bits
 .Op Fl f Ar config_file
@@ -52,6 +53,7 @@
 .Op Fl o Ar option
 .Op Fl p Ar port
 .Op Fl u Ar len
+.Ek
 .Sh DESCRIPTION
 .Nm
 (SSH Daemon) is the daemon program for
@@ -75,7 +77,7 @@
 .Nm
 supports both SSH protocol version 1 and 2 simultaneously.
 .Nm
-works as follows.
+works as follows:
 .Pp
 .Ss SSH protocol version 1
 .Pp
@@ -86,7 +88,7 @@
 This key is normally regenerated every hour if it has been used, and
 is never stored on disk.
 .Pp
-Whenever a client connects the daemon responds with its public
+Whenever a client connects, the daemon responds with its public
 host and server keys.
 The client compares the
 RSA host key against its own database to verify that it has not changed.
@@ -116,14 +118,14 @@
 because it is fundamentally insecure, but can be enabled in the server
 configuration file if desired.
 System security is not improved unless
-.Xr rshd 8 ,
-.Xr rlogind 8 ,
+.Nm rshd ,
+.Nm rlogind ,
 and
-.Xr rexecd 8
+.Nm rexecd
 are disabled (thus completely disabling
-.Xr rlogin 1
+.Xr rlogin
 and
-.Xr rsh 1
+.Xr rsh
 into the machine).
 .Pp
 .Ss SSH protocol version 2
@@ -189,7 +191,9 @@
 log, and does not put itself in the background.
 The server also will not fork and will only process one connection.
 This option is only intended for debugging for the server.
-Multiple -d options increase the debugging level.
+Multiple
+.Fl d
+options increase the debugging level.
 Maximum is 3.
 .It Fl e
 When this option is specified,
@@ -203,7 +207,7 @@
 refuses to start if there is no configuration file.
 .It Fl g Ar login_grace_time
 Gives the grace time for clients to authenticate themselves (default
-600 seconds).
+120 seconds).
 If the client fails to authenticate the user within
 this many seconds, the server disconnects and exits.
 A value of zero indicates no limit.
@@ -225,7 +229,8 @@
 .It Fl i
 Specifies that
 .Nm
-is being run from inetd.
+is being run from
+.Xr inetd 8 .
 .Nm
 is normally not run
 from inetd because it needs to generate the server key before it can
@@ -282,7 +287,7 @@
 .Pa utmp
 file.
 .Fl u0
-is also be used to prevent
+may also be used to prevent
 .Nm
 from making DNS requests unless the authentication
 mechanism or configuration requires it.
@@ -320,630 +325,8 @@
 (or the file specified with
 .Fl f
 on the command line).
-The file contains keyword-argument pairs, one per line.
-Lines starting with
-.Ql #
-and empty lines are interpreted as comments.
-.Pp
-The possible
-keywords and their meanings are as follows (note that
-keywords are case-insensitive and arguments are case-sensitive):
-.Bl -tag -width Ds
-.It Cm AFSTokenPassing
-Specifies whether an AFS token may be forwarded to the server.
-Default is
-.Dq yes .
-.It Cm 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.
-.Ql \&*
-and
-.Ql ?
-can be used as
-wildcards in the patterns.
-Only group names are valid; a numerical group ID is not recognized.
-By default, login is allowed for all groups.
-.Pp
-.It Cm AllowTcpForwarding
-Specifies whether TCP forwarding is permitted.
-The default is
-.Dq yes .
-Note that disabling TCP forwarding does not improve security unless
-users are also denied shell access, as they can always install their
-own forwarders.
-.Pp
-.It Cm AllowUsers
-This keyword can be followed by a list of user name patterns, separated
-by spaces.
-If specified, login is allowed only for users names that
-match one of the patterns.
-.Ql \&*
-and
-.Ql ?
-can be used as
-wildcards in 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.
-.Pp
-.It Cm AuthorizedKeysFile
-Specifies the file that contains the public keys that can be used
-for user authentication.
-.Cm AuthorizedKeysFile
-may contain tokens of the form %T which are substituted during connection
-set-up. The following tokens are defined: %% is replaced by a literal '%',
-%h is replaced by the home directory of the user being authenticated and
-%u is replaced by the username of that user.
-After expansion,
-.Cm AuthorizedKeysFile
-is taken to be an absolute path or one relative to the user's home
-directory.
-The default is
-.Dq .ssh/authorized_keys .
-.It Cm Banner
-In some jurisdictions, sending a warning message before authentication
-may be relevant for getting legal protection.
-The contents of the specified file are sent to the remote user before
-authentication is allowed.
-This option is only available for protocol version 2.
-By default, no banner is displayed.
-.Pp
-.It Cm ChallengeResponseAuthentication
-Specifies whether challenge response authentication is allowed.
-All authentication styles from
-.Xr login.conf 5
-are supported.
-The default is
-.Dq yes .
-.It Cm Ciphers
-Specifies the ciphers allowed for protocol version 2.
-Multiple ciphers must be comma-separated.
-The default is
-.Pp
-.Bd -literal
-  ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
-    aes192-cbc,aes256-cbc''
-.Ed
-.It Cm ClientAliveInterval
-Sets a timeout interval in seconds after which if no data has been received
-from the client,
-.Nm
-will send a message through the encrypted
-channel to request a response from the client.
-The default
-is 0, indicating that these messages will not be sent to the client.
-This option applies to protocol version 2 only.
-.It Cm ClientAliveCountMax
-Sets the number of client alive messages (see above) which may be
-sent without
-.Nm
-receiving any messages back from the client. If this threshold is
-reached while client alive messages are being sent,
-.Nm
-will disconnect the client, terminating the session. It is important
-to note that the use of client alive messages is very different from
-.Cm KeepAlive
-(below). The client alive messages are sent through the
-encrypted channel and therefore will not be spoofable. The TCP keepalive
-option enabled by
-.Cm KeepAlive
-is spoofable. The client alive mechanism is valuable when the client or
-server depend on knowing when a connection has become inactive.
-.Pp
-The default value is 3. If
-.Cm ClientAliveInterval
-(above) is set to 15, and
-.Cm ClientAliveCountMax
-is left at the default, unresponsive ssh clients
-will be disconnected after approximately 45 seconds.
-.It Cm 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.
-.Ql \&*
-and
-.Ql ?
-can be used as
-wildcards in the patterns.
-Only group names are valid; a numerical group ID is not recognized.
-By default, login is allowed for all groups.
-.Pp
-.It Cm 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.
-.Ql \&*
-and
-.Ql ?
-can be used as wildcards in 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.
-.It Cm GatewayPorts
-Specifies whether remote hosts are allowed to connect to ports
-forwarded for the client.
-By default,
-.Nm
-binds remote port forwardings to the loopback addresss.  This
-prevents other remote hosts from connecting to forwarded ports.
-.Cm GatewayPorts
-can be used to specify that
-.Nm
-should bind remote port forwardings to the wildcard address,
-thus allowing remote hosts to connect to forwarded ports.
-The argument must be
-.Dq yes
-or
-.Dq no .
-The default is
-.Dq no .
-.It Cm HostbasedAuthentication
-Specifies whether rhosts or /etc/hosts.equiv authentication together
-with successful public key client host authentication is allowed
-(hostbased authentication).
-This option is similar to
-.Cm RhostsRSAAuthentication
-and applies to protocol version 2 only.
-The default is
-.Dq no .
-.It Cm HostKey
-Specifies a file containing a private host key
-used by SSH.
-The default is
-.Pa /etc/ssh/ssh_host_key
-for protocol version 1, and
-.Pa /etc/ssh/ssh_host_rsa_key
-and
-.Pa /etc/ssh/ssh_host_dsa_key
-for protocol version 2.
-Note that
-.Nm
-will refuse to use a file if it is group/world-accessible.
-It is possible to have multiple host key files.
-.Dq rsa1
-keys are used for version 1 and
-.Dq dsa
-or
-.Dq rsa
-are used for version 2 of the SSH protocol.
-.It Cm IgnoreRhosts
-Specifies that
-.Pa .rhosts
-and
-.Pa .shosts
-files will not be used in
-.Cm RhostsAuthentication ,
-.Cm RhostsRSAAuthentication
-or
-.Cm HostbasedAuthentication .
-.Pp
-.Pa /etc/hosts.equiv
-and
-.Pa /etc/shosts.equiv
-are still used.
-The default is
-.Dq yes .
-.It Cm IgnoreUserKnownHosts
-Specifies whether
-.Nm
-should ignore the user's
-.Pa $HOME/.ssh/known_hosts
-during
-.Cm RhostsRSAAuthentication
-or
-.Cm HostbasedAuthentication .
-The default is
-.Dq no .
-.It Cm KeepAlive
-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 keepalives are not sent,
-sessions may hang indefinitely on the server, leaving
-.Dq ghost
-users and consuming server resources.
-.Pp
-The default is
-.Dq yes
-(to send keepalives), and the server will notice
-if the network goes down or the client host crashes.
-This avoids infinitely hanging sessions.
-.Pp
-To disable keepalives, the value should be set to
-.Dq no .
-.It Cm KerberosAuthentication
-Specifies whether Kerberos authentication is allowed.
-This can be in the form of a Kerberos ticket, or if
-.Cm PasswordAuthentication
-is yes, the password provided by the user 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.
-Default is
-.Dq yes .
-.It Cm KerberosOrLocalPasswd
-If set then if password authentication through Kerberos fails then
-the password will be validated via any additional local mechanism
-such as
-.Pa /etc/passwd .
-Default is
-.Dq yes .
-.It Cm KerberosTgtPassing
-Specifies whether a Kerberos TGT may be forwarded to the server.
-Default is
-.Dq no ,
-as this only works when the Kerberos KDC is actually an AFS kaserver.
-.It Cm KerberosTicketCleanup
-Specifies whether to automatically destroy the user's ticket cache
-file on logout.
-Default is
-.Dq yes .
-.It Cm KeyRegenerationInterval
-In protocol version 1, the ephemeral server key is automatically regenerated
-after this many seconds (if it has been used).
-The purpose of regeneration is to prevent
-decrypting captured sessions by later breaking into the machine and
-stealing the keys.
-The key is never stored anywhere.
-If the value is 0, the key is never regenerated.
-The default is 3600 (seconds).
-.It Cm ListenAddress
-Specifies the local addresses
-.Nm
-should listen on.
-The following forms may be used:
-.Pp
-.Bl -item -offset indent -compact
-.It
-.Cm ListenAddress
-.Sm off
-.Ar host No | Ar IPv4_addr No | Ar IPv6_addr
-.Sm on
-.It
-.Cm ListenAddress
-.Sm off
-.Ar host No | Ar IPv4_addr No : Ar port
-.Sm on
-.It
-.Cm ListenAddress
-.Sm off
-.Oo
-.Ar host No | Ar IPv6_addr Oc : Ar port
-.Sm on
-.El
-.Pp
-If
-.Ar port
-is not specified,
-.Nm
-will listen on the address and all prior
-.Cm Port
-options specified. The default is to listen on all local
-addresses.  Multiple
-.Cm ListenAddress
-options are permitted. Additionally, any
-.Cm Port
-options must precede this option for non port qualified addresses.
-.It Cm 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 600 (seconds).
-.It Cm LogLevel
-Gives the verbosity level that is used when logging messages from
-.Nm sshd .
-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.
-.It Cm MACs
-Specifies the available MAC (message authentication code) algorithms.
-The MAC algorithm is used in protocol version 2
-for data integrity protection.
-Multiple algorithms must be comma-separated.
-The default is
-.Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
-.It Cm MaxStartups
-Specifies the maximum number of concurrent unauthenticated connections to the
-.Nm
-daemon.
-Additional connections will be dropped until authentication succeeds or the
-.Cm LoginGraceTime
-expires for a connection.
-The default is 10.
-.Pp
-Alternatively, random early drop can be enabled by specifying
-the three colon separated values
-.Dq start:rate:full
-(e.g., "10:30:60").
-.Nm
-will refuse connection attempts with a probability of
-.Dq rate/100
-(30%)
-if there are currently
-.Dq start
-(10)
-unauthenticated connections.
-The probability increases linearly and all connection attempts
-are refused if the number of unauthenticated connections reaches
-.Dq full
-(60).
-.It Cm PasswordAuthentication
-Specifies whether password authentication is allowed.
-The default is
-.Dq yes .
-.It Cm PermitEmptyPasswords
-When password authentication is allowed, it specifies whether the
-server allows login to accounts with empty password strings.
-The default is
-.Dq no .
-.It Cm PermitRootLogin
-Specifies whether root can login using
-.Xr ssh 1 .
-The argument must be
-.Dq yes ,
-.Dq without-password ,
-.Dq forced-commands-only
-or
-.Dq no .
-The default is
-.Dq yes .
-.Pp
-If this option is set to
-.Dq without-password
-password authentication is disabled for root.
-.Pp
-If this option is set to
-.Dq forced-commands-only
-root login with public key authentication will be allowed,
-but only if the
-.Ar 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.
-.Pp
-If this option is set to
-.Dq no
-root is not allowed to login.
-.It Cm PidFile
-Specifies the file that contains the process identifier of the
-.Nm
-daemon.
-The default is
-.Pa /var/run/sshd.pid .
-.It Cm Port
-Specifies the port number that
-.Nm
-listens on.
-The default is 22.
-Multiple options of this type are permitted.
-See also
-.Cm ListenAddress .
-.It Cm PrintLastLog
-Specifies whether
-.Nm
-should print the date and time when the user last logged in.
-The default is
-.Dq yes .
-.It Cm PrintMotd
-Specifies whether
-.Nm
-should print
-.Pa /etc/motd
-when a user logs in interactively.
-(On some systems it is also printed by the shell,
-.Pa /etc/profile ,
-or equivalent.)
-The default is
-.Dq yes .
-.It Cm Protocol
-Specifies the protocol versions
-.Nm
-should support.
-The possible values are
-.Dq 1
-and
-.Dq 2 .
-Multiple versions must be comma-separated.
-The default is
-.Dq 2,1 .
-.It Cm PubkeyAuthentication
-Specifies whether public key authentication is allowed.
-The default is
-.Dq yes .
-Note that this option applies to protocol version 2 only.
-.It Cm RhostsAuthentication
-Specifies whether authentication using rhosts or /etc/hosts.equiv
-files is sufficient.
-Normally, this method should not be permitted because it is insecure.
-.Cm RhostsRSAAuthentication
-should be used
-instead, because it performs RSA-based host authentication in addition
-to normal rhosts or /etc/hosts.equiv authentication.
-The default is
-.Dq no .
-This option applies to protocol version 1 only.
-.It Cm RhostsRSAAuthentication
-Specifies whether rhosts or /etc/hosts.equiv authentication together
-with successful RSA host authentication is allowed.
-The default is
-.Dq no .
-This option applies to protocol version 1 only.
-.It Cm RSAAuthentication
-Specifies whether pure RSA authentication is allowed.
-The default is
-.Dq yes .
-This option applies to protocol version 1 only.
-.It Cm ServerKeyBits
-Defines the number of bits in the ephemeral protocol version 1 server key.
-The minimum value is 512, and the default is 768.
-.It Cm StrictModes
-Specifies whether
-.Nm
-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
-.Dq yes .
-.It Cm Subsystem
-Configures an external subsystem (e.g., file transfer daemon).
-Arguments should be a subsystem name and a command to execute upon subsystem
-request.
-The command
-.Xr sftp-server 8
-implements the
-.Dq sftp
-file transfer subsystem.
-By default no subsystems are defined.
-Note that this option applies to protocol version 2 only.
-.It Cm SyslogFacility
-Gives the facility code that is used when logging messages from
-.Nm sshd .
-The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
-LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
-The default is AUTH.
-.It Cm UseLogin
-Specifies whether
-.Xr login 1
-is used for interactive login sessions.
-The default is
-.Dq no .
-Note that
-.Xr login 1
-is never used for remote command execution.
-Note also, that if this is enabled,
-.Cm X11Forwarding
-will be disabled because
-.Xr login 1
-does not know how to handle
-.Xr xauth 1
-cookies.  If
-.Cm UsePrivilegeSeparation
-is specified, it will be disabled after authentication.
-.It Cm UsePrivilegeSeparation
-Specifies whether
-.Nm
-separated privileges by creating an unprivileged child process
-to deal with incoming network traffic.  After successful authentication,
-another process will be created that has the privilege of the authenticated
-user.  The goal of privilege separation is to prevent privilege
-escalation by containing any corruption within the unprivileged processes.
-The default is
-.Dq no .
-.It Cm VerifyReverseMapping
-Specifies whether
-.Nm
-should try to verify the remote host name and check that
-the resolved host name for the remote IP address maps back to the
-very same IP address.
-The default is
-.Dq no .
-.It Cm X11DisplayOffset
-Specifies the first display number available for
-.Nm sshd Ns 's
-X11 forwarding.
-This prevents
-.Nm
-from interfering with real X11 servers.
-The default is 10.
-.It Cm X11Forwarding
-Specifies whether X11 forwarding is permitted.
-The default is
-.Dq no .
-Note that disabling X11 forwarding does not improve security in any
-way, as users can always install their own forwarders.
-X11 forwarding is automatically disabled if
-.Cm UseLogin
-is enabled.
-.It Cm X11UseLocalhost
-Specifies whether
-.Nm
-should bind the X11 forwarding server to the loopback address or to
-the wildcard address.  By default,
-.Nm
-binds the forwarding server to the loopback address and sets the
-hostname part of the
-.Ev DISPLAY
-environment variable to
-.Dq localhost .
-This prevents remote hosts from connecting to the fake display.
-However, some older X11 clients may not function with this
-configuration.
-.Cm X11UseLocalhost
-may be set to
-.Dq no
-to specify that the forwarding server should be bound to the wildcard
-address.
-The argument must be
-.Dq yes
-or
-.Dq no .
-The default is
-.Dq yes .
-.It Cm XAuthLocation
-Specifies the location of the
-.Xr xauth 1
-program.
-The default is
-.Pa /usr/X11R6/bin/xauth .
-.El
-.Ss Time Formats
-.Pp
-.Nm
-command-line arguments and configuration file options that specify time
-may be expressed using a sequence of the form:
-.Sm off
-.Ar time Oo Ar qualifier Oc ,
-.Sm on
-where
-.Ar time
-is a positive integer value and
-.Ar qualifier
-is one of the following:
-.Pp
-.Bl -tag -width Ds -compact -offset indent
-.It Cm <none>
-seconds
-.It Cm s | Cm S
-seconds
-.It Cm m | Cm M
-minutes
-.It Cm h | Cm H
-hours
-.It Cm d | Cm D
-days
-.It Cm w | Cm W
-weeks
-.El
-.Pp
-Each member of the sequence is added together to calculate
-the total time value.
-.Pp
-Time format examples:
-.Pp
-.Bl -tag -width Ds -compact -offset indent
-.It 600
-600 seconds (10 minutes)
-.It 10m
-10 minutes
-.It 1h30m
-1 hour 30 minutes (90 minutes)
-.El
+The file format and configuration options are described in
+.Xr sshd_config 5 .
 .Sh LOGIN PROCESS
 When a user successfully logs in,
 .Nm
@@ -972,7 +355,11 @@
 .It
 Reads
 .Pa $HOME/.ssh/environment
-if it exists.
+if it exists and users are allowed to change their environment.
+See the
+.Cm PermitUserEnvironment
+option in
+.Xr sshd_config 5 .
 .It
 Changes to user's home directory.
 .It
@@ -1007,9 +394,9 @@
 spaces: options, bits, exponent, modulus, comment.
 Each protocol version 2 public key consists of:
 options, keytype, base64 encoded key, comment.
-The options fields
-are optional; its presence is determined by whether the line starts
-with a number or not (the option field never starts with a number).
+The options field
+is optional; its presence is determined by whether the line starts
+with a number or not (the options field never starts with a number).
 The bits, exponent, modulus and comment fields give the RSA key for
 protocol version 1; the
 comment field is not used for anything (but may be convenient for the
@@ -1020,7 +407,7 @@
 .Dq ssh-rsa .
 .Pp
 Note that lines in this file are usually several hundred bytes long
-(because of the size of the RSA key modulus).
+(because of the size of the public key encoding).
 You don't want to type them in; instead, copy the
 .Pa identity.pub ,
 .Pa id_dsa.pub
@@ -1039,7 +426,7 @@
 that option keywords are case-insensitive):
 .Bl -tag -width Ds
 .It Cm from="pattern-list"
-Specifies that in addition to RSA authentication, the canonical name
+Specifies that in addition to public key authentication, the canonical name
 of the remote host must be present in the comma-separated list of
 patterns
 .Pf ( Ql *
@@ -1051,7 +438,7 @@
 .Ql ! ;
 if the canonical host name matches a negated pattern, the key is not accepted.
 The purpose
-of this option is to optionally increase security: RSA authentication
+of this option is to optionally increase security: public key authentication
 by itself does not trust the network or name servers or anything (but
 the key); however, if somebody somehow steals the key, the key
 permits an intruder to log in from anywhere in the world.
@@ -1064,12 +451,12 @@
 The command supplied by the user (if any) is ignored.
 The command is run on a pty if the client requests a pty;
 otherwise it is run without a tty.
-If a 8-bit clean channel is required,
+If an 8-bit clean channel is required,
 one must not request a pty or should specify
 .Cm no-pty .
 A quote may be included in the command by quoting it with a backslash.
 This option might be useful
-to restrict certain RSA keys to perform just a specific operation.
+to restrict certain public keys to perform just a specific operation.
 An example might be a key that permits remote backups but nothing else.
 Note that the client may specify TCP/IP and/or X11
 forwarding unless they are explicitly prohibited.
@@ -1080,6 +467,10 @@
 Environment variables set this way
 override other default environment values.
 Multiple options of this type are permitted.
+Environment processing is disabled by default and is
+controlled via the
+.Cm PermitUserEnvironment
+option.
 This option is automatically disabled if
 .Cm UseLogin
 is enabled.
@@ -1120,7 +511,7 @@
 permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23.\|.\|.\|2323
 .Sh SSH_KNOWN_HOSTS FILE FORMAT
 The
-.Pa /etc/ssh/ssh_known_hosts ,
+.Pa /etc/ssh/ssh_known_hosts
 and
 .Pa $HOME/.ssh/known_hosts
 files contain host public keys for all known hosts.
@@ -1179,8 +570,8 @@
 .It Pa /etc/ssh/sshd_config
 Contains configuration data for
 .Nm sshd .
-This file should be writable by root only, but it is recommended
-(though not necessary) that it be world-readable.
+The file format and configuration options are described in
+.Xr sshd_config 5 .
 .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
 These three files contain the private parts of the host keys.
 These files should only be owned by root, readable only by root, and not
@@ -1200,11 +591,20 @@
 .Xr ssh-keygen 1 .
 .It Pa /etc/moduli
 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
+The file format is described in
+.Xr moduli 5 .
+.It Pa /var/empty
+.Xr chroot 2
+directory used by
+.Nm
+during privilege separation in the pre-authentication phase.
+The directory should not contain any files and must be owned by root
+and not group or world-writable.
 .It Pa /var/run/sshd.pid
 Contains the process ID of the
 .Nm
 listening for connections (if there are several daemons running
-concurrently for different ports, this contains the pid of the one
+concurrently for different ports, this contains the process ID of the one
 started last).
 The content of this file is not sensitive; it can be world-readable.
 .It Pa $HOME/.ssh/authorized_keys
@@ -1232,7 +632,7 @@
 .Pa /etc/ssh/ssh_known_hosts
 should be world-readable, and
 .Pa $HOME/.ssh/known_hosts
-can but need not be world-readable.
+can, but need not be, world-readable.
 .It Pa /etc/nologin
 If this file exists,
 .Nm
@@ -1249,7 +649,7 @@
 This file contains host-username pairs, separated by a space, one per
 line.
 The given user on the corresponding host is permitted to log in
-without password.
+without a password.
 The same file is used by rlogind and rshd.
 The file must
 be writable only by the user; it is recommended that it not be
@@ -1313,8 +713,14 @@
 and assignment lines of the form name=value.
 The file should be writable
 only by the user; it need not be readable by anyone else.
+Environment processing is disabled by default and is
+controlled via the
+.Cm PermitUserEnvironment
+option.
 .It Pa $HOME/.ssh/rc
-If this file exists, it is run with /bin/sh after reading the
+If this file exists, it is run with
+.Pa /bin/sh
+after reading the
 environment files but before starting the user's shell or command.
 It must not produce any output on stdout; stderr must be used
 instead.
@@ -1338,12 +744,12 @@
 if read proto cookie && [ -n "$DISPLAY" ]; then
 	if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then
 		# X11UseLocalhost=yes
-		xauth add unix:`echo $DISPLAY |
+		echo add unix:`echo $DISPLAY |
 		    cut -c11-` $proto $cookie
 	else
 		# X11UseLocalhost=no
-		xauth add $DISPLAY $proto $cookie
-	fi
+		echo add $DISPLAY $proto $cookie
+	fi | xauth -q -
 fi
 .Ed
 .Pp
@@ -1381,6 +787,7 @@
 .Xr ssh-keygen 1 ,
 .Xr login.conf 5 ,
 .Xr moduli 5 ,
+.Xr sshd_config 5 ,
 .Xr sftp-server 8
 .Rs
 .%A T. Ylonen