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Diff for /src/usr.bin/ssh/sshd.8 between version 1.176.2.6 and 1.177

version 1.176.2.6, 2003/04/03 22:35:18 version 1.177, 2002/04/21 16:19:27
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 .Nd OpenSSH SSH daemon  .Nd OpenSSH SSH daemon
 .Sh SYNOPSIS  .Sh SYNOPSIS
 .Nm sshd  .Nm sshd
 .Bk -words  
 .Op Fl deiqtD46  .Op Fl deiqtD46
 .Op Fl b Ar bits  .Op Fl b Ar bits
 .Op Fl f Ar config_file  .Op Fl f Ar config_file
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 .Op Fl o Ar option  .Op Fl o Ar option
 .Op Fl p Ar port  .Op Fl p Ar port
 .Op Fl u Ar len  .Op Fl u Ar len
 .Ek  
 .Sh DESCRIPTION  .Sh DESCRIPTION
 .Nm  .Nm
 (SSH Daemon) is the daemon program for  (SSH Daemon) is the daemon program for
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 .Nm  .Nm
 supports both SSH protocol version 1 and 2 simultaneously.  supports both SSH protocol version 1 and 2 simultaneously.
 .Nm  .Nm
 works as follows:  works as follows.
 .Pp  .Pp
 .Ss SSH protocol version 1  .Ss SSH protocol version 1
 .Pp  .Pp
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 This key is normally regenerated every hour if it has been used, and  This key is normally regenerated every hour if it has been used, and
 is never stored on disk.  is never stored on disk.
 .Pp  .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.  host and server keys.
 The client compares the  The client compares the
 RSA host key against its own database to verify that it has not changed.  RSA host key against its own database to verify that it has not changed.
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 because it is fundamentally insecure, but can be enabled in the server  because it is fundamentally insecure, but can be enabled in the server
 configuration file if desired.  configuration file if desired.
 System security is not improved unless  System security is not improved unless
 .Nm rshd ,  .Xr rshd 8 ,
 .Nm rlogind ,  .Xr rlogind 8 ,
 and  and
 .Nm rexecd  .Xr rexecd 8
 are disabled (thus completely disabling  are disabled (thus completely disabling
 .Xr rlogin  .Xr rlogin 1
 and  and
 .Xr rsh  .Xr rsh 1
 into the machine).  into the machine).
 .Pp  .Pp
 .Ss SSH protocol version 2  .Ss SSH protocol version 2
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 log, and does not put itself in the background.  log, and does not put itself in the background.
 The server also will not fork and will only process one connection.  The server also will not fork and will only process one connection.
 This option is only intended for debugging for the server.  This option is only intended for debugging for the server.
 Multiple  Multiple -d options increase the debugging level.
 .Fl d  
 options increase the debugging level.  
 Maximum is 3.  Maximum is 3.
 .It Fl e  .It Fl e
 When this option is specified,  When this option is specified,
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 refuses to start if there is no configuration file.  refuses to start if there is no configuration file.
 .It Fl g Ar login_grace_time  .It Fl g Ar login_grace_time
 Gives the grace time for clients to authenticate themselves (default  Gives the grace time for clients to authenticate themselves (default
 120 seconds).  600 seconds).
 If the client fails to authenticate the user within  If the client fails to authenticate the user within
 this many seconds, the server disconnects and exits.  this many seconds, the server disconnects and exits.
 A value of zero indicates no limit.  A value of zero indicates no limit.
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 .It Fl i  .It Fl i
 Specifies that  Specifies that
 .Nm  .Nm
 is being run from  is being run from inetd.
 .Xr inetd 8 .  
 .Nm  .Nm
 is normally not run  is normally not run
 from inetd because it needs to generate the server key before it can  from inetd because it needs to generate the server key before it can
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 .Pa utmp  .Pa utmp
 file.  file.
 .Fl u0  .Fl u0
 may also be used to prevent  is also be used to prevent
 .Nm  .Nm
 from making DNS requests unless the authentication  from making DNS requests unless the authentication
 mechanism or configuration requires it.  mechanism or configuration requires it.
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 (or the file specified with  (or the file specified with
 .Fl f  .Fl f
 on the command line).  on the command line).
 The file format and configuration options are described in  The file contains keyword-argument pairs, one per line.
 .Xr sshd_config 5 .  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 no .
   .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
 .Sh LOGIN PROCESS  .Sh LOGIN PROCESS
 When a user successfully logs in,  When a user successfully logs in,
 .Nm  .Nm
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 .It  .It
 Reads  Reads
 .Pa $HOME/.ssh/environment  .Pa $HOME/.ssh/environment
 if it exists and users are allowed to change their environment.  if it exists.
 See the  
 .Cm PermitUserEnvironment  
 option in  
 .Xr sshd_config 5 .  
 .It  .It
 Changes to user's home directory.  Changes to user's home directory.
 .It  .It
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 spaces: options, bits, exponent, modulus, comment.  spaces: options, bits, exponent, modulus, comment.
 Each protocol version 2 public key consists of:  Each protocol version 2 public key consists of:
 options, keytype, base64 encoded key, comment.  options, keytype, base64 encoded key, comment.
 The options field  The options fields
 is optional; its presence is determined by whether the line starts  are optional; its presence is determined by whether the line starts
 with a number or not (the options field never starts with a number).  with a number or not (the option field never starts with a number).
 The bits, exponent, modulus and comment fields give the RSA key for  The bits, exponent, modulus and comment fields give the RSA key for
 protocol version 1; the  protocol version 1; the
 comment field is not used for anything (but may be convenient for the  comment field is not used for anything (but may be convenient for the
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 .Dq ssh-rsa .  .Dq ssh-rsa .
 .Pp  .Pp
 Note that lines in this file are usually several hundred bytes long  Note that lines in this file are usually several hundred bytes long
 (because of the size of the public key encoding).  (because of the size of the RSA key modulus).
 You don't want to type them in; instead, copy the  You don't want to type them in; instead, copy the
 .Pa identity.pub ,  .Pa identity.pub ,
 .Pa id_dsa.pub  .Pa id_dsa.pub
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 that option keywords are case-insensitive):  that option keywords are case-insensitive):
 .Bl -tag -width Ds  .Bl -tag -width Ds
 .It Cm from="pattern-list"  .It Cm from="pattern-list"
 Specifies that in addition to public key authentication, the canonical name  Specifies that in addition to RSA authentication, the canonical name
 of the remote host must be present in the comma-separated list of  of the remote host must be present in the comma-separated list of
 patterns  patterns
 .Pf ( Ql *  .Pf ( Ql *
Line 438 
Line 1051 
 .Ql ! ;  .Ql ! ;
 if the canonical host name matches a negated pattern, the key is not accepted.  if the canonical host name matches a negated pattern, the key is not accepted.
 The purpose  The purpose
 of this option is to optionally increase security: public key authentication  of this option is to optionally increase security: RSA authentication
 by itself does not trust the network or name servers or anything (but  by itself does not trust the network or name servers or anything (but
 the key); however, if somebody somehow steals the key, the key  the key); however, if somebody somehow steals the key, the key
 permits an intruder to log in from anywhere in the world.  permits an intruder to log in from anywhere in the world.
Line 451 
Line 1064 
 The command supplied by the user (if any) is ignored.  The command supplied by the user (if any) is ignored.
 The command is run on a pty if the client requests a pty;  The command is run on a pty if the client requests a pty;
 otherwise it is run without a tty.  otherwise it is run without a tty.
 If an 8-bit clean channel is required,  If a 8-bit clean channel is required,
 one must not request a pty or should specify  one must not request a pty or should specify
 .Cm no-pty .  .Cm no-pty .
 A quote may be included in the command by quoting it with a backslash.  A quote may be included in the command by quoting it with a backslash.
 This option might be useful  This option might be useful
 to restrict certain public keys to perform just a specific operation.  to restrict certain RSA keys to perform just a specific operation.
 An example might be a key that permits remote backups but nothing else.  An example might be a key that permits remote backups but nothing else.
 Note that the client may specify TCP/IP and/or X11  Note that the client may specify TCP/IP and/or X11
 forwarding unless they are explicitly prohibited.  forwarding unless they are explicitly prohibited.
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Line 1080 
 Environment variables set this way  Environment variables set this way
 override other default environment values.  override other default environment values.
 Multiple options of this type are permitted.  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  This option is automatically disabled if
 .Cm UseLogin  .Cm UseLogin
 is enabled.  is enabled.
Line 511 
Line 1120 
 permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23.\|.\|.\|2323  permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23.\|.\|.\|2323
 .Sh SSH_KNOWN_HOSTS FILE FORMAT  .Sh SSH_KNOWN_HOSTS FILE FORMAT
 The  The
 .Pa /etc/ssh/ssh_known_hosts  .Pa /etc/ssh/ssh_known_hosts ,
 and  and
 .Pa $HOME/.ssh/known_hosts  .Pa $HOME/.ssh/known_hosts
 files contain host public keys for all known hosts.  files contain host public keys for all known hosts.
Line 570 
Line 1179 
 .It Pa /etc/ssh/sshd_config  .It Pa /etc/ssh/sshd_config
 Contains configuration data for  Contains configuration data for
 .Nm sshd .  .Nm sshd .
 The file format and configuration options are described in  This file should be writable by root only, but it is recommended
 .Xr sshd_config 5 .  (though not necessary) that it be world-readable.
 .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key  .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 three files contain the private parts of the host keys.
 These files should only be owned by root, readable only by root, and not  These files should only be owned by root, readable only by root, and not
Line 591 
Line 1200 
 .Xr ssh-keygen 1 .  .Xr ssh-keygen 1 .
 .It Pa /etc/moduli  .It Pa /etc/moduli
 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".  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  .It Pa /var/run/sshd.pid
 Contains the process ID of the  Contains the process ID of the
 .Nm  .Nm
 listening for connections (if there are several daemons running  listening for connections (if there are several daemons running
 concurrently for different ports, this contains the process ID of the one  concurrently for different ports, this contains the pid of the one
 started last).  started last).
 The content of this file is not sensitive; it can be world-readable.  The content of this file is not sensitive; it can be world-readable.
 .It Pa $HOME/.ssh/authorized_keys  .It Pa $HOME/.ssh/authorized_keys
Line 632 
Line 1232 
 .Pa /etc/ssh/ssh_known_hosts  .Pa /etc/ssh/ssh_known_hosts
 should be world-readable, and  should be world-readable, and
 .Pa $HOME/.ssh/known_hosts  .Pa $HOME/.ssh/known_hosts
 can, but need not be, world-readable.  can but need not be world-readable.
 .It Pa /etc/nologin  .It Pa /etc/nologin
 If this file exists,  If this file exists,
 .Nm  .Nm
Line 649 
Line 1249 
 This file contains host-username pairs, separated by a space, one per  This file contains host-username pairs, separated by a space, one per
 line.  line.
 The given user on the corresponding host is permitted to log in  The given user on the corresponding host is permitted to log in
 without a password.  without password.
 The same file is used by rlogind and rshd.  The same file is used by rlogind and rshd.
 The file must  The file must
 be writable only by the user; it is recommended that it not be  be writable only by the user; it is recommended that it not be
Line 713 
Line 1313 
 and assignment lines of the form name=value.  and assignment lines of the form name=value.
 The file should be writable  The file should be writable
 only by the user; it need not be readable by anyone else.  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  .It Pa $HOME/.ssh/rc
 If this file exists, it is run with  If this file exists, it is run with /bin/sh after reading the
 .Pa /bin/sh  
 after reading the  
 environment files but before starting the user's shell or command.  environment files but before starting the user's shell or command.
 It must not produce any output on stdout; stderr must be used  It must not produce any output on stdout; stderr must be used
 instead.  instead.
Line 744 
Line 1338 
 if read proto cookie && [ -n "$DISPLAY" ]; then  if read proto cookie && [ -n "$DISPLAY" ]; then
         if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then          if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then
                 # X11UseLocalhost=yes                  # X11UseLocalhost=yes
                 echo add unix:`echo $DISPLAY |                  xauth add unix:`echo $DISPLAY |
                     cut -c11-` $proto $cookie                      cut -c11-` $proto $cookie
         else          else
                 # X11UseLocalhost=no                  # X11UseLocalhost=no
                 echo add $DISPLAY $proto $cookie                  xauth add $DISPLAY $proto $cookie
         fi | xauth -q -          fi
 fi  fi
 .Ed  .Ed
 .Pp  .Pp
Line 787 
Line 1381 
 .Xr ssh-keygen 1 ,  .Xr ssh-keygen 1 ,
 .Xr login.conf 5 ,  .Xr login.conf 5 ,
 .Xr moduli 5 ,  .Xr moduli 5 ,
 .Xr sshd_config 5 ,  
 .Xr sftp-server 8  .Xr sftp-server 8
 .Rs  .Rs
 .%A T. Ylonen  .%A T. Ylonen
Legend:
Removed from v.1.176.2.6  
changed lines
  Added in v.1.177