version 1.70, 2000/10/16 09:38:44 |
version 1.70.2.7, 2001/11/15 22:50:30 |
|
|
.\" incompatible with the protocol description in the RFC file, it must be |
.\" incompatible with the protocol description in the RFC file, it must be |
.\" called by a name other than "ssh" or "Secure Shell". |
.\" called by a name other than "ssh" or "Secure Shell". |
.\" |
.\" |
.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. |
.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. |
.\" Copyright (c) 1999 Aaron Campbell. All rights reserved. |
.\" Copyright (c) 1999 Aaron Campbell. All rights reserved. |
.\" Copyright (c) 1999 Theo de Raadt. All rights reserved. |
.\" Copyright (c) 1999 Theo de Raadt. All rights reserved. |
.\" |
.\" |
.\" Redistribution and use in source and binary forms, with or without |
.\" Redistribution and use in source and binary forms, with or without |
.\" modification, are permitted provided that the following conditions |
.\" modification, are permitted provided that the following conditions |
|
|
.Os |
.Os |
.Sh NAME |
.Sh NAME |
.Nm sshd |
.Nm sshd |
.Nd secure shell daemon |
.Nd OpenSSH SSH daemon |
.Sh SYNOPSIS |
.Sh SYNOPSIS |
.Nm sshd |
.Nm sshd |
.Op Fl diqQ46 |
.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 |
.Op Fl g Ar login_grace_time |
.Op Fl g Ar login_grace_time |
|
|
.Op Fl k Ar key_gen_time |
.Op Fl k Ar key_gen_time |
.Op Fl p Ar port |
.Op Fl p Ar port |
.Op Fl u Ar len |
.Op Fl u Ar len |
.Op Fl V Ar client_protocol_id |
|
.Sh DESCRIPTION |
.Sh DESCRIPTION |
.Nm |
.Nm |
(Secure Shell Daemon) is the daemon program for |
(SSH Daemon) is the daemon program for |
.Xr ssh 1 . |
.Xr ssh 1 . |
Together these programs replace rlogin and rsh, and |
Together these programs replace rlogin and rsh, and |
provide secure encrypted communications between two untrusted hosts |
provide secure encrypted communications between two untrusted hosts |
|
|
System security is not improved unless |
System security is not improved unless |
.Xr rshd 8 , |
.Xr rshd 8 , |
.Xr rlogind 8 , |
.Xr rlogind 8 , |
.Xr rexecd 8 , |
|
and |
and |
.Xr rexd 8 |
.Xr rexecd 8 |
are disabled (thus completely disabling |
are disabled (thus completely disabling |
.Xr rlogin 1 |
.Xr rlogin 1 |
and |
and |
|
|
.Ss SSH protocol version 2 |
.Ss SSH protocol version 2 |
.Pp |
.Pp |
Version 2 works similarly: |
Version 2 works similarly: |
Each host has a host-specific DSA key used to identify the host. |
Each host has a host-specific key (RSA or DSA) used to identify the host. |
However, when the daemon starts, it does not generate a server key. |
However, when the daemon starts, it does not generate a server key. |
Forward security is provided through a Diffie-Hellman key agreement. |
Forward security is provided through a Diffie-Hellman key agreement. |
This key agreement results in a shared session key. |
This key agreement results in a shared session key. |
The rest of the session is encrypted |
.Pp |
using a symmetric cipher, currently |
The rest of the session is encrypted using a symmetric cipher, currently |
Blowfish, 3DES or CAST128 in CBC mode or Arcfour. |
128 bit AES, Blowfish, 3DES, CAST128, Arcfour, 192 bit AES, or 256 bit AES. |
The client selects the encryption algorithm |
The client selects the encryption algorithm |
to use from those offered by the server. |
to use from those offered by the server. |
Additionally, session integrity is provided |
Additionally, session integrity is provided |
|
|
(hmac-sha1 or hmac-md5). |
(hmac-sha1 or hmac-md5). |
.Pp |
.Pp |
Protocol version 2 provides a public key based |
Protocol version 2 provides a public key based |
user authentication method (DSAAuthentication) |
user (PubkeyAuthentication) or |
and conventional password authentication. |
client host (HostbasedAuthentication) authentication method, |
|
conventional password authentication and challenge response based methods. |
.Pp |
.Pp |
.Ss Command execution and data forwarding |
.Ss Command execution and data forwarding |
.Pp |
.Pp |
|
|
.Pp |
.Pp |
.Nm |
.Nm |
rereads its configuration file when it receives a hangup signal, |
rereads its configuration file when it receives a hangup signal, |
.Dv SIGHUP . |
.Dv SIGHUP , |
|
by executing itself with the name it was started as, i.e., |
|
.Pa /usr/sbin/sshd . |
.Pp |
.Pp |
The options are as follows: |
The options are as follows: |
.Bl -tag -width Ds |
.Bl -tag -width Ds |
.It Fl b Ar bits |
.It Fl b Ar bits |
Specifies the number of bits in the server key (default 768). |
Specifies the number of bits in the ephemeral protocol version 1 |
.Pp |
server key (default 768). |
.It Fl d |
.It Fl d |
Debug mode. |
Debug mode. |
The server sends verbose debug output to the system |
The server sends verbose debug output to the system |
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 -d options increases the debugging level. |
Multiple -d options increase the debugging level. |
Maximum is 3. |
Maximum is 3. |
|
.It Fl e |
|
When this option is specified, |
|
.Nm |
|
will send the output to the standard error instead of the system log. |
.It Fl f Ar configuration_file |
.It Fl f Ar configuration_file |
Specifies the name of the configuration file. |
Specifies the name of the configuration file. |
The default is |
The default is |
|
|
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 |
300 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. |
.It Fl h Ar host_key_file |
.It Fl h Ar host_key_file |
Specifies the file from which the RSA host key is read (default |
Specifies the file from which the host key is read (default |
.Pa /etc/ssh_host_key ) . |
.Pa /etc/ssh_host_key ) . |
This option must be given if |
This option must be given if |
.Nm |
.Nm |
is not run as root (as the normal |
is not run as root (as the normal |
host file is normally not readable by anyone but root). |
host file is normally not readable by anyone but root). |
|
It is possible to have multiple host key files for |
|
the different protocol versions and host key algorithms. |
.It Fl i |
.It Fl i |
Specifies that |
Specifies that |
.Nm |
.Nm |
|
|
from inetd may |
from inetd may |
be feasible. |
be feasible. |
.It Fl k Ar key_gen_time |
.It Fl k Ar key_gen_time |
Specifies how often the server key is regenerated (default 3600 |
Specifies how often the ephemeral protocol version 1 server key is |
seconds, or one hour). |
regenerated (default 3600 seconds, or one hour). |
The motivation for regenerating the key fairly |
The motivation for regenerating the key fairly |
often is that the key is not stored anywhere, and after about an hour, |
often is that the key is not stored anywhere, and after about an hour, |
it becomes impossible to recover the key for decrypting intercepted |
it becomes impossible to recover the key for decrypting intercepted |
|
|
Nothing is sent to the system log. |
Nothing is sent to the system log. |
Normally the beginning, |
Normally the beginning, |
authentication, and termination of each connection is logged. |
authentication, and termination of each connection is logged. |
|
.It Fl t |
|
Test mode. |
|
Only check the validity of the configuration file and sanity of the keys. |
|
This is useful for updating |
|
.Nm |
|
reliably as configuration options may change. |
.It Fl u Ar len |
.It Fl u Ar len |
This option is used to specify the size of the field |
This option is used to specify the size of the field |
in the |
in the |
|
|
should be put into the |
should be put into the |
.Pa utmp |
.Pa utmp |
file. |
file. |
.It Fl Q |
.Fl u0 |
Do not print an error message if RSA support is missing. |
is also be used to prevent |
.It Fl V Ar client_protocol_id |
.Nm |
SSH-2 compatibility mode. |
from making DNS requests unless the authentication |
|
mechanism or configuration requires it. |
|
Authentication mechanisms that may require DNS include |
|
.Cm RhostsAuthentication , |
|
.Cm RhostsRSAAuthentication , |
|
.Cm HostbasedAuthentication |
|
and using a |
|
.Cm from="pattern-list" |
|
option in a key file. |
|
.It Fl D |
When this option is specified |
When this option is specified |
.Nm |
.Nm |
assumes the client has sent the supplied version string |
will not detach and does not become a daemon. |
and skips the |
This allows easy monitoring of |
Protocol Version Identification Exchange. |
.Nm sshd . |
This option is not intended to be called directly. |
|
.It Fl 4 |
.It Fl 4 |
Forces |
Forces |
.Nm |
.Nm |
|
|
(or the file specified with |
(or the file specified with |
.Fl f |
.Fl f |
on the command line). |
on the command line). |
The file contains keyword-value pairs, one per line. |
The file contains keyword-argument pairs, one per line. |
Lines starting with |
Lines starting with |
.Ql # |
.Ql # |
and empty lines are interpreted as comments. |
and empty lines are interpreted as comments. |
.Pp |
.Pp |
The following keywords are possible. |
The possible |
|
keywords and their meanings are as follows (note that |
|
keywords are case-insensitive and arguments are case-sensitive): |
.Bl -tag -width Ds |
.Bl -tag -width Ds |
.It Cm AFSTokenPassing |
.It Cm AFSTokenPassing |
Specifies whether an AFS token may be forwarded to the server. |
Specifies whether an AFS token may be forwarded to the server. |
Default is |
Default is |
.Dq yes . |
.Dq yes . |
.It Cm AllowGroups |
.It Cm AllowGroups |
This keyword can be followed by a number of group names, separated |
This keyword can be followed by a list of group names, separated |
by spaces. |
by spaces. |
If specified, login is allowed only for users whose primary |
If specified, login is allowed only for users whose primary |
group matches one of the patterns. |
group or supplementary group list matches one of the patterns. |
.Ql \&* |
.Ql \&* |
and |
and |
.Ql ? |
.Ql ? |
can be used as |
can be used as |
wildcards in the patterns. |
wildcards in the patterns. |
Only group names are valid; a numerical group ID isn't recognized. |
Only group names are valid; a numerical group ID is not recognized. |
By default login is allowed regardless of the primary group. |
By default login is allowed regardless of the group list. |
.Pp |
.Pp |
.It Cm AllowTcpForwarding |
.It Cm AllowTcpForwarding |
Specifies whether TCP forwarding is permitted. |
Specifies whether TCP forwarding is permitted. |
|
|
own forwarders. |
own forwarders. |
.Pp |
.Pp |
.It Cm AllowUsers |
.It Cm AllowUsers |
This keyword can be followed by a number of user names, separated |
This keyword can be followed by a list of user names, separated |
by spaces. |
by spaces. |
If specified, login is allowed only for users names that |
If specified, login is allowed only for users names that |
match one of the patterns. |
match one of the patterns. |
|
|
.Ql ? |
.Ql ? |
can be used as |
can be used as |
wildcards in the patterns. |
wildcards in the patterns. |
Only user names are valid; a numerical user ID isn't recognized. |
Only user names are valid; a numerical user ID is not recognized. |
By default login is allowed regardless of the user name. |
By default login is allowed regardless of the user name. |
|
If the pattern takes the form USER@HOST then USER and HOST |
|
are separately checked, restricting logins to particular |
|
users from particular hosts. |
.Pp |
.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. |
|
.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 |
.It Cm Ciphers |
Specifies the ciphers allowed for protocol version 2. |
Specifies the ciphers allowed for protocol version 2. |
Multiple ciphers must be comma-separated. |
Multiple ciphers must be comma-separated. |
The default is |
The default is |
.Dq 3des-cbc,blowfish-cbc,arcfour,cast128-cbc . |
.Dq aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour. |
.It Cm CheckMail |
.It Cm ClientAliveInterval |
Specifies whether |
Sets a timeout interval in seconds after which if no data has been received |
|
from the client, |
.Nm |
.Nm |
should check for new mail for interactive logins. |
will send a message through the encrypted |
The default is |
channel to request a response from the client. |
.Dq no . |
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 |
.It Cm DenyGroups |
This keyword can be followed by a number of group names, separated |
This keyword can be followed by a number of group names, separated |
by spaces. |
by spaces. |
Users whose primary group matches one of the patterns |
Users whose primary group or supplementary group list matches |
aren't allowed to log in. |
one of the patterns aren't allowed to log in. |
.Ql \&* |
.Ql \&* |
and |
and |
.Ql ? |
.Ql ? |
can be used as |
can be used as |
wildcards in the patterns. |
wildcards in the patterns. |
Only group names are valid; a numerical group ID isn't recognized. |
Only group names are valid; a numerical group ID is not recognized. |
By default login is allowed regardless of the primary group. |
By default login is allowed regardless of the group list. |
.Pp |
.Pp |
.It Cm DenyUsers |
.It Cm DenyUsers |
This keyword can be followed by a number of user names, separated |
This keyword can be followed by a number of user names, separated |
|
|
and |
and |
.Ql ? |
.Ql ? |
can be used as wildcards in the patterns. |
can be used as wildcards in the patterns. |
Only user names are valid; a numerical user ID isn't recognized. |
Only user names are valid; a numerical user ID is not recognized. |
By default login is allowed regardless of the user name. |
By default login is allowed regardless of the user name. |
.It Cm DSAAuthentication |
|
Specifies whether DSA authentication is allowed. |
|
The default is |
|
.Dq yes . |
|
Note that this option applies to protocol version 2 only. |
|
.It Cm GatewayPorts |
.It Cm GatewayPorts |
Specifies whether remote hosts are allowed to connect to ports |
Specifies whether remote hosts are allowed to connect to ports |
forwarded for the client. |
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 |
The argument must be |
.Dq yes |
.Dq yes |
or |
or |
.Dq no . |
.Dq no . |
The default is |
The default is |
.Dq no . |
.Dq no . |
.It Cm HostDSAKey |
.It Cm HostbasedAuthentication |
Specifies the file containing the private DSA host key (default |
Specifies whether rhosts or /etc/hosts.equiv authentication together |
.Pa /etc/ssh_host_dsa_key ) |
with successful public key client host authentication is allowed |
used by SSH protocol 2.0. |
(hostbased authentication). |
Note that |
This option is similar to |
.Nm |
.Cm RhostsRSAAuthentication |
disables protocol 2.0 if this file is group/world-accessible. |
and applies to protocol version 2 only. |
|
The default is |
|
.Dq no . |
.It Cm HostKey |
.It Cm HostKey |
Specifies the file containing the private RSA host key (default |
Specifies the file containing the private host keys (default |
.Pa /etc/ssh_host_key ) |
.Pa /etc/ssh_host_key ) |
used by SSH protocols 1.3 and 1.5. |
used by SSH protocol versions 1 and 2. |
Note that |
Note that |
.Nm |
.Nm |
disables protocols 1.3 and 1.5 if this file is group/world-accessible. |
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 |
.It Cm IgnoreRhosts |
Specifies that |
Specifies that |
.Pa .rhosts |
.Pa .rhosts |
and |
and |
.Pa .shosts |
.Pa .shosts |
files will not be used in authentication. |
files will not be used in |
|
.Cm RhostsAuthentication , |
|
.Cm RhostsRSAAuthentication |
|
or |
|
.Cm HostbasedAuthentication . |
|
.Pp |
.Pa /etc/hosts.equiv |
.Pa /etc/hosts.equiv |
and |
and |
.Pa /etc/shosts.equiv |
.Pa /etc/shosts.equiv |
|
|
should ignore the user's |
should ignore the user's |
.Pa $HOME/.ssh/known_hosts |
.Pa $HOME/.ssh/known_hosts |
during |
during |
.Cm RhostsRSAAuthentication . |
.Cm RhostsRSAAuthentication |
|
or |
|
.Cm HostbasedAuthentication . |
The default is |
The default is |
.Dq no . |
.Dq no . |
.It Cm KeepAlive |
.It Cm KeepAlive |
|
|
Default is |
Default is |
.Dq yes . |
.Dq yes . |
.It Cm KeyRegenerationInterval |
.It Cm KeyRegenerationInterval |
The server key is automatically regenerated after this many seconds |
In protocol version 1, the ephemeral server key is automatically regenerated |
(if it has been used). |
after this many seconds (if it has been used). |
The purpose of regeneration is to prevent |
The purpose of regeneration is to prevent |
decrypting captured sessions by later breaking into the machine and |
decrypting captured sessions by later breaking into the machine and |
stealing the keys. |
stealing the keys. |
|
|
If the value is 0, the key is never regenerated. |
If the value is 0, the key is never regenerated. |
The default is 3600 (seconds). |
The default is 3600 (seconds). |
.It Cm ListenAddress |
.It Cm ListenAddress |
Specifies what local address |
Specifies the local addresses |
.Nm |
.Nm |
should listen on. |
should listen on. |
The default is to listen to all local addresses. |
The following forms may be used: |
Multiple options of this type are permitted. |
.Pp |
Additionally, the |
.Bl -item -offset indent -compact |
.Cm Ports |
.It |
options must precede this option. |
.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 |
.It Cm LoginGraceTime |
The server disconnects after this time if the user has not |
The server disconnects after this time if the user has not |
successfully logged in. |
successfully logged in. |
|
|
The default is INFO. |
The default is INFO. |
Logging with level DEBUG violates the privacy of users |
Logging with level DEBUG violates the privacy of users |
and is not recommended. |
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 |
.It Cm MaxStartups |
Specifies the maximum number of concurrent unauthenticated connections to the |
Specifies the maximum number of concurrent unauthenticated connections to the |
.Nm |
.Nm |
|
|
.Dq start:rate:full |
.Dq start:rate:full |
(e.g., "10:30:60"). |
(e.g., "10:30:60"). |
.Nm |
.Nm |
will refuse connection attempts with a probabillity of |
will refuse connection attempts with a probability of |
.Dq rate/100 |
.Dq rate/100 |
(30%) |
(30%) |
if there are currently |
if there are currently |
.Dq start |
.Dq start |
(10) |
(10) |
unauthenticated connections. |
unauthenticated connections. |
The probabillity increases linearly and all connection attempts |
The probability increases linearly and all connection attempts |
are refused if the number of unauthenticated connections reaches |
are refused if the number of unauthenticated connections reaches |
.Dq full |
.Dq full |
(60). |
(60). |
|
|
Specifies whether password authentication is allowed. |
Specifies whether password authentication is allowed. |
The default is |
The default is |
.Dq yes . |
.Dq yes . |
Note that this option applies to both protocol versions 1 and 2. |
|
.It Cm PermitEmptyPasswords |
.It Cm PermitEmptyPasswords |
When password authentication is allowed, it specifies whether the |
When password authentication is allowed, it specifies whether the |
server allows login to accounts with empty password strings. |
server allows login to accounts with empty password strings. |
The default is |
The default is |
.Dq no . |
.Dq no . |
.It Cm PermitRootLogin |
.It Cm PermitRootLogin |
Specifies whether the root can log in using |
Specifies whether root can login using |
.Xr ssh 1 . |
.Xr ssh 1 . |
The argument must be |
The argument must be |
.Dq yes , |
.Dq yes , |
.Dq without-password |
.Dq without-password , |
|
.Dq forced-commands-only |
or |
or |
.Dq no . |
.Dq no . |
The default is |
The default is |
.Dq yes . |
.Dq yes . |
If this options is set to |
.Pp |
|
If this option is set to |
.Dq without-password |
.Dq without-password |
only password authentication is disabled for root. |
password authentication is disabled for root. |
.Pp |
.Pp |
Root login with RSA authentication when the |
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 |
.Ar command |
option has been |
option has been specified |
specified will be allowed regardless of the value of this setting |
|
(which may be useful for taking remote backups even if root login is |
(which may be useful for taking remote backups even if root login is |
normally not allowed). |
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 |
.It Cm PidFile |
Specifies the file that contains the process identifier of the |
Specifies the file that contains the process identifier of the |
.Nm |
.Nm |
|
|
listens on. |
listens on. |
The default is 22. |
The default is 22. |
Multiple options of this type are permitted. |
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 |
.It Cm PrintMotd |
Specifies whether |
Specifies whether |
.Nm |
.Nm |
|
|
.Dq 2 . |
.Dq 2 . |
Multiple versions must be comma-separated. |
Multiple versions must be comma-separated. |
The default is |
The default is |
.Dq 1 . |
.Dq 2,1 . |
.It Cm RandomSeed |
.It Cm PubkeyAuthentication |
Obsolete. |
Specifies whether public key authentication is allowed. |
Random number generation uses other techniques. |
The default is |
|
.Dq yes . |
|
Note that this option applies to protocol version 2 only. |
|
.It Cm ReverseMappingCheck |
|
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 RhostsAuthentication |
.It Cm RhostsAuthentication |
Specifies whether authentication using rhosts or /etc/hosts.equiv |
Specifies whether authentication using rhosts or /etc/hosts.equiv |
files is sufficient. |
files is sufficient. |
|
|
to normal rhosts or /etc/hosts.equiv authentication. |
to normal rhosts or /etc/hosts.equiv authentication. |
The default is |
The default is |
.Dq no . |
.Dq no . |
|
This option applies to protocol version 1 only. |
.It Cm RhostsRSAAuthentication |
.It Cm RhostsRSAAuthentication |
Specifies whether rhosts or /etc/hosts.equiv authentication together |
Specifies whether rhosts or /etc/hosts.equiv authentication together |
with successful RSA host authentication is allowed. |
with successful RSA host authentication is allowed. |
The default is |
The default is |
.Dq no . |
.Dq no . |
|
This option applies to protocol version 1 only. |
.It Cm RSAAuthentication |
.It Cm RSAAuthentication |
Specifies whether pure RSA authentication is allowed. |
Specifies whether pure RSA authentication is allowed. |
The default is |
The default is |
.Dq yes . |
.Dq yes . |
Note that this option applies to protocol version 1 only. |
This option applies to protocol version 1 only. |
.It Cm ServerKeyBits |
.It Cm ServerKeyBits |
Defines the number of bits in the server key. |
Defines the number of bits in the ephemeral protocol version 1 server key. |
The minimum value is 512, and the default is 768. |
The minimum value is 512, and the default is 768. |
.It Cm SkeyAuthentication |
|
Specifies whether |
|
.Xr skey 1 |
|
authentication is allowed. |
|
The default is |
|
.Dq yes . |
|
Note that s/key authentication is enabled only if |
|
.Cm PasswordAuthentication |
|
is allowed, too. |
|
.It Cm StrictModes |
.It Cm StrictModes |
Specifies whether |
Specifies whether |
.Nm |
.Nm |
|
|
Specifies whether |
Specifies whether |
.Xr login 1 |
.Xr login 1 |
is used for interactive login sessions. |
is used for interactive login sessions. |
|
The default is |
|
.Dq no . |
Note that |
Note that |
.Xr login 1 |
.Xr login 1 |
is never used for remote command execution. |
is never used for remote command execution. |
The default is |
Note also, that if this is enabled, |
.Dq no . |
.Cm X11Forwarding |
|
will be disabled because |
|
.Xr login 1 |
|
does not know how to handle |
|
.Xr xauth 1 |
|
cookies. |
.It Cm X11DisplayOffset |
.It Cm X11DisplayOffset |
Specifies the first display number available for |
Specifies the first display number available for |
.Nm sshd Ns 's |
.Nm sshd Ns 's |
|
|
.Dq no . |
.Dq no . |
Note that disabling X11 forwarding does not improve security in any |
Note that disabling X11 forwarding does not improve security in any |
way, as users can always install their own forwarders. |
way, as users can always install their own forwarders. |
|
X11 forwarding is automatically disabled if |
|
.Cm UseLogin |
|
is enabled. |
.It Cm XAuthLocation |
.It Cm XAuthLocation |
Specifies the location of the |
Specifies the location of the |
.Xr xauth 1 |
.Xr xauth 1 |
|
|
The default is |
The default is |
.Pa /usr/X11R6/bin/xauth . |
.Pa /usr/X11R6/bin/xauth . |
.El |
.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 |
|
|
Runs user's shell or command. |
Runs user's shell or command. |
.El |
.El |
.Sh AUTHORIZED_KEYS FILE FORMAT |
.Sh AUTHORIZED_KEYS FILE FORMAT |
The |
|
.Pa $HOME/.ssh/authorized_keys |
.Pa $HOME/.ssh/authorized_keys |
file lists the RSA keys that are |
is the default file that lists the public keys that are |
permitted for RSA authentication in SSH protocols 1.3 and 1.5 |
permitted for RSA authentication in protocol version 1 |
Similarly, the |
and for public key authentication (PubkeyAuthentication) |
.Pa $HOME/.ssh/authorized_keys2 |
in protocol version 2. |
file lists the DSA keys that are |
.Cm AuthorizedKeysFile |
permitted for DSA authentication in SSH protocol 2.0. |
may be used to specify an alternative file. |
|
.Pp |
Each line of the file contains one |
Each line of the file contains one |
key (empty lines and lines starting with a |
key (empty lines and lines starting with a |
.Ql # |
.Ql # |
are ignored as |
are ignored as |
comments). |
comments). |
Each line consists of the following fields, separated by |
Each RSA public key consists of the following fields, separated by |
spaces: options, bits, exponent, modulus, comment. |
spaces: options, bits, exponent, modulus, comment. |
The options field |
Each protocol version 2 public key consists of: |
is optional; its presence is determined by whether the line starts |
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). |
with a number or not (the option field never starts with a number). |
The bits, exponent, modulus and comment fields give the RSA key; the |
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 |
comment field is not used for anything (but may be convenient for the |
user to identify the key). |
user to identify the key). |
|
For protocol version 2 the keytype is |
|
.Dq ssh-dss |
|
or |
|
.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 RSA key modulus). |
(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 |
|
or the |
|
.Pa id_rsa.pub |
file and edit it. |
file and edit it. |
.Pp |
.Pp |
The options (if present) consist of comma-separated option |
The options (if present) consist of comma-separated option |
specifications. |
specifications. |
No spaces are permitted, except within double quotes. |
No spaces are permitted, except within double quotes. |
The following option specifications are supported: |
The following option specifications are supported (note |
|
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 RSA authentication, the canonical name |
Specifies that in addition to RSA authentication, the canonical name |
|
|
Specifies that the command is executed whenever this key is used for |
Specifies that the command is executed whenever this key is used for |
authentication. |
authentication. |
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 connection 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 a 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. |
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 RSA 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. |
|
Note that this option applies to shell, command or subsystem execution. |
.It Cm environment="NAME=value" |
.It Cm environment="NAME=value" |
Specifies that the string is to be added to the environment when |
Specifies that the string is to be added to the environment when |
logging in using this key. |
logging in using this key. |
|
|
authentication. |
authentication. |
.It Cm no-pty |
.It Cm no-pty |
Prevents tty allocation (a request to allocate a pty will fail). |
Prevents tty allocation (a request to allocate a pty will fail). |
|
.It Cm permitopen="host:port" |
|
Limit local |
|
.Li ``ssh -L'' |
|
port forwarding such that it may only connect to the specified host and |
|
port. |
|
IPv6 addresses can be specified with an alternative syntax: |
|
.Ar host/port . |
|
Multiple |
|
.Cm permitopen |
|
options may be applied separated by commas. No pattern matching is |
|
performed on the specified hostnames, they must be literal domains or |
|
addresses. |
.El |
.El |
.Ss Examples |
.Ss Examples |
1024 33 12121.\|.\|.\|312314325 ylo@foo.bar |
1024 33 12121.\|.\|.\|312314325 ylo@foo.bar |
|
|
from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula |
from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula |
.Pp |
.Pp |
command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi |
command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi |
|
.Pp |
|
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_known_hosts , |
.Pa /etc/ssh_known_hosts , |
.Pa /etc/ssh_known_hosts2 , |
|
.Pa $HOME/.ssh/known_hosts , |
|
and |
and |
.Pa $HOME/.ssh/known_hosts2 |
.Pa $HOME/.ssh/known_hosts |
files contain host public keys for all known hosts. |
files contain host public keys for all known hosts. |
The global file should |
The global file should |
be prepared by the administrator (optional), and the per-user file is |
be prepared by the administrator (optional), and the per-user file is |
|
|
.Pa /etc/ssh_host_key.pub |
.Pa /etc/ssh_host_key.pub |
and adding the host names at the front. |
and adding the host names at the front. |
.Ss Examples |
.Ss Examples |
closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi |
.Bd -literal |
|
closenet,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi |
|
cvs.openbsd.org,199.185.137.3 ssh-rsa AAAA1234.....= |
|
.Ed |
.Sh FILES |
.Sh FILES |
.Bl -tag -width Ds |
.Bl -tag -width Ds |
.It Pa /etc/sshd_config |
.It Pa /etc/sshd_config |
|
|
.Nm sshd . |
.Nm sshd . |
This file should be writable by root only, but it is recommended |
This file should be writable by root only, but it is recommended |
(though not necessary) that it be world-readable. |
(though not necessary) that it be world-readable. |
.It Pa /etc/ssh_host_key |
.It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key |
Contains the private part of the host key. |
These three files contain the private parts of the host keys. |
This file 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 |
accessible to others. |
accessible to others. |
Note that |
Note that |
.Nm |
.Nm |
does not start if this file is group/world-accessible. |
does not start if this file is group/world-accessible. |
.It Pa /etc/ssh_host_key.pub |
.It Pa /etc/ssh_host_key.pub, /etc/ssh_host_dsa_key.pub, /etc/ssh_host_rsa_key.pub |
Contains the public part of the host key. |
These three files contain the public parts of the host keys. |
This file should be world-readable but writable only by |
These files should be world-readable but writable only by |
root. |
root. |
Its contents should match the private part. |
Their contents should match the respective private parts. |
This file is not |
These files are not |
really used for anything; it is only provided for the convenience of |
really used for anything; they are provided for the convenience of |
the user so its contents can be copied to known hosts files. |
the user so their contents can be copied to known hosts files. |
These two files are created using |
These files are created using |
.Xr ssh-keygen 1 . |
.Xr ssh-keygen 1 . |
|
.It Pa /etc/moduli |
|
Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange". |
.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 |
|
|
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 |
Lists the RSA keys that can be used to log into the user's account. |
Lists the public keys (RSA or DSA) that can be used to log into the user's account. |
This file must be readable by root (which may on some machines imply |
This file must be readable by root (which may on some machines imply |
it being world-readable if the user's home directory resides on an NFS |
it being world-readable if the user's home directory resides on an NFS |
volume). |
volume). |
It is recommended that it not be accessible by others. |
It is recommended that it not be accessible by others. |
The format of this file is described above. |
The format of this file is described above. |
Users will place the contents of their |
Users will place the contents of their |
.Pa identity.pub |
.Pa identity.pub , |
files into this file, as described in |
|
.Xr ssh-keygen 1 . |
|
.It Pa $HOME/.ssh/authorized_keys2 |
|
Lists the DSA keys that can be used to log into the user's account. |
|
This file must be readable by root (which may on some machines imply |
|
it being world-readable if the user's home directory resides on an NFS |
|
volume). |
|
It is recommended that it not be accessible by others. |
|
The format of this file is described above. |
|
Users will place the contents of their |
|
.Pa id_dsa.pub |
.Pa id_dsa.pub |
|
and/or |
|
.Pa id_rsa.pub |
files into this file, as described in |
files into this file, as described in |
.Xr ssh-keygen 1 . |
.Xr ssh-keygen 1 . |
.It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts" |
.It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts" |
These files are consulted when using rhosts with RSA host |
These files are consulted when using rhosts with RSA host |
authentication to check the public key of the host. |
authentication or protocol version 2 hostbased authentication |
|
to check the public key of the host. |
The key must be listed in one of these files to be accepted. |
The key must be listed in one of these files to be accepted. |
The client uses the same files |
The client uses the same files |
to verify that the remote host is the one it intended to connect. |
to verify that it is connecting to the correct remote host. |
These files should be writable only by root/the owner. |
These files should be writable only by root/the owner. |
.Pa /etc/ssh_known_hosts |
.Pa /etc/ssh_known_hosts |
should be world-readable, and |
should be world-readable, and |
|
|
refused. |
refused. |
The file should be world-readable. |
The file should be world-readable. |
.It Pa /etc/hosts.allow, /etc/hosts.deny |
.It Pa /etc/hosts.allow, /etc/hosts.deny |
If compiled with |
Access controls that should be enforced by tcp-wrappers are defined here. |
.Sy LIBWRAP |
Further details are described in |
support, tcp-wrappers access controls may be defined here as described in |
|
.Xr hosts_access 5 . |
.Xr hosts_access 5 . |
.It Pa $HOME/.rhosts |
.It Pa $HOME/.rhosts |
This file contains host-username pairs, separated by a space, one per |
This file contains host-username pairs, separated by a space, one per |
|
|
accessible; AFS is a particular example of such an environment. |
accessible; AFS is a particular example of such an environment. |
.Pp |
.Pp |
This file will probably contain some initialization code followed by |
This file will probably contain some initialization code followed by |
something similar to: "if read proto cookie; then echo add $DISPLAY |
something similar to: |
$proto $cookie | xauth -q -; fi". |
.Bd -literal |
|
if read proto cookie; then |
|
echo add $DISPLAY $proto $cookie | xauth -q - |
|
fi |
|
.Ed |
.Pp |
.Pp |
If this file does not exist, |
If this file does not exist, |
.Pa /etc/sshrc |
.Pa /etc/sshrc |
|
|
machine-specific login-time initializations globally. |
machine-specific login-time initializations globally. |
This file should be writable only by root, and should be world-readable. |
This file should be writable only by root, and should be world-readable. |
.El |
.El |
.Sh AUTHOR |
.Sh AUTHORS |
OpenSSH |
OpenSSH is a derivative of the original and free |
is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen, |
ssh 1.2.12 release by Tatu Ylonen. |
but with bugs removed and newer features re-added. |
Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, |
Rapidly after the |
Theo de Raadt and Dug Song |
1.2.12 release, newer versions of the original ssh bore successively |
removed many bugs, re-added newer features and |
more restrictive licenses, and thus demand for a free version was born. |
created OpenSSH. |
.Pp |
Markus Friedl contributed the support for SSH |
This version of OpenSSH |
protocol versions 1.5 and 2.0. |
.Bl -bullet |
|
.It |
|
has all components of a restrictive nature (i.e., patents, see |
|
.Xr ssl 8 ) |
|
directly removed from the source code; any licensed or patented components |
|
are chosen from |
|
external libraries. |
|
.It |
|
has been updated to support SSH protocol 1.5 and 2, making it compatible with |
|
all other SSH clients and servers. |
|
.It |
|
contains added support for |
|
.Xr kerberos 8 |
|
authentication and ticket passing. |
|
.It |
|
supports one-time password authentication with |
|
.Xr skey 1 . |
|
.El |
|
.Pp |
|
OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl, |
|
Niels Provos, Theo de Raadt, and Dug Song. |
|
.Pp |
|
The support for SSH protocol 2 was written by Markus Friedl. |
|
.Sh SEE ALSO |
.Sh SEE ALSO |
.Xr scp 1 , |
.Xr scp 1 , |
.Xr sftp-server 8 , |
.Xr sftp 1 , |
.Xr ssh 1 , |
.Xr ssh 1 , |
.Xr ssh-add 1 , |
.Xr ssh-add 1 , |
.Xr ssh-agent 1 , |
.Xr ssh-agent 1 , |
.Xr ssh-keygen 1 , |
.Xr ssh-keygen 1 , |
.Xr ssl 8 , |
.Xr login.conf 5 , |
.Xr rlogin 1 , |
.Xr moduli 5 , |
.Xr rsh 1 |
.Xr sftp-server 8 |
|
.Rs |
|
.%A T. Ylonen |
|
.%A T. Kivinen |
|
.%A M. Saarinen |
|
.%A T. Rinne |
|
.%A S. Lehtinen |
|
.%T "SSH Protocol Architecture" |
|
.%N draft-ietf-secsh-architecture-09.txt |
|
.%D July 2001 |
|
.%O work in progress material |
|
.Re |
|
.Rs |
|
.%A M. Friedl |
|
.%A N. Provos |
|
.%A W. A. Simpson |
|
.%T "Diffie-Hellman Group Exchange for the SSH Transport Layer Protocol" |
|
.%N draft-ietf-secsh-dh-group-exchange-01.txt |
|
.%D April 2001 |
|
.%O work in progress material |
|
.Re |