SYNOPSIS
ssh [-l login_name] [hostname | user@hostname] [command]
ssh [-afgknqstvxACNPTX1246] [-c cipher_spec] [-e es-
cape_char] [-i
identity_file] [-l login_name] [-m mac_spec] [-o option]
[-p port]
[-L port:host:hostport] [-R port:host:hostport] [host-
name |
user@hostname] [command]
DESCRIPTION
ssh (SSH client) is a program for logging into a remote ma-
chine and for
executing commands on a remote machine. It is intended to
replace rlogin
and rsh, and provide secure encrypted communications between
two untrustM--
ed hosts over an insecure network. X11 connections and ar-
bitrary TCP/IP
ports can also be forwarded over the secure channel.
ssh connects and logs into the specified hostname. The user
must prove
his/her identity to the remote machine using one of several
methods deM--
pending on the protocol version used:
SSH protocol version 1
First, if the machine the user logs in from is listed in
/etc/hosts.equiv
or /etc/shosts.equiv on the remote machine, and the user
names are the
same on both sides, the user is immediately permitted to log
in. Second,
if .rhosts or .shosts exists in the user's home directory on
the remote
machine and contains a line containing the name of the
client machine and
the name of the user on that machine, the user is permitted
to log in.
This form of authentication alone is normally not allowed by
the server
because it is not secure.
The second authentication method is the rhosts or
hosts.equiv method comM--
bined with RSA-based host authentication. It means that if
the login
would be permitted by $HOME/.rhosts, $HOME/.shosts,
/etc/hosts.equiv, or
As a third authentication method, ssh supports RSA based au-
thentication.
The scheme is based on public-key cryptography: there are
cryptosystems
where encryption and decryption are done using separate
keys, and it is
not possible to derive the decryption key from the encryp-
tion key. RSA
is one such system. The idea is that each user creates a
public/private
key pair for authentication purposes. The server knows the
public key,
and only the user knows the private key. The file
$HOME/.ssh/authorized_keys lists the public keys that are
permitted for
logging in. When the user logs in, the ssh program tells
the server
which key pair it would like to use for authentication. The
server
checks if this key is permitted, and if so, sends the user
(actually the
ssh program running on behalf of the user) a challenge, a
random number,
encrypted by the user's public key. The challenge can only
be decrypted
using the proper private key. The user's client then de-
crypts the chalM--
lenge using the private key, proving that he/she knows the
private key
but without disclosing it to the server.
ssh implements the RSA authentication protocol automatical-
ly. The user
creates his/her RSA key pair by running ssh-keygen(1). This
stores the
private key in $HOME/.ssh/identity and the public key in
$HOME/.ssh/identity.pub in the user's home directory. The
user should
then copy the identity.pub to $HOME/.ssh/authorized_keys in
his/her home
directory on the remote machine (the authorized_keys file
corresponds to
the conventional $HOME/.rhosts file, and has one key per
line, though the
lines can be very long). After this, the user can log in
without giving
the password. RSA authentication is much more secure than
rhosts authenM--
tication.
The most convenient way to use RSA authentication may be
authenticaM--
tion methods are available. Using the default values for
PreferredAuthentications, the client will try to authenti-
cate first using
the public key method; if this method fails password authen-
tication is
attempted, and finally if this method fails keyboard-inter-
active authenM--
tication is attempted. If this method fails password au-
thentication is
tried.
The public key method is similar to RSA authentication de-
scribed in the
previous section and allows the RSA or DSA algorithm to be
used: The
client uses his private key, $HOME/.ssh/id_dsa or
$HOME/.ssh/id_rsa, to
sign the session identifier and sends the result to the
server. The
server checks whether the matching public key is listed in
$HOME/.ssh/authorized_keys2 and grants access if both the
key is found
and the signature is correct. The session identifier is de-
rived from a
shared Diffie-Hellman value and is only known to the client
and the servM--
er.
If public key authentication fails or is not available a
password can be
sent encrypted to the remote host for proving the user's
identity.
Additionally, ssh supports hostbased or challenge response
authenticaM--
tion.
Protocol 2 provides additional mechanisms for confidentiali-
ty (the trafM--
fic is encrypted using 3DES, Blowfish, CAST128 or Arcfour)
and integrity
(hmac-md5, hmac-sha1). Note that protocol 1 lacks a strong
mechanism for
ensuring the integrity of the connection.
Login session and remote execution
When the user's identity has been accepted by the server,
the server eiM--
ther executes the given command, or logs into the machine
and gives the
if a tty is used.
The session terminates when the command or shell on the re-
mote machine
exits and all X11 and TCP/IP connections have been closed.
The exit staM--
tus of the remote program is returned as the exit status of
ssh.
Escape Characters
When a pseudo terminal has been requested, ssh supports a
number of funcM--
tions through the use of an escape character.
A single tilde character can be sent as ~~ (or by following
the tilde by
a character other than those described above). The escape
character must
always follow a newline to be interpreted as special. The
escape characM--
ter can be changed in configuration files using the Es-
capeChar configuraM--
tion directive or on the command line by the -e option.
The supported escapes (assuming the default `~') are:
~. Disconnect
~^Z Background ssh
~# List forwarded connections
~& Background ssh at logout when waiting for forwarded
connection /
X11 sessions to terminate (protocol version 1 only)
~? Display a list of escape characters
~R Request rekeying of the connection (only useful for
SSH protocol
version 2 and if the peer supports it)
X11 and TCP forwarding
If the user is using X11 (the DISPLAY environment variable
is set), the
connection to the X11 display is automatically forwarded to
the remote
side in such a way that any X11 programs started from the
shell (or comM--
connections over the encrypted channel.
ssh will also automatically set up Xauthority data on the
server machine.
For this purpose, it will generate a random authorization
cookie, store
it in Xauthority on the server, and verify that any forward-
ed connections
carry this cookie and replace it by the real cookie when the
connection
is opened. The real authentication cookie is never sent to
the server
machine (and no cookies are sent in the plain).
If the user is using an authentication agent, the connection
to the agent
is automatically forwarded to the remote side unless dis-
abled on command
line or in a configuration file.
Forwarding of arbitrary TCP/IP connections over the secure
channel can be
specified either on command line or in a configuration file.
One possiM--
ble application of TCP/IP forwarding is a secure connection
to an elecM--
tronic purse; another is going through firewalls.
Server authentication
ssh automatically maintains and checks a database containing
identificaM--
tions for all hosts it has ever been used with. RSA host
keys are stored
in $HOME/.ssh/known_hosts and host keys used in the protocol
version 2
are stored in $HOME/.ssh/known_hosts2 in the user's home di-
rectory. AdM--
ditionally, the files /etc/ssh_known_hosts and
/etc/ssh_known_hosts2 are
automatically checked for known hosts. Any new hosts are
automatically
added to the user's file. If a host's identification ever
changes, ssh
warns about this and disables password authentication to
prevent a trojan
horse from getting the user's password. Another purpose of
this mechaM--
nism is to prevent man-in-the-middle attacks which could
otherwise be
used to circumvent the encryption. The StrictHostKeyCheck-
ing option (see
-c blowfish|3des
Selects the cipher to use for encrypting the ses-
sion. 3des is
used by default. It is believed to be secure. 3des
(triple-des)
is an encrypt-decrypt-encrypt triple with three dif-
ferent keys.
It is presumably more secure than the des cipher
which is no
longer fully supported in ssh. blowfish is a fast
block cipher,
it appears very secure and is much faster than 3des.
-c cipher_spec
Additionally, for protocol version 2 a comma-sepa-
rated list of
ciphers can be specified in order of preference.
See Ciphers for
more information.
-e ch|^ch|none
Sets the escape character for sessions with a pty
(default: `~').
The escape character is only recognized at the be-
ginning of a
line. The escape character followed by a dot (`.')
closes the
connection, followed by control-Z suspends the con-
nection, and
followed by itself sends the escape character once.
Setting the
character to ``none'' disables any escapes and makes
the session
fully transparent.
-f Requests ssh to go to background just before command
execution.
This is useful if ssh is going to ask for passwords
or passphrasM--
es, but the user wants it in the background. This
implies -n.
The recommended way to start X11 programs at a re-
mote site is
with something like ssh -f host xterm.
-g Allows remote hosts to connect to local forwarded
ports.
-i identity_file
Selects the file from which the identity (private
key) for RSA or
-l login_name
Specifies the user to log in as on the remote ma-
chine. This also
may be specified on a per-host basis in the configu-
ration file.
-m mac_spec
Additionally, for protocol version 2 a comma-sepa-
rated list of
MAC (message authentication code) algorithms can be
specified in
order of preference. See the MACs keyword for more
information.
-n Redirects stdin from /dev/null (actually, prevents
reading from
stdin). This must be used when ssh is run in the
background. A
common trick is to use this to run X11 programs on a
remote maM--
chine. For example, ssh -n shadows.cs.hut.fi emacs
& will start
an emacs on shadows.cs.hut.fi, and the X11 connec-
tion will be auM--
tomatically forwarded over an encrypted channel.
The ssh program
will be put in the background. (This does not work
if ssh needs
to ask for a password or passphrase; see also the -f
option.)
-N Do not execute a remote command. This is useful if
you just want
to forward ports (protocol version 2 only).
-o option
Can be used to give options in the format used in
the config
file. This is useful for specifying options for
which there is
no separate command-line flag. The option has the
same format as
a line in the configuration file.
-p port
Port to connect to on the remote host. This can be
specified on
a per-host basis in the configuration file.
-P Use a non-privileged port for outgoing connections.
This can be
cilitate the use of SSH as a secure transport for
other applicaM--
tion (eg. sftp). The subsystem is specified as the
remote comM--
mand.
-t Force pseudo-tty allocation. This can be used to
execute arbiM--
trary screen-based programs on a remote machine,
which can be
very useful, e.g., when implementing menu services.
Multiple -t
options force tty allocation, even if ssh has no lo-
cal tty.
-T Disable pseudo-tty allocation.
-v Verbose mode. Causes ssh to print debugging mes-
sages about its
progress. This is helpful in debugging connection,
authenticaM--
tion, and configuration problems. Multiple -v op-
tions increases
the verbosity. Maximum is 3.
-x Disables X11 forwarding.
-X Enables X11 forwarding. This can also be specified
on a per-host
basis in a configuration file.
-C Requests compression of all data (including stdin,
stdout,
stderr, and data for forwarded X11 and TCP/IP con-
nections). The
compression algorithm is the same used by gzip(1),
and the
``level'' can be controlled by the CompressionLevel
option (see
below). Compression is desirable on modem lines and
other slow
connections, but will only slow down things on fast
networks.
The default value can be set on a host-by-host basis
in the conM--
figuration files; see the Compress option below.
-L port:host:hostport
Specifies that the given port on the local (client)
host is to be
alternative syntax: port/host/hostport
-R port:host:hostport
Specifies that the given port on the remote (server)
host is to
be forwarded to the given host and port on the local
side. This
works by allocating a socket to listen to port on
the remote
side, and whenever a connection is made to this
port, the connecM--
tion is forwarded over the secure channel, and a
connection is
made to host port hostport from the local machine.
Port forwardM--
ings can also be specified in the configuration
file. Privileged
ports can be forwarded only when logging in as root
on the remote
machine. IPv6 addresses can be specified with an
alternative
syntax: port/host/hostport
-1 Forces ssh to try protocol version 1 only.
-2 Forces ssh to try protocol version 2 only.
-4 Forces ssh to use IPv4 addresses only.
-6 Forces ssh to use IPv6 addresses only.
CONFIGURATION FILES
ssh obtains configuration data from the following sources
(in this orM--
der): command line options, user's configuration file
($HOME/.ssh/config), and system-wide configuration file
(/etc/ssh_config). For each parameter, the first obtained
value will be
used. The configuration files contain sections bracketed by
``Host''
specifications, and that section is only applied for hosts
that match one
of the patterns given in the specification. The matched
host name is the
one given on the command line.
Since the first obtained value for each parameter is used,
more host-speM--
cific declarations should be given near the beginning of the
file, and
general defaults at the end.
given after the keyword. `*' and `?' can be used as
wildcards in
the patterns. A single `*' as a pattern can be used
to provide
global defaults for all hosts. The host is the
hostname argument
given on the command line (i.e., the name is not
converted to a
canonicalized host name before matching).
AFSTokenPassing
Specifies whether to pass AFS tokens to remote host.
The arguM--
ment to this keyword must be ``yes'' or ``no''. This
option apM--
plies to protocol version 1 only.
BatchMode
If set to ``yes'', passphrase/password querying will
be disabled.
This option is useful in scripts and other batch
jobs where you
have no user to supply the password. The argument
must be
``yes'' or ``no''. The default is ``no''.
CheckHostIP
If this flag is set to ``yes'', ssh will additional-
ly check the
host IP address in the known_hosts file. This al-
lows ssh to deM--
tect if a host key changed due to DNS spoofing. If
the option is
set to ``no'', the check will not be executed. The
default is
``yes''.
Cipher Specifies the cipher to use for encrypting the ses-
sion in protoM--
col version 1. Currently, ``blowfish'' and ``3des''
are supportM--
ed. The default is ``3des''.
Ciphers
Specifies the ciphers allowed for protocol version 2
in order of
preference. Multiple ciphers must be comma-separat-
ed. The deM--
fault is
``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,ar-
plications. The
meaning of the values is the same as in gzip(1).
Note that this
option applies to protocol version 1 only.
ConnectionAttempts
Specifies the number of tries (one per second) to
make before
falling back to rsh or exiting. The argument must
be an integer.
This may be useful in scripts if the connection
sometimes fails.
The default is 4.
EscapeChar
Sets the escape character (default: `~'). The escape
character
can also be set on the command line. The argument
should be a
single character, `^' followed by a letter, or
``none'' to disM--
able the escape character entirely (making the con-
nection transM--
parent for binary data).
FallBackToRsh
Specifies that if connecting via ssh fails due to a
connection
refused error (there is no sshd(8) listening on the
remote host),
rsh(1) should automatically be used instead (after a
suitable
warning about the session being unencrypted). The
argument must
be ``yes'' or ``no''. The default is ``no''.
ForwardAgent
Specifies whether the connection to the authentica-
tion agent (if
any) will be forwarded to the remote machine. The
argument must
be ``yes'' or ``no''. The default is ``no''.
ForwardX11
Specifies whether X11 connections will be automati-
cally redirectM--
ed over the secure channel and DISPLAY set. The ar-
gument must be
``yes'' or ``no''. The default is ``no''.
GatewayPorts
Specifies whether remote hosts are allowed to con-
HostbasedAuthentication
Specifies whether to try rhosts based authentication
with public
key authentication. The argument must be ``yes'' or
``no''. The
default is ``yes''. This option applies to protocol
version 2 onM--
ly and is similar to RhostsRSAAuthentication.
HostKeyAlgorithms
Specfies the protocol version 2 host key algorithms
that the
client wants to use in order of preference. The de-
fault for this
option is: ``ssh-rsa,ssh-dss''
HostKeyAlias
Specifies an alias that should be used instead of
the real host
name when looking up or saving the host key in the
host key
database files. This option is useful for tunneling
ssh connecM--
tions or if you have multiple servers running on a
single host.
HostName
Specifies the real host name to log into. This can
be used to
specify nicknames or abbreviations for hosts. De-
fault is the
name given on the command line. Numeric IP address-
es are also
permitted (both on the command line and in HostName
specificaM--
tions).
IdentityFile
Specifies the file from which the user's RSA or DSA
authenticaM--
tion identity is read (default $HOME/.ssh/identity
in the user's
home directory). Additionally, any identities rep-
resented by the
authentication agent will be used for authentica-
tion. The file
name may use the tilde syntax to refer to a user's
home directoM--
ry. It is possible to have multiple identity files
specified in
configuration files; all these identities will be
The default is ``yes'' (to send keepalives), and the
client will
notice if the network goes down or the remote host
dies. This is
important in scripts, and many users want it too.
To disable keepalives, the value should be set to
``no'' in both
the server and the client configuration files.
KerberosAuthentication
Specifies whether Kerberos authentication will be
used. The arM--
gument to this keyword must be ``yes'' or ``no''.
KerberosTgtPassing
Specifies whether a Kerberos TGT will be forwarded
to the server.
This will only work if the Kerberos server is actu-
ally an AFS
kaserver. The argument to this keyword must be
``yes'' or
``no''.
LocalForward
Specifies that a TCP/IP port on the local machine be
forwarded
over the secure channel to given host:port from the
remote maM--
chine. The first argument must be a port number,
and the second
must be host:port. Multiple forwardings may be
specified, and
additional forwardings can be given on the command
line. Only
the superuser can forward privileged ports.
LogLevel
Gives the verbosity level that is used when logging
messages from
ssh. The possible values are: QUIET, FATAL, ERROR,
INFO, VERBOSE
and DEBUG. The default is INFO.
MACs Specifies the MAC (message authentication code) al-
gorithms in orM--
der of preference. The MAC algorithm is used in
protocol version
2 for data integrity protection. Multiple algo-
rithms must be
comma-separated. The default is
to this keyword must be ``yes'' or ``no''. The de-
fault is
``yes''.
Port Specifies the port number to connect on the remote
host. Default
is 22.
PreferredAuthentications
Specifies the order in which the client should try
protocol 2 auM--
thentication methods. This allows a client to prefer
one method
(e.g. keyboard-interactive) over another method
(e.g. password)
The default for this option is: ``publickey, pass-
word, keyboard-
interactive''
Protocol
Specifies the protocol versions ssh should support
in order of
preference. The possible values are ``1'' and
``2''. Multiple
versions must be comma-separated. The default is
``2,1''. This
means that ssh tries version 2 and falls back to
version 1 if
version 2 is not available.
ProxyCommand
Specifies the command to use to connect to the serv-
er. The comM--
mand string extends to the end of the line, and is
executed with
/bin/sh. In the command string, `%h' will be substi-
tuted by the
host name to connect and `%p' by the port. The com-
mand can be
basically anything, and should read from its stan-
dard input and
write to its standard output. It should eventually
connect an
sshd(8) server running on some machine, or execute
sshd -i someM--
where. Host key management will be done using the
HostName of
the host being connected (defaulting to the name
typed by the usM--
er). Note that CheckHostIP is not available for
connects with a
proxy command.
chine. The first argument must be a port number,
and the second
must be host:port. Multiple forwardings may be
specified, and
additional forwardings can be given on the command
line. Only
the superuser can forward privileged ports.
RhostsAuthentication
Specifies whether to try rhosts based authentica-
tion. Note that
this declaration only affects the client side and
has no effect
whatsoever on security. Disabling rhosts authenti-
cation may reM--
duce authentication time on slow connections when
rhosts authenM--
tication is not used. Most servers do not permit
RhostsAuthentiM--
cation because it is not secure (see RhostsRSAAu-
thentication ).
The argument to this keyword must be ``yes'' or
``no''. The deM--
fault is ``yes''. This option applies to protocol
version 1 only.
RhostsRSAAuthentication
Specifies whether to try rhosts based authentication
with RSA
host authentication. The argument must be ``yes''
or ``no''. The
default is ``yes''. This option applies to protocol
version 1 onM--
ly.
RSAAuthentication
Specifies whether to try RSA authentication. The
argument to
this keyword must be ``yes'' or ``no''. RSA authen-
tication will
only be attempted if the identity file exists, or an
authenticaM--
tion agent is running. The default is ``yes''. Note
that this
option applies to protocol version 1 only.
ChallengeResponseAuthentication
Specifies whether to use challenge response authen-
tication. CurM--
rently there is only support for skey(1) authentica-
tion. The arM--
gument to this keyword must be ``yes'' or ``no''.
/etc/ssh_known_hosts2 files installed and frequently
connect to
new hosts. This option forces the user to manually
add all new
hosts. If this flag is set to ``no'', ssh will au-
tomatically add
new host keys to the user known hosts files. If
this flag is set
to ``ask'', new host keys will be added to the user
known host
files only after the user has confirmed that is what
they really
want to do, and ssh will refuse to connect to hosts
whose host
key has changed. The host keys of known hosts will
be verified
automatically in all cases. The argument must be
``yes'', ``no''
or ``ask''. The default is ``ask''.
UsePrivilegedPort
Specifies whether to use a privileged port for out-
going connecM--
tions. The argument must be ``yes'' or ``no''. The
default is
``no''. Note that you need to set this option to
``yes'' if you
want to use RhostsAuthentication and RhostsRSAAu-
thentication with
older servers.
User Specifies the user to log in as. This can be useful
if you have
a different user name on different machines. This
saves the
trouble of having to remember to give the user name
on the comM--
mand line.
UserKnownHostsFile
Specifies a file to use for the protocol version 1
user host key
database instead of $HOME/.ssh/known_hosts.
UserKnownHostsFile2
Specifies a file to use for the protocol version 2
user host key
database instead of $HOME/.ssh/known_hosts2.
UseRsh Specifies that rlogin/rsh should be used for this
host. It is
possible that the host does not at all support the
DISPLAY
The DISPLAY variable indicates the location of the
X11 server.
It is automatically set by ssh to point to a value
of the form
``hostname:n'' where hostname indicates the host
where the shell
runs, and n is an integer >= 1. ssh uses this spe-
cial value to
forward X11 connections over the secure channel.
The user should
normally not set DISPLAY explicitly, as that will
render the X11
connection insecure (and will require the user to
manually copy
any required authorization cookies).
HOME Set to the path of the user's home directory.
LOGNAME
Synonym for USER; set for compatibility with systems
that use
this variable.
MAIL Set to point the user's mailbox.
PATH Set to the default PATH, as specified when compiling
ssh.
SSH_AUTH_SOCK
indicates the path of a unix-domain socket used to
communicate
with the agent.
SSH_CLIENT
Identifies the client end of the connection. The
variable conM--
tains three space-separated values: client ip-ad-
dress, client
port number, and server port number.
SSH_ORIGINAL_COMMAND
The variable contains the original command line if a
forced comM--
mand is executed. It can be used to extract the
original arguM--
ments.
SSH_TTY
This is set to the name of the tty (path to the de-
vice) associatM--
format ``VARNAME=value'' to the environment.
FILES
$HOME/.ssh/known_hosts, $HOME/.ssh/known_hosts2
Records host keys for all hosts the user has logged
into (that
are not in /etc/ssh_known_hosts for protocol version
1 or
/etc/ssh_known_hosts2 for protocol version 2). See
sshd(8).
$HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa
Contains the authentication identity of the user.
They are for
protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA,
respectively.
These files contain sensitive data and should be
readable by the
user but not accessible by others (read/write/exe-
cute). Note
that ssh ignores a private key file if it is acces-
sible by othM--
ers. It is possible to specify a passphrase when
generating the
key; the passphrase will be used to encrypt the sen-
sitive part of
this file using 3DES.
$HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub,
$HOME/.ssh/id_rsa.pub
Contains the public key for authentication (public
part of the
identity file in human-readable form). The contents
of the
$HOME/.ssh/identity.pub file should be added to
$HOME/.ssh/authorized_keys on all machines where you
wish to log
in using protocol version 1 RSA authentication. The
contents of
the $HOME/.ssh/id_dsa.pub and $HOME/.ssh/id_rsa.pub
file should
be added to $HOME/.ssh/authorized_keys2 on all ma-
chines where you
wish to log in using protocol version 2 DSA/RSA au-
thentication.
These files are not sensitive and can (but need not)
be readable
by anyone. These files are never used automatically
and are not
necessary; they are only provided for the conve-
nience of the usM--
er.
as this user.
The format of this file is described in the sshd(8)
manual page.
In the simplest form the format is the same as the
.pub identity
files (that is, each line contains the number of
bits in modulus,
public exponent, modulus, and comment fields, sepa-
rated by
spaces). This file is not highly sensitive, but the
recommended
permissions are read/write for the user, and not ac-
cessible by
others.
$HOME/.ssh/authorized_keys2
Lists the public keys (RSA/DSA) that can be used for
logging in
as this user. This file is not highly sensitive,
but the recomM--
mended permissions are read/write for the user, and
not accessiM--
ble by others.
/etc/ssh_known_hosts, /etc/ssh_known_hosts2
Systemwide list of known host keys.
/etc/ssh_known_hosts conM--
tains RSA and /etc/ssh_known_hosts2 contains RSA or
DSA keys for
protocol version 2. These files should be prepared
by the system
administrator to contain the public host keys of all
machines in
the organization. This file should be world-read-
able. This file
contains public keys, one per line, in the following
format
(fields separated by spaces): system name, number of
bits in modM--
ulus, public exponent, modulus, and optional comment
field. When
different names are used for the same machine, all
such names
should be listed, separated by commas. The format
is described
on the sshd(8) manual page.
The canonical system name (as returned by name
servers) is used
by sshd(8) to verify the client host when logging
in; other names
are needed because ssh does not convert the user-
This file must be world-readable.
$HOME/.rhosts
This file is used in .rhosts authentication to list
the host/user
pairs that are permitted to log in. (Note that this
file is also
used by rlogin and rsh, which makes using this file
insecure.)
Each line of the file contains a host name (in the
canonical form
returned by name servers), and then a user name on
that host,
separated by a space. On some machines this file
may need to be
world-readable if the user's home directory is on a
NFS partiM--
tion, because sshd(8) reads it as root. Additional-
ly, this file
must be owned by the user, and must not have write
permissions
for anyone else. The recommended permission for
most machines is
read/write for the user, and not accessible by oth-
ers.
Note that by default sshd(8) will be installed so
that it reM--
quires successful RSA host authentication before
permitting
.rhosts authentication. If your server machine does
not have the
client's host key in /etc/ssh_known_hosts, you can
store it in
$HOME/.ssh/known_hosts. The easiest way to do this
is to connect
back to the client from the server machine using
ssh; this will
automatically add the host key to
$HOME/.ssh/known_hosts.
$HOME/.shosts
This file is used exactly the same way as .rhosts.
The purpose
for having this file is to be able to use rhosts au-
thentication
with ssh without permitting login with rlogin(1) or
rsh(1).
/etc/hosts.equiv
This file is used during .rhosts authentication. It
contains
This file may
be useful to permit logins using ssh but not using
rsh/rlogin.
/etc/sshrc
Commands in this file are executed by ssh when the
user logs in
just before the user's shell (or command) is start-
ed. See the
sshd(8) manual page for more information.
$HOME/.ssh/rc
Commands in this file are executed by ssh when the
user logs in
just before the user's shell (or command) is start-
ed. See the
sshd(8) manual page for more information.
$HOME/.ssh/environment
Contains additional definitions for environment
variables, see
section ENVIRONMENT above.
AUTHORS
OpenSSH is a derivative of the original and free ssh 1.2.12
release by
Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels
Provos, Theo
de Raadt and Dug Song removed many bugs, re-added newer fea-
tures and creM--
ated OpenSSH. Markus Friedl contributed the support for SSH
protocol
versions 1.5 and 2.0.
SEE ALSO
rlogin(1), rsh(1), scp(1), sftp(1), ssh-add(1), ssh-
agent(1), ssh-
keygen(1), telnet(1), sshd(8)
T. Ylonen, T. Kivinen, M. Saarinen, T. Rinne, and S. Lehti-
nen, SSH
Protocol Architecture, draft-ietf-secsh-architecture-07.txt,
January
2001, work in progress material.
BSD Experimental September 25, 1999
14
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