SSH(1) UNIX System V (September 25, 1999) SSH(1)
NAME
ssh - OpenSSH SSH client (remote login program)
SYNOPSIS
ssh [-1246AaCfgkMNnqsTtVvXxY] [-b bind_address] [-c
cipher_spec] [-D port] [-e escape_char] [-F configfile] [-i
identity_file] [-L port:host:hostport] [-l login_name] [-m
mac_spec] [-o option] [-p port] [-R port:host:hostport] [-S
ctl] [user@]hostname [command]
DESCRIPTION
ssh (SSH client) is a program for logging into a remote
machine and for executing commands on a remote machine. It
is intended to replace rlogin and rsh, and provide secure
encrypted communications between two untrusted hosts over an
insecure network. X11 connections and arbitrary TCP/IP
ports can also be forwarded over the secure channel.
ssh connects and logs into the specified hostname (with
optional user name). The user must prove his/her identity
to the remote machine using one of several methods depending
on the protocol version used.
If command is specified, command is executed on the remote
host instead of a login shell.
SSH protocol version 1
First, if the machine the user logs in from is listed in
/etc/hosts.equiv or /etc/openssh/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 combined with RSA-based host
authentication. It means that if the login would be
permitted by $HOME/.rhosts, $HOME/.shosts, /etc/hosts.equiv,
or /etc/openssh/shosts.equiv, and if additionally the server
can verify the client's host key (see
/etc/openssh/ssh_known_hosts and $HOME/.ssh/known_hosts in
the FILES section), only then is login permitted. This
authentication method closes security holes due to IP
spoofing, DNS spoofing and routing spoofing. [Note to the
administrator: /etc/hosts.equiv, $HOME/.rhosts, and the
rlogin/rsh protocol in general, are inherently insecure and
should be disabled if security is desired.]
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As a third authentication method, ssh supports RSA based
authentication. 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 encryption
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 decrypts the challenge 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
automatically. The user creates his/her RSA key pair by
running ssh-keygen(1). This stores the private key in
$HOME/.ssh/identity and stores 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 authentication.
The most convenient way to use RSA authentication may be
with an authentication agent. See ssh-agent(1) for more
information.
If other authentication methods fail, ssh prompts the user
for a password. The password is sent to the remote host for
checking; however, since all communications are encrypted,
the password cannot be seen by someone listening on the
network.
SSH protocol version 2
When a user connects using protocol version 2, similar
authentication methods are available. Using the default
values for PreferredAuthentications, the client will try to
authenticate first using the hostbased method; if this
method fails, public key authentication is attempted, and
finally if this method fails, keyboard-interactive and
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password authentication are tried.
The public key method is similar to RSA authentication
described 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_keys and grants access if both the key
is found and the signature is correct. The session
identifier is derived from a shared Diffie-Hellman value and
is only known to the client and the server.
If public key authentication fails or is not available, a
password can be sent encrypted to the remote host to prove
the user's identity.
Additionally, ssh supports hostbased or challenge response
authentication.
Protocol 2 provides additional mechanisms for
confidentiality (the traffic is encrypted using AES, 3DES,
Blowfish, CAST128 or Arcfour) and integrity (hmac-md5,
hmac-sha1, hmac-ripemd160). 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 either executes the given command, or logs into
the machine and gives the user a normal shell on the remote
machine. All communication with the remote command or shell
will be automatically encrypted.
If a pseudo-terminal has been allocated (normal login
session), the user may use the escape characters noted
below.
If no pseudo-tty has been allocated, the session is
transparent and can be used to reliably transfer binary
data. On most systems, setting the escape character to
``none'' will also make the session transparent even if a
tty is used.
The session terminates when the command or shell on the
remote machine exits and all X11 and TCP/IP connections have
been closed. The exit status 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 functions through the use of an escape character.
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A single tilde character can be sent as ~~ or by following
the tilde by a character other than those described below.
The escape character must always follow a newline to be
interpreted as special. The escape character can be changed
in configuration files using the EscapeChar configuration
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.
~? Display a list of escape characters.
~B Send a BREAK to the remote system (only useful for SSH
protocol version 2 and if the peer supports it).
~C Open command line. Currently this allows the addition
of port forwardings using the -L and -R options (see
below). It also allows the cancellation of existing
remote port-forwardings using -KR hostport. Basic help
is available, using the -h option.
~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 ForwardX11 variable is set to ``yes'' (or see the
description of the -X and -x options described later) and
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 command) will go through
the encrypted channel, and the connection to the real X
server will be made from the local machine. The user should
not manually set DISPLAY. Forwarding of X11 connections can
be configured on the command line or in configuration files.
The DISPLAY value set by ssh will point to the server
machine, but with a display number greater than zero. This
is normal, and happens because ssh creates a ``proxy'' X
server on the server machine for forwarding the 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
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authorization cookie, store it in Xauthority on the server,
and verify that any forwarded 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 ForwardAgent variable is set to ``yes'' (or see the
description of the -A and -a options described later) and
the user is using an authentication agent, the connection to
the agent is automatically forwarded to the remote side.
Forwarding of arbitrary TCP/IP connections over the secure
channel can be specified either on the command line or in a
configuration file. One possible application of TCP/IP
forwarding is a secure connection to an electronic purse;
another is going through firewalls.
Server authentication
ssh automatically maintains and checks a database containing
identifications for all hosts it has ever been used with.
Host keys are stored in $HOME/.ssh/known_hosts in the user's
home directory. Additionally, the file
/etc/openssh/ssh_known_hosts is 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 mechanism is to prevent man-in-the-
middle attacks which could otherwise be used to circumvent
the encryption. The StrictHostKeyChecking option can be
used to prevent logins to machines whose host key is not
known or has changed.
ssh can be configured to verify host identification using
fingerprint resource records (SSHFP) published in DNS. The
VerifyHostKeyDNS option can be used to control how DNS
lookups are performed. SSHFP resource records can be
generated using ssh-keygen(1).
The options are as follows:
-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.
-A Enables forwarding of the authentication agent
connection. This can also be specified on a per-host
basis in a configuration file.
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Agent forwarding should be enabled with caution. Users
with the ability to bypass file permissions on the
remote host (for the agent's Unix-domain socket) can
access the local agent through the forwarded
connection. An attacker cannot obtain key material
from the agent, however they can perform operations on
the keys that enable them to authenticate using the
identities loaded into the agent.
-a Disables forwarding of the authentication agent
connection.
-b bind_address
Specify the interface to transmit from on machines with
multiple interfaces or aliased addresses.
-C Requests compression of all data (including stdin,
stdout, stderr, and data for forwarded X11 and TCP/IP
connections). The compression algorithm is the same
used by gzip(1), and the ``level'' can be controlled by
the CompressionLevel option for protocol version 1.
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 configuration files; see the
Compression option.
-c cipher_spec
Selects the cipher specification for encrypting the
session.
Protocol version 1 allows specification of a single
cipher. The suported values are ``3des'', ``blowfish''
and ``des''. 3des (triple-des) is an encrypt-decrypt-
encrypt triple with three different keys. It is
believed to be secure. blowfish is a fast block
cipher; it appears very secure and is much faster than
3des. des is only supported in the ssh client for
interoperability with legacy protocol 1 implementations
that do not support the 3des cipher. Its use is
strongly discouraged due to cryptographic weaknesses.
The default is ``3des''.
For protocol version 2 cipher_spec is a comma-separated
list of ciphers listed in order of preference. The
supported ciphers are ``3des-cbc'', ``aes128-cbc'',
``aes192-cbc'', ``aes256-cbc'', ``aes128-ctr'',
``aes192-ctr'', ``aes256-ctr'', ``arcfour'',
``blowfish-cbc'', and ``cast128-cbc''. The default is
``aes128-cbc,3des-cbc,blowfish-cbc,cast128-
cbc,arcfour,
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aes192-cbc,aes256-cbc''
-D port
Specifies a local ``dynamic'' application-level port
forwarding. This works by allocating a socket to
listen to port on the local side, and whenever a
connection is made to this port, the connection is
forwarded over the secure channel, and the application
protocol is then used to determine where to connect to
from the remote machine. Currently the SOCKS4 and
SOCKS5 protocols are supported, and ssh will act as a
SOCKS server. Only root can forward privileged ports.
Dynamic port forwardings can also be specified in the
configuration file.
-e ch | ^ch | none
Sets the escape character for sessions with a pty
(default: `~' ) . The escape character is only
recognized at the beginning of a line. The escape
character followed by a dot (`.') closes the
connection; followed by control-Z suspends the
connection; and followed by itself sends the escape
character once. Setting the character to ``none''
disables any escapes and makes the session fully
transparent.
-F configfile
Specifies an alternative per-user configuration file.
If a configuration file is given on the command line,
the system-wide configuration file
(/etc/openssh/ssh_config) will be ignored. The default
for the per-user configuration file is
$HOME/.ssh/config.
-f Requests ssh to go to background just before command
execution. This is useful if ssh is going to ask for
passwords or passphrases, but the user wants it in the
background. This implies -n. The recommended way to
start X11 programs at a remote site is with something
like ssh-f host xterm.
-g Allows remote hosts to connect to local forwarded
ports.
-I smartcard_device
Specifies which smartcard device to use. The argument
is the device ssh should use to communicate with a
smartcard used for storing the user's private RSA key.
-i identity_file
Selects a file from which the identity (private key)
for RSA or DSA authentication is read. The default is
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$HOME/.ssh/identity for protocol version 1, and
$HOME/.ssh/id_rsa and $HOME/.ssh/id_dsa for protocol
version 2. Identity files may also be specified on a
per-host basis in the configuration file. It is
possible to have multiple -i options (and multiple
identities specified in configuration files).
-k Disables forwarding (delegation) of GSSAPI credentials
to the server.
-L port:host:hostport
Specifies that the given port on the local (client)
host is to be forwarded to the given host and port on
the remote side. This works by allocating a socket to
listen to port on the local side, and whenever a
connection is made to this port, the connection is
forwarded over the secure channel, and a connection is
made to host port hostport from the remote machine.
Port forwardings can also be specified in the
configuration file. Only root can forward privileged
ports. IPv6 addresses can be specified with an
alternative syntax:
port/host/ hostport.
-l login_name
Specifies the user to log in as on the remote machine.
This also may be specified on a per-host basis in the
configuration file.
-M Places the ssh client into ``master'' mode for
connection sharing. Refer to the description of
ControlMaster in ssh_config(5) for details.
-m mac_spec
Additionally, for protocol version 2 a comma-separated
list of MAC (message authentication code) algorithms
can be specified in order of preference. See the MACs
keyword for more information.
-N Do not execute a remote command. This is useful for
just forwarding ports (protocol version 2 only).
-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 machine. For example, ssh-n shadows.cs.hut.fi emacs & will start an emacs on
shadows.cs.hut.fi, and the X11 connection will be
automatically 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.)
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Can be used to give options in the format used in the
configuration file. This is useful for specifying
options for which there is no separate command-line
flag. For full details of the options listed below,
and their possible values, see ssh_config(5).
AddressFamily
BatchMode
BindAddress
ChallengeResponseAuthentication
CheckHostIP
Cipher
Ciphers
ClearAllForwardings
Compression
CompressionLevel
ConnectionAttempts
ConnectTimeout
ControlMaster
ControlPath
DynamicForward
EscapeChar
ForwardAgent
ForwardX11
ForwardX11Trusted
GatewayPorts
GlobalKnownHostsFile
GSSAPIAuthentication
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GSSAPIDelegateCredentials
Host
HostbasedAuthentication
HostKeyAlgorithms
HostKeyAlias
HostName
IdentityFile
IdentitiesOnly
LocalForward
LogLevel
MACs
NoHostAuthenticationForLocalhost
NumberOfPasswordPrompts
PasswordAuthentication
Port
PreferredAuthentications
Protocol
ProxyCommand
PubkeyAuthentication
RemoteForward
RhostsRSAAuthentication
RSAAuthentication
SendEnv
ServerAliveInterval
ServerAliveCountMax
SmartcardDevice
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StrictHostKeyChecking
TCPKeepAlive
UsePrivilegedPort
User
UserKnownHostsFile
VerifyHostKeyDNS
XAuthLocation
-p port
Port to connect to on the remote host. This can be
specified on a per-host basis in the configuration
file.
-q Quiet mode. Causes all warning and diagnostic messages
to be suppressed.
-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 connection is
forwarded over the secure channel, and a connection is
made to host port hostport from the local machine.
Port forwardings 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.
-S ctl
Specifies the location of a control socket for
connection sharing. Refer to the description of
ControlPath and ControlMaster in ssh_config(5) for
details.
-s May be used to request invocation of a subsystem on the
remote system. Subsystems are a feature of the SSH2
protocol which facilitate the use of SSH as a secure
transport for other applications (eg. sftp(1)) . The
subsystem is specified as the remote command.
-T Disable pseudo-tty allocation.
-t Force pseudo-tty allocation. This can be used to
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execute arbitrary 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 local tty.
-V Display the version number and exit.
-v Verbose mode. Causes ssh to print debugging messages
about its progress. This is helpful in debugging
connection, authentication, and configuration problems.
Multiple -v options increase the verbosity. The
maximum is 3.
-X Enables X11 forwarding. This can also be specified on
a per-host basis in a configuration file.
X11 forwarding should be enabled with caution. Users
with the ability to bypass file permissions on the
remote host (for the user's X authorization database)
can access the local X11 display through the forwarded
connection. An attacker may then be able to perform
activities such as keystroke monitoring.
-x Disables X11 forwarding.
-Y Enables trusted X11 forwarding.
CONFIGURATION FILES
ssh may additionally obtain configuration data from a per-
user configuration file and a system-wide configuration
file. The file format and configuration options are
described in ssh_config(5).
ENVIRONMENT
ssh will normally set the following environment variables:
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 special 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
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that use this variable.
MAIL Set to the path of the user's mailbox.
PATH Set to the default PATH, as specified when compiling
ssh.
SSH_ASKPASS
If ssh needs a passphrase, it will read the passphrase
from the current terminal if it was run from a
terminal. If ssh does not have a terminal associated
with it but DISPLAY and SSH_ASKPASS are set, it will
execute the program specified by SSH_ASKPASS and open
an X11 window to read the passphrase. This is
particularly useful when calling ssh from a .Xsession
or related script. (Note that on some machines it may
be necessary to redirect the input from /dev/null to
make this work.)
SSH_AUTH_SOCK
Identifies the path of a unix-domain socket used to
communicate with the agent.
SSH_CONNECTION
Identifies the client and server ends of the
connection. The variable contains four space-separated
values: client ip-address, client port number, server
ip-address and server port number.
SSH_ORIGINAL_COMMAND
The variable contains the original command line if a
forced command is executed. It can be used to extract
the original arguments.
SSH_TTY
This is set to the name of the tty (path to the device)
associated with the current shell or command. If the
current session has no tty, this variable is not set.
TZ The timezone variable is set to indicate the present
timezone if it was set when the daemon was started
(i.e., the daemon passes the value on to new
connections).
USER Set to the name of the user logging in.
Additionally, ssh reads $HOME/.ssh/environment, and
adds lines of the format ``VARNAME=value'' to the
environment if the file exists and if users are allowed
to change their environment. For more information, see
the PermitUserEnvironment option in sshd_config(5).
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FILES
$HOME/.ssh/known_hosts
Records host keys for all hosts the user has logged
into that are not in /etc/openssh/ssh_known_hosts. 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/execute). Note that ssh ignores
a private key file if it is accessible by others. It
is possible to specify a passphrase when generating the
key; the passphrase will be used to encrypt the
sensitive part of this file using 3DES.
$HOME/.ssh/id_rsa.pub
$HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.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 the file $HOME/.ssh/authorized_keys on all
machines where the user wishes 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_keys on all
machines where the user wishes to log in using protocol
version 2 DSA/RSA authentication. 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 convenience
of the user.
$HOME/.ssh/config
This is the per-user configuration file. The file
format and configuration options are described in
ssh_config(5). Because of the potential for abuse,
this file must have strict permissions: read/write for
the user, and not accessible by others.
$HOME/.ssh/authorized_keys
Lists the public keys (RSA/DSA) that can be used for
logging in 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.
This file is not highly sensitive, but the recommended
permissions are read/write for the user, and not
accessible by others.
/etc/openssh/ssh_known_hosts
Systemwide list of known host keys. This file should
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be prepared by the system administrator to contain the
public host keys of all machines in the organization.
This file should be world-readable. This file contains
public keys, one per line, in the following format
(fields separated by spaces): system name, public key
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
in 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-supplied name to a canonical name
before checking the key, because someone with access to
the name servers would then be able to fool host
authentication.
/etc/openssh/ssh_config
Systemwide configuration file. The file format and
configuration options are described in ssh_config(5).
/etc/openssh/ssh_host_rsa_key
/etc/openssh/ssh_host_key, /etc/openssh/ssh_host_dsa_key,
These three files contain the private parts of the host
keys and are used for RhostsRSAAuthentication and
HostbasedAuthentication. If the protocol version 1
RhostsRSAAuthentication method is used, ssh must be
setuid root, since the host key is readable only by
root. For protocol version 2, ssh uses ssh-keysign(8)
to access the host keys for HostbasedAuthentication.
This eliminates the requirement that ssh be setuid root
when that authentication method is used. By default
ssh is not setuid root.
$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 partition, because sshd(8) reads it as
root. Additionally, 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 others.
Note that by default sshd(8) will be installed so that
it requires successful RSA host authentication before
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permitting rhosts authentication. If the server
machine does not have the client's host key in
/etc/openssh/ssh_known_hosts, it can be stored 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 authentication with ssh without permitting login
with rlogin() or rsh(1).
/etc/hosts.equiv
This file is used during rhosts authentication. It
contains canonical hosts names, one per line (the full
format is described in the sshd(8) manual page). If
the client host is found in this file, login is
automatically permitted provided client and server user
names are the same. Additionally, successful RSA host
authentication is normally required. This file should
only be writable by root.
/etc/openssh/shosts.equiv
This file is processed exactly as /etc/hosts.equiv.
This file may be useful to permit logins using ssh but
not using rsh/rlogin.
/etc/openssh/sshrc
Commands in this file are executed by ssh when the user
logs in just before the user's shell (or command) is
started. 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
started. See the sshd(8) manual page for more
information.
$HOME/.ssh/environment
Contains additional definitions for environment
variables, see section ENVIRONMENT above.
DIAGNOSTICS
ssh exits with the exit status of the remote command or with
255 if an error occurred.
SEE ALSO
gzip(1), rsh(1), scp(1), sftp(1), ssh-add(1), ssh-agent(1),
ssh-keygen(1), telnet(1), hosts.equiv(5), ssh_config(5),
Page 16 (printed 10/26/05)
SSH(1) UNIX System V (September 25, 1999) SSH(1)ssh-keysign(8), sshd(8)
S. Lehtinen, T. Rinne, M. Saarinen, T. Kivinen and T.
Ylonen, SSH Protocol Architecture, draft-ietf-secsh-
architecture-12.txt, January 2002, work in progress
material.
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 features and created OpenSSH.
Markus Friedl contributed the support for SSH protocol
versions 1.5 and 2.0.
Page 17 (printed 10/26/05)
