ssh - OpenSSH SSH client (remote login program)
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]
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 [Toc] [Back]
The first authentication method is the rhosts or hosts.equiv
method combined
with RSA-based host authentication. 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, or
if the files
$HOME/.rhosts or $HOME/.shosts exist in the user's home directory on the
remote machine and contain a line containing the name of the
client machine
and the name of the user on that machine, the user is
considered
for log in. Additionally, if the server can verify the
client's host key
(see /etc/ssh/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.]
As a second 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.
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 [Toc] [Back]
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
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 [Toc] [Back]
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 [Toc] [Back]
When a pseudo-terminal has been requested, ssh supports a
number of functions
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 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 [Toc] [Back]
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 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 [Toc] [Back]
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/ssh/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 manin-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.
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 hostby-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,
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/ssh/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
$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.)
-o option
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
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
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 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
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.
ssh may additionally obtain configuration data from a peruser configuration
file and a system-wide configuration file. The file
format and configuration
options are described in ssh_config(5).
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 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).
$HOME/.ssh/known_hosts
Records host keys for all hosts the user has logged
into that are
not in /etc/ssh/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/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 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/ssh/ssh_known_hosts
Systemwide list of known host keys. This file
should be prepared
by the system administrator to contain the public
host keys of
all machines in the organization. This file should
be worldreadable.
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 usersupplied 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/ssh/ssh_config
Systemwide configuration file. The file format and
configuration
options are described in ssh_config(5).
/etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key,
/etc/ssh/ssh_host_rsa_key
These three files contain the private parts of the
host keys 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 sshkeysign(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 RhostsRSAAuthentication and
HostbasedAuthentication 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 sshd(8) allows authentication only in combination with
client host key authentication before permitting log
in. If the
server machine does not have the client's host key
in
/etc/ssh/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 useRhostsRSAAuthentication [Toc] [Back] and HostbasedAuthentication authentication without
permitting login
with rlogin or rsh(1).
/etc/hosts.equiv
This file is used during RhostsRSAAuthentication and
HostbasedAuthentication 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 client
host key authentication
is required. This file should only be
writable by
root.
/etc/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/ssh/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.
ssh exits with the exit status of the remote command or with
255 if an
error occurred.
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),
ssh-keysign(8),
sshd(8)
T. Ylonen, T. Kivinen, M. Saarinen, T. Rinne, and S. Lehtinen, SSH
Protocol Architecture, draft-ietf-secsh-architecture-12.txt,
January
2002, work in progress material.
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.
OpenBSD 3.6 September 25, 1999
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