mirror of
git://anongit.mindrot.org/openssh.git
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5428f646ad
- Merged OpenBSD CVS changes: - [channels.c] report from mrwizard@psu.edu via djm@ibs.com.au - [channels.c] set SO_REUSEADDR and SO_LINGER for forwarded ports. chip@valinux.com via damien@ibs.com.au - [nchan.c] it's not an error() if shutdown_write failes in nchan. - [readconf.c] remove dead #ifdef-0-code - [readconf.c servconf.c] strcasecmp instead of tolower - [scp.c] progress meter overflow fix from damien@ibs.com.au - [ssh-add.1 ssh-add.c] SSH_ASKPASS support - [ssh.1 ssh.c] postpone fork_after_authentication until command execution, request/patch from jahakala@cc.jyu.fi via damien@ibs.com.au plus: use daemon() for backgrounding
988 lines
32 KiB
Groff
988 lines
32 KiB
Groff
.\" -*- nroff -*-
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.\"
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.\" ssh.1.in
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.\"
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.\" Author: Tatu Ylonen <ylo@cs.hut.fi>
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.\"
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.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
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.\" All rights reserved
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.\"
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.\" Created: Sat Apr 22 21:55:14 1995 ylo
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.\"
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.\" $Id: ssh.1,v 1.10 1999/11/25 00:54:59 damien Exp $
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.\"
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.Dd September 25, 1999
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.Dt SSH 1
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.Os
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.Sh NAME
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.Nm ssh
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.Nd OpenSSH secure shell client (remote login program)
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.Sh SYNOPSIS
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.Nm ssh
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.Op Fl l Ar login_name
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.Op Ar hostname | user@hostname
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.Op Ar command
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.Pp
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.Nm ssh
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.Op Fl afgknqtvxCPX
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.Op Fl c Ar blowfish | 3des
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.Op Fl e Ar escape_char
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.Op Fl i Ar identity_file
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.Op Fl l Ar login_name
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.Op Fl o Ar option
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.Op Fl p Ar port
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.Oo Fl L Xo
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.Sm off
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.Ar host :
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.Ar port :
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.Ar hostport
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.Sm on
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.Xc
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.Oc
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.Oo Fl R Xo
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.Sm off
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.Ar host :
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.Ar port :
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.Ar hostport
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.Sm on
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.Xc
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.Oc
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.Op Ar hostname | user@hostname
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.Op Ar command
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.Sh DESCRIPTION
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.Nm
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(Secure Shell) is a program for logging into a remote machine and for
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executing commands on a remote machine. It is intended to replace
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rlogin and rsh, and provide secure encrypted communications between
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two untrusted hosts over an insecure network. X11 connections and
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arbitrary TCP/IP ports can also be forwarded over the secure channel.
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.Pp
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.Nm
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connects and logs into the specified
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.Ar hostname .
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The user must prove
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his/her identity to the remote machine using one of several methods.
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.Pp
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First, if the machine the user logs in from is listed in
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.Pa /etc/hosts.equiv
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or
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.Pa /etc/ssh/shosts.equiv
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on the remote machine, and the user names are
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the same on both sides, the user is immediately permitted to log in.
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Second, if
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.Pa \&.rhosts
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or
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.Pa \&.shosts
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exists in the user's home directory on the
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remote machine and contains a line containing the name of the client
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machine and the name of the user on that machine, the user is
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permitted to log in. This form of authentication alone is normally not
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allowed by the server because it is not secure.
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.Pp
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The second (and primary) authentication method is the
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.Pa rhosts
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or
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.Pa hosts.equiv
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method combined with RSA-based host authentication. It
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means that if the login would be permitted by
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.Pa \&.rhosts ,
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.Pa \&.shosts ,
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.Pa /etc/hosts.equiv ,
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or
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.Pa /etc/ssh/shosts.equiv ,
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and if additionally the server can verify the client's
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host key (see
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.Pa /etc/ssh/ssh_known_hosts
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and
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.Pa $HOME/.ssh/known_hosts
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in the
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.Sx FILES
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section), only then login is
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permitted. This authentication method closes security holes due to IP
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spoofing, DNS spoofing and routing spoofing. [Note to the
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administrator:
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.Pa /etc/hosts.equiv ,
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.Pa \&.rhosts ,
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and the rlogin/rsh protocol in general, are inherently insecure and should be
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disabled if security is desired.]
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.Pp
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As a third authentication method,
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.Nm
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supports RSA based authentication.
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The scheme is based on public-key cryptography: there are cryptosystems
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where encryption and decryption are done using separate keys, and it
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is not possible to derive the decryption key from the encryption key.
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RSA is one such system. The idea is that each user creates a public/private
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key pair for authentication purposes. The
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server knows the public key, and only the user knows the private key.
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The file
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.Pa $HOME/.ssh/authorized_keys
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lists the public keys that are permitted for logging
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in. When the user logs in, the
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.Nm
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program tells the server which key pair it would like to use for
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authentication. The server checks if this key is permitted, and if
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so, sends the user (actually the
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.Nm
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program running on behalf of the user) a challenge, a random number,
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encrypted by the user's public key. The challenge can only be
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decrypted using the proper private key. The user's client then decrypts the
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challenge using the private key, proving that he/she knows the private
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key but without disclosing it to the server.
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.Pp
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.Nm
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implements the RSA authentication protocol automatically. The user
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creates his/her RSA key pair by running
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.Xr ssh-keygen 1 .
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This stores the private key in
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.Pa \&.ssh/identity
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and the public key in
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.Pa \&.ssh/identity.pub
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in the user's home directory. The user should then
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copy the
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.Pa identity.pub
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to
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.Pa \&.ssh/authorized_keys
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in his/her home directory on the remote machine (the
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.Pa authorized_keys
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file corresponds to the conventional
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.Pa \&.rhosts
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file, and has one key
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per line, though the lines can be very long). After this, the user
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can log in without giving the password. RSA authentication is much
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more secure than rhosts authentication.
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.Pp
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The most convenient way to use RSA authentication may be with an
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authentication agent. See
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.Xr ssh-agent 1
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for more information.
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.Pp
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If other authentication methods fail,
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.Nm
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prompts the user for a password. The password is sent to the remote
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host for checking; however, since all communications are encrypted,
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the password cannot be seen by someone listening on the network.
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.Pp
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When the user's identity has been accepted by the server, the server
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either executes the given command, or logs into the machine and gives
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the user a normal shell on the remote machine. All communication with
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the remote command or shell will be automatically encrypted.
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.Pp
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If a pseudo-terminal has been allocated (normal login session), the
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user can disconnect with
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.Ic ~. ,
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and suspend
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.Nm
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with
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.Ic ~^Z .
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All forwarded connections can be listed with
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.Ic ~#
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and if
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the session blocks waiting for forwarded X11 or TCP/IP
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connections to terminate, it can be backgrounded with
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.Ic ~&
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(this should not be used while the user shell is active, as it can cause the
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shell to hang). All available escapes can be listed with
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.Ic ~? .
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.Pp
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A single tilde character can be sent as
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.Ic ~~
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(or by following the tilde by a character other than those described above).
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The escape character must always follow a newline to be interpreted as
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special. The escape character can be changed in configuration files
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or on the command line.
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.Pp
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If no pseudo tty has been allocated, the
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session is transparent and can be used to reliably transfer binary
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data. On most systems, setting the escape character to
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.Dq none
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will also make the session transparent even if a tty is used.
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.Pp
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The session terminates when the command or shell in on the remote
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machine exists and all X11 and TCP/IP connections have been closed.
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The exit status of the remote program is returned as the exit status
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of
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.Nm ssh .
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.Pp
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If the user is using X11 (the
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.Ev DISPLAY
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environment variable is set), the connection to the X11 display is
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automatically forwarded to the remote side in such a way that any X11
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programs started from the shell (or command) will go through the
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encrypted channel, and the connection to the real X server will be made
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from the local machine. The user should not manually set
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.Ev DISPLAY .
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Forwarding of X11 connections can be
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configured on the command line or in configuration files.
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.Pp
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The
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.Ev DISPLAY
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value set by
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.Nm
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will point to the server machine, but with a display number greater
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than zero. This is normal, and happens because
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.Nm
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creates a
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.Dq proxy
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X server on the server machine for forwarding the
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connections over the encrypted channel.
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.Pp
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.Nm
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will also automatically set up Xauthority data on the server machine.
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For this purpose, it will generate a random authorization cookie,
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store it in Xauthority on the server, and verify that any forwarded
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connections carry this cookie and replace it by the real cookie when
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the connection is opened. The real authentication cookie is never
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sent to the server machine (and no cookies are sent in the plain).
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.Pp
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If the user is using an authentication agent, the connection to the agent
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is automatically forwarded to the remote side unless disabled on
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command line or in a configuration file.
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.Pp
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Forwarding of arbitrary TCP/IP connections over the secure channel can
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be specified either on command line or in a configuration file. One
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possible application of TCP/IP forwarding is a secure connection to an
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electronic purse; another is going trough firewalls.
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.Pp
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.Nm
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automatically maintains and checks a database containing RSA-based
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identifications for all hosts it has ever been used with. The
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database is stored in
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.Pa \&.ssh/known_hosts
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in the user's home directory. Additionally, the file
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.Pa /etc/ssh/ssh_known_hosts
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is automatically checked for known hosts. Any new hosts are
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automatically added to the user's file. If a host's identification
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ever changes,
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.Nm
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warns about this and disables password authentication to prevent a
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trojan horse from getting the user's password. Another purpose of
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this mechanism is to prevent man-in-the-middle attacks which could
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otherwise be used to circumvent the encryption. The
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.Cm StrictHostKeyChecking
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option (see below) can be used to prevent logins to machines whose
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host key is not known or has changed.
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.Sh OPTIONS
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.Bl -tag -width Ds
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.It Fl a
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Disables forwarding of the authentication agent connection. This may
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also be specified on a per-host basis in the configuration file.
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.It Fl c Ar blowfish|3des
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Selects the cipher to use for encrypting the session.
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.Ar 3des
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is used by default. It is believed to be secure.
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.Ar 3des
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(triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
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It is presumably more secure than the
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.Ar des
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cipher which is no longer supported in ssh.
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.Ar blowfish
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is a fast block cipher, it appears very secure and is much faster than
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.Ar 3des .
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.It Fl e Ar ch|^ch|none
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Sets the escape character for sessions with a pty (default:
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.Ql ~ ) .
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The escape character is only recognized at the beginning of a line. The
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escape character followed by a dot
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.Pq Ql \&.
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closes the connection, followed
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by control-Z suspends the connection, and followed by itself sends the
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escape character once. Setting the character to
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.Dq none
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disables any escapes and makes the session fully transparent.
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.It Fl f
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Requests
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.Nm
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to go to background just before command execution. This is useful
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if
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.Nm
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is going to ask for passwords or passphrases, but the user
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wants it in the background. This implies
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.Fl n .
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The recommended way to start X11 programs at a remote site is with
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something like
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.Ic ssh -f host xterm .
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.It Fl i Ar identity_file
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Selects the file from which the identity (private key) for
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RSA authentication is read. Default is
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.Pa \&.ssh/identity
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in the user's home directory. Identity files may also be specified on
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a per-host basis in the configuration file. It is possible to have
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multiple
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.Fl i
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options (and multiple identities specified in
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configuration files).
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.It Fl g
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Allows remote hosts to connect to local forwarded ports.
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.It Fl k
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Disables forwarding of Kerberos tickets and AFS tokens. This may
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also be specified on a per-host basis in the configuration file.
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.It Fl l Ar login_name
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Specifies the user to log in as on the remote machine. This may also
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be specified on a per-host basis in the configuration file.
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.It Fl n
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Redirects stdin from
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.Pa /dev/null
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(actually, prevents reading from stdin).
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This must be used when
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.Nm
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is run in the background. A common trick is to use this to run X11
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programs in a remote machine. For example,
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.Ic ssh -n shadows.cs.hut.fi emacs &
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will start an emacs on shadows.cs.hut.fi, and the X11
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connection will be automatically forwarded over an encrypted channel.
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The
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.Nm
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program will be put in the background.
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(This does not work if
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.Nm
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needs to ask for a password or passphrase; see also the
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.Fl f
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option.)
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.It Fl o Ar option
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Can be used to give options in the format used in the config file.
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This is useful for specifying options for which there is no separate
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command-line flag. The option has the same format as a line in the
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configuration file.
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.It Fl p Ar port
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Port to connect to on the remote host. This can be specified on a
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per-host basis in the configuration file.
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.It Fl P
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Use a non-privileged port for outgoing connections.
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This can be used if your firewall does
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not permit connections from privileged ports.
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Note that this option turns of
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.Cm RhostsAuthentication
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and
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.Cm RhostsRSAAuthentication .
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.It Fl q
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Quiet mode. Causes all warning and diagnostic messages to be
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suppressed. Only fatal errors are displayed.
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.It Fl t
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Force pseudo-tty allocation. This can be used to execute arbitary
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screen-based programs on a remote machine, which can be very useful
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e.g. when implementing menu services.
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.It Fl v
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Verbose mode. Causes
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.Nm
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to print debugging messages about its progress. This is helpful in
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debugging connection, authentication, and configuration problems.
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The verbose mode is also used to display
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.Xr skey 1
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challenges, if the user entered "s/key" as password.
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.It Fl x
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Disables X11 forwarding. This can also be specified on a per-host
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basis in a configuration file.
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.It Fl X
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Enables X11 forwarding.
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.It Fl C
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Requests compression of all data (including stdin, stdout, stderr, and
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data for forwarded X11 and TCP/IP connections). The compression
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algorithm is the same used by gzip, and the
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.Dq level
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can be controlled by the
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.Cm CompressionLevel
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option (see below). Compression is desirable on modem lines and other
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slow connections, but will only slow down things on fast networks.
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The default value can be set on a host-by-host basis in the
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configuration files; see the
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.Cm Compress
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option below.
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.It Fl L Ar port:host:hostport
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Specifies that the given port on the local (client) host is to be
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forwarded to the given host and port on the remote side. This works
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by allocating a socket to listen to
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.Ar port
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on the local side, and whenever a connection is made to this port, the
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connection is forwarded over the secure channel, and a connection is
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made to
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.Ar host:hostport
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from the remote machine. Port forwardings can also be specified in the
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configuration file. Only root can forward privileged ports.
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.It Fl R Ar port:host:hostport
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Specifies that the given port on the remote (server) host is to be
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forwarded to the given host and port on the local side. This works
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by allocating a socket to listen to
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.Ar port
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on the remote side, and whenever a connection is made to this port, the
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connection is forwarded over the secure channel, and a connection is
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made to
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.Ar host:hostport
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from the local machine. Port forwardings can also be specified in the
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configuration file. Privileged ports can be forwarded only when
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logging in as root on the remote machine.
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.El
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.Sh CONFIGURATION FILES
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.Nm
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obtains configuration data from the following sources (in this order):
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command line options, user's configuration file
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.Pq Pa $HOME/.ssh/config ,
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and system-wide configuration file
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.Pq Pa /etc/ssh/ssh_config .
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For each parameter, the first obtained value
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will be used. The configuration files contain sections bracketed by
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"Host" specifications, and that section is only applied for hosts that
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match one of the patterns given in the specification. The matched
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host name is the one given on the command line.
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.Pp
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Since the first obtained value for each parameter is used, more
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host-specific declarations should be given near the beginning of the
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file, and general defaults at the end.
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.Pp
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The configuration file has the following format:
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.Pp
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Empty lines and lines starting with
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.Ql #
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are comments.
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.Pp
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Otherwise a line is of the format
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.Dq keyword arguments .
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The possible
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keywords and their meanings are as follows (note that the
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configuration files are case-sensitive):
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.Bl -tag -width Ds
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.It Cm Host
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Restricts the following declarations (up to the next
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.Cm Host
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keyword) to be only for those hosts that match one of the patterns
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given after the keyword.
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.Ql \&*
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and
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.Ql ?
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can be used as wildcards in the
|
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patterns. A single
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.Ql \&*
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as a pattern can be used to provide global
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defaults for all hosts. The host is the
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.Ar hostname
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|
argument given on the command line (i.e., the name is not converted to
|
|
a canonicalized host name before matching).
|
|
.It Cm AFSTokenPassing
|
|
Specifies whether to pass AFS tokens to remote host. The argument to
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this keyword must be
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.Dq yes
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or
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.Dq no .
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.It Cm BatchMode
|
|
If set to
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.Dq yes ,
|
|
passphrase/password querying will be disabled. This
|
|
option is useful in scripts and other batch jobs where you have no
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user to supply the password. The argument must be
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.Dq yes
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or
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.Dq no .
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.It Cm Cipher
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|
Specifies the cipher to use for encrypting the session. Currently,
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|
.Dq blowfish ,
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and
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.Dq 3des
|
|
are supported. The default is
|
|
.Dq 3des .
|
|
.It Cm Compression
|
|
Specifies whether to use compression. The argument must be
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.Dq yes
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or
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.Dq no .
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.It Cm CompressionLevel
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|
Specifies the compression level to use if compression is enable. The
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argument must be an integer from 1 (fast) to 9 (slow, best). The
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default level is 6, which is good for most applications. The meaning
|
|
of the values is the same as in GNU GZIP.
|
|
.It Cm 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.
|
|
.It Cm EscapeChar
|
|
Sets the escape character (default:
|
|
.Ql ~ ) .
|
|
The escape character can also
|
|
be set on the command line. The argument should be a single
|
|
character,
|
|
.Ql ^
|
|
followed by a letter, or
|
|
.Dq none
|
|
to disable the escape
|
|
character entirely (making the connection transparent for binary
|
|
data).
|
|
.It Cm FallBackToRsh
|
|
Specifies that if connecting via
|
|
.Nm
|
|
fails due to a connection refused error (there is no
|
|
.Xr sshd 8
|
|
listening on the remote host),
|
|
.Xr rsh 1
|
|
should automatically be used instead (after a suitable warning about
|
|
the session being unencrypted). The argument must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
.It Cm ForwardAgent
|
|
Specifies whether the connection to the authentication agent (if any)
|
|
will be forwarded to the remote machine. The argument must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
.It Cm ForwardX11
|
|
Specifies whether X11 connections will be automatically redirected
|
|
over the secure channel and
|
|
.Ev DISPLAY
|
|
set. The argument must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
.It Cm GatewayPorts
|
|
Specifies whether remote hosts are allowed to connect to local
|
|
forwarded ports.
|
|
The argument must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
The default is
|
|
.Dq no .
|
|
.It Cm GlobalKnownHostsFile
|
|
Specifies a file to use instead of
|
|
.Pa /etc/ssh/ssh_known_hosts .
|
|
.It Cm HostName
|
|
Specifies the real host name to log into. This can be used to specify
|
|
nicnames or abbreviations for hosts. Default is the name given on the
|
|
command line. Numeric IP addresses are also permitted (both on the
|
|
command line and in
|
|
.Cm HostName
|
|
specifications).
|
|
.It Cm IdentityFile
|
|
Specifies the file from which the user's RSA authentication identity
|
|
is read (default
|
|
.Pa .ssh/identity
|
|
in the user's home directory).
|
|
Additionally, any identities represented by the authentication agent
|
|
will be used for authentication. The file name may use the tilde
|
|
syntax to refer to a user's home directory. It is possible to have
|
|
multiple identity files specified in configuration files; all these
|
|
identities will be tried in sequence.
|
|
.It Cm KeepAlive
|
|
Specifies whether the system should send keepalive messages to the
|
|
other side. If they are sent, death of the connection or crash of one
|
|
of the machines will be properly noticed. However, this means that
|
|
connections will die if the route is down temporarily, and some people
|
|
find it annoying.
|
|
.Pp
|
|
The default is
|
|
.Dq 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.
|
|
.Pp
|
|
To disable keepalives, the value should be set to
|
|
.Dq no
|
|
in both the server and the client configuration files.
|
|
.It Cm KerberosAuthentication
|
|
Specifies whether Kerberos authentication will be used. The argument to
|
|
this keyword must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
.It Cm KerberosTgtPassing
|
|
Specifies whether a Kerberos TGT will be forwarded to the server. This
|
|
will only work if the Kerberos server is actually an AFS kaserver. The
|
|
argument to this keyword must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
.It Cm LocalForward
|
|
Specifies that a TCP/IP port on the local machine be forwarded over
|
|
the secure channel to given host:port from the remote machine. 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 root can
|
|
forward privileged ports.
|
|
.It Cm PasswordAuthentication
|
|
Specifies whether to use password authentication. The argument to
|
|
this keyword must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
.It Cm LogLevel
|
|
Gives the verbosity level that is used when logging messages from
|
|
.Nm ssh .
|
|
The possible values are:
|
|
QUIET, FATAL, ERROR, INFO, CHAT and DEBUG.
|
|
The default is INFO.
|
|
.It Cm NumberOfPasswordPrompts
|
|
Specifies the number of password prompts before giving up. The
|
|
argument to this keyword must be an integer. Default is 3.
|
|
.It Cm Port
|
|
Specifies the port number to connect on the remote host. Default is
|
|
22.
|
|
.It Cm ProxyCommand
|
|
Specifies the command to use to connect to the server. The command
|
|
string extends to the end of the line, and is executed with /bin/sh.
|
|
In the command string, %h will be substituted by the host name to
|
|
connect and %p by the port. The command can be basically anything,
|
|
and should read from its stdin and write to its stdout. It should
|
|
eventually connect an
|
|
.Xr sshd 8
|
|
server running on some machine, or execute
|
|
.Ic sshd -i
|
|
somewhere. Host key management will be done using the
|
|
HostName of the host being connected (defaulting to the name typed by
|
|
the user).
|
|
.Pp
|
|
.It Cm RemoteForward
|
|
Specifies that a TCP/IP port on the remote machine be forwarded over
|
|
the secure channel to given host:port from the local machine. 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 root can
|
|
forward privileged ports.
|
|
.It Cm RhostsAuthentication
|
|
Specifies whether to try rhosts based authentication. Note that this
|
|
declaration only affects the client side and has no effect whatsoever
|
|
on security. Disabling rhosts authentication may reduce
|
|
authentication time on slow connections when rhosts authentication is
|
|
not used. Most servers do not permit RhostsAuthentication because it
|
|
is not secure (see RhostsRSAAuthentication). The argument to this
|
|
keyword must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
.It Cm RhostsRSAAuthentication
|
|
Specifies whether to try rhosts based authentication with RSA host
|
|
authentication. This is the primary authentication method for most
|
|
sites. The argument must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
.It Cm RSAAuthentication
|
|
Specifies whether to try RSA authentication. The argument to this
|
|
keyword must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
RSA authentication will only be
|
|
attempted if the identity file exists, or an authentication agent is
|
|
running.
|
|
.It Cm SkeyAuthentication
|
|
Specifies whether to use
|
|
.Xr skey 1
|
|
authentication. The argument to
|
|
this keyword must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
The default is
|
|
.Dq no .
|
|
.It Cm CheckHostIP
|
|
If this flag is set to
|
|
.Dq yes ,
|
|
ssh will additionally check the host ip address in the
|
|
.Pa known_hosts
|
|
file. This allows ssh to detect if a host key changed due to DNS spoofing.
|
|
If the option is set to
|
|
.Dq no ,
|
|
the check will not be executed.
|
|
.It Cm StrictHostKeyChecking
|
|
If this flag is set to
|
|
.Dq yes ,
|
|
.Nm
|
|
ssh will never automatically add host keys to the
|
|
.Pa $HOME/.ssh/known_hosts
|
|
file, and refuses to connect hosts whose host key has changed. This
|
|
provides maximum protection against trojan horse attacks. However, it
|
|
can be somewhat annoying if you don't have good
|
|
.Pa /etc/ssh/ssh_known_hosts
|
|
files installed and frequently
|
|
connect new hosts. Basically this option forces the user to manually
|
|
add any new hosts. Normally this option is disabled, and new hosts
|
|
will automatically be added to the known host files. The host keys of
|
|
known hosts will be verified automatically in either case. The
|
|
argument must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
.It Cm User
|
|
Specifies the user to log in as. This can be useful if you have a
|
|
different user name in different machines. This saves the trouble of
|
|
having to remember to give the user name on the command line.
|
|
.It Cm UserKnownHostsFile
|
|
Specifies a file to use instead of
|
|
.Pa $HOME/.ssh/known_hosts .
|
|
.It Cm UsePrivilegedPort
|
|
Specifies whether to use a privileged port for outgoing connections.
|
|
The argument must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
The default is
|
|
.Dq yes .
|
|
Note that setting this option to
|
|
.Dq no
|
|
turns of
|
|
.Cm RhostsAuthentication
|
|
and
|
|
.Cm RhostsRSAAuthentication .
|
|
.It Cm UseRsh
|
|
Specifies that rlogin/rsh should be used for this host. It is
|
|
possible that the host does not at all support the
|
|
.Nm
|
|
protocol. This causes
|
|
.Nm
|
|
to immediately exec
|
|
.Xr rsh 1 .
|
|
All other options (except
|
|
.Cm HostName )
|
|
are ignored if this has been specified. The argument must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
.Sh ENVIRONMENT
|
|
.Nm
|
|
will normally set the following environment variables:
|
|
.Bl -tag -width Ds
|
|
.It Ev DISPLAY
|
|
The
|
|
.Ev DISPLAY
|
|
variable indicates the location of the X11 server. It is
|
|
automatically set by
|
|
.Nm
|
|
to point to a value of the form
|
|
.Dq 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).
|
|
.It Ev HOME
|
|
Set to the path of the user's home directory.
|
|
.It Ev LOGNAME
|
|
Synonym for
|
|
.Ev USER ;
|
|
set for compatibility with systems that use this variable.
|
|
.It Ev MAIL
|
|
Set to point the user's mailbox.
|
|
.It Ev PATH
|
|
Set to the default
|
|
.Ev PATH ,
|
|
as specified when compiling
|
|
.Nm ssh .
|
|
.It Ev SSH_AUTH_SOCK
|
|
indicates the path of a unix-domain socket used to communicate with the
|
|
agent.
|
|
.It Ev SSH_CLIENT
|
|
Identifies the client end of the connection. The variable contains
|
|
three space-separated values: client ip-address, client port number,
|
|
and server port number.
|
|
.It Ev 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.
|
|
.It Ev TZ
|
|
The timezone variable is set to indicate the present timezone if it
|
|
was set when the daemon was started (e.i., the daemon passes the value
|
|
on to new connections).
|
|
.It Ev USER
|
|
Set to the name of the user logging in.
|
|
.El
|
|
.Pp
|
|
Additionally,
|
|
.Nm
|
|
reads
|
|
.Pa $HOME/.ssh/environment ,
|
|
and adds lines of the format
|
|
.Dq VARNAME=value
|
|
to the environment.
|
|
.Sh FILES
|
|
.Bl -tag -width $HOME/.ssh/known_hosts
|
|
.It Pa $HOME/.ssh/known_hosts
|
|
Records host keys for all hosts the user has logged into (that are not
|
|
in
|
|
.Pa /etc/ssh/ssh_known_hosts ) .
|
|
See
|
|
.Xr sshd 8 .
|
|
.It Pa $HOME/.ssh/random_seed
|
|
Used for seeding the random number generator. This file contains
|
|
sensitive data and should read/write for the user and not accessible
|
|
for others. This file is created the first time the program is run
|
|
and updated automatically. The user should never need to read or
|
|
modify this file.
|
|
.It Pa $HOME/.ssh/identity
|
|
Contains the RSA authentication identity of the user. This file
|
|
contains sensitive data and should be readable by the user but not
|
|
accessible by others (read/write/execute).
|
|
Note that
|
|
.Nm
|
|
ignores this 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.
|
|
.It Pa $HOME/.ssh/identity.pub
|
|
Contains the public key for authentication (public part of the
|
|
identity file in human-readable form). The contents of this file
|
|
should be added to
|
|
.Pa $HOME/.ssh/authorized_keys
|
|
on all machines
|
|
where you wish to log in using RSA authentication. This file is not
|
|
sensitive and can (but need not) be readable by anyone. This file is
|
|
never used automatically and is not necessary; it is only provided for
|
|
the convenience of the user.
|
|
.It Pa $HOME/.ssh/config
|
|
This is the per-user configuration file. The format of this file is
|
|
described above. This file is used by the
|
|
.Nm
|
|
client. This file does not usually contain any sensitive information,
|
|
but the recommended permissions are read/write for the user, and not
|
|
accessible by others.
|
|
.It Pa $HOME/.ssh/authorized_keys
|
|
Lists the RSA keys that can be used for logging in as this user. The
|
|
format of this file is described in the
|
|
.Xr 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, separated by
|
|
spaces). This file is not highly sensitive, but the recommended
|
|
permissions are read/write for the user, and not accessible by others.
|
|
.It Pa /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 world-readable. This file contains
|
|
public keys, one per line, in the following format (fields separated
|
|
by spaces): system name, number of bits in modulus, 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
|
|
.Xr sshd 8
|
|
manual page.
|
|
.Pp
|
|
The canonical system name (as returned by name servers) is used by
|
|
.Xr sshd 8
|
|
to verify the client host when logging in; other names are needed because
|
|
.Nm
|
|
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.
|
|
.It Pa /etc/ssh/ssh_config
|
|
Systemwide configuration file. This file provides defaults for those
|
|
values that are not specified in the user's configuration file, and
|
|
for those users who do not have a configuration file. This file must
|
|
be world-readable.
|
|
.It Pa $HOME/.rhosts
|
|
This file is used in
|
|
.Pa \&.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. One some machines this file may need to be
|
|
world-readable if the user's home directory is on a NFS partition,
|
|
because
|
|
.Xr 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.
|
|
.Pp
|
|
Note that by default
|
|
.Xr sshd 8
|
|
will be installed so that it requires successful RSA host
|
|
authentication before permitting \s+2.\s0rhosts authentication. If your
|
|
server machine does not have the client's host key in
|
|
.Pa /etc/ssh/ssh_known_hosts ,
|
|
you can store it in
|
|
.Pa $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 inxi
|
|
.Pa $HOME/.ssh/known_hosts .
|
|
.It Pa $HOME/.shosts
|
|
This file is used exactly the same way as
|
|
.Pa \&.rhosts .
|
|
The purpose for
|
|
having this file is to be able to use rhosts authentication with
|
|
.Nm
|
|
without permitting login with
|
|
.Xr rlogin 1
|
|
or
|
|
.Xr rsh 1 .
|
|
.It Pa /etc/hosts.equiv
|
|
This file is used during
|
|
.Pa \&.rhosts authentication. It contains
|
|
canonical hosts names, one per line (the full format is described on
|
|
the
|
|
.Xr 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.
|
|
.It Pa /etc/ssh/shosts.equiv
|
|
This file is processed exactly as
|
|
.Pa /etc/hosts.equiv .
|
|
This file may be useful to permit logins using
|
|
.Nm
|
|
but not using rsh/rlogin.
|
|
.It Pa /etc/ssh/sshrc
|
|
Commands in this file are executed by
|
|
.Nm
|
|
when the user logs in just before the user's shell (or command) is started.
|
|
See the
|
|
.Xr sshd 8
|
|
manual page for more information.
|
|
.It Pa $HOME/.ssh/rc
|
|
Commands in this file are executed by
|
|
.Nm
|
|
when the user logs in just before the user's shell (or command) is
|
|
started.
|
|
See the
|
|
.Xr sshd 8
|
|
manual page for more information.
|
|
.It Pa libcrypto.so.X.1
|
|
A version of this library which includes support for the RSA algorithm
|
|
is required for proper operation.
|
|
.Sh AUTHOR
|
|
Tatu Ylonen <ylo@cs.hut.fi>
|
|
.Pp
|
|
Issues can be found from the SSH WWW home page:
|
|
.Pp
|
|
.Dl http://www.cs.hut.fi/ssh
|
|
.Pp
|
|
OpenSSH
|
|
is a derivative of the original (free) ssh 1.2.12 release, but with bugs
|
|
removed and newer features re-added. Rapidly after the 1.2.12 release,
|
|
newer versions bore successively more restrictive licenses. This version
|
|
of OpenSSH
|
|
.Bl -bullet
|
|
.It
|
|
has all components of a restrictive nature (ie. 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.
|
|
.It
|
|
contains added support for
|
|
.Xr kerberos 8
|
|
authentication and ticket passing.
|
|
.It
|
|
supports one-time password authentication with
|
|
.Xr skey 1 .
|
|
.El
|
|
.Pp
|
|
The libraries described in
|
|
.Xr ssl 8
|
|
are required for proper operation.
|
|
.Pp
|
|
OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl,
|
|
Niels Provos, Theo de Raadt, and Dug Song.
|
|
.Sh SEE ALSO
|
|
.Xr rlogin 1 ,
|
|
.Xr rsh 1 ,
|
|
.Xr scp 1 ,
|
|
.Xr ssh-add 1 ,
|
|
.Xr ssh-agent 1 ,
|
|
.Xr ssh-keygen 1 ,
|
|
.Xr telnet 1 ,
|
|
.Xr sshd 8 ,
|
|
.Xr ssl 8
|