View Source: ssh-agent(1) - Waikato Linux Users Group

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__NAME__


ssh-agent - authentication agent
__SYNOPSIS__


ssh-agent [[-c | -s] [[-d] [[command [[args ...]]


ssh-agent [[-c | -s] -k
__DESCRIPTION__


ssh-agent is a program to hold private keys used for public
key authentication (RSA, DSA). The idea is that ssh-agent is
started in the beginning of an X-session or a login ses-
sion, and all other windows or programs are started as
clients to the ssh-agent program. Through use of environ-
ment variables the agent can be located and automatically
used for authentication when logging in to other machines
using ssh(1).


The options are as follows:
       -c   Generate C-shell commands on  stdout
. This is the default if SHELL looks like it's
a csh style of shell.


-s
Generate Bourne shell commands on stdout. This is the default if SHELL does not look like it's a csh style of shell.


-k
Kill the current agent (given by the SSH_AGENT_PID
environment variable).


-d
Debug mode. When this option is specified ssh-agent will not
fork.


If a commandline is given, this is executed as a subprocess
of the agent. When the command dies, so does the
agent.


The agent initially does not have any private keys. Keys are
added using ssh-add(1). When executed without argu-
ments, ssh-add(1) adds the
$HOME/.ssh/identity file. If the identity has a
passphrase, ssh-add(1) asks for the passphrase
(using a small X11 application if running under X11, or from
the terminal if running without X). It then sends the
identity to the agent. Several identities can be stored in
the agent; the agent can automatically use any of these
identities. ssh-add -l displays the identities cur- rently
held by the agent.


The idea is that the agent is run in the user's local PC,
laptop, or terminal. Authentication data need not be stored
on any other machine, and authentication passphrases never
go over the network. However, the connection to the agent is
forwarded over SSH remote logins, and the user can thus use
the privileges given by the identities anywhere in the
network in a secure way.


There are two main ways to get an agent setup: Either the
agent starts a new subcommand into which some environment
variables are exported, or the agent prints the needed shell
commands (either sh(1) or csh(1) syntax
can be generated) which can be evalled in the calling shell.
Later ssh(1) looks at these variables and uses them
to establish a con- nection to the agent.


A unix-domain socket is created
(/tmp/ssh-XXXXXXXX/agent.), and the name
of this socket is stored in the SSH_AUTH_SOCK
environment variable. The socket is made accessible only to
the current user. This method is easily abused by root or
another instance of the same user.


The SSH_AGENT_PID environment variable holds the
agent's PID.


The agent exits automatically when the command given on the
command line terminates.


__FILES__
       $HOME/.ssh/identity


Contains the protocol version 1 RSA authentication identity
of the user. This file should not be read- able by anyone
but the user. It is possible to spec- ify a passphrase when
generating the key; that passphrase will be used to encrypt
the private part of this file. This file is not used by
ssh-agent but is normally added to the agent using
ssh-add(1) at login time.


$HOME/.ssh/id_dsa
Contains the protocol version 2 DSA authentication identity
of the user.


$HOME/.ssh/id_rsa
Contains the protocol version 2 RSA authentication identity
of the user.


/tmp/ssh-XXXXXXXX/agent.
Unix-domain sockets used to contain the connection to the
authentication agent. These sockets should only be readable
by the owner. The sockets should get automatically removed
when the agent exits.


__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 ver-
sions 1.5 and 2.0.
__SEE ALSO__


ssh(1), ssh-add(1),
ssh-keygen(1), sshd(8)


BSD September 25, 1999 1
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14 pages link to ssh-agent(1):
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Last edited on Monday, June 3, 2002 11:56:09 pm by "perry"
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