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SSH-AGENT(1) System Reference Manual SSH-AGENT(1)
NAME
ssh-agent - authentication agent
SYNOPSIS
ssh-agent [-c | -s] [-k] [command [args ...]]
DESCRIPTION
ssh-agent is a program to hold private keys used for RSA authentication.
The idea is that ssh-agent is started in the beginning of an X-session or
a login session, and all other windows or programs are started as clients
to the ssh-agent program. Through use of environment variables the agent
can be located and automatically used for RSA 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).
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 arguments, 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 iden-
tity 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 currently held by the agent.
The idea is that the agent is run in the user's local PC, laptop, or ter-
minal. Authentication data need not be stored on any other machine, and
authentication passphrases never go over the network. However, the con-
nection to the agent is forwarded over SSH remote logins, and the user
can thus use the privileges given by the identities anywhere in the net-
work in a secure way.
There are two main ways to get an agent setup: Either you let the agent
start a new subcommand into which some environment variables are export-
ed, or you let the agent print 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) look at these variables and use them to establish a
connection to the agent.
A unix-domain socket is created (/tmp/ssh-XXXXXXXX/agent.<pid>), 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 RSA authentication identity of the user. This file
should not be readable by anyone but the user. It is possible to
specify 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.
/tmp/ssh-XXXX/agent.<pid>,
Unix-domain sockets used to contain the connection to the authen-
tication agent. These sockets should only be readable by the
owner. The sockets should get automatically removed when the
agent exits.
AUTHOR
Tatu Ylonen <ylo@cs.hut.fi>
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
o has all components of a restrictive nature (i.e., patents) directly
removed from the source code; any licensed or patented components are
chosen from external libraries.
o has been updated to support ssh protocol 1.5.
o contains added support for kerberos(8) authentication and ticket
passing.
o supports one-time password authentication with skey(1).
SEE ALSO
ssh(1), ssh-add(1), ssh-keygen(1), sshd(8),
BSD Experimental September 25, 1999 2
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