ssh-agent command args ...
ssh-agent [-c | -s]
ssh-agent -k
DESCRIPTION
ssh-agent is a program to hold private keys used for public key authenti
cation (RSA, DSA). The idea is that ssh-agent is started in the begin
ning of an X-session or a login session, and all other windows or pro
grams are started as clients to the ssh-agent program. Through use of
environment 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).
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) looks at these variables and uses 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.
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.<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.
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 cre
ated OpenSSH. Markus Friedl contributed the support for SSH protocol
versions 1.5 and 2.0.
SEE ALSO
ssh(1), ssh-add(1), ssh-keygen(1), sshd(8)
BSD Experimental September 25, 1999 2
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