118 lines
5.3 KiB
Plaintext
118 lines
5.3 KiB
Plaintext
SSH-AGENT(1) OpenBSD Reference Manual SSH-AGENT(1)
|
|
|
|
NAME
|
|
ssh-agent - authentication agent
|
|
|
|
SYNOPSIS
|
|
ssh-agent [-c | -s] [-d] [-a bind_address] [-t life] [command [arg ...]]
|
|
ssh-agent [-c | -s] -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:
|
|
|
|
-a bind_address
|
|
Bind the agent to the unix-domain socket bind_address. The de-
|
|
fault is /tmp/ssh-XXXXXXXXXX/agent.<ppid>.
|
|
|
|
-c Generate C-shell commands on stdout. This is the default if
|
|
SHELL looks like it's a csh style of shell.
|
|
|
|
-d Debug mode. When this option is specified ssh-agent will not
|
|
fork.
|
|
|
|
-k Kill the current agent (given by the SSH_AGENT_PID environment
|
|
variable).
|
|
|
|
-s Generate Bourne shell commands on stdout. This is the default if
|
|
SHELL does not look like it's a csh style of shell.
|
|
|
|
-t life
|
|
Set a default value for the maximum lifetime of identities added
|
|
to the agent. The lifetime may be specified in seconds or in a
|
|
time format specified in sshd_config(5). A lifetime specified
|
|
for an identity with ssh-add(1) overrides this value. Without
|
|
this option the default maximum lifetime is forever.
|
|
|
|
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 files
|
|
~/.ssh/id_rsa, ~/.ssh/id_dsa and ~/.ssh/identity. If the identity has a
|
|
passphrase, ssh-add(1) asks for the passphrase (using a small X11 appli-
|
|
cation 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 identi-
|
|
ties. 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 set up: The first is that the
|
|
agent starts a new subcommand into which some environment variables are
|
|
exported, eg ssh-agent xterm &. The second is that the agent prints the
|
|
needed shell commands (either sh(1) or csh(1) syntax can be generated)
|
|
which can be evaluated in the calling shell, eg eval `ssh-agent -s` for
|
|
Bourne-type shells such as sh(1) or ksh(1) and eval `ssh-agent -c` for
|
|
csh(1) and derivatives.
|
|
|
|
Later ssh(1) looks at these variables and uses them to establish a con-
|
|
nection to the agent.
|
|
|
|
The agent will never send a private key over its request channel. In-
|
|
stead, operations that require a private key will be performed by the
|
|
agent, and the result will be returned to the requester. This way, pri-
|
|
vate keys are not exposed to clients using the agent.
|
|
|
|
A unix-domain socket is created 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 anoth-
|
|
er instance of the same user.
|
|
|
|
The SSH_AGENT_PID environment variable holds the agent's process ID.
|
|
|
|
The agent exits automatically when the command given on the command line
|
|
terminates.
|
|
|
|
FILES
|
|
~/.ssh/identity
|
|
Contains the protocol version 1 RSA authentication identity of
|
|
the user.
|
|
|
|
~/.ssh/id_dsa
|
|
Contains the protocol version 2 DSA authentication identity of
|
|
the user.
|
|
|
|
~/.ssh/id_rsa
|
|
Contains the protocol version 2 RSA authentication identity of
|
|
the user.
|
|
|
|
/tmp/ssh-XXXXXXXXXX/agent.<ppid>
|
|
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.
|
|
|
|
SEE ALSO
|
|
ssh(1), ssh-add(1), ssh-keygen(1), sshd(8)
|
|
|
|
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.
|
|
|
|
OpenBSD 4.6 March 26, 2009 2
|