Manual Pages for UNIX Darwin command on man ssh-agent

SSH-AGENT(1) BSD General Commands Manual SSH-AGENT(1)

NAME

sssshh-aaggeenntt - authentication agent

SYNOPSIS

sssshh-aaggeenntt [-cc | -ss] [-dd] [-aa bindaddress] [-tt life] [command [arg ...]]

sssshh-aaggeenntt [-cc | -ss] -kk

DESCRIPTION

sssshh-aaggeenntt is a program to hold private keys used for public key authenti-

cation (RSA, DSA). The idea is that sssshh-aaggeenntt 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:

-aa bindaddress

Bind the agent to the unix-domain socket bindaddress. The

default is /tmp/ssh-XXXXXXXXXX/agent..

-cc Generate C-shell commands on stdout. This is the default if

SHELL looks like it's a csh style of shell.

-dd Debug mode. When this option is specified sssshh-aaggeenntt will not

fork.

-kk Kill the current agent (given by the SSHAGENTPID environment

variable).

-ss Generate Bourne shell commands on stdout. This is the default if

SHELL does not look like it's a csh style of shell.

-tt 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 sshdconfig(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/idrsa, ~/.ssh/iddsa 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. sssshh-aadddd -ll 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 sssshh-aaggeenntt xxtteerrmm &&. The second is that 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, eg eevvaall ``sssshh-aaggeenntt -ss`` for

Bourne-type shells such as sh(1) or ksh(1) and eevvaall ``sssshh-aaggeenntt -cc`` 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. Instead, 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 SSHAUTHSOCK 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 SSHAGENTPID 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/iddsa Contains the protocol version 2 DSA authentication identity of the user. ~/.ssh/idrsa Contains the protocol version 2 RSA authentication identity of the user.

/tmp/ssh-XXXXXXXXXX/agent.

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.