MAN page from Trustix openssh-clients-3.6.1p2-5tr.i586.rpm


Section: User Commands (1)
BSD mandoc


ssh-agent - authentication agent 


ssh-agent[-a bind_address][-c | -s][-t life][-d][command [args ...]]
ssh-agent[-c | -s]-k 


ssh-agentis a program to hold private keys used for public key authentication(RSA, DSA).The idea is thatssh-agentis started in the beginning of an X-session or a login session, andall other windows or programs are started as clients to the ssh-agentprogram.Through use of environment variables the agent can be locatedand automatically used for authentication when logging in to othermachines usingssh(1).

The options are as follows:

-a bind_address
Bind the agent to the unix-domain socketbind_address The default is/tmp/ssh-XXXXXXXX/agent.<ppid>
Generate C-shell commands onstdout This is the default ifSHELLlooks like it's a csh style of shell.
Generate Bourne shell commands onstdout This is the default ifSHELLdoes not look like it's a csh style of shell.
Kill the current agent (given by theSSH_AGENT_PIDenvironment variable).
-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 insshd(8).A lifetime specified for an identity withssh-add1overrides this value.Without this option the default maximum lifetime is forever.
Debug mode.When this option is specifiedssh-agentwill 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 usingssh-add1.When executed without arguments,ssh-add1adds the files$HOME/.ssh/id_rsa $HOME/.ssh/id_dsaand$HOME/.ssh/identity If the identity has a passphrase,ssh-add1asks for the passphrase (using a small X11 application if runningunder X11, or from the terminal if running without X).It then sends the identity to the agent.Several identities can be stored in theagent; the agent can automatically use any of these identities.ssh-add -ldisplays the identities currently held by the agent.

The idea is that the agent is run in the user's local PC, laptop, orterminal.Authentication data need not be stored on any othermachine, and authentication passphrases never go over the network.However, the connection to the agent is forwarded over SSHremote logins, and the user can thus use the privileges given by theidentities 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 environmentvariables are exported, or the agent prints the needed shell commands(eithersh(1)orcsh(1)syntax can be generated) which can be evalled in the calling shell.Laterssh(1)looks at these variables and uses them to establish a connection to the agent.

The agent will never send a private key over its request channel.Instead, operations that require a private key will be performedby the agent, and the result will be returned to the requester.This way, private keys are not exposed to clients using the agent.

A unix-domain socket is createdand the name of this socket is stored in theSSH_AUTH_SOCKenvironmentvariable.The socket is made accessible only to the current user.This method is easily abused by root or another instance of the sameuser.

TheSSH_AGENT_PIDenvironment variable holds the agent's process ID.

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


Contains the protocol version 1 RSA authentication identity of the user.
Contains the protocol version 2 DSA authentication identity of the user.
Contains the protocol version 2 RSA authentication identity of the user.
Unix-domain sockets used to contain the connection to theauthentication agent.These sockets should only be readable by the owner.The sockets should get automatically removed when the agent exits.



OpenSSH is a derivative of the original and freessh 1.2.12 release by Tatu Ylonen.Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,Theo de Raadt and Dug Songremoved many bugs, re-added newer features andcreated OpenSSH.Markus Friedl contributed the support for SSHprotocol versions 1.5 and 2.0. 






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