1.\" $OpenBSD: ssh-agent.1,v 1.35 2002/06/24 13:12:23 markus Exp $ 2.\" 3.\" Author: Tatu Ylonen <ylo@cs.hut.fi> 4.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland 5.\" All rights reserved 6.\" 7.\" As far as I am concerned, the code I have written for this software 8.\" can be used freely for any purpose. Any derived versions of this 9.\" software must be clearly marked as such, and if the derived work is 10.\" incompatible with the protocol description in the RFC file, it must be 11.\" called by a name other than "ssh" or "Secure Shell". 12.\" 13.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. 14.\" Copyright (c) 1999 Aaron Campbell. All rights reserved. 15.\" Copyright (c) 1999 Theo de Raadt. All rights reserved. 16.\" 17.\" Redistribution and use in source and binary forms, with or without 18.\" modification, are permitted provided that the following conditions 19.\" are met: 20.\" 1. Redistributions of source code must retain the above copyright 21.\" notice, this list of conditions and the following disclaimer. 22.\" 2. Redistributions in binary form must reproduce the above copyright 23.\" notice, this list of conditions and the following disclaimer in the 24.\" documentation and/or other materials provided with the distribution. 25.\" 26.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 27.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 28.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 29.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 30.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 31.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 32.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 33.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 34.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 35.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 36.\" 37.Dd September 25, 1999 38.Dt SSH-AGENT 1 39.Os 40.Sh NAME 41.Nm ssh-agent 42.Nd authentication agent 43.Sh SYNOPSIS 44.Nm ssh-agent 45.Op Fl a Ar bind_address 46.Op Fl c Li | Fl s 47.Op Fl d 48.Op Ar command Op Ar args ... 49.Nm ssh-agent 50.Op Fl c Li | Fl s 51.Fl k 52.Sh DESCRIPTION 53.Nm 54is a program to hold private keys used for public key authentication 55(RSA, DSA). 56The idea is that 57.Nm 58is started in the beginning of an X-session or a login session, and 59all other windows or programs are started as clients to the ssh-agent 60program. 61Through use of environment variables the agent can be located 62and automatically used for authentication when logging in to other 63machines using 64.Xr ssh 1 . 65.Pp 66The options are as follows: 67.Bl -tag -width Ds 68.It Fl a Ar bind_address 69Bind the agent to the unix-domain socket 70.Ar bind_address . 71The default is 72.Pa /tmp/ssh-XXXXXXXX/agent.<ppid> . 73.It Fl c 74Generate C-shell commands on 75.Dv stdout . 76This is the default if 77.Ev SHELL 78looks like it's a csh style of shell. 79.It Fl s 80Generate Bourne shell commands on 81.Dv stdout . 82This is the default if 83.Ev SHELL 84does not look like it's a csh style of shell. 85.It Fl k 86Kill the current agent (given by the 87.Ev SSH_AGENT_PID 88environment variable). 89.It Fl d 90Debug mode. When this option is specified 91.Nm 92will not fork. 93.El 94.Pp 95If a commandline is given, this is executed as a subprocess of the agent. 96When the command dies, so does the agent. 97.Pp 98The agent initially does not have any private keys. 99Keys are added using 100.Xr ssh-add 1 . 101When executed without arguments, 102.Xr ssh-add 1 103adds the files 104.Pa $HOME/.ssh/id_rsa , 105.Pa $HOME/.ssh/id_dsa 106and 107.Pa $HOME/.ssh/identity . 108If the identity has a passphrase, 109.Xr ssh-add 1 110asks for the passphrase (using a small X11 application if running 111under X11, or from the terminal if running without X). 112It then sends the identity to the agent. 113Several identities can be stored in the 114agent; the agent can automatically use any of these identities. 115.Ic ssh-add -l 116displays the identities currently held by the agent. 117.Pp 118The idea is that the agent is run in the user's local PC, laptop, or 119terminal. 120Authentication data need not be stored on any other 121machine, and authentication passphrases never go over the network. 122However, the connection to the agent is forwarded over SSH 123remote logins, and the user can thus use the privileges given by the 124identities anywhere in the network in a secure way. 125.Pp 126There are two main ways to get an agent setup: 127Either the agent starts a new subcommand into which some environment 128variables are exported, or the agent prints the needed shell commands 129(either 130.Xr sh 1 131or 132.Xr csh 1 133syntax can be generated) which can be evalled in the calling shell. 134Later 135.Xr ssh 1 136looks at these variables and uses them to establish a connection to the agent. 137.Pp 138The agent will never send a private key over its request channel. 139Instead, operations that require a private key will be performed 140by the agent, and the result will be returned to the requester. 141This way, private keys are not exposed to clients using the agent. 142.Pp 143A unix-domain socket is created 144and the name of this socket is stored in the 145.Ev SSH_AUTH_SOCK 146environment 147variable. 148The socket is made accessible only to the current user. 149This method is easily abused by root or another instance of the same 150user. 151.Pp 152The 153.Ev SSH_AGENT_PID 154environment variable holds the agent's process ID. 155.Pp 156The agent exits automatically when the command given on the command 157line terminates. 158.Sh FILES 159.Bl -tag -width Ds 160.It Pa $HOME/.ssh/identity 161Contains the protocol version 1 RSA authentication identity of the user. 162.It Pa $HOME/.ssh/id_dsa 163Contains the protocol version 2 DSA authentication identity of the user. 164.It Pa $HOME/.ssh/id_rsa 165Contains the protocol version 2 RSA authentication identity of the user. 166.It Pa /tmp/ssh-XXXXXXXX/agent.<ppid> 167Unix-domain sockets used to contain the connection to the 168authentication agent. 169These sockets should only be readable by the owner. 170The sockets should get automatically removed when the agent exits. 171.El 172.Sh AUTHORS 173OpenSSH is a derivative of the original and free 174ssh 1.2.12 release by Tatu Ylonen. 175Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 176Theo de Raadt and Dug Song 177removed many bugs, re-added newer features and 178created OpenSSH. 179Markus Friedl contributed the support for SSH 180protocol versions 1.5 and 2.0. 181.Sh SEE ALSO 182.Xr ssh 1 , 183.Xr ssh-add 1 , 184.Xr ssh-keygen 1 , 185.Xr sshd 8 186