1.\" $OpenBSD: ssh-agent.1,v 1.53 2010/11/21 01:01:13 djm Exp $ 2.\" $FreeBSD$ 3.\" 4.\" Author: Tatu Ylonen <ylo@cs.hut.fi> 5.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland 6.\" All rights reserved 7.\" 8.\" As far as I am concerned, the code I have written for this software 9.\" can be used freely for any purpose. Any derived versions of this 10.\" software must be clearly marked as such, and if the derived work is 11.\" incompatible with the protocol description in the RFC file, it must be 12.\" called by a name other than "ssh" or "Secure Shell". 13.\" 14.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. 15.\" Copyright (c) 1999 Aaron Campbell. All rights reserved. 16.\" Copyright (c) 1999 Theo de Raadt. All rights reserved. 17.\" 18.\" Redistribution and use in source and binary forms, with or without 19.\" modification, are permitted provided that the following conditions 20.\" are met: 21.\" 1. Redistributions of source code must retain the above copyright 22.\" notice, this list of conditions and the following disclaimer. 23.\" 2. Redistributions in binary form must reproduce the above copyright 24.\" notice, this list of conditions and the following disclaimer in the 25.\" documentation and/or other materials provided with the distribution. 26.\" 27.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 28.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 29.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 30.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 31.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 32.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 33.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 34.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 35.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 36.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 37.\" 38.Dd November 21, 2010 39.Dt SSH-AGENT 1 40.Os 41.Sh NAME 42.Nm ssh-agent 43.Nd authentication agent 44.Sh SYNOPSIS 45.Nm ssh-agent 46.Op Fl c | s 47.Op Fl dx 48.Op Fl a Ar bind_address 49.Op Fl t Ar life 50.Op Ar command Op Ar arg ... 51.Nm ssh-agent 52.Op Fl c | s 53.Fl k 54.Sh DESCRIPTION 55.Nm 56is a program to hold private keys used for public key authentication 57(RSA, DSA, ECDSA). 58The idea is that 59.Nm 60is started in the beginning of an X-session or a login session, and 61all other windows or programs are started as clients to the ssh-agent 62program. 63Through use of environment variables the agent can be located 64and automatically used for authentication when logging in to other 65machines using 66.Xr ssh 1 . 67.Pp 68The options are as follows: 69.Bl -tag -width Ds 70.It Fl a Ar bind_address 71Bind the agent to the 72.Ux Ns -domain 73socket 74.Ar bind_address . 75The default is 76.Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt . 77.It Fl c 78Generate C-shell commands on 79.Dv stdout . 80This is the default if 81.Ev SHELL 82looks like it's a csh style of shell. 83.It Fl d 84Debug mode. 85When this option is specified 86.Nm 87will not fork. 88.It Fl k 89Kill the current agent (given by the 90.Ev SSH_AGENT_PID 91environment variable). 92.It Fl s 93Generate Bourne shell commands on 94.Dv stdout . 95This is the default if 96.Ev SHELL 97does not look like it's a csh style of shell. 98.It Fl t Ar life 99Set a default value for the maximum lifetime of identities added to the agent. 100The lifetime may be specified in seconds or in a time format specified in 101.Xr sshd_config 5 . 102A lifetime specified for an identity with 103.Xr ssh-add 1 104overrides this value. 105Without this option the default maximum lifetime is forever. 106.It Fl x 107Exit after the last client has disconnected. 108.El 109.Pp 110If a commandline is given, this is executed as a subprocess of the agent. 111When the command dies, so does the agent. 112.Pp 113The agent initially does not have any private keys. 114Keys are added using 115.Xr ssh-add 1 . 116When executed without arguments, 117.Xr ssh-add 1 118adds the files 119.Pa ~/.ssh/id_rsa , 120.Pa ~/.ssh/id_dsa , 121.Pa ~/.ssh/id_ecdsa 122and 123.Pa ~/.ssh/identity . 124If the identity has a passphrase, 125.Xr ssh-add 1 126asks for the passphrase on the terminal if it has one or from a small X11 127program if running under X11. 128If neither of these is the case then the authentication will fail. 129It then sends the identity to the agent. 130Several identities can be stored in the 131agent; the agent can automatically use any of these identities. 132.Ic ssh-add -l 133displays the identities currently held by the agent. 134.Pp 135The idea is that the agent is run in the user's local PC, laptop, or 136terminal. 137Authentication data need not be stored on any other 138machine, and authentication passphrases never go over the network. 139However, the connection to the agent is forwarded over SSH 140remote logins, and the user can thus use the privileges given by the 141identities anywhere in the network in a secure way. 142.Pp 143There are two main ways to get an agent set up: 144The first is that the agent starts a new subcommand into which some environment 145variables are exported, eg 146.Cm ssh-agent xterm & . 147The second is that the agent prints the needed shell commands (either 148.Xr sh 1 149or 150.Xr csh 1 151syntax can be generated) which can be evaluated in the calling shell, eg 152.Cm eval `ssh-agent -s` 153for Bourne-type shells such as 154.Xr sh 1 155or 156.Xr ksh 1 157and 158.Cm eval `ssh-agent -c` 159for 160.Xr csh 1 161and derivatives. 162.Pp 163Later 164.Xr ssh 1 165looks at these variables and uses them to establish a connection to the agent. 166.Pp 167The agent will never send a private key over its request channel. 168Instead, operations that require a private key will be performed 169by the agent, and the result will be returned to the requester. 170This way, private keys are not exposed to clients using the agent. 171.Pp 172A 173.Ux Ns -domain 174socket is created and the name of this socket is stored in the 175.Ev SSH_AUTH_SOCK 176environment 177variable. 178The socket is made accessible only to the current user. 179This method is easily abused by root or another instance of the same 180user. 181.Pp 182The 183.Ev SSH_AGENT_PID 184environment variable holds the agent's process ID. 185.Pp 186The agent exits automatically when the command given on the command 187line terminates. 188.Sh FILES 189.Bl -tag -width Ds 190.It Pa ~/.ssh/identity 191Contains the protocol version 1 RSA authentication identity of the user. 192.It Pa ~/.ssh/id_dsa 193Contains the protocol version 2 DSA authentication identity of the user. 194.It Pa ~/.ssh/id_ecdsa 195Contains the protocol version 2 ECDSA authentication identity of the user. 196.It Pa ~/.ssh/id_rsa 197Contains the protocol version 2 RSA authentication identity of the user. 198.It Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt 199.Ux Ns -domain 200sockets used to contain the connection to the authentication agent. 201These sockets should only be readable by the owner. 202The sockets should get automatically removed when the agent exits. 203.El 204.Sh SEE ALSO 205.Xr ssh 1 , 206.Xr ssh-add 1 , 207.Xr ssh-keygen 1 , 208.Xr sshd 8 209.Sh AUTHORS 210OpenSSH is a derivative of the original and free 211ssh 1.2.12 release by Tatu Ylonen. 212Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 213Theo de Raadt and Dug Song 214removed many bugs, re-added newer features and 215created OpenSSH. 216Markus Friedl contributed the support for SSH 217protocol versions 1.5 and 2.0. 218