1.\" $OpenBSD: ssh-agent.1,v 1.49 2009/10/22 15:02:12 sobrado 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 $Mdocdate: October 22 2009 $ 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 c Li | Fl s 46.Op Fl d 47.Op Fl a Ar bind_address 48.Op Fl t Ar life 49.Op Ar command Op Ar arg ... 50.Nm ssh-agent 51.Op Fl c Li | Fl s 52.Fl k 53.Sh DESCRIPTION 54.Nm 55is a program to hold private keys used for public key authentication 56(RSA, DSA). 57The idea is that 58.Nm 59is started in the beginning of an X-session or a login session, and 60all other windows or programs are started as clients to the ssh-agent 61program. 62Through use of environment variables the agent can be located 63and automatically used for authentication when logging in to other 64machines using 65.Xr ssh 1 . 66.Pp 67The options are as follows: 68.Bl -tag -width Ds 69.It Fl a Ar bind_address 70Bind the agent to the 71.Ux Ns -domain 72socket 73.Ar bind_address . 74The default is 75.Pa /tmp/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt . 76.It Fl c 77Generate C-shell commands on 78.Dv stdout . 79This is the default if 80.Ev SHELL 81looks like it's a csh style of shell. 82.It Fl d 83Debug mode. 84When this option is specified 85.Nm 86will not fork. 87.It Fl k 88Kill the current agent (given by the 89.Ev SSH_AGENT_PID 90environment variable). 91.It Fl s 92Generate Bourne shell commands on 93.Dv stdout . 94This is the default if 95.Ev SHELL 96does not look like it's a csh style of shell. 97.It Fl t Ar life 98Set a default value for the maximum lifetime of identities added to the agent. 99The lifetime may be specified in seconds or in a time format specified in 100.Xr sshd_config 5 . 101A lifetime specified for an identity with 102.Xr ssh-add 1 103overrides this value. 104Without this option the default maximum lifetime is forever. 105.El 106.Pp 107If a commandline is given, this is executed as a subprocess of the agent. 108When the command dies, so does the agent. 109.Pp 110The agent initially does not have any private keys. 111Keys are added using 112.Xr ssh-add 1 . 113When executed without arguments, 114.Xr ssh-add 1 115adds the files 116.Pa ~/.ssh/id_rsa , 117.Pa ~/.ssh/id_dsa 118and 119.Pa ~/.ssh/identity . 120If the identity has a passphrase, 121.Xr ssh-add 1 122asks for the passphrase (using a small X11 application if running 123under X11, or from the terminal if running without X). 124It then sends the identity to the agent. 125Several identities can be stored in the 126agent; the agent can automatically use any of these identities. 127.Ic ssh-add -l 128displays the identities currently held by the agent. 129.Pp 130The idea is that the agent is run in the user's local PC, laptop, or 131terminal. 132Authentication data need not be stored on any other 133machine, and authentication passphrases never go over the network. 134However, the connection to the agent is forwarded over SSH 135remote logins, and the user can thus use the privileges given by the 136identities anywhere in the network in a secure way. 137.Pp 138There are two main ways to get an agent set up: 139The first is that the agent starts a new subcommand into which some environment 140variables are exported, eg 141.Cm ssh-agent xterm & . 142The second is that the agent prints the needed shell commands (either 143.Xr sh 1 144or 145.Xr csh 1 146syntax can be generated) which can be evaluated in the calling shell, eg 147.Cm eval `ssh-agent -s` 148for Bourne-type shells such as 149.Xr sh 1 150or 151.Xr ksh 1 152and 153.Cm eval `ssh-agent -c` 154for 155.Xr csh 1 156and derivatives. 157.Pp 158Later 159.Xr ssh 1 160looks at these variables and uses them to establish a connection to the agent. 161.Pp 162The agent will never send a private key over its request channel. 163Instead, operations that require a private key will be performed 164by the agent, and the result will be returned to the requester. 165This way, private keys are not exposed to clients using the agent. 166.Pp 167A 168.Ux Ns -domain 169socket is created and the name of this socket is stored in the 170.Ev SSH_AUTH_SOCK 171environment 172variable. 173The socket is made accessible only to the current user. 174This method is easily abused by root or another instance of the same 175user. 176.Pp 177The 178.Ev SSH_AGENT_PID 179environment variable holds the agent's process ID. 180.Pp 181The agent exits automatically when the command given on the command 182line terminates. 183.Sh FILES 184.Bl -tag -width Ds 185.It Pa ~/.ssh/identity 186Contains the protocol version 1 RSA authentication identity of the user. 187.It Pa ~/.ssh/id_dsa 188Contains the protocol version 2 DSA authentication identity of the user. 189.It Pa ~/.ssh/id_rsa 190Contains the protocol version 2 RSA authentication identity of the user. 191.It Pa /tmp/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt 192.Ux Ns -domain 193sockets used to contain the connection to the authentication agent. 194These sockets should only be readable by the owner. 195The sockets should get automatically removed when the agent exits. 196.El 197.Sh SEE ALSO 198.Xr ssh 1 , 199.Xr ssh-add 1 , 200.Xr ssh-keygen 1 , 201.Xr sshd 8 202.Sh AUTHORS 203OpenSSH is a derivative of the original and free 204ssh 1.2.12 release by Tatu Ylonen. 205Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 206Theo de Raadt and Dug Song 207removed many bugs, re-added newer features and 208created OpenSSH. 209Markus Friedl contributed the support for SSH 210protocol versions 1.5 and 2.0. 211