1.\" $OpenBSD: ssh-agent.1,v 1.54 2013/12/07 11:58:46 naddy 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: December 7 2013 $ 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 | 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 | s 52.Fl k 53.Sh DESCRIPTION 54.Nm 55is a program to hold private keys used for public key authentication 56(RSA, DSA, ECDSA, ED25519). 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 $TMPDIR/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 , 118.Pa ~/.ssh/id_ecdsa , 119.Pa ~/.ssh/id_ed25519 120and 121.Pa ~/.ssh/identity . 122If the identity has a passphrase, 123.Xr ssh-add 1 124asks for the passphrase on the terminal if it has one or from a small X11 125program if running under X11. 126If neither of these is the case then the authentication will fail. 127It then sends the identity to the agent. 128Several identities can be stored in the 129agent; the agent can automatically use any of these identities. 130.Ic ssh-add -l 131displays the identities currently held by the agent. 132.Pp 133The idea is that the agent is run in the user's local PC, laptop, or 134terminal. 135Authentication data need not be stored on any other 136machine, and authentication passphrases never go over the network. 137However, the connection to the agent is forwarded over SSH 138remote logins, and the user can thus use the privileges given by the 139identities anywhere in the network in a secure way. 140.Pp 141There are two main ways to get an agent set up: 142The first is that the agent starts a new subcommand into which some environment 143variables are exported, eg 144.Cm ssh-agent xterm & . 145The second is that the agent prints the needed shell commands (either 146.Xr sh 1 147or 148.Xr csh 1 149syntax can be generated) which can be evaluated in the calling shell, eg 150.Cm eval `ssh-agent -s` 151for Bourne-type shells such as 152.Xr sh 1 153or 154.Xr ksh 1 155and 156.Cm eval `ssh-agent -c` 157for 158.Xr csh 1 159and derivatives. 160.Pp 161Later 162.Xr ssh 1 163looks at these variables and uses them to establish a connection to the agent. 164.Pp 165The agent will never send a private key over its request channel. 166Instead, operations that require a private key will be performed 167by the agent, and the result will be returned to the requester. 168This way, private keys are not exposed to clients using the agent. 169.Pp 170A 171.Ux Ns -domain 172socket is created and the name of this socket is stored in the 173.Ev SSH_AUTH_SOCK 174environment 175variable. 176The socket is made accessible only to the current user. 177This method is easily abused by root or another instance of the same 178user. 179.Pp 180The 181.Ev SSH_AGENT_PID 182environment variable holds the agent's process ID. 183.Pp 184The agent exits automatically when the command given on the command 185line terminates. 186.Sh FILES 187.Bl -tag -width Ds 188.It Pa ~/.ssh/identity 189Contains the protocol version 1 RSA authentication identity of the user. 190.It Pa ~/.ssh/id_dsa 191Contains the protocol version 2 DSA authentication identity of the user. 192.It Pa ~/.ssh/id_ecdsa 193Contains the protocol version 2 ECDSA authentication identity of the user. 194.It Pa ~/.ssh/id_ed25519 195Contains the protocol version 2 ED25519 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