1.\" $OpenBSD: ssh-agent.1,v 1.59 2015/04/24 06:26:49 jmc 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 $Mdocdate: April 24 2015 $ 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 Ddx 48.Op Fl a Ar bind_address 49.Op Fl E Ar fingerprint_hash 50.Op Fl t Ar life 51.Op Ar command Op Ar arg ... 52.Nm ssh-agent 53.Op Fl c | s 54.Fl k 55.Sh DESCRIPTION 56.Nm 57is a program to hold private keys used for public key authentication 58(RSA, DSA, ECDSA, Ed25519). 59.Nm 60is usually 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 agent initially does not have any private keys. 69Keys are added using 70.Xr ssh-add 1 . 71Multiple identities may be stored in 72.Nm 73concurrently and 74.Xr ssh 1 75will automatically use them if present. 76.Xr ssh-add 1 77is also used to remove keys from 78.Nm 79and to query the keys that are held in one. 80.Pp 81The options are as follows: 82.Bl -tag -width Ds 83.It Fl a Ar bind_address 84Bind the agent to the 85.Ux Ns -domain 86socket 87.Ar bind_address . 88The default is 89.Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt . 90.It Fl c 91Generate C-shell commands on 92.Dv stdout . 93This is the default if 94.Ev SHELL 95looks like it's a csh style of shell. 96.It Fl D 97Foreground mode. 98When this option is specified 99.Nm 100will not fork. 101.It Fl d 102Debug mode. 103When this option is specified 104.Nm 105will not fork and will write debug information to standard error. 106.It Fl E Ar fingerprint_hash 107Specifies the hash algorithm used when displaying key fingerprints. 108Valid options are: 109.Dq md5 110and 111.Dq sha256 . 112The default is 113.Dq sha256 . 114.It Fl k 115Kill the current agent (given by the 116.Ev SSH_AGENT_PID 117environment variable). 118.It Fl s 119Generate Bourne shell commands on 120.Dv stdout . 121This is the default if 122.Ev SHELL 123does not look like it's a csh style of shell. 124.It Fl t Ar life 125Set a default value for the maximum lifetime of identities added to the agent. 126The lifetime may be specified in seconds or in a time format specified in 127.Xr sshd_config 5 . 128A lifetime specified for an identity with 129.Xr ssh-add 1 130overrides this value. 131Without this option the default maximum lifetime is forever. 132.It Fl x 133Exit after the last client has disconnected. 134.El 135.Pp 136If a commandline is given, this is executed as a subprocess of the agent. 137When the command dies, so does the agent. 138.Pp 139The idea is that the agent is run in the user's local PC, laptop, or 140terminal. 141Authentication data need not be stored on any other 142machine, and authentication passphrases never go over the network. 143However, the connection to the agent is forwarded over SSH 144remote logins, and the user can thus use the privileges given by the 145identities anywhere in the network in a secure way. 146.Pp 147There are two main ways to get an agent set up: 148The first is that the agent starts a new subcommand into which some environment 149variables are exported, eg 150.Cm ssh-agent xterm & . 151The second is that the agent prints the needed shell commands (either 152.Xr sh 1 153or 154.Xr csh 1 155syntax can be generated) which can be evaluated in the calling shell, eg 156.Cm eval `ssh-agent -s` 157for Bourne-type shells such as 158.Xr sh 1 159or 160.Xr ksh 1 161and 162.Cm eval `ssh-agent -c` 163for 164.Xr csh 1 165and derivatives. 166.Pp 167Later 168.Xr ssh 1 169looks at these variables and uses them to establish a connection to the agent. 170.Pp 171The agent will never send a private key over its request channel. 172Instead, operations that require a private key will be performed 173by the agent, and the result will be returned to the requester. 174This way, private keys are not exposed to clients using the agent. 175.Pp 176A 177.Ux Ns -domain 178socket is created and the name of this socket is stored in the 179.Ev SSH_AUTH_SOCK 180environment 181variable. 182The socket is made accessible only to the current user. 183This method is easily abused by root or another instance of the same 184user. 185.Pp 186The 187.Ev SSH_AGENT_PID 188environment variable holds the agent's process ID. 189.Pp 190The agent exits automatically when the command given on the command 191line terminates. 192.Sh FILES 193.Bl -tag -width Ds 194.It Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt 195.Ux Ns -domain 196sockets used to contain the connection to the authentication agent. 197These sockets should only be readable by the owner. 198The sockets should get automatically removed when the agent exits. 199.El 200.Sh SEE ALSO 201.Xr ssh 1 , 202.Xr ssh-add 1 , 203.Xr ssh-keygen 1 , 204.Xr sshd 8 205.Sh AUTHORS 206OpenSSH is a derivative of the original and free 207ssh 1.2.12 release by Tatu Ylonen. 208Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 209Theo de Raadt and Dug Song 210removed many bugs, re-added newer features and 211created OpenSSH. 212Markus Friedl contributed the support for SSH 213protocol versions 1.5 and 2.0. 214