1.\" $NetBSD: ssh-agent.1,v 1.13 2018/07/10 22:12:08 sevan Exp $ 2.\" $OpenBSD: ssh-agent.1,v 1.64 2016/11/30 06:54:26 jmc Exp $ 3.\" 4.\" 5.\" Author: Tatu Ylonen <ylo@cs.hut.fi> 6.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland 7.\" All rights reserved 8.\" 9.\" As far as I am concerned, the code I have written for this software 10.\" can be used freely for any purpose. Any derived versions of this 11.\" software must be clearly marked as such, and if the derived work is 12.\" incompatible with the protocol description in the RFC file, it must be 13.\" called by a name other than "ssh" or "Secure Shell". 14.\" 15.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. 16.\" Copyright (c) 1999 Aaron Campbell. All rights reserved. 17.\" Copyright (c) 1999 Theo de Raadt. All rights reserved. 18.\" 19.\" Redistribution and use in source and binary forms, with or without 20.\" modification, are permitted provided that the following conditions 21.\" are met: 22.\" 1. Redistributions of source code must retain the above copyright 23.\" notice, this list of conditions and the following disclaimer. 24.\" 2. Redistributions in binary form must reproduce the above copyright 25.\" notice, this list of conditions and the following disclaimer in the 26.\" documentation and/or other materials provided with the distribution. 27.\" 28.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 29.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 30.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 31.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 32.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 33.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 34.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 35.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 36.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 37.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 38.\" 39.Dd November 30 2016 40.Dt SSH-AGENT 1 41.Os 42.Sh NAME 43.Nm ssh-agent 44.Nd authentication agent 45.Sh SYNOPSIS 46.Nm ssh-agent 47.Op Fl c | s 48.Op Fl \&Dd 49.Op Fl a Ar bind_address 50.Op Fl E Ar fingerprint_hash 51.Op Fl P Ar pkcs11_whitelist 52.Op Fl t Ar life 53.Op Ar command Op Ar arg ... 54.Nm ssh-agent 55.Op Fl c | s 56.Fl k 57.Sh DESCRIPTION 58.Nm 59is a program to hold private keys used for public key authentication 60(RSA, DSA, ECDSA, Ed25519). 61.Nm 62is usually started in the beginning of an X-session or a login session, and 63all other windows or programs are started as clients to the ssh-agent 64program. 65Through use of environment variables the agent can be located 66and automatically used for authentication when logging in to other 67machines using 68.Xr ssh 1 . 69.Pp 70The agent initially does not have any private keys. 71Keys are added using 72.Xr ssh 1 73(see 74.Cm AddKeysToAgent 75in 76.Xr ssh_config 5 77for details) 78or 79.Xr ssh-add 1 . 80Multiple identities may be stored in 81.Nm 82concurrently and 83.Xr ssh 1 84will automatically use them if present. 85.Xr ssh-add 1 86is also used to remove keys from 87.Nm 88and to query the keys that are held in one. 89.Pp 90The options are as follows: 91.Bl -tag -width Ds 92.It Fl a Ar bind_address 93Bind the agent to the 94.Ux Ns -domain 95socket 96.Ar bind_address . 97The default is 98.Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt . 99.It Fl c 100Generate C-shell commands on 101.Dv stdout . 102This is the default if 103.Ev SHELL 104looks like it's a csh style of shell. 105.It Fl D 106Foreground mode. 107When this option is specified 108.Nm 109will not fork. 110.It Fl d 111Debug mode. 112When this option is specified 113.Nm 114will not fork and will write debug information to standard error. 115.It Fl E Ar fingerprint_hash 116Specifies the hash algorithm used when displaying key fingerprints. 117Valid options are: 118.Dq md5 119and 120.Dq sha256 . 121The default is 122.Dq sha256 . 123.It Fl k 124Kill the current agent (given by the 125.Ev SSH_AGENT_PID 126environment variable). 127.It Fl P Ar pkcs11_whitelist 128Specify a pattern-list of acceptable paths for PKCS#11 shared libraries 129that may be added using the 130.Fl s 131option to 132.Xr ssh-add 1 . 133The default is to allow loading PKCS#11 libraries from 134.Dq /usr/lib/*,/usr/pkg/lib/* . 135PKCS#11 libraries that do not match the whitelist will be refused. 136See PATTERNS in 137.Xr ssh_config 5 138for a description of pattern-list syntax. 139.It Fl s 140Generate Bourne shell commands on 141.Dv stdout . 142This is the default if 143.Ev SHELL 144does not look like it's a csh style of shell. 145.It Fl t Ar life 146Set a default value for the maximum lifetime of identities added to the agent. 147The lifetime may be specified in seconds or in a time format specified in 148.Xr sshd_config 5 . 149A lifetime specified for an identity with 150.Xr ssh-add 1 151overrides this value. 152Without this option the default maximum lifetime is forever. 153.El 154.Pp 155If a command line is given, this is executed as a subprocess of the agent. 156When the command dies, so does the agent. 157.Pp 158The idea is that the agent is run in the user's local PC, laptop, or 159terminal. 160Authentication data need not be stored on any other 161machine, and authentication passphrases never go over the network. 162However, the connection to the agent is forwarded over SSH 163remote logins, and the user can thus use the privileges given by the 164identities anywhere in the network in a secure way. 165.Pp 166There are two main ways to get an agent set up: 167The first is that the agent starts a new subcommand into which some environment 168variables are exported, eg 169.Cm ssh-agent xterm & . 170The second is that the agent prints the needed shell commands (either 171.Xr sh 1 172or 173.Xr csh 1 174syntax can be generated) which can be evaluated in the calling shell, eg 175.Cm eval `ssh-agent -s` 176for Bourne-type shells such as 177.Xr sh 1 178or 179.Xr ksh 1 180and 181.Cm eval `ssh-agent -c` 182for 183.Xr csh 1 184and derivatives. 185.Pp 186Later 187.Xr ssh 1 188looks at these variables and uses them to establish a connection to the agent. 189.Pp 190The agent will never send a private key over its request channel. 191Instead, operations that require a private key will be performed 192by the agent, and the result will be returned to the requester. 193This way, private keys are not exposed to clients using the agent. 194.Pp 195A 196.Ux Ns -domain 197socket is created and the name of this socket is stored in the 198.Ev SSH_AUTH_SOCK 199environment 200variable. 201The socket is made accessible only to the current user. 202This method is easily abused by root or another instance of the same 203user. 204.Pp 205The 206.Ev SSH_AGENT_PID 207environment variable holds the agent's process ID. 208.Pp 209The agent exits automatically when the command given on the command 210line terminates. 211.Sh FILES 212.Bl -tag -width Ds 213.It Pa $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid> 214.Ux Ns -domain 215sockets used to contain the connection to the authentication agent. 216These sockets should only be readable by the owner. 217The sockets should get automatically removed when the agent exits. 218.El 219.Sh SEE ALSO 220.Xr ssh 1 , 221.Xr ssh-add 1 , 222.Xr ssh-keygen 1 , 223.Xr sshd 8 224.Sh AUTHORS 225.An -nosplit 226OpenSSH is a derivative of the original and free ssh 1.2.12 release by 227.An Tatu Ylonen . 228.An Aaron Campbell , Bob Beck , Markus Friedl , Niels Provos , Theo de Raadt 229and 230.An Dug Song 231removed many bugs, re-added newer features and created OpenSSH. 232.An Markus Friedl 233contributed the support for SSH protocol versions 1.5 and 2.0. 234