SSH-AGENT(1) BSD General Commands Manual SSH-AGENT(1)
NAME
ssh-agent — authentication agent
SYNOPSIS
ssh-agent [-c | -s] [-d] [-a bind_address] [-t life]
[command [arg …]]
ssh-agent [-c | -s] -k
DESCRIPTION
ssh-agent is a program to hold private keys used for public key authen‐
tication (RSA, DSA, ECDSA, ED25519). ssh-agent is usually started in
the beginning of an X-session or a login session, and all other windows
or programs are started as clients to the ssh-agent program. Through
use of environment variables the agent can be located and automatically
used for authentication when logging in to other machines using ssh(1).
The agent initially does not have any private keys. Keys are added
using ssh-add(1). Multiple identities may be stored in ssh-agent con‐
currently and ssh(1) will automatically use them if present.
ssh-add(1) is also used to remove keys from ssh-agent and to query the
keys that are held in one.
The options are as follows:
-a bind_address
Bind the agent to the UNIX-domain socket bind_address. The
default is $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid>.
-c Generate C-shell commands on stdout. This is the default if
SHELL looks like it’s a csh style of shell.
-d Debug mode. When this option is specified ssh-agent will not
fork.
-k Kill the current agent (given by the SSH_AGENT_PID environment
variable).
-s Generate Bourne shell commands on stdout. This is the default
if SHELL does not look like it’s a csh style of shell.
-t life
Set a default value for the maximum lifetime of identities
added to the agent. The lifetime may be specified in seconds
or in a time format specified in sshd_config(5). A lifetime
specified for an identity with ssh-add(1) overrides this value.
Without this option the default maximum lifetime is forever.
If a commandline is given, this is executed as a subprocess of the
agent. When the command dies, so does the agent.
The idea is that the agent is run in the user’s local PC, laptop, or
terminal. Authentication data need not be stored on any other machine,
and authentication passphrases never go over the network. However, the
connection to the agent is forwarded over SSH remote logins, and the
user can thus use the privileges given by the identities anywhere in
the network in a secure way.
There are two main ways to get an agent set up: The first is that the
agent starts a new subcommand into which some environment variables are
exported, eg ssh-agent xterm &. The second is that the agent prints
the needed shell commands (either sh(1) or csh(1) syntax can be gener‐
ated) which can be evaluated in the calling shell, eg eval `ssh-agent
-s` for Bourne-type shells such as sh(1) or ksh(1) and eval `ssh-agent
-c` for csh(1) and derivatives.
Later ssh(1) looks at these variables and uses them to establish a con‐
nection to the agent.
The agent will never send a private key over its request channel.
Instead, operations that require a private key will be performed by the
agent, and the result will be returned to the requester. This way,
private keys are not exposed to clients using the agent.
A UNIX-domain socket is created and the name of this socket is stored
in the SSH_AUTH_SOCK environment variable. The socket is made accessi‐
ble only to the current user. This method is easily abused by root or
another instance of the same user.
The SSH_AGENT_PID environment variable holds the agent’s process ID.
The agent exits automatically when the command given on the command
line terminates.
FILES
$TMPDIR/ssh-XXXXXXXXXX/agent.<ppid>
UNIX-domain sockets used to contain the connection to the
authentication agent. These sockets should only be readable by
the owner. The sockets should get automatically removed when
the agent exits.
SEE ALSO
ssh(1), ssh-add(1), ssh-keygen(1), sshd(8)
AUTHORS
OpenSSH is a derivative of the original and free ssh 1.2.12 release by
Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
Theo de Raadt and Dug Song removed many bugs, re-added newer features
and created OpenSSH. Markus Friedl contributed the support for SSH
protocol versions 1.5 and 2.0.
COLOPHON
This page is part of the openssh (Portable OpenSSH) project. Informa‐
tion about the project can be found at
http://www.openssh.com/portable.html. If you have a bug report for
this manual page, see http://www.openssh.com/report.html. This page
was obtained from the tarball openssh-6.7p1.tar.gz fetched from
http://ftp.eu.openbsd.org/pub/OpenBSD/OpenSSH/portable/ on 2014-12-30.
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BSD December 31, 2014 BSD