SSH-AGENT(1) | General Commands Manual | SSH-AGENT(1) |
ssh-agent
—
OpenSSH authentication agent
ssh-agent |
[-c | -s ]
[-Dd ] [-a
bind_address] [-E
fingerprint_hash] [-O
option] [-P
allowed_providers] [-t
life] |
ssh-agent |
[-a bind_address]
[-E fingerprint_hash]
[-O option]
[-P allowed_providers]
[-t life]
command [arg ...] |
ssh-agent |
[-c | -s ]
-k |
ssh-agent
is a program to hold private
keys used for public key authentication. 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 options are as follows:
-a
bind_address-c
stdout
. This is the
default if SHELL
looks like it's a csh style of
shell.-D
ssh-agent
will not fork.-d
ssh-agent
will not fork and will write debug
information to standard error.-E
fingerprint_hash-k
SSH_AGENT_PID
environment variable).-O
optionssh-agent
.
Currently two options are supported:
allow-remote-pkcs11
and
no-restrict-websafe
.
The allow-remote-pkcs11
option allows
clients of a forwarded ssh-agent
to load PKCS#11
or FIDO provider libraries. By default only local clients may perform
this operation. Note that signalling that an
ssh-agent
client is remote is performed by
ssh(1), and use of other tools to
forward access to the agent socket may circumvent this restriction.
The no-restrict-websafe
option
instructs ssh-agent
to permit signatures using
FIDO keys that might be web authentication requests. By default,
ssh-agent
refuses signature requests for FIDO
keys where the key application string does not start with
“ssh:” and when the data to be signed does not appear to
be a ssh(1) user authentication
request or a ssh-keygen(1)
signature. The default behaviour prevents forwarded access to a FIDO key
from also implicitly forwarding the ability to authenticate to
websites.
-P
allowed_providers-S
or -s
options to
ssh-add(1). Libraries that do not
match the pattern list will be refused. See PATTERNS in
ssh_config(5) for a description
of pattern-list syntax. The default list is
“usr/lib*/*,/usr/local/lib*/*”.-s
stdout
. This is
the default if SHELL
does not look like it's a csh
style of shell.-t
lifeThere are two main ways to get an agent set up. The first is at
the start of an X session, where all other windows or programs are started
as children of the ssh-agent
program. The agent
starts a command under which its environment variables are exported, for
example ssh-agent xterm &
. When the command
terminates, so does the agent.
The second method is used for a login session. When
ssh-agent
is started, it prints the shell commands
required to set its environment variables, which in turn can be evaluated in
the calling shell, for example eval `ssh-agent
-s`
.
In both cases, ssh(1) looks at these environment variables and uses them to establish a connection to the agent.
The agent initially does not have any private keys. Keys are added
using ssh-add(1) or by
ssh(1) when
AddKeysToAgent
is set in
ssh_config(5). Multiple identities
may be stored in ssh-agent
concurrently 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.
Connections to ssh-agent
may be forwarded
from further remote hosts using the -A
option to
ssh(1) (but see the caveats documented
therein), avoiding the need for authentication data to be stored on other
machines. Authentication passphrases and private keys never go over the
network: the connection to the agent is forwarded over SSH remote
connections and the result is returned to the requester, allowing the user
access to their identities anywhere in the network in a secure fashion.
SSH_AGENT_PID
ssh-agent
starts, it stores the name of the
agent's process ID (PID) in this variable.SSH_AUTH_SOCK
ssh-agent
starts, it creates a
UNIX-domain socket and stores its pathname in this
variable. It is accessible only to the current user, but is easily abused
by root or another instance of the same user.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.
August 10, 2023 | macOS 14.6 |