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] [-P
allowed_providers] [-t
life] |
ssh-agent |
[-a bind_address]
[-E fingerprint_hash]
[-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).-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.In Debian, ssh-agent
is installed with the
set-group-id bit set, to prevent ptrace(2) attacks
retrieving private key material. This has the side-effect of causing the
run-time linker to remove certain environment variables which might have
security implications for set-id programs, including
LD_PRELOAD
, LD_LIBRARY_PATH
,
and TMPDIR
. If you need to set any of these
environment variables, you will need to do so in the program executed by
ssh-agent.
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.
June 22, 2020 | Debian |