ssh-agent - OpenSSH authentication agent
ssh-agent [-c | s] [-Ddx] [-a bind_address]
[-E fingerprint_hash] [-P allowed_providers]
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
The options are as follows:
- -a bind_address
- Bind the agent to the UNIX-domain socket bind_address. The default
- Generate C-shell commands on stdout. This is the default if
SHELL looks like it's a csh style of shell.
- Foreground mode. When this option is specified ssh-agent will not
- Debug mode. When this option is specified ssh-agent will not fork
and will write debug information to standard error.
- -E fingerprint_hash
- Specifies the hash algorithm used when displaying key fingerprints. Valid
options are: ``md5'' and ``sha256''. The default is ``sha256''.
- Kill the current agent (given by the SSH_AGENT_PID environment
- -P allowed_providers
- Specify a pattern-list of acceptable paths for PKCS#11 provider and FIDO
authenticator middleware shared libraries that may be used with the
-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/*''.
- 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.
- Exit after the last client has disconnected.
- command [arg...]
- If a command (and optional arguments) is given, this is executed as a
subprocess of the agent. The agent exits automatically when the command
given on the command line terminates.
There 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
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
- When ssh-agent starts, it stores the name of the agent's process ID
(PID) in this variable.
- When 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.
ssh(1), ssh-add(1), ssh-keygen(1), ssh_config(5),
-nosplit OpenSSH is a derivative of the original and free ssh 1.2.12 release by
- 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.
Tatu Ylonen .
Aaron Campbell , Bob Beck , Markus Friedl , Niels Provos , Theo de
Dug Song removed many bugs, re-added newer features and created
Markus Friedl contributed the support for SSH protocol versions
1.5 and 2.0.