NAME
ssh-agent2 - authentication agent
SYNOPSIS
ssh-agent2 command
eval `ssh-agent2 [-s] [-c] [-1]`
DESCRIPTION
ssh-agent2 is a program to hold authentication private keys.
The idea is that ssh-agent2 is started in the beginning of
an X-session or a login session, and all other windows or
programs are started as children of the ssh-agent2 program
(the command normally starts X or is the user shell). The
programs started under the agent inherit a connection to the
agent, and the agent is automatically used for public key
authentication when logging to other machines using ssh.
If the ssh-agent2 is started without any arguments (no com-
mand) it will fork and start the agent as a background pro-
cess. The agent also prints a command that can be evaluated
in sh or csh like shells, setting the SSH2_AUTH_SOCK and
SSH2_AGENT_PID environment variables. The SSH2_AGENT_PID
environment variable can be used to kill the agent away when
it is no longer needed (when you logout from X-session etc).
If no options are given, the ssh-agent2 uses the SHELL
environment variable to detect what kind of shell you have
(*csh or sh-style shell). The -c option will force csh-style
shell, and -s option will force sh-style shell.
Note that in SysV variants (at least IRIX and Solaris) the
environment variable SHELL might not contain the actual
value of the shell executing the evaluation. If ALTSHELL is
set to YES in /etc/default/login, the SHELL environment
variable is set to the login shell of the user.
The agent initially does not have any private keys. Keys
are added using ssh-add2. Several identities can be stored
in the agent; the agent can automatically use any of these
identities. ssh-add2 -l displays the identities currently
held by the agent.
The idea is that the agent is run in the user's local PC,
laptop, or terminal. Authentication data does not have to
be stored on any other machine, and authentication
passphrases never go over the network. However, the connec-
tion 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.
A connection to the agent is inherited by child programs. A
unix-domain socket is created (/tmp/ssh-$USER/agent-socket-
<pid>), where the <pid> is the process id of the listener
(agent or sshd proxying the agent). The name of this socket
is stored in the SSH2_AUTH_SOCK environment variable. The
socket is made accessible only to the current user. This
method can easily be abused by root or another instance of
the same user. Older versions of ssh used inherited file
descriptors for contacting the agent and used the unix-
domain sockets in an incompatible way.
If the command is given as an argument to ssh-agent2, the
agent exits automatically when the command given on the com-
mand line terminates. The command is executed even if the
agent fails to start its key storing and challenge process-
ing services.
COMPATIBILITY
With the option -1 ssh-agent2 can also serve old ssh1 appli-
cations and can also be accessed with ssh-add program in
ssh1 releases. If the option -1 is given to the ssh-agent2,
the program will also set the environment variables
SSH_AUTH_SOCK and SSH_AGENT_PID and share keys with both
protocols.
FILES
$HOME/.ssh2/id_KEYTYPE_KEYLEN_XX
Contains the private key authentication identity of the
user. This file should not be readable by anyone but
the user. It is possible to specify a passphrase when
generating the key; that passphrase will be used to
encrypt the private part of this file. This file is
not used by ssh-agent2, but is normally added to the
agent using ssh-add2 at login time.
/tmp/ssh-$USER/agent-socket-<pid>
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 automat-
ically removed when the agent exits. The parent direc-
tory of ssh2-$USER must have its sticky bit set.
AUTHORS
SSH Communications Security Corp
For more information, see http://www.ssh.com.
SEE ALSO
ssh-add2(1), ssh-keygen2(1), ssh2(1), sshd2(8), sftp(1)
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