1SSH-AGENT(1) BSD General Commands Manual SSH-AGENT(1)
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4 ssh-agent — OpenSSH authentication agent
5
7 ssh-agent [-c | -s] [-Dd] [-a bind_address] [-E fingerprint_hash]
8 [-P provider_whitelist] [-t life] [command [arg ...]]
9 ssh-agent [-c | -s] -k
10
12 ssh-agent is a program to hold private keys used for public key authenti‐
13 cation. Through use of environment variables the agent can be located
14 and automatically used for authentication when logging in to other
15 machines using ssh(1).
16 The options are as follows:
18 -a bind_address
20 Bind the agent to the UNIX-domain socket bind_address. The
21 default is $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid>.
22 -c Generate C-shell commands on stdout. This is the default if
24 SHELL looks like it's a csh style of shell.
25 -D Foreground mode. When this option is specified ssh-agent will
27 not fork.
28 -d Debug mode. When this option is specified ssh-agent will not
30 fork and will write debug information to standard error.
31 -E fingerprint_hash
33 Specifies the hash algorithm used when displaying key finger‐
34 prints. Valid options are: “md5” and “sha256”. The default is
35 “sha256”.
36 -k Kill the current agent (given by the SSH_AGENT_PID environment
38 variable).
39 -P provider_whitelist
41 Specify a pattern-list of acceptable paths for PKCS#11 and FIDO
42 authenticator shared libraries that may be used with the -S or -s
43 options to ssh-add(1). Libraries that do not match the whitelist
44 will be refused. See PATTERNS in ssh_config(5) for a description
45 of pattern-list syntax. The default whitelist is
46 “/usr/lib/*,/usr/local/lib/*”.
47 -s Generate Bourne shell commands on stdout. This is the default if
49 SHELL does not look like it's a csh style of shell.
50 -t life
52 Set a default value for the maximum lifetime of identities added
53 to the agent. The lifetime may be specified in seconds or in a
54 time format specified in sshd_config(5). A lifetime specified
55 for an identity with ssh-add(1) overrides this value. Without
56 this option the default maximum lifetime is forever.
57 command [arg ...]
59 If a command (and optional arguments) is given, this is executed
60 as a subprocess of the agent. The agent exits automatically when
61 the command given on the command line terminates.
62 There are two main ways to get an agent set up. The first is at the
64 start of an X session, where all other windows or programs are started as
65 children of the ssh-agent program. The agent starts a command under
66 which its environment variables are exported, for example ssh-agent xterm
67 &. When the command terminates, so does the agent.
68 The second method is used for a login session. When ssh-agent is
70 started, it prints the shell commands required to set its environment
71 variables, which in turn can be evaluated in the calling shell, for exam‐
72 ple eval `ssh-agent -s`.
73 In both cases, ssh(1) looks at these environment variables and uses them
75 to establish a connection to the agent.
76 The agent initially does not have any private keys. Keys are added using
78 ssh-add(1) or by ssh(1) when AddKeysToAgent is set in ssh_config(5).
79 Multiple identities may be stored in ssh-agent concurrently and ssh(1)
80 will automatically use them if present. ssh-add(1) is also used to
81 remove keys from ssh-agent and to query the keys that are held in one.
82 Connections to ssh-agent may be forwarded from further remote hosts using
84 the -A option to ssh(1) (but see the caveats documented therein), avoid‐
85 ing the need for authentication data to be stored on other machines.
86 Authentication passphrases and private keys never go over the network:
87 the connection to the agent is forwarded over SSH remote connections and
88 the result is returned to the requester, allowing the user access to
89 their identities anywhere in the network in a secure fashion.
90
92 SSH_AGENT_PID When ssh-agent starts, it stores the name of the agent's
93 process ID (PID) in this variable.
94 SSH_AUTH_SOCK When ssh-agent starts, it creates a UNIX-domain socket and
96 stores its pathname in this variable. It is accessible
97 only to the current user, but is easily abused by root or
98 another instance of the same user.
99
101 $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid>
102 UNIX-domain sockets used to contain the connection to the authen‐
103 tication agent. These sockets should only be readable by the
104 owner. The sockets should get automatically removed when the
105 agent exits.
106
108 ssh(1), ssh-add(1), ssh-keygen(1), ssh_config(5), sshd(8)
109
111 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
112 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
113 de Raadt and Dug Song removed many bugs, re-added newer features and cre‐
114 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
115 versions 1.5 and 2.0.
116BSD May 10, 2020 BSD