ssh will normally set the following environment variables:
DISPLAY The DISPLAY variable indicates the location
of the X11 server. It is automatically set
by ssh to point to a value of the form
'hostname:n', where 'hostname' indicates the
host where the shell runs, and 'n' is an
integer ≥ 1. ssh uses this special value to
forward X11 connections over the secure
channel. The user should normally not set
DISPLAY explicitly, as that will render the
X11 connection insecure (and will require the
user to manually copy any required
authorization cookies).
HOME Set to the path of the user's home directory.
LOGNAME Synonym for USER; set for compatibility with
systems that use this variable.
MAIL Set to the path of the user's mailbox.
PATH Set to the default PATH, as specified when
compiling ssh.
SSH_ASKPASS If ssh needs a passphrase, it will read the
passphrase from the current terminal if it
was run from a terminal. If ssh does not
have a terminal associated with it but
DISPLAY and SSH_ASKPASS are set, it will
execute the program specified by SSH_ASKPASS
and open an X11 window to read the
passphrase. This is particularly useful when
calling ssh from a .xsession or related
script. (Note that on some machines it may
be necessary to redirect the input from
/dev/null to make this work.)
SSH_ASKPASS_REQUIRE Allows further control over the use of an
askpass program. If this variable is set to
'never' then ssh will never attempt to use
one. If it is set to 'prefer', then ssh will
prefer to use the askpass program instead of
the TTY when requesting passwords. Finally,
if the variable is set to 'force', then the
askpass program will be used for all
passphrase input regardless of whether
DISPLAY is set.
SSH_AUTH_SOCK Identifies the path of a UNIX-domain socket
used to communicate with the agent.
SSH_CONNECTION Identifies the client and server ends of the
connection. The variable contains four
space-separated values: client IP address,
client port number, server IP address, and
server port number.
SSH_ORIGINAL_COMMAND This variable contains the original command
line if a forced command is executed. It can
be used to extract the original arguments.
SSH_TTY This is set to the name of the tty (path to
the device) associated with the current shell
or command. If the current session has no
tty, this variable is not set.
SSH_TUNNEL Optionally set by sshd(8) to contain the
interface names assigned if tunnel forwarding
was requested by the client.
SSH_USER_AUTH Optionally set by sshd(8), this variable may
contain a pathname to a file that lists the
authentication methods successfully used when
the session was established, including any
public keys that were used.
TZ This variable is set to indicate the present
time zone if it was set when the daemon was
started (i.e. the daemon passes the value on
to new connections).
USER Set to the name of the user logging in.
Additionally, ssh reads ~/.ssh/environment, and adds lines of the
format 'VARNAME=value' to the environment if the file exists and
users are allowed to change their environment. For more
information, see the PermitUserEnvironment option in
sshd_config(5).
