is "pat". To
connect to your remote account from your friend's account on
over the Internet, asking
to be logged into the remote account with username pat.
secure channel between the client and
the server so all transmissions between them are encrypted. The
client then prompts for your password, which it supplies to the
server over the secure channel. The server authenticates you by
checking that the password is correct and permits the login. All
subsequent client/server exchanges are protected by that secure
channel, including the contents of the email you proceed to read
using a mail program on
.
It's important to remember that the secure channel exists only
between the SSH client and server machines. After logging into
is not
secure. However, you can run another
, creating
another secure channel, which keeps the chain of connections secure.
We've covered only the simplest use of
2.2.1. File Transfer with scp
Continuing the story, suppose that
while reading your email, you encounter a message with an attached
file you'd like to print. In order to send the file to a local
printer at the university, you must first transfer the file to
local.university.edu. Once
again, you reject as insecure the traditional file-transfer programs,
such as
ftp and
rcp. Instead,
you use another SSH client program,
scp, to copy
the file across the network via a secure channel.
First, you write the attachment to a file in your home directory on
shell.isp.com using your
mail client, naming the file
print-me. When
you've finished reading your other email messages, log out of
shell.isp.com, ending the
SSH session and returning to the shell prompt on
local.university.edu. You're now
ready to copy the file securely.
The
scp program has syntax much like the
traditional Unix
cp program and nearly identical
to the insecure
rcp program. It is roughly:
scp name-of-source name-of-destination
In this example,
scp copies the file
print-me on
shell.isp.com over the network to a
local file in your friend's account on
local.university.edu, also called
print-me :
$ scp [email protected]:print-me print-me
The file is transferred over an SSH-secured connection. The source
and destination files may be specified not only by filename, but also
by username ("pat" in our example) and hostname
(
shell.isp.com), indicating
the location of the file on the network. Depending on your needs,
various parts of the source or destination name can be omitted, and
defaults values used. For example, omitting the username and the
"at" sign (pat@) makes
scp assume that
the remote username is the same as the local one.
Like
ssh,
scp prompts for your
remote password and passes it to the SSH server for verification. If
successful,
scp logs into the pat account on
shell.isp.com, copies your
remote file
print-me to the local file
print-me, and logs out of
shell.isp.com. The local file
print-me may now be sent to a printer.
The destination filename need not be the same as the remote one. For
example, if you're feeling French, you could call the local
file
imprime-moi :
$ scp [email protected]:print-me imprime-moi
The full syntax of
scp can represent local and
remote files in powerful ways, and the program also has numerous
command-line options. [
Section 7.5, "Secure Copy with scp"]
