Copying Files Between Windows and Linux using PuTTY
Here's a neat way to transfer files between your Windows PC and your Linux (Ubuntu) project using Ethernet.
PuTTY is a program that connects one device to another over the network. It supports SSH and Telnet, among others.
PuTTY is a “client” application that talks to a “host”. The host must be running an SSH server (which is often the case for iMX Linux enabled systems).
A Windows version exists and this is ideal for transferring files between your Windows PC and a Linux Platform.
Select the Windows Installer version. This installs the programs and help files you will need.
File transfers can be done using PSCP (Putty Secure CoPy) or by using PSFTP (Putty Secure File Transfer Protocol).
PSFTP can be launched from the Windows Start.
PSCP must be launched from within a DOS box (StartWingdings"">àRun and enter cmd, then press OK). Before
running PSCP, you need to set the path variable. At the DOS command prompt, type
set PATH=C:\Program Files\PuTTY
This assumes you installed PuTTY in C:\Program Files\PuTTY (default). Note the “\” slash.
This will only work for the lifetime of that particular console window. To set your PATH more permanently on Windows NT, 2000, and XP, use the Advanced tab of the System Control Panel (right-click on MyComputer then select Properties). Click the Environment Variables button, high-light “path” and edit it. Add “;C:\Program Files\PuTTY” at the end of
the line. You can then verify the path is correct by typing “path” at the DOS prompt.
The format for pscp is straight forward:
pscp [options] source destination
To copy a Windows file to Linux system, at the DOS prompt, type
pscp c:/music.mp3 ubuntu@10.0.0.3:/home/ubuntu/Music
which will copy the file music.mp3 to my Music folder into Linux. My Ubuntu EVK has an ip address as 10.0.0.3. (Note that you can use either / or \ for the Windows files and directories, but you must use / when specifying the Linux files.)
The reverse works as well (copy Linux file to Windows)
pscp ubuntu@10.0.0.3:/home/ubuntu/Music/music.mp3 c:/
This copies the music.mp3 file from Linux into my C root directory.
There are many other options available, including the ability to use the ftp protocol as well. See the help file for more information.
Starting PSCP
PSCP is a command line application. This means that you cannot just double-click on its icon to run it and instead you have to bring up a
console window. With Windows NT, 2000, and XP, it is called a ‘Command Prompt’.
The basics
To
receive (a) file(s) from a remote server:
pscp [options] [user@]host:source target
So to copy the file
/etc/hosts from the server
example.com as user
fred to the file
c:\temp\example-hosts.txt, you would type:
pscp fred@example.com:/etc/hosts c:\temp\example-hosts.txt
To
send (a) file(s) to a remote server:
pscp [options] source [source...] [user@]host:target
So to copy the local file
c:\documents\foo.txt to the server
example.com as user
fred to the file
/tmp/foo you would type:
pscp c:\documents\foo.txt fred@example.com:/tmp/foo
You can use
wildcards to transfer multiple files in either direction, like this:
pscp c:\documents\*.doc fred@example.com:docfiles
pscp fred@example.com:source/*.c c:\source
However, in the second case (using a wildcard for multiple remote files) you may see a warning saying something like ‘warning: remote host tried to write to a file called ‘
terminal.c’ when we requested a file called ‘
*.c’. If this is a wildcard, consider upgrading to SSH-2 or using the ‘
-unsafe’ option. Renaming of this file has been disallowed’.
This is due to a
fundamental insecurity in the old-style
SCP protocol: the client sends the wildcard string (
*.c) to the server, and the server sends back a sequence of file names that match the wildcard pattern. However, there is nothing to stop the server sending back a
different pattern and writing over one of your other files: if you request
*.c, the server might send back the file name
AUTOEXEC.BAT and install a virus for you. Since the wildcard matching rules are decided by the server, the client cannot reliably verify that the filenames sent back match the pattern.
PSCP will attempt to use the newer
SFTP protocol (part of SSH-2) where possible, which does not suffer from this security flaw. If you are talking to an SSH-2 server which supports SFTP, you will never see this warning. (You can force use of the SFTP protocol, if available, with
-sftp - see
section 5.2.2.6.)
If you really need to use a server-side wildcard with an SSH-1 server, you can use the
-unsafe command line option with PSCP:
pscp -unsafe fred@example.com:source/*.c c:\source
This will suppress the warning message and the file transfer will happen. However, you should be aware that by using this option you are giving the server the ability to write to
any file in the target directory, so you should only use this option if you trust the server administrator not to be malicious (and not to let the server machine be cracked by malicious people). Alternatively, do any such download in a newly created empty directory. (Even in ‘unsafe’ mode, PSCP will still protect you against the server trying to get out of that directory using pathnames including ‘
..’.)
5.2.1.1 user
The
login name on the remote server. If this is omitted, and
host is a PuTTY saved session, PSCP will use any username specified by that saved session. Otherwise, PSCP will attempt to use the local Windows username.
5.2.1.2 host
The name of the remote server, or the name of an existing PuTTY saved session. In the latter case, the session's settings for hostname, port number, cipher type and username will be used.
5.2.1.3 source
One or more source files.
Wildcards are allowed. The syntax of wildcards depends on the system to which they apply, so if you are copying
from a Windows system
to a UNIX system, you should use Windows wildcard syntax (e.g.
*.*), but if you are copying
from a UNIX system
to a Windows system, you would use the wildcard syntax allowed by your UNIX shell (e.g.
*).
If the source is a remote server and you do not specify a full pathname (in UNIX, a pathname beginning with a
/ (slash) character), what you specify as a source will be interpreted relative to your
home directory on the remote server.
5.2.1.4 target
The filename or directory to put the file(s). When copying from a remote server to a local host, you may wish simply to place the file(s) in the current directory. To do this, you should specify a target of
.. For example:
pscp fred@example.com:/home/tom/.emacs .
...would copy
/home/tom/.emacs on the remote server to the current directory.
As with the
source parameter, if the target is on a remote server and is not a full path name, it is interpreted relative to your home directory on the remote server.
5.2.2 Options
PSCP accepts all the general command line options supported by the PuTTY tools, except the ones which make no sense in a file transfer utility. See
section 3.8.3 for a description of these options. (The ones not supported by PSCP are clearly marked.)
PSCP also supports some of its own options. The following sections describe PSCP's specific command-line options.
5.2.2.1 -ls list remote files
If the
-ls option is given, no files are transferred; instead, remote files are listed. Only a hostname specification and optional remote file specification need be given. For example:
pscp -ls fred@example.com:dir1
The SCP protocol does not contain within itself a means of listing files. If SCP is in use, this option therefore assumes that the server responds appropriately to the command
ls -la; this may not work with all servers.
If SFTP is in use, this option should work with all servers.
5.2.2.2 -p preserve file attributes
By default, files copied with PSCP are
timestamped with the date and time they were copied. The
-p option preserves the original timestamp on copied files.
5.2.2.3 -q quiet, don't show statistics
By default, PSCP displays a meter displaying the progress of the current transfer:
mibs.tar | 168 kB | 84.0 kB/s | ETA: 00:00:13 | 13%
The fields in this display are (from left to right), filename, size (in kilobytes) of file transferred so far, estimate of how fast the file is being transferred (in kilobytes per second), estimated time that the transfer will be complete, and percentage of the file so far transferred. The
-q option to PSCP suppresses the printing of these statistics.
5.2.2.4 -r copies directories recursively
By default, PSCP will only copy files. Any directories you specify to copy will be skipped, as will their contents. The
-r option tells PSCP to descend into any directories you specify, and to copy them and their contents. This allows you to use PSCP to transfer whole directory structures between machines.
5.2.2.5 -batch avoid interactive prompts
If you use the
-batch option, PSCP will never give an interactive prompt while establishing the connection. If the server's host key is invalid, for example (see
section 2.2), then the connection will simply be abandoned instead of asking you what to do next.
This may help PSCP's behaviour when it is used in automated scripts: using
-batch, if something goes wrong at connection time, the batch job will fail rather than hang.
5.2.2.6 -sftp, -scp force use of particular protocol
As mentioned in
section 5.2.1, there are two different file transfer protocols in use with SSH. Despite its name, PSCP (like many other ostensible
scp clients) can use either of these protocols.
The older
SCP protocol does not have a written specification and leaves a lot of detail to the server platform.
Wildcards are expanded on the server. The simple design means that any wildcard specification supported by the server platform (such as brace expansion) can be used, but also leads to interoperability issues such as with filename quoting (for instance, where filenames contain spaces), and also the security issue described in
section 5.2.1.
The newer
SFTP protocol, which is usually associated with SSH-2 servers, is specified in a more platform independent way, and leaves issues such as wildcard syntax up to the client. (PuTTY's SFTP wildcard syntax is described in
section 6.2.2.) This makes it more consistent across platforms, more suitable for scripting and automation, and avoids security issues with wildcard matching.
Normally PSCP will attempt to use the SFTP protocol, and only fall back to the SCP protocol if SFTP is not available on the server.
The
-scp option forces PSCP to use the SCP protocol or quit.
The
-sftp option forces PSCP to use the SFTP protocol or quit. When this option is specified, PSCP looks harder for an SFTP server, which may allow use of SFTP with SSH-1 depending on server setup.
5.2.3 Return value
PSCP returns an
ERRORLEVEL of zero (success) only if the files were correctly transferred. You can test for this in a
batch file, using code such as this:
pscp file*.* user@hostname:
if errorlevel 1 echo There was an error
5.2.4 Using public key authentication with PSCP
Like PuTTY, PSCP can authenticate using a public key instead of a password. There are three ways you can do this.
Firstly, PSCP can use PuTTY saved sessions in place of hostnames (see
section 5.2.1.2). So you would do this:
- Run PuTTY, and create a PuTTY saved session (see section 4.1.2) which specifies your private key file (see section 4.20.7). You will probably also want to specify a username to log in as (see section 4.14.1).
- In PSCP, you can now use the name of the session instead of a hostname: type
pscp sessionname:file localfile, where sessionname is replaced by the name of your saved session.
Secondly, you can supply the name of a private key file on the command line, with the
-i option. See
section 3.8.3.18 for more information.
Thirdly, PSCP will attempt to authenticate using Pageant if Pageant is running (see
chapter 9). So you would do this:
- Ensure Pageant is running, and has your private key stored in it.
- Specify a user and host name to PSCP as normal. PSCP will automatically detect Pageant and try to use the keys within it.
For more general information on public-key authentication, see
chapter 8.
