File transfer to/from Unix/Linux machines

Updated: 2011-03-26 07:16 EDT

1 Introduction to File Transfer Index up to index

This file explains how to copy files between Unix/Linux machines and between Unix/Linux and other machines (e.g. to/from your home Linux or Windows machine or to/from a Windows machine in an Access Lab).

How you transfer files depends on where you log in, and which machine is “local” and which machine is “remote”. The existence of firewalls that restrict connections makes things more complex than usual.

1.1 Connecting from other machines to the Course Linux Server Index up to index

The Course Linux Server idallen-alinux is located behind an Algonquin College firewall but has some limited access from the Public Internet.

The Course Linux Server has two public ports, one HTTP and one SSH, mapped through a Public gateway machine cst8281.idallen.ca. This gateway machine and these two ports are visible anywhere on the Internet, giving you limited access to the machine without needing to use the VPN.

1.2 Connecting from the Course Linux Server to other machines Index up to index

Connecting from the Course Linux Server out to a remote machine (e.g. using a command-line ftp or ssh command) usually requires that the remote machine have its own IP adddress - it should not itself be behind a firewall, unless you have arranged a pass-through port on that firewall.

1.3 Connecting to Algonquin Lab machines Index up to index

All Algonquin Access Labs are behind firewalls; you cannot use anything to connect into Algonquin machines from off-campus. Only the Algonquin Unix machine ACADUNIX is not hidden behind a firewall; it accepts both insecure FTP and secure SCP/SFTP connections. If you have an ACADUNIX account, sometimes you have to use ACADUNIX as a staging area to hold a file for copying.

2 File Permissions and Web Permissions Index up to index

You may be able to access a file via your file transfer program that cannot be displayed in a web browser, since the file transfer program is logged in as your account name and the web browser accesses your files as “other”.

To be displayed by the web server, your files must have read permissions for “other” after you transfer them to the Course Linux Server. The Unix/Linux chmod command can change file permissions.

3 Text File Line End Differences Index up to index

Note that the line end character in text files is not the same between Unix and Windows. A text file written on Unix contains only linefeed (LF or NL or “\n”) characters at the ends of lines; Windows expects lines in text files to end in both a carriage-return (CR or “\r”) and a linefeed character. This may result in “staircasing” text if you send a Unix text file to a Windows printer from some programs (e.g. Notepad).

Print a small sample first, and on Windows try using “Write” or “Wordpad” to read or print a Unix file instead of “Notepad”.

Web pages can be stored in either Unix or Windows format.

4 Unix/Linux SCP and SFTP - Secure Copy Program, Secure FTP Index up to index

The SCP and SFTP programs should be used to transfer files between machines when a userid/password is required (e.g. to/from the Course Linux Server). Both these programs use the underlying SSH (Secure SHell) protocol that encrypts both your password and the data being transferred.

Avoid the standard FTP program - it sends passwords in clear text across the Internet. (You are slightly safer using the FTP program locall here at school, but realize that anyone snooping packets on your local network will still see your password.)

For Windows users, scroll down to the Microsoft Windows Users section.

4.1 Unix/Linux: Copy a file from a remote machine to the local machine Index up to index

Using SCP from a Unix/Linux or Cygwin command line:

    $ scp -p userid@remote.host.name:remote_file local_file

The “userid@” part contains your login userid on “remote.host.name”. You can leave off “userid@” if your remote userid is the same as your userid on the local machine. You will be prompted to enter your password for the remote machine. The “remote_file” may be an absolute pathname (on “remote.host.name”), or it may be a pathname relative to your home directory on “remote.host.name”. The “-p” option to SCP preserves the modify time of the transferred file. Examples:

If the remote machine is not behind a firewall and uses a standard SSH port:

    $ scp -p abcd0001@acadunix.algonquincollege.com:dodo.txt happy.txt
    $ scp -p acadunix.algonquincollege.com:/tmp/foo mydir/bar

If the remote machine is behind a firewall and requires a special port to be used, the -P option (upper case P) must be used to set the firewall pass-through port:

$ scp -p -P 2222 abcd0001@example.com:dodo.txt happy.txt

4.2 Unix/Linux: Copy a file from the local machine to a remote machine Index up to index

To copy from local to remote via a Unix/Linux or Cygwin command line, just reverse the order of the arguments to SCP:

    $ scp -p local_file userid@remote.host.name:remote_file

If the remote machine is not behind a firewall and uses a standard SSH port:

    $ scp -p happy.txt abcd0001@acadunix.algonquincollege.com:dodo.txt
    $ scp -p mydir/foo acadunix.algonquincollege.com:/tmp/bar

If the remote machine is behind a firewall and requires a special port to be used, the -P option (upper case P) must be used to set the firewall pass-through port:

    $ scp -p -P 2222 happy.txt abcd0001@example.com:dodo.txt 

4.3 Unix/Linux: Using SFTP (includes Cygwin) Index up to index

The SFTP program is a cover for SSH and SCP that makes things look like you are using the insecure FTP program; however, the actual connection and transfer is done using the secure SSH protocol. From a Unix/Linux (or Cygwin) command line, you can start SFTP like this:

    $ sftp abcd0001@acadunix.algonquincollege.com
    Connecting to acadunix.algonquincollege.com...
    abcd0001@acadunix.algonquincollege.com's password: 
    sftp> help
    [... output similar to using insecure FTP ...]
    sftp> quit

If you are familiar with insecure FTP (see below), SFTP will operate much the same way. As with insecure FTP, you can list the contents of remote directories and transfer files both ways (using “put” and “get”) on the same connection.

Some versions of SFTP use -P to set the port number; others have an awkward way to specify the port number:

    $ sftp -oPort=2222 example.com
    Connecting to example.com...
    idallen@example.com's password: 
    sftp> help
    [... output similar to using insecure FTP ...]
    sftp> quit

5 Unix/Linux Insecure FTP - File Transfer Protocol (do not use) Index up to index

The Course Linux Server does not support insecure FTP, but you can use SFTP instead with many of the same command meanings.

The old way to move files between machines was the insecure FTP (File Transfer Protocol) program. FTP is an insecure form of file transfer; because, any password you type into insecure FTP is visible across the network. Don’t use insecure FTP for transfer between machines requiring userids and passwords over an insecure network (e.g. the Internet).

If you log in to the Course Linux Server (using secure SSH), you can then use the insecure “ftp” or “lftp” commands on the Server to connect out from the Server to other remote machines (e.g. insecure FTP to your home computer or to ACADUNIX), if those other machines accept insecure FTP connections.

If you set up your home computer with an insecure FTP server [be careful!], you may use the insecure “ftp” command on the Course Linux Server to connect to your home machine, if your home machine has a public IP address and isn’t behind a firewall or NAT router. (Use SFTP instead.)

Once you have an insecure FTP connection set up, you can copy files in either direction using the “put” and “get” commands, as you wish.

Many Internet sites support a form of “anonymous” insecure FTP that lets you connect to a site without requring a password, using the special insecure FTP userid “anonymous” or “ftp”. Since it requires no password, this form of insecure FTP is safe to use over the Internet. It is how software is often provided for download to Unix/Linux users.

Command-line insecure FTP is a “subsystem” kind of program with its own set of subcommands. Once inside the insecure FTP program, your prompt becomes “ftp>”. Inside insecure FTP, the “help” command will list the possible insecure FTP commands available, and “help commandname” will give you a bit more help on the given FTP command name.

The Unix manual page for insecure FTP (“man ftp”) explains the individual insecure FTP subcommands in much better detail.

Do not confuse Unix commands with insecure FTP subcommands. Pay attention to which program is prompting you for input. To quit FTP, type “quit”.

The command-line insecure FTP program is also available under Windows. (You may need to install insecure FTP from the Windows CDROM.) The list of insecure FTP commands is slightly different; but, the basic commands (ls, cd, get, put) are the same as for Unix. (You can run command-line insecure FTP from a DOS window or using the “Run” dialog box.) Remember: FTP is not secure.

Insecure FTP will not transfer entire directories; it may only be used to transfer files one at a time. (There are ways to get insecure FTP to fetch multiple files at once; but, the files must all be in the same directory; you can’t fetch multiple directories. See the help for the “mget” insecure FTP subcommand.)

Below is an example command-line insecure FTP session to a public FTP server. This insecure FTP command could be run on a Unix/Linux machine or under Windows.

    $ ftp ftp.gnu.org
    Connected to ftp.gnu.org.
    220 GNU FTP server ready.
    530 Please login with USER and PASS.
    Name (ftp.gnu.org:idallen): anonymous   # NOTE: special userid used
    230 Login successful.                   # NOTE: no password needed!
    Remote system type is UNIX.
    Using binary mode to transfer files.
    ftp> help
    [... many lines of FTP commands show here ...]
    ftp> help ls
    ls              list contents of remote directory
    ftp> help get
    get             receive file
    ftp> help cd
    cd              change remote working directory
    ftp> ls
    150 Here comes the directory listing.
    [... many files show here ...]
    ftp> cd gnu
    ftp> ls
    150 Here comes the directory listing.
    [... many files show here ...]
    ftp> cd chess
    ftp> ls
    150 Here comes the directory listing.
    [... many files show here ...]
    ftp> get README.gnuchess
    local: README.gnuchess remote: README.gnuchess
    150 Opening BINARY mode data connection for README.gnuchess (89 bytes).
    226 File send OK.
    89 bytes received in 0.0066 seconds (13 Kbytes/s)
    ftp> quit
    221 Goodbye.
    $ ls -l README.gnuchess
    -rw-r--r--   1 idallen  idallen   89 Oct  2 00:49 README.gnuchess

5.1 FTP Binary Mode vs. Text Mode file transfer Index up to index

Insecure FTP can transfer files in either “text” or “binary” mode. Almost always use “binary” mode, which makes an exact copy of the file.

“Text” mode can be used to translate line ends when copying plain text files between dissimilar systems, e.g. between Unix and Windows, but the line-end translation will corrupt all other non-text files (i.e. images sent in text mode will be corrupted).

5.2 Insecure FTP vs. the Unix Shells Index up to index

The syntax of insecure FTP commands is not the same as the syntax of Unix commands. This insecure FTP command doesn’t do what you think it does:

    ftp> ls -l filename
    output to local-file: filename?

If you answer “yes” to this prompt, you will copy the output of “ls -l” into the file “filename” in your current directory, erasing what was there before. This is probably not what you want. Don’t do it.

The insecure FTP command names resemble Unix command names; but, they are not Unix commands. The syntax is different. You are not typing into a shell, you are typing into the insecure FTP program. Be careful.

Also, don’t type insecure FTP commands into Unix and expect that they will work, e.g. the BASH shell doesn’t understand “put filename”.

6 Microsoft Windows Users Index up to index

MS Windows does not ship with any secure file transfer programs such as SCP or SFTP, even though versions exist that are open source and free software. You can buy expensive commercial versions of SSH/SCP/SFTP for Windows from various vendors; or, you can download and install some free (source code available) programs:

6.1 The WinSCP GUI Client Index up to index

WinSCP is a graphical SCP/SFTP client for Windows. It has two GUI interface modes: Commander and Explorer. Use the Explorer interface if you are not familiar with the two-pane format of Norton Commander. Use the Commander interface if you want to move files quickly using mouse-free keyboard shortcuts.

WinSCP lets you edit files locally or remotely directly from the GUI, but be careful that you don’t make remote edits to files that you later overwrite with older versions by doing file transfer from your hard drive.

This is the easiest way to copy files into the Course Linux Server, but it cannot be automated or scripted. For use in scripts, see the PuTTY suite.

6.2 The PuTTY suite of programs (PSCP, PSFTP) Index up to index

PuTTY is a graphical telnet/SSH client and a suite of command-line (DOS window) file transfer clients.

If you download and install the full PuTTY program suite under Windows (PuTTY comes with an executable auto-installer that will do this for you), you will find the programs PSCP and PSFTP under the installation directory (usually under C:\Program Files\PuTTY). Start up a DOS command prompt, change to this directory, and run the secure commands you need to copy files to/from other systems. See below for examples of how to do this.

Unless you change your DOS search PATH, you will only be able to execute the PSCP and PSFTP commands from the directory into which you downloaded them.

When transferring files between Windows and Unix/Linux machines, remember that pathnames on the Windows machines contain backward slashes while pathnames on Unix/Linux machines contain forward slashes. For example, you might find yourself typing something like this:

    psftp> put "d:\folder\myfile.txt" "public_html/dir/page.txt"
    local:d:\dir\myfile.txt => remote:/home/abcd0001/public_html/page.txt

Windows pathnames contain backslashes and the Unix/Linux pathnames contain forward slashes. Some versions of PSFTP also accept forward slashes for Windows pathnames. You must surround the pathnames with double quotes if the pathnames contain blanks.

6.2.1 PSCP Index up to index

PSCP is a command-line copy program, similar to the Unix/Linux SCP program.

If the remote machine is behind a firewall and requires a gateway and special port to be used, the -P option (upper case P) must be used to set the firewall pass-through port. Leave it out otherwise.

The backslash at the end of a line below indicates that the line continues. Type what is written all on one line without the backslash.

    C:\> cd "C:\Program Files\PuTTY"

    C:\Program Files\PuTTY> pscp -h
...the -h displays a short help listing here...

    C:\Program Files\PuTTY> \
        pscp -P 2222 "abcd0001@example.com:dir/foo.txt" "folder\bar.txt"
    abcd0001@example.com's password:
...only use the -P option if you need the special port number...
...you may be asked to accept the host key here (say yes)...
...file transfers remote "dir/foo.txt" to local "folder\bar.txt"...
  • You must use your own userid on the remote machine. You must replace “example.com” with the machine name or IP address to which you wish to connect. The -P option sets a non-standard port number, if you need it.

  • Windows pathnames should contain backslashes and the Unix/Linux pathnames contain forward slashes. Some versions of PSCP accept forward slashes for Windows pathnames. You must surround the pathnames with double quotes if the pathnames contain blanks.

6.2.2 PSFTP Index up to index

PSFTP is a secure command-line FTP-like program, similar to standard FTP.

If the remote machine is behind a firewall and requires a special port to be used, the -P option (upper case P) must be used to set the firewall pass-through port. Leave it out otherwise.

    C:\> cd "C:\Program Files\PuTTY"

    C:\Program Files\PuTTY> psftp -h
...the -h displays a short help listing here...

    C:\Program Files\PuTTY> psftp -P 2222 abcd0001@example.com
...only use the -P option if you need the special port number...
...you may be asked to accept the host key here (say yes)...
    abcd0001@example.com's password:
    Remote working directory is /home/abcd0001
    psftp> help
...short help listing displays here...
    psftp> ls
...listing of directory displays here...
    psftp> get ".bashrc" "foo.txt"
    remote:/home/abcd0001/.bashrc => local:foo.txt
    psftp> put "d:\dir\myfile.txt" "public_html/page.txt"
    local:d:\dir\myfile.txt => remote:/home/abcd0001/public_html/page.txt psftp> quit
...file "foo.txt" is now in the current directory...
  • You must use your own userid on the remote machine. You must replace “example.com” with the machine name or IP address to which you wish to connect. The -P option sets a non-standard port number, if you need it.

  • Windows pathnames should contain backslashes and the Unix/Linux pathnames contain forward slashes. Some versions of PSFTP accept forward slashes for Windows pathnames. You must surround the pathnames with double quotes if the pathnames contain blanks.

  • The options to the PuTTY Windows version of SFTP (named PSFTP) are not the same as the options to the Unix/Linux version of SFTP. In particular, the option “-P” has different meanings!

6.2.3 Example SCP and SFTP Windows Command Lines Index up to index

First, here are some typical PSCP command lines for file transfer from a local (Windows) computer to the public_html directory of the abcd0001 account on the Course Linux Server. The first line uses the Public gateway and special port 2222; the second uses the Private IP address (via the VPN or On-Campus):

    pscp -P 2222 d:\dir\image.jpg abcd0001@cst8281.idallen.ca:public_html/a10/image.jpg

    pscp d:\dir\image.jpg abcd0001@10.50.254.148:public_html/a10/image.jpg

Second, here is the same transfer using the PSFTP command instead of PSCP:

    psftp -P 2222 abcd0001@cst8281.idallen.ca
    password:
    psftp> put d:\dir\image.jpg public_html/a10/image.jpg
    psftp> help

    psftp abcd0001@10.50.254.148
    password:
    psftp> put d:\dir\image.jpg public_html/a10/image.jpg
    psftp> help
  1. You must replace abcd0001 with your own userid. You will be asked for your password on the Course Linux Server. If you are asked to accept the server encryption key, say “yes”.

  2. You must remember to insert the web directory name “public_html” into all your file names for the Course Linux Server, since that is where the web server looks in your account. Files put into your home directory will not be visible on the Web.

  3. Slashes go backwards for Windows pathnames and forwards for Unix pathnames.

  4. The psftp and pscp commands may not be in your Windows DOS search PATH. You can add the directory containing these commands to your DOS search PATH, or you can change to the directory containing these commands when you want to run them, or you can type the absolute path of the command names if you aren’t in the right directory.

6.3 Windows Insecure FTP (do not use) Index up to index

The Course Linux Server does not support insecure FTP.

MS Windows has a command-line version of insecure FTP available from a DOS prompt or in a DOS window. You can also download various graphical insecure FTP clients. Many recommend the insecure programs “FileZilla” or “WS_FTP”.

6.3.1 Using Windows GUI via Windows Explorer Index up to index

Some versions of Windows also let you use an insecure FTP URI to connect to an insecure FTP server and log in and transfer files, e.g. using this form of URI:

    ftp://ftp.algonquincollege.com/

The Windows Explorer (not Internet Explorer!) will let you open an insecure FTP URI such as the one above and drag-and-drop files between your machine and a remote machine graphically. Underneath, Windows is using the insecure FTP protocol and your data and passwords are visible to anyone who can snoop your network connection. Don’t use this.

  1. You must log in with your own Linux userid. You will be asked for your FTP password.

  2. Your password and data are not encrypted when you use insecure FTP. Do not use this method on an untrusted network (i.e. Internet).

  3. You may be able to access a file via FTP that cannot be displayed in a web browser, since the FTP program is logged in as your account name and the web browser accesses your files as “other”. You must ensure that your files have read permissions for “other” after you transfer them to the Course Linux Server.

  4. Windows Explorer, using insecure FTP, may create directories and files with the wrong Linux permissions. Directories under your public_html directory must be readable and searchable (not writable!) by “other”. Files under your public_html directory must also be readable (not writable or executable!) by others. Inaccessible files and directories will generate “Permission Denied” errors in your web browser. Files and directories with unwanted “write” permissions will allow other users to delete or erase your web pages.

7 File Transfer Hacks Index up to index

Here are some ways to move files around without using a file transfer program:

7.1 Use the Web Index up to index

If you run a web server on your machine, you can move a file into the web directory and access it remotely via any browser and HTTP.

The Unix/Linux command “wget” can fetch files (web pages) for you:

    $ wget http://cst8281.idallen.ca:8080/~abcd0001/foo.txt
    $ wget http://idallen.com/

7.2 Use EMail for text files Index up to index

If the file you want to take home from Unix is a text file (not an image), you can usually EMail it to yourself somewhere using a command-line Unix EMail program with standard input redirected to come from the file you want. Unix mail programs that work this way are “mutt”, “Mail”, “mailx”, and “mail”. For example:

    $ mutt  abcd0001@algonquincollege.com  <.bashrc
    $ mutt  me@hotmail.com  <.bashrc

You can only send text files this way, and you can only send one file per mail message using file input redirection (unless you concatenate many files together first). See “man mail” for further details.

To send binary programs via email you must encode them as ASCII first and decode them after receiving them. See “man uuencode”.

Author: 
| Ian! D. Allen  -  idallen@idallen.ca  -  Ottawa, Ontario, Canada
| Home Page: http://idallen.com/   Contact Improv: http://contactimprov.ca/
| College professor (Free/Libre GNU+Linux) at: http://teaching.idallen.com/
| Defend digital freedom:  http://eff.org/  and have fun:  http://fools.ca/

Plain Text - plain text version of this page in Pandoc Markdown format


Campaign for non-browser-specific HTML   Valid XHTML 1.0 Transitional   Valid CSS!   Creative Commons by nc sa 3.0   Hacker Ideals Emblem   Author Ian! D. Allen