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SFTP

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SFTP is normally used as an interactive application/protocol, but also can be put into a batch mode with the -b flag. This can be specified with a file or can be directed stdin from an external script.

The password can not be passed by either process.

sftp [-1Cv] [-b batchfile] [-F SSH_config] [-o SSH_option] [-s subsystem | sftp_server] [-S program] host

sftp [[user@]host[:file [file]]]

sftp [[user@]host[:dir[/]]]

But mostly SFTP is used as an interactive file transfer program.

With FTP one might try to copy up all their JPG files to their image directory like this:

ftp> cd /home/user/images/
ftp> bin
ftp> prompt
ftp> mput *.jpg

With SFTP it is much simpler..

sftp> cd /home/user/images/
sftp> put *.jpgtt>

List of SFTP commands (SFTP will abort if any of the following commands fail):

List of other commands:

SFTP may also use many features of SSH, such as public key authentication and compression. SFTP connects and logs into the specified host, then enters an interactive command mode. The second usage format will retrieve files automatically if a noninteractive authentication method is used; otherwise it will do so after successful interactive authentication. The last usage format allows the sftp client to start in a remote directory. 

Here are the options used:


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[Sep 28, 2017] Transferring Files with Secure FTP (sftp)

Part of the OpenSSH (Open Source Secure Shell) project, Secure FTP (sftp) is another file-transfer program that works in a similar way to FTP but encrypts the transfer so that it cannot be intercepted or read by intermediary computers. The encryption process increases the amount of data and slows the transfer but provides protection for confidential information.

You must specify the computer and user account on the sftp command line. SFTP prompts you for the password.

$ sftp root@our_web_site.com:/etc/httpd/httpd.conf
Connecting to our_web_site.com...
root@our_web_site.coms password:
Fetching /etc/httpd/httpd.conf to httpd.conf

For security purposes, SFTP normally asks the user for the Linux login password. It doesn't request the password from standard input but from the controlling terminal. This means you can't include the password in the batch file. The solution to this problem is to use SSH's public key authentication using the ssh-keygen command. If you have not already done so, generate a new key pair as follows.

$ ssh-keygen -t rsa
				

A pair of authentication keys are stored under .ssh in your home directory. You must copy the public key (a file ending in .pub) to the remote machine and add it to a text file called ~/.sshd/authorized_keys. Each local login accessing the remote login needs a public key in authorized_keys. If a key pair exists, SFTP automatically uses the keys instead of the Linux login password.

Like FTP, SFTP needs a list of commands to carry out. SFTP includes a -b (batch) switch to specify a separate batch file containing the commands to execute. To use a convenient here file in your script, use a batch file called /dev/stdin.

The commands that SFTP understands are similar to FTP. For purposes of shell scripting, the basic transfer commands are the same. Transfers are always "binary." There is a -v (verbose) switch, but it produces a lot of information. When the -b switch is used, SFTP shows the commands that are executed so the -v switch is not necessary for logging what happened during the transfer.

sftp -C -b /dev/stdin root@our_web_site.com <<!
cd /etc/httpd
get httpd.conf
!
STATUS=$?
if [ $STATUS -ne 0 ] ; then
   printf "%s\n" "Error: SFTP transfer failed" >&2
   exit $STATUS
fi

The -C (compress) option attempts to compress the data for faster transfers.

For more information about ssh, sftp, and related programs, visit http://www.openssh.org/.

[Mar 16, 2010] Resuming interrupted sftp transfers in Linux " Free Software

Even though the Linux version of the sftp client doesn't offer a direct way to resume an interrupted transfer, doing so is quite simple by using common shell tools, as long as you are able to login to the remote server through a console. Assuming that you are transferring data.zip from source_server to target_server and the transfer was interrupted, you can do the following:

This works for both text and binary files. Apparently a better way would be integrating this ability into the sftp client, which is the way some clients such as putty and winscp work, but until that happy day you can use the tips above as a workaround.

Comments

mikeX:

lftp is a very nice command line ftp client, which supports tab completion, directory mirroring and of course resuming of interrupted downloads. It can also work as an sftp client, with the right protocol prefix, e.g. lftp sftp://user@host, and can even be used in batch mode. You can find a copy at http://lftp.yar.ru/. Still, nice trick :)

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