Posts Tagged ‘scp’

Resume sftp / scp cancelled (interrupted) network transfer – Continue (large) partially downloaded files on Linux / Windows

Thursday, April 23rd, 2015

Reading Time: 3minutes

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I've recentely have a task to transfer some huge Application server long time stored data (about 70GB) of data after being archived between an old Linux host server and a new one to where the new Tomcat Application (Linux) server will be installed to fit the increased sites accessibility (server hardware overload).

The two systems are into a a paranoid DMZ network and does not have access between each other via SSH / FTP / FTPs and even no Web Access on port (80 or SSL – 443) between the two hosts, so in order to move the data I had to use a third HOP station Windows (server) which have a huge SAN network attached storage of 150 TB (as a Mapped drive I:/).

On the Windows HOP station which is giving me access via Citrix Receiver to the DMZ-ed network I'm using mobaxterm so I have the basic UNIX commands such as sftp / scp already existing on the Windows system via it.
Thus to transfer the Chronos Tomcat application stored files .tar.gz archived I've sftp-ed into the Linux host and used get command to retrieve it, e.g.:

 

sftp UserName@Linux-server.net
Password:
Connected to Linux-server.
sftp> get Chronos_Application_23_04_2015.tar.gz

….


The Secured DMZ Network seemed to have a network shaper limiting my get / Secured SCP download to be at 2.5MBytes / sec, thus the overall file transfer seemed to require a lot of time about 08:30 hours to complete. As it was the middle of day about 13:00 and my work day ends at 18:00 (this meant I would be able to keep the file retrieval session for a maximum of 5 hrs) and thus file transfer would cancel when I logout of the HOP station (after 18:00). However I've already left the file transfer to continue for 2hrs and thus about 23% of file were retrieved, thus I wondered whether SCP / SFTP Protocol file downloads could be resumed. I've checked thoroughfully all the options within sftp (interactive SCP client) and the scp command manual itself however none of it doesn't have a way to do a resume option. Then I thought for a while what I can use to continue the interrupted download and I remembered good old rsync (versatile remote and local file copying tool) which I often use to create customer backup stragies has the ability to resume partially downloaded files I wondered whether this partially downloaded file resume could be done only if file transfer was only initiated through rsync itself and luckilyrsync is able to continue interrupted file transfers no matter what kind of HTTP / HTTPS / SCP / FTP program was used to start file retrievalrsync is able to continue cancelled / failed transfer due to network problems or user interaction activity), that turned even pretty easy to continue failed file transferdownload from where it was interrupted I had to change to directory where file is located:
 

cd /path/to/interrupted_file/


and issue command:
 

rsync -av –partial username@Linux-server.net:/path/to/file .


the –partial option is the one that does the file resume trick, -a option stands for –archive and turns on the archive mode; equals -rlptgoD (no -H,-A,-X) arguments and -v option shows a file transfer percantage status line and an avarage estimated time for transfer to complete, an easier to remember rsync resume is like so:
 

rsync -avP username@Linux-server.net:/path/to/file .
Password:
receiving incremental file list
chronos_application_23_04_2015.tar.gz
  4364009472   8%    2.41MB/s    5:37:34

To continue a failed file upload with rsync (e.g. if you used sftp put command and the upload transfer failed or have been cancalled:
 

rsync -avP chronos_application_23_04_2015.tar.gz username@Linux-server.net:/path/where_to/upload


Of course for the rsync resume to work remote Linux system had installed rsync (package), if rsync was not available on remote system this would have not work, so before using this method make sure remote Linux / Windows server has rsync installed. There is anrsync port also for Windows so to resume large Giga or Terabyte file archive downloads easily between two Windows hosts use cwRsync.

How to copy / clone installed packages from one Debian server to another

Friday, April 13th, 2012

Reading Time: 3minutes

1. Dump all installed server packages from Debian Linux server1

First it is necessery to dump a list of all installed packages on the server from which the intalled deb packages 'selection' will be replicated.

debian-server1:~# dpkg --get-selections \* > packages.txt

The format of the produced packages.txt file will have only two columns, in column1 there will be the package (name) installed and in column 2, the status of the package e.g.: install or deinstall

Note that you can only use the –get-selections as root superuser, trying to run it with non-privileged user I got:

hipo@server1:~$ dpkg --set-selections > packages.txt
dpkg: operation requires read/write access to dpkg status area

2. Copy packages.txt file containing the installed deb packages from server1 to server2

There is many way to copy the packages.txt package description file, one can use ftp, sftp, scp, rsync … lftp or even copy it via wget if placed in some Apache directory on server1.

A quick and convenient way to copy the file from Debian server1 to server2 is with scp as it can also be used easily for an automated script to do the packages.txt file copying (if for instance you have to implement package cloning on multiple Debian Linux servers).

root@debian-server1:~# scp ./packages.txt hipo@server-hostname2:~/packages.txt
The authenticity of host '83.170.97.153 (83.170.97.153)' can't be established. RSA key fingerprint is 38:da:2a:79:ad:38:5b:64:9e:8b:b4:81:09:cd:94:d4. Are you sure you want to continue connecting (yes/no)? yes Warning: Permanently added '83.170.97.153' (RSA) to the list of known hosts. hipo@83.170.97.153's password:
packages.txt

As this is the first time I make connection to server2 from server1, I'm prompted to accept the host RSA unique fingerprint.

3. Install the copied selection from server1 on server2 with apt-get or dselect

debian-server2:/home/hipo# apt-get update
...
debian-server2:/home/hipo# apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
debian-server2:/home/hipo# dpkg --set-selections < packages.txt
debian-server2:/home/hipo# apt-get -u dselect-upgrade --yes

The first apt-get update command assures the server will have the latest version of the packages currently installed, this will save you from running an outdated versions of the installed packages on debian-server2

Bear in mind that using apt-get sometimes, might create dependency issues. This is depending on the exact package names, being replicated in between the servers

Therefore it is better to use another approach with bash for loop to "replicate" installed packages between two servers, like so:

debian-server2:/home/hipo# for i in $(cat packages.txt |awk '{ print $1 }'); do aptitude install $i; done

If you want to automate the questioning about aptitude operations pass on the -y

debian-server2:/home/hipo# for i in $(cat packages.txt |awk '{ print $1 }'); do aptitude -y install $i; done

Be cautious if the -y is passed as sometimes some packages might be removed from the server to resolve dependency issues, if you need this packages you will have to again install them manually.

4. Mirroring package selection from server1 to server2 using one liner

A quick one liner, that does replicate a set of preselected packages from server1 to server2 is also possible with either a combination of apt, ssh, awk and dpkg or with ssh + dpkg + dselect :

a) One-liner code with apt-get unifying the installed packages between 2 or more servers

debian-server2:~# apt-get --yes install `ssh root@debian-server1 "dpkg -l | grep -E ^ii" | awk '{print $2}'`
...

If it is necessery to install on more than just debian-server2, copy paste the above code to all servers you want to have identical installed packages as with debian-server1 or use a shor for loop to run the commands for each and every host of multiple servers group.

In some cases it might be better to use dselect instead as in some situations using apt-get might not correctly solve the package dependencies, if encountering problems with dependencies better run:

debian-server2:/home/hipo# ssh root@debian-server1 'dpkg --get-selections' | dpkg --set-selections && dselect install

As you can see using this second dselect installed "package" mirroring is also way easier to read and understand than the prior "cryptic" method with apt-get, hence I personally think using dselect method is a better.

Well that's basically it. If you need to synchronize also configurations, either an rsync/scp shell script, should be used with all defined server1 config files or in case if a cloning of packages between identical server machines is necessery dd or some other tool like Norton Ghost could be used.
Hope this helps, someone.

Using rsync to copy / synchronize files or backups between Linux / BSD / Unix servers

Monday, November 21st, 2011

Reading Time: 2minutes

Rsync and Rsync over ssh logo picture

Many of us have already taken advantage of the powerful Rsync proggie, however I'm quite sure there are still people who never used rsync to transfer files between servers.. That's why I came with this small post to possibly introduce rsync to my blog readers.
Why Rsync and not Scp or SFTP? Well Rsync is designed from the start for large files transfer and optimized to do the file copying job really efficient. Some tests with scp against rsync will clearly show rsync's superiority.
Rsync is also handy to contiue copying of half copied files or backups and thus in many cases saves bandwidth and machine hdd i/o operations.

The most simple way to use rsync is:

server:~# rsync -avz -e ssh remoteuser@remotehost:/remote/directory /local/directory/

Where remoteuser@remotehost — is the the username and hostname of remote server to copy files to.
/remote/directory — is the directory where the rsync copied files should be stored
/local/directory — is the local directory from which files will be copied to remote directory

If not a preliminary passwordless ssh key (RSA / DSA) authentication is configured on remote server, the above command will prompt for a password otherwise the rsync will start doing the transfer.

If one needs to have a RSA or DSA (public / private key) passwordless SSH key authentication , a RSA key first should be generated and copied over to the remote server, like so:

server:~# ssh-keygen -t dsa
...
server:~# ssh-copy-id -i ~/.ssh/id_dsa.pub root@remotehost
...

That's all folks, enjoy rsyncing 😉