Posts Tagged ‘dump’

Linux: List last 10 (newest) and 10 oldest modified files in a directory with ls

Tuesday, April 8th, 2014

Reading Time: < 1minute

An useful thing on GNU / Linux sometimes is to list last or oldest modified files in directory.

Lets say you want to list last 10 modified files with ls from today / yesterday. Here is how:

ls -1t | head -10


To list 10 oldest modified files on Linux:


ls -1t | tail -10

Cheers 😉

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 ' (' 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 '' (RSA) to the list of known hosts. hipo@'s password:

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.

Tiny PHP script to dump your browser set HTTP headers (useful in debugging)

Friday, March 30th, 2012

Reading Time: 2minutes

While browsing I stumbled upon a nice blog article

Dumping HTTP headers

The arcitle, points at few ways to DUMP the HTTP headers obtained from user browser.
As I'm not proficient with Ruby, Java and AOL Server what catched my attention is a tiny php for loop, which loops through all the HTTP_* browser set variables and prints them out. Here is the PHP script code:

<?php<br />
foreach($_SERVER as $h=>$v)<br />
if(ereg('HTTP_(.+)',$h,$hp))<br />
echo "<li>$h = $v</li>\n";<br />
header('Content-type: text/html');<br />

The script is pretty easy to use, just place it in a directory on a WebServer capable of executing php and save it under a name like:

If you don't want to bother copy pasting above code, you can also download the dump_HTTP_headers.php script here , rename the dump_HTTP_headers.php.txt to dump_HTTP_headers.php and you're ready to go.

Follow to the respective url to exec the script. I've installed the script on my webserver, so if you are curious of the output the script will be returning check your own browser HTTP set values by clicking here.
PHP will produce output like the one in the screenshot you see below, the shot is taken from my Opera browser:

Screenshot show HTTP headers.php script Opera Debian Linux

Another sample of the text output the script produce whilst invoked in my Epiphany GNOME browser is:

HTTP_USER_AGENT = Mozilla/5.0 (X11; U; Linux x86_64; en-us) AppleWebKit/531.2+ (KHTML, like Gecko) Version/5.0 Safari/531.2+ Debian/squeeze (2.30.6-1) Epiphany/2.30.6
HTTP_ACCEPT = application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
HTTP_ACCEPT_LANGUAGE = en-us, en;q=0.90
HTTP_COOKIE = __qca=P0-2141911651-1294433424320;
__utma_a2a=8614995036.1305562814.1274005888.1319809825.1320152237.2021;wooMeta=MzMxJjMyOCY1NTcmODU1MDMmMTMwODQyNDA1MDUyNCYxMzI4MjcwNjk0ODc0JiYxMDAmJjImJiYm; 3ec0a0ded7adebfeauth=22770a75911b9fb92360ec8b9cf586c9;
__utmb=238407297.1.10.1333023754; __utmc=238407297;|utmccn=(referral)|utmcmd=referral|utmcct=/blog/

You see the script returns, plenty of useful information for debugging purposes:
HTTP_HOST – Virtual Host Webserver name
HTTP_USER_AGENT – The browser exact type useragent returnedHTTP_ACCEPT – the type of MIME applications accepted by the WebServerHTTP_ACCEPT_LANGUAGE – The language types the browser has support for
HTTP_ACCEPT_ENCODING – This PHP variable is usually set to gzip or deflate by the browser if the browser has support for webserver returned content gzipping.
If HTTP_ACCEPT_ENCODING is there, then this means remote webserver is configured to return its HTML and static files in gzipped form.
HTTP_COOKIE – Information about browser cookies, this info can be used for XSS attacks etc. 🙂
HTTP_COOKIE also contains the referrar which in the above case is:|utmccn=(referral)
The Cookie information HTTP var also contains information of the exact link referrar:

For the sake of comparison show_HTTP_headers.php script output from elinks text browser is like so:

* HTTP_USER_AGENT = Links (2.3pre1; Linux 2.6.32-5-amd64 x86_64; 143x42)
* HTTP_ACCEPT_ENCODING = gzip,deflate * HTTP_ACCEPT_CHARSET = us-ascii, ISO-8859-1, ISO-8859-2, ISO-8859-3, ISO-8859-4, ISO-8859-5, ISO-8859-6, ISO-8859-7, ISO-8859-8, ISO-8859-9, ISO-8859-10, ISO-8859-13, ISO-8859-14, ISO-8859-15, ISO-8859-16, windows-1250, windows-1251, windows-1252, windows-1256,
windows-1257, cp437, cp737, cp850, cp852, cp866, x-cp866-u, x-mac, x-mac-ce, x-kam-cs, koi8-r, koi8-u, koi8-ru, TCVN-5712, VISCII,utf-8 * HTTP_ACCEPT_LANGUAGE = en,*;q=0.1
* HTTP_CONNECTION = keep-alive
One good reason, why it is good to give this script a run is cause it can help you reveal problems with HTTP headers impoperly set cookies, language encoding problems, security holes etc. Also the script is a good example, for starters in learning PHP programming.


List and get rid of obsolete program core dump files and completely disable core files on FreeBSD

Tuesday, November 1st, 2011

Reading Time: < 1minute
My FreeBSD router has started running out of space, I looked for ways to clean up some space. So I remembered some programs are generating core files while they crash. Some of these files are really huge and ban be from 1Mb to > 1G.

I used find to first list all my produced core files starting from root directory (/) , like so:

find / -name core -exec du -hsc {} ;

Having a list of my core files with the respective core file size and after reviewing, I deleted one by one the cores which were there just taking up space.
It’s a wise idea that core dumps file generation on program crash is completely disabled, however I forgot to disable cores, so I had plenty of the cores – (crash files which are handy for debug purposes and fixing the bug that caused the crash).

Further on I used an /etc/rc.confdumpdev=NO , variable which instructs the kernel to not generate core files on program crash:

freebsd# echo 'dumpdev=NO' >> /etc/rc.conf

Next, to make dumpdev=NO , take affect I rebooted the server:

freebsd# shutdown -r now

There is a way to instruct every server running daemon to know about the newly set dumpdev=NO by restarting each of the services with their init scripts individually, but I was too lazy to do that.