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Force your users to change their passwords frequently

ggarron — Sat, 04 Oct 2008 07:18:36 -0700

The users of a Linux Operating system computer, should always take care about security and if you are the admin of a Linux box with lots of users, you are responsible for the security of it, and maybe you should "force" the other users to change their passwords from time to time, to make this use the command chage

Apply this to a user, lets say guillermo

sudo chage --list guillermo

something like this may appear.

$sudo chage --list guillermo
Last password change                                    : May 10, 2008
Password expires                                        : never
Password inactive                                       : never
Account expires                                         : never
Minimum number of days between password change          : 0
Maximum number of days between password change          : 99999
Number of days of warning before password expires       : 7

Now lets change change its expiry password date.

sudo chage -M 30 guillermo

This will make its password to expire after 30 days of the last change date.

See now the new info:

$ sudo chage --list guillermo
Last password change                                    : May 10, 2008
Password expires                                        : Jun 09, 2008
Password inactive                                       : never
Account expires                                         : never
Minimum number of days between password change          : 0
Maximum number of days between password change          : 30
Number of days of warning before password expires       : 7

Now when I try to login as guillermo, this is what I got:

$ su - guillermo
Password: 
You are required to change your password immediately (password aged)
Changing password for guillermo.
(current) UNIX password: 
Enter new UNIX password: 
Retype new UNIX password: 
Password unchanged
Enter new UNIX password: 
Retype new UNIX password:

I tried to use the same password again the Linux refused to let me use it, so I was forced to pick a new password.

It is good to have the warn days to 3 or more days, so the user may have time to think a new good password, otherwise will use the first thing he/she may read around resulting in a weak password, which is worse that not changing the original one.

To set the warn days use this command.

sudo chage -W 4 guillermo

Now lets check the info for user guillermo

$ sudo chage --list guillermo
Last password change					: Oct 04, 2008
Password expires					: Nov 03, 2008
Password inactive					: never
Account expires						: never
Minimum number of days between password change		: 0
Maximum number of days between password change		: 30
Number of days of warning before password expires	: 4

Now you may see the new expiry date is Nov 3, 2008 and he will have a 4 days warning about the expiry of his password.

Editing "bluring" your images with GIMP to create bokeh effect

ggarron — Sat, 04 Oct 2008 06:56:26 -0700

If you like the bokeh effect in some pictures you can create it with GIMP, it may not be the same as created at the time of taking the picture (With lenses).

Check out this bokeh pictures

Well now lets see how to create kind of bokeh effect using GIMP

This is the original image:

What we first need to do, is to use the GIMP free select tool.

Then select the contour of the image you want to be highlighted, in this case the flower.

Now with the selection done, press "Ctrl+c" and then "Ctrl+v", and go to layers view.

As you can see it appeared a new layer, a "floating selection (pasted layer)", now right-click on it and select "new layer"

Ok, now we have two layers one with the full image and the other with only our selection.

Select now the layer with the full image, and right-click over the image itself, select the menu "filters" and then, "blur" and then "Gaussian blur".

Select the value that better works for your image.

And the final job is here:

Hope you enjoy it, and thanks goes to: Digital Photography blogs

Alias - create alias for your commands

ggarron — Sat, 20 Sep 2008 08:38:11 -0700

Alias is a command that lets you create command aliases, it is very useful when you usually use commands with options.

As an example in my case I use a lot these commands

du -h

and

df -h

In both cases the "-h" option makes the output be in Kbytes or Mbytes instead of bytes, so it is more human redeable.

To create aliases for this commands just need to enter.

alias du='du -h'

and

alias df='df -h'

Now both du and df will be executed with its -h option.

If you need to de-alias the command just enter:

unalias du

And the alias for du will be deleted.

To view a list of all aliases just type alias with no arguments on the command line.

Running a program in the background

ggarron — Sat, 20 Sep 2008 08:09:09 -0700

If you need to start a program from the command line, and want to recover the command prompt, just add the & symbol to the command.

Example.

firefox

This command will start firefox, but the command prompt will not be available for you to continue working.

firefox &

With this other you will get the prompt back to you, and you can continue using the console for other tasks, It also returns you a number that number is the PID of the application just started.

Making grub menu to wait for you -change timeout-

ggarron — Sat, 20 Sep 2008 07:34:09 -0700

On my PC I have installed, Mandriva, Ubuntu, Gentoo, Sabayon and Debian (my main Linux operating system), but when I turn it on, usually I did not get the grub menu, and I am forwarded directly to Debian, sometimes I have to restart the system to start another Linux flavor.

So, the solution was to put the timeout of grub menu to 15 seconds, so I have enough time to react even when I am not paying attention to the PC startup.

The timeout parameter is stored in the file

/boot/grub/menu.lst

So, to change it edit that file with your favorite text editor. (mine is vim)

sudo vim /boot/grub/menu.lst

and look for the line that contains the string "timeout"

This is how my file looks

## timeout sec
# Set a timeout, in SEC seconds, before automatically booting the default entry
# (normally the first entry defined).
timeout         15

please note that the above text is only part of my menu.lst.

If you want grub to wait for you to take an action before continue, comment the timeout line, or erase it.

whowatch - Monitor who is doing what on your system

ggarron — Fri, 12 Sep 2008 14:17:55 -0700

whowatch is a console application that lets you monitor what different users are doing on the Linux operating system in a given moment, it works in real time.

First install it

sudo aptitude install whowatch

Now to run it just enter whowath in the command line, some screen like this will appear.

If you press ENTER while on a given username you will see the info about the programs that user is running.

Like this:

As you can see below you may see some command that lets you get more info about the user, and the programs being run by him.

If you go to "menu" by pressing F9 from the main menu, you will also be able among other things to send kill, HUB or TERM signals to the processes running, you can also use the keyboard for that with

^K for Kill
^U for HUP
^T for TERM

A pretty useful tool for admins

dpkg: ../../src/packages.c:221: process_queue: Assertion `dependtry <= 4' failed

ggarron — Tue, 09 Sep 2008 14:36:39 -0700

I run a

sudo aptitude full-upgrade

On my Debian Lenny, but once all the packages were downloaded and started to be installed, suddenly the process stopped, then when I run

sudo aptitude reinstall

I got this:

sudo aptitude reinstall
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Reading extended state information      
Initializing package states... Done
Writing extended state information... Done
Reading task descriptions... Done         
The following partially installed packages will be configured:
  cups-driver-gutenprint cupsys-driver-gutenprint debian-faq gxine 
  libregexp-java menu 
0 packages upgraded, 0 newly installed, 0 to remove and 170 not upgraded.
Need to get 0B of archives. After unpacking 0B will be used.
Writing extended state information... Done
dpkg: error processing iptables (--configure):
 package iptables is not ready for configuration
 cannot configure (current status `triggers-awaited')
dpkg: error processing nano (--configure):
 package nano is not ready for configuration
 cannot configure (current status `triggers-awaited')
dpkg: error processing debian-faq (--configure):
 package debian-faq is not ready for configuration
 cannot configure (current status `triggers-awaited')
dpkg: error processing cups (--configure):
 package cups is not ready for configuration
 cannot configure (current status `triggers-awaited')
dpkg: error processing libxine1-bin (--configure):
 package libxine1-bin is not ready for configuration
 cannot configure (current status `triggers-awaited')
dpkg: error processing libregexp-java (--configure):
 package libregexp-java is not ready for configuration
 cannot configure (current status `triggers-awaited')
dpkg: error processing menu (--configure):
 package menu is not ready for configuration
 cannot configure (current status `triggers-awaited')
dpkg: ../../src/packages.c:221: process_queue: Assertion `dependtry <= 4' failed.
E: Sub-process /usr/bin/dpkg exited unexpectedly
A package failed to install.  Trying to recover:
dpkg: ../../src/packages.c:221: process_queue: Assertion `dependtry <= 4' failed.
Reading package lists... Done             
Building dependency tree       
Reading state information... Done
Reading extended state information      
Initializing package states... Done
Reading task descriptions... Done

So, after googling a little, I used dpkg to uninstall manually all the packages listed above,

sudo dpkg -r cups-driver-gutenprint cupsys-driver-gutenprint debian-faq gxine

Then the command

sudo aptitude reinstall

worked again, and I was able to install those packages again.

VMware Server 1.05 fails to start with version 2:1.1.4-2 of libx11-6

ggarron — Sun, 31 Aug 2008 07:34:06 -0700

Some days ago I have updated my Lenny and VMware stop working, this time it was not a problem of a new kernel usually solved reconfiguring vmware, this time the problem was the new version of libx11-6 does not work with vmware, so the solution is to downgrade it to the Etch version.

First create a file called

/etc/apt/preferences

put this content inside:

Package: libx11-6
Pin: release a=stable
Pin-Priority: 1001

Package: *
Pin: release a=testing
Pin-Priority: 500

Then modify your /etc/apt/sources.list

and add the stable (or Etch) lines, mine looks like this:

deb http://ftp.debian.org/debian/ testing main non-free contrib
#deb-src http://mirrors.kernel.org/debian/ lenny main non-free contrib

#deb http://mirrors.xenir.com/debian/ lenny main non-free contrib

deb http://security.debian.org/ testing/updates main contrib non-free
#deb-src http://security.debian.org/ lenny/updates main contrib non-free

deb http://download.skype.com/linux/repos/debian/ stable non-free

deb http://deb.opera.com/opera lenny non-free
#

#stable
deb http://ftp.debian.org/debian/ stable main non-free contrib

Now run

sudo aptitude update

to update your database.

Now run:

sudo apt-get -t stable install libx11-6

that command will downgrade the libx11-6 package to a version that will work with VMWare.

be sure that your output when running VMware is like this to be sure this is your solution:

Locking assertion failure.  Backtrace:
#0 /usr/lib/libxcb-xlib.so.0 [0xb6f43767]
#1 /usr/lib/libxcb-xlib.so.0(xcb_xlib_unlock+0x31) [0xb6f438b1]
#2 /usr/lib/libX11.so.6(_XReply+0x244) [0xb7dc2c14]
#3 /usr/lib/vmware/lib/libXrender.so.1/libXrender.so.1(XRenderQueryFormats+0x109) [0xb7cae969]
#4 /usr/lib/vmware/lib/libXrender.so.1/libXrender.so.1(XRenderFindFormat+0x4c) [0xb7caef4c]
#5 /usr/lib/vmware/lib/libgdk-x11-2.0.so.0/libgdk-x11-2.0.so.0 [0xb7af4180]
#6 /usr/lib/vmware/lib/libgdk-x11-2.0.so.0/libgdk-x11-2.0.so.0 [0xb7af4d2c]
#7 /usr/lib/vmware/lib/libgdk-x11-2.0.so.0/libgdk-x11-2.0.so.0(gdk_draw_pixbuf+0x270) [0xb7ac4c14]
#8 /usr/lib/vmware/lib/libgdk-x11-2.0.so.0/libgdk-x11-2.0.so.0 [0xb7ad124f]
#9 /usr/lib/vmware/lib/libgdk-x11-2.0.so.0/libgdk-x11-2.0.so.0(gdk_draw_pixbuf+0x270) [0xb7ac4c14]
#10 /usr/lib/vmware/lib/libgdk-x11-2.0.so.0/libgdk-x11-2.0.so.0(gdk_pixbuf_render_pixmap_and_mask_for_colormap+0x255) [0xb7ad0b34]
#11 /usr/lib/vmware/lib/libgtk-x11-2.0.so.0/libgtk-x11-2.0.so.0 [0xb79d5298]
#12 /usr/lib/vmware/lib/libgtk-x11-2.0.so.0/libgtk-x11-2.0.so.0 [0xb79d5586]
#13 /usr/lib/vmware/lib/libgtk-x11-2.0.so.0/libgtk-x11-2.0.so.0 [0xb79d777e]
#14 /usr/lib/vmware/lib/libgobject-2.0.so.0/libgobject-2.0.so.0(g_cclosure_marshal_VOID__VOID+0xd1)
[0xb7bea459]
#15 /usr/lib/vmware/lib/libgobject-2.0.so.0/libgobject-2.0.so.0 [0xb7bd23a1]
#16 /usr/lib/vmware/lib/libgobject-2.0.so.0/libgobject-2.0.so.0(g_closure_invoke+0x1b1) [0xb7bd2076]
#17 /usr/lib/vmware/lib/libgobject-2.0.so.0/libgobject-2.0.so.0 [0xb7be96eb]
#18 /usr/lib/vmware/lib/libgobject-2.0.so.0/libgobject-2.0.so.0(g_signal_emit_valist+0x91e) [0xb7be8d46]
#19 /usr/lib/vmware/lib/libgobject-2.0.so.0/libgobject-2.0.so.0(g_signal_emit+0x38) [0xb7be90b8]
Locking assertion failure.  Backtrace:
#0 /usr/lib/libxcb-xlib.so.0 [0xb6f43767]
#1 /usr/lib/libxcb-xlib.so.0(xcb_xlib_lock+0x2e) [0xb6f4381e]
#2 /usr/lib/libX11.so.6 [0xb7dc1dc9]
#3 /usr/lib/libX11.so.6(XAddExtension+0x2c) [0xb7da423c]
#4 /usr/lib/vmware/lib/libXft.so.2/libXft.so.2(_XftDisplayInfoGet+0x77) [0xb7ca6ed7]
#5 /usr/lib/vmware/lib/libXft.so.2/libXft.so.2 [0xb7ca58b1]
#6 /usr/lib/vmware/lib/libXft.so.2/libXft.so.2 [0xb7ca5d39]
#7 /usr/lib/vmware/lib/libXft.so.2/libXft.so.2(XftDrawPicture+0x10) [0xb7ca5ec0]
#8 /usr/lib/vmware/lib/libgdk-x11-2.0.so.0/libgdk-x11-2.0.so.0 [0xb7af29b6]
#9 /usr/lib/vmware/lib/libgdk-x11-2.0.so.0/libgdk-x11-2.0.so.0 [0xb7af4d75]
#10 /usr/lib/vmware/lib/libgdk-x11-2.0.so.0/libgdk-x11-2.0.so.0(gdk_draw_pixbuf+0x270) [0xb7ac4c14]
#11 /usr/lib/vmware/lib/libgdk-x11-2.0.so.0/libgdk-x11-2.0.so.0 [0xb7ad124f]
#12 /usr/lib/vmware/lib/libgdk-x11-2.0.so.0/libgdk-x11-2.0.so.0(gdk_draw_pixbuf+0x270) [0xb7ac4c14]
#13 /usr/lib/vmware/lib/libgdk-x11-2.0.so.0/libgdk-x11-2.0.so.0(gdk_pixbuf_render_pixmap_and_mask_for_colormap+0x255) [0xb7ad0b34]
#14 /usr/lib/vmware/lib/libgtk-x11-2.0.so.0/libgtk-x11-2.0.so.0 [0xb79d5298]
#15 /usr/lib/vmware/lib/libgtk-x11-2.0.so.0/libgtk-x11-2.0.so.0 [0xb79d5586]
#16 /usr/lib/vmware/lib/libgtk-x11-2.0.so.0/libgtk-x11-2.0.so.0 [0xb79d777e]
#17 /usr/lib/vmware/lib/libgobject-2.0.so.0/libgobject-2.0.so.0(g_cclosure_marshal_VOID__VOID+0xd1) [0xb7bea459]
#18 /usr/lib/vmware/lib/libgobject-2.0.so.0/libgobject-2.0.so.0 [0xb7bd23a1]
#19 /usr/lib/vmware/lib/libgobject-2.0.so.0/libgobject-2.0.so.0(g_closure_invoke+0x1b1) [0xb7bd2076]
vmware: ../../src/xcb_lock.c:77: _XGetXCBBuffer: Assertion `((int) ((xcb_req) - (dpy->request)) >= 0)' failed.

You may want to read:

How to apt-get

at - command to schedule actions

ggarron — Wed, 06 Aug 2008 13:35:12 -0700

One of the most uses I give to this command is to turn the PC off after some time, sure there are other ways.

I like the way you may execute batch jobs at a given time, all you need is:

1. Write your shell script

Which actually is a list of commands in a text file

2. Execute the at command

at now + 5 minutes < $HOME/listofcommands.txt

You can use times like "now", "noon", "midnight", or a date in the format of DD.MM.YY

check man at in order to have more details

Nice IBM adverticing about Linux

ggarron — Wed, 16 Jul 2008 06:28:19 -0700

Hi,

I have found this video on Youtube, take a look at it.

Installing and uninstalling .deb package

ggarron — Sat, 12 Jul 2008 07:05:39 -0700

Debian uses .deb binary packages and you manually install and uninstall them using dpkg tool.

dpkg has lots of options but maybe the most important or used ones are:

-i: Installs and configures a package
-r: Removes the package but keeps the configuration files on your systems, thus you may reinstall it later and does not need to configure it again
-p: Purges a package, meaning it will remove the package and also all configuration files

How to use it

- To install a .deb package

sudo dpkg -i package.deb

- To uninstall a .deb package

sudo dpkg -r package

- To purge a .deb package

sudo dpkg -p package

Moving a window in GNOME

ggarron — Sat, 21 Jun 2008 19:07:37 -0700

If you someday have a window out of your screen or at least the title bar out of your screen as I had today, I was surfing the web using Opera and when I pressed CTRL+F to look for a text in the page the little window appeared too high in the screen that I could not click on the title bar and move it a little down.

Well the solution for this is to press the and hold the ALT key, and click any place on the window to move it.

Tip: If you use the righ button of the mose you can resize it without need to click on the border of the window.

Hope this may help you.

du - Shows the disk space a file or directory is using in your disk

ggarron — Sat, 21 Jun 2008 18:40:21 -0700

This is a very useful command you may use to find which file or directory is filling you disk.

So if you need to check the file and directory size in your home directory you can enter

to switch to your home directory

du -S * | sort -n

This is going to list all files, directiries and sub-directories in size order, and will not include sub-directories' size in directories' size, if you want to have a total size of a directory including its sub-directories, you will have to remove the -S

du * | sort -n

If you want to have the sizes in "human language" I mean in kilos and megas, add the -h parameter.

How to play a DVD video ISO image

ggarron — Sun, 08 Jun 2008 20:47:14 -0700

I have this new video camera Sony that records on mini DVDs, and I got a video from my daughter dancing for the mother's day, I copied it as an image to the hard disk of my Linux Operating System machine

cat /dev/dvd/ > $HOME/video.iso

But now how to play that iso image from my disk with out using my DVD player?

These are the simple commands needed.

sudo mkdir /media/iso

To create a mount point

sudo mount -t iso9660 -o loop /home/ggarron/dvd_video.iso /media/iso

To mount the iso as a DVD

sudo aptitude install gxine

To install the player

gxine dvd://media/iso/video_ts/

To play the DVD movie.

How to delete / purge an email from postfix queue

ggarron — Tue, 03 Jun 2008 05:55:05 -0700

Today I sent an email to a person with an attachment that was not supposed to be sent, so I had to log into my postfix server and delete it from the queue before it leaves the server.

Fortunately, I realized before it leaves, and thanks God the email was big enough for me to have time to log in, find the message and delete it.

If you ever need to delete an email from Postfix queue, you have to follow this steps.

Once logged in your server find the message you are looking for.

sudo postqueue -p

This is going to list the current active queue in your server, something like this.

5642B4D8647* 1683500 Tue Jun  3 08:37:27  xxxxxx@xxxxxxx.com
                                         rrrrrrrrr@hotmail.com

9359B4D82B1* 1635730 Tue Jun  3 08:36:53  xxxxxx@xxxxxxx.com
                                         yyyyyyyy@hotmail.com

The first number is the message ID, the asterisk behind it, denotes that the messages is currently in the process of being sent, to delete it enter.

postsuper -d 9359B4D82B1

This is going to delete message ID=9359B4D82B1, from the queue.

Gmail Manager - Firefox Extension

ggarron — Fri, 23 May 2008 06:51:04 -0700

I want to write a little about this good Firefox extension, maybe lots of you already know it, but for those who does not, here it goes.

As its name says, this extension lets Firefox access your Gmail account, install it from:

Gmail Manager Firefox extension once installed you will have it located at the bottom of your screen, you can manage lots of accounts, which is great, you can see how many emails you have unread, which labels they have, all of that at a glance.

It is also good that you can add sound when there is incoming email, you can also make firefox to directly open your account and create an email when you click on an email address link.

Check it you will love it!, if you are gmail users :)

How to find files, using command line (locate)

ggarron — Wed, 21 May 2008 13:27:20 -0700

Continuing reviewing some of my old posts, I found this one Examples of find command, now I want to show you a faster and easier way to find files.

We are going to use the commands updatedb and locate

updatedb

This command will update the database of the files in a given file system, with no arguments, it will read from / to all file system structure looking for files and archiving the data in the database, located in Debian (/var/cache/locate/locatedb).

There is an option for those using NFS (like me) that you can use to include your NFS file system in the database.

--netpaths=’path1 path2...’

So you can enter a command like this:

sudo updatedb --netpaths=/media/nfs_drive

Now that you have your database updated lets find files.

locate

You just need to enter:

locate filename

and the file named filename will be showed, example:

locate apt-cacher -b

The output is:

/etc/apache2/conf.d/apt-cacher.conf
/etc/apt-cacher
/etc/apt-cacher/apt-cacher.conf
/etc/cron.daily/apt-cacher
/etc/default/apt-cacher
/etc/init.d/apt-cacher
/etc/logrotate.d/apt-cacher
/etc/rc0.d/K20apt-cacher
/etc/rc1.d/K20apt-cacher
/etc/rc2.d/K20apt-cacher
/etc/rc3.d/S20apt-cacher
/etc/rc4.d/S20apt-cacher
/etc/rc5.d/S20apt-cacher
/etc/rc6.d/K20apt-cacher
/etc/rcS.d/S20apt-cacher
/usr/lib/cgi-bin/apt-cacher
/usr/sbin/apt-cacher
/usr/share/apt-cacher
/usr/share/apt-cacher/apt-cacher
/usr/share/apt-cacher/apt-cacher-cleanup.pl
/usr/share/apt-cacher/apt-cacher-format-transition.pl
/usr/share/apt-cacher/apt-cacher-import.pl
/usr/share/apt-cacher/apt-cacher-lib-cs.pl
/usr/share/apt-cacher/apt-cacher-lib.pl
/usr/share/apt-cacher/apt-cacher.pl
/usr/share/apt-cacher/apt-cacher-precache.pl
/usr/share/apt-cacher/apt-cacher-report.pl
/usr/share/apt-cacher/apt-proxy-to-apt-cacher
/usr/share/doc/apt-cacher
/usr/share/man/man1/apt-cacher.1.gz
/var/cache/apt-cacher
/var/cache/apt-cacher/headers/apt-cacher_1.6.1_all.deb
/var/cache/apt-cacher/packages/apt-cacher_1.6.1_all.deb
/var/cache/apt-cacher/private/apt-cacher_1.6.1_all.deb.complete
/var/lib/dpkg/info/apt-cacher.conffiles
/var/lib/dpkg/info/apt-cacher.list
/var/lib/dpkg/info/apt-cacher.md5sums
/var/lib/dpkg/info/apt-cacher.postinst
/var/lib/dpkg/info/apt-cacher.postrm
/var/lib/dpkg/info/apt-cacher.prerm
/var/log/apt-cacher
/var/run/apt-cacher.pid

With the option -b only shows the files where the final part of the name matches the given file name, otherwise, it will show you the full content of the directory /etc/apt-cacher.

Which runlevel are you in?

ggarron — Wed, 21 May 2008 13:06:04 -0700

I wrote a little runlevel explanation, now I will show you how to know in which runlevel your Linux Operating System is actually running.

Which runlevel are you in?

Enter the following command:

sudo runlevel

My output is:

N 2

Switch to other runlevel

To do that enter:

telinit [number of runlevel]

This will change your runlevel to whatever number you enter there, be careful with this command as you can loose data, some programs may not close in an appropriate way.

telinit is actually the same as init, or better said:

telinit = tell init to do change runlevel to:...

1001 RSS readers

ggarron — Wed, 21 May 2008 12:46:09 -0700

Hi, this post is to thank you all for reading this blog, I want to celebrate with you "my readers" because today we surpassed the line of 1000 readers, we are now 1001 readers of this blog.

These are the statics from feedburner.

Thanks again to all of you, and hope you continue reading the posts, and more important that what I write could be useful for your

Automatic Login - Gnome

ggarron — Tue, 20 May 2008 13:11:48 -0700

I think this should work for any Linux operating system using Gnome, I have tested on Debian and Ubuntu.

Well, automatic login will let you avoid to enter your login and password each time you turn on your PC, this could be insecure, but if your computer is physically secured it is Ok to enable this, that could make your booting more smooth.

How to do it?

On Gnome go to:

Systems->Administration->Login Window, you will be prompted for the administrator password, enter it and then select Security tab, once in there select Enable automatic login and select the user you want to be automatically logged in, each time you turn on your PC.

Showing line numbers on vim

ggarron — Tue, 20 May 2008 06:45:10 -0700

Sometimes you really need to see the number of the line where you are while editing a text file, if you like vi / vim, this will help you how to turn on and off the numbering of lines.

Turn on the number display on vim

While editing the file enter:

:set nu

:set number

Turn off the number display on vim

While editing the file enter:

:set nonu

:set nonumber

Printing the numbers

Sometimes you want to print those numbers, specially if you are debugging software, so enter:

:set printoptions=number:y

Note: Remember that you can always put these commands in your $HOME/.vimrc in order to have them as defaults

How to find which service is listening on a given port

ggarron — Mon, 19 May 2008 07:39:54 -0700

It is really important to know which ports are open in your PC, this is not only useful for Linux, but also for other operating systems, Linux has a lot of tools to check which ports are open, the most common is nmap which is a command line tool, but also exist a Graphical frontEnd for it if you prefer that way.

So to scan you own PC and find open ports you can enter:

sudo nmap -T Aggressive -A -v 127.0.0.1 -p 1-65000

That will scan all ports and you will an output like this:

Starting Nmap 4.53 ( http://insecure.org ) at 2008-05-19 10:20 BOT
Initiating SYN Stealth Scan at 10:20
Scanning localhost (127.0.0.1) [65000 ports]
Discovered open port 113/tcp on 127.0.0.1
Discovered open port 22/tcp on 127.0.0.1
Discovered open port 80/tcp on 127.0.0.1
Discovered open port 443/tcp on 127.0.0.1
Discovered open port 902/tcp on 127.0.0.1
Discovered open port 55378/tcp on 127.0.0.1
Discovered open port 3143/tcp on 127.0.0.1
Discovered open port 8307/tcp on 127.0.0.1
Discovered open port 631/tcp on 127.0.0.1
Discovered open port 8222/tcp on 127.0.0.1
Discovered open port 8308/tcp on 127.0.0.1
Discovered open port 8009/tcp on 127.0.0.1
Discovered open port 111/tcp on 127.0.0.1
Discovered open port 8005/tcp on 127.0.0.1
Discovered open port 8123/tcp on 127.0.0.1
Discovered open port 38599/tcp on 127.0.0.1
Completed SYN Stealth Scan at 10:20, 1.47s elapsed (65000 total ports)
Initiating Service scan at 10:20
Scanning 16 services on localhost (127.0.0.1)
Completed Service scan at 10:21, 88.68s elapsed (16 services on 1 host)
Initiating OS detection (try #1) against localhost (127.0.0.1)
Initiating RPCGrind Scan against localhost (127.0.0.1) at 10:21
Completed RPCGrind Scan against localhost (127.0.0.1) at 10:21, 0.12s elapsed (3 ports)
SCRIPT ENGINE: Initiating script scanning.
SCRIPT ENGINE: rpcinfo.nse is not a file.
SCRIPT ENGINE: Aborting script scan.
Host localhost (127.0.0.1) appears to be up ... good.
Interesting ports on localhost (127.0.0.1):
Not shown: 64984 closed ports
PORT      STATE SERVICE         VERSION
22/tcp    open  ssh             OpenSSH 4.7p1 Debian 9 (protocol 2.0)
80/tcp    open  http            Apache httpd 2.2.8 ((Debian))
111/tcp   open  rpcbind          2 (rpc #100000)
113/tcp   open  ident
443/tcp   open  https?
631/tcp   open  ipp             CUPS 1.2
902/tcp   open  ssl/vmware-auth VMware GSX Authentication Daemon 1.10 (Uses VNC, SOAP)
3143/tcp  open  unknown
8005/tcp  open  unknown
8009/tcp  open  ajp13?
8123/tcp  open  http-proxy      Polipo http proxy
8222/tcp  open  unknown
8307/tcp  open  unknown
8308/tcp  open  http            Apache Tomcat/Coyote JSP engine 1.1
38599/tcp open  status           1 (rpc #100024)
55378/tcp open  nlockmgr         1-4 (rpc #100021)

As you can see, it tries to guess which service is listening on each port, but it can make mistakes, so if you want to be sure you need to use some other tools, we will see three different now.

netstat

With netstat the command you need to enter is:

sudo netstat --tcp --udp --listening --program

The output could be something like this:

Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 *:902                   *:*                     LISTEN      3441/inetd      
tcp        0      0 *:38599                 *:*                     LISTEN      2926/rpc.statd  
tcp        0      0 *:3143                  *:*                     LISTEN      2763/perl       
tcp        0      0 *:sunrpc                *:*                     LISTEN      2919/portmap    
tcp        0      0 *:auth                  *:*                     LISTEN      3441/inetd      
tcp        0      0 *:55378                 *:*                     LISTEN      -               
tcp        0      0 *:8307                  *:*                     LISTEN      4096/vmware-hostd
tcp        0      0 localhost:ipp           *:*                     LISTEN      3407/cupsd      
tcp        0      0 *:https                 *:*                     LISTEN      4096/vmware-hostd
tcp        0      0 *:8123                  *:*                     LISTEN      3455/polipo     
tcp        0      0 *:8222                  *:*                     LISTEN      4096/vmware-hostd
tcp6       0      0 localhost:8005          [::]:*                  LISTEN      3956/webAccess  
tcp6       0      0 [::]:8009               [::]:*                  LISTEN      3956/webAccess  
tcp6       0      0 [::]:www                [::]:*                  LISTEN      4175/apache2    
tcp6       0      0 [::]:8308               [::]:*                  LISTEN      3956/webAccess  
tcp6       0      0 [::]:ssh                [::]:*                  LISTEN      3281/sshd       
udp        0      0 *:44807                 *:*                                 2926/rpc.statd  
udp        0      0 *:36555                 *:*                                 3467/avahi-daemon: 
udp        0      0 *:982                   *:*                                 2926/rpc.statd  
udp        0      0 *:mdns                  *:*                                 3467/avahi-daemon: 
udp        0      0 *:sunrpc                *:*                                 2919/portmap    
udp        0      0 *:ipp                   *:*                                 3407/cupsd      
udp6       0      0 [::]:51107              [::]:*                              3467/avahi-daemon: 
udp6       0      0 [::]:mdns               [::]:*                              3467/avahi-daemon:

Now you can see which programs are opening/listening on those ports.

lsof

With this command you need to enter

sudo lsof +M -i4

You will get an output like this:

COMMAND    PID     USER   FD   TYPE DEVICE SIZE NODE NAME
apt-cache 2763 www-data    3u  IPv4   6403       TCP *:3143 (LISTEN)
portmap   2919   daemon    3u  IPv4   6686       UDP *:sunrpc[portmapper] 
portmap   2919   daemon    4u  IPv4   6687       TCP *:sunrpc[portmapper] (LISTEN)
rpc.statd 2926    statd    5u  IPv4   6726       UDP *:982 
rpc.statd 2926    statd    7u  IPv4   6736       UDP *:44807[status] 
rpc.statd 2926    statd    8u  IPv4   6741       TCP *:38599[status] (LISTEN)
cupsd     3407     root    0u  IPv4  20058       TCP localhost:ipp (LISTEN)
cupsd     3407     root    3u  IPv4  20061       UDP *:ipp 
inetd     3441     root    4u  IPv4   7612       TCP *:auth (LISTEN)
inetd     3441     root    5u  IPv4   7615       TCP *:902 (LISTEN)
polipo    3455    proxy    0u  IPv4   7649       TCP *:8123 (LISTEN)
polipo    3455    proxy    2u  IPv4  11350       UDP debian.go2linux.org:59528->vnsc-bak.sys.gtei.net:domain 
polipo    3455    proxy    5u  IPv4  21863       TCP localhost:8123->localhost:56811 (ESTABLISHED)
polipo    3455    proxy    8u  IPv4  21405       TCP localhost:8123->localhost:50403 (ESTABLISHED)
polipo    3455    proxy   22u  IPv4  21872       TCP localhost:8123->localhost:56813 (ESTABLISHED)
polipo    3455    proxy   42u  IPv4  21965       TCP localhost:8123->localhost:56828 (ESTABLISHED)
avahi-dae 3467    avahi   14u  IPv4   7702       UDP *:mdns 
avahi-dae 3467    avahi   16u  IPv4   7704       UDP *:36555 
vmware-ho 4096     root    6u  IPv4   9022       TCP *:https (LISTEN)
vmware-ho 4096     root    7u  IPv4   9023       TCP *:8222 (LISTEN)
vmware-ho 4096     root   30u  IPv4   9455       TCP *:8307 (LISTEN)
firefox-b 4431  ggarron   58u  IPv4  21862       TCP localhost:56811->localhost:8123 (ESTABLISHED)
firefox-b 4431  ggarron   61u  IPv4  21871       TCP localhost:56813->localhost:8123 (ESTABLISHED)
firefox-b 4431  ggarron   62u  IPv4  21964       TCP localhost:56828->localhost:8123 (ESTABLISHED)
firefox-b 4431  ggarron   68u  IPv4  21404       TCP localhost:50403->localhost:8123 (ESTABLISHED)

Now you have the program running, as an example, netstat showed on 3143 (Perl) but lsoft showed (apt-cacher), which is a perl script.

fuser

Fuser, does help, but is not like those other tools, with fuser you can also kill the process which is listening on a given port.

sudo fuser -v 3143/tcp

The output is:

                     USER        PID ACCESS COMMAND
3143/tcp:            www-data   2763 F.... apt-cacher

If you need to kill the process enter

sudo fuser -vk 3143/tcp

Do not forget to read the man pages of this tools to have more info about its uses.

Another way to populate your apt-cacher

ggarron — Fri, 16 May 2008 14:56:31 -0700

If you have some Debian machines already installed, and you plan to install some others, you maybe are going to use the net-install CD, which is the most common way to install Debian.

That may take a long time, to install all the Desktop Gnome or KDE, all the applications or servers, etc, and if you have just installed your apt-cacher server as me, you will not be able to use it this first time .... unless you populate it.

Usually at nights you are not working and your bandwidth is wasted, so at night you can enter this command to one or more Debian machines, (all pointed to the apt-cacher server see how to install apt-cacher).

for pkg in `dpkg --get-selections | awk '{print $1}'`; do sudo aptitude download $pkg; sudo rm $pkg; done

and you will have your machines downloading all its installed packages, and thus populating the apt-cacher database.

Be sure to have issued

sudo aptitude update && sudo aptitude safe-upgrade

in those machines before, so they download the latest versions of the packages, according to the manual this is not needed but I prefer to be sure.

Now, when the bid day arrives and you need to install that new Debian machine, you will have almost all the needed packages already in your proxy disk, and will waste not time.

The "Ubuntu Story" site

ggarron — Fri, 16 May 2008 04:59:22 -0700

I just stumbled on this site, it is a promotional site devoted to Ubuntu, you might be thinking, "well yet another Ubuntu site" but I think this one deserves a visit, it does not have how-tos, or such kind of info, it is mainly promotional, it has some information about Ubuntu's, Flexibility, Speed, Simplicity, Appearance, Stability, Freedom, Security and Community, which are the columns where Ubuntu rests.

You can also share your story (your Ubuntu's Story) with others, and you can read other's story, there are some good ones, you find how Ubuntu helps people in all areas, from students, to web developers, to sales people, as a matter of fact in all possible areas.

So, I encourage you to share your Ubuntu story in that site, if you are an Ubuntu user off course.

I also like the design with flash, the colours, effects, etc. nice artwork.

Ubuntu Story

How did Ubuntu end up so popular?

ggarron — Fri, 16 May 2008 03:49:32 -0700

As a matter of fact, I made myself that question more than a few times, but never took the time to try to find an answer, because Ubuntu is a relatively new Distro, it comes from Debian when Mark Shuttleworth, who was part of the Debian project decided that Debian was not focused on the final user as it should, and made its own distribution.

Well, I have found an article which touches some facts about why is Ubuntu so popular today, and we have to say that, in less time than RedHat, Suse, or Debian.

Of course as almost everything in this globalization era, is marketing, but instead of starting an analysis, you better read the article I have found, and then comment about it. (Due to spam, I have to approve the comments before they go online).

How did Ubuntu end up so popular?

wget - Resume downloads, limit the speed and much

ggarron — Thu, 15 May 2008 16:09:24 -0700

wget is a command line tool used to download files, or complete webpages, it is a great utility with lots of options, as you can see if you read the wget man page

Some months ago, I have written about how to download files with wget, now I want to add some other tips to those already explained that day.

Resume a download

If you need to stop a current download, and pretend to resume it later, you should use the -c option i.e.:

wget http://some.server.com/file -c

Traffic shaping, or limiting the speed of the download

I really use this feature a lot, as my home ADSL is not as big as I would like, I have to use the speed limiter, when downloading ISOs, otherwise I just can not continue working, to limit the speed of the download use the --limit-rate option.

wget http://some.server.com/file --limit-rate=20k

That line is going to limit the download speed to 20 Kbytes per second, or 160 kbps.

Let wget working after log out from ssh connection

I usually connect through ssh to my office (better ADSL than my home's) and download the files there over the night, the next day I bring them home.

So, to make wget continue working after the log out, because I do not want to let my home PC on all night long, so the command is:

wget -b http://some.server.com/file

Logging the output to a file

This is useful when you are working with wget in the background, to be able to know what was wrong if anything goes wrong, use the -o option and specify a file to store the logs.

wget http://some.server.com/file -o $HOME/log.txt

Of course you can combine the options, and put something like this:

wget -b -c http://some.server.com/file --limit-rate=20K -o $HOME/log.txt

The /etc/default/rcS file

ggarron — Thu, 15 May 2008 12:40:00 -0700

There is some behavior of your Linux Operating System which is easy to change, but not too common to know how.

The things you can change are:

Frequency to erase /tmp/ directory
Use UTC or local time
How Verbose are the boot messages of your Linux
If a disk error should be always repaired while booting automatically

There are more than those, but I will touch only those, for the rest, you can enter:

man /etc/default/rcS

Well, this is what we can do:

Change the frequency of cleaning /tmp/ directory

The variable that controls that is TMPTIME, its default value is 0, so the /tmp/ directory will be cleaned no matter the age of the files in there, if you want you can specify that the files there should be a week old to be erasable, to do that change the value to 7, if you enter a negative value -1 for instance, then /tmp/ will never be cleaned.

UTC or Local time

The UTC variable, controls that you can enter yes or no, to tell Linux that your hardware clock is set to local time or to UTC.

Verbose boot process

You can change VERBOSE variable from no to yes to have more messages during the boot process, or less if you enter no

Repair disks error automatically or not

When Linux checks the file system, and find error, fsck is called with -a option, and will only repair if no major damages are found, but if you want that fsck to try to fix the file system no matter the magnitude of the error, change FSCKFIX variable to yes

Tip: Importing your /var/cache/apt/ files to apt-cacher database

ggarron — Thu, 15 May 2008 07:46:26 -0700

Yesterday, I wrote about apt-cacher, and when you first install it, its database is empty, and of course the server where it is installed could have a lot of .deb files, in the /var/log/apt/archives/, so it would be great to use those packages in our new ATP proxy.

To do that we need one of the perl scripts that come with apt-cacher, and that are stored in:

/usr/share/apt-cacher

The right script for this task is: apt-cacher-import.pl , so run:

sudo /usr/share/apt-cacher/apt-cacher-import.pl /var/cache/apt/archives

That is all, now you have all those packages available in your new Proxy server, to save disk space your can then run:

sudo aptitude clean

How to: Find the fastest apt mirror server

ggarron — Wed, 14 May 2008 13:51:57 -0700

If you want to use the fastest mirror to download the .deb files you may need to upgrade or update your Debian machines, you have to remember that not always your nearest server is the fastest one, and that could be because not only the distance the server is from you but also the network congestion is a factor when talking about network speed.

For instance, your ISP may have a direct satellite connection to another country, and thus your nearest server should be in that country, to avoid you the hassle to get that info, Debian give you some tools, I will touch two of them here.

netselect-apt

This tool will download the full list of mirrors and will quickly explore throw them for the fastest mirror for you, the use of it really easy and reliable.

Installation

You just need to run:

sudo aptitude install netselect-apt

Running it

Once installed, run

sudo netselect-apt -n -s lenny

Be sure to change lenny for your appropriate version, you can use the name of the version, (edge, lenny, sid) or the words stable, testing, unstable, experimental.

It will then write a sources.list file in the current directory, you may then copy that file to /etc/apt/sources.list or just edit and copy the lines you need from one to the other.

If you see, I have used -n and -s options, because I wanted to get the non-free section, and deb-src to be able to use apt-get source

apt-spy

apt-spy is a little bit more flexible, well maybe flexible is not the right word, as in netselect-apt you can also select some specific mirrors to explore, you have to edit the mirrors_full file, while with apt-spy you just enter the countries you may want to explore for servers.

Installation

To install it run:

sudo aptitude install apt-spy

Running it

You first need to get the mirrors file, and contrary to netselect-apt apt-spy does not do that automatically, so first run:

sudo apt-spy update

Now it is time to run the tool:

sudo apt-spy -a North-America -a Europe

To check for available servers in Noerth-America and Europe, if you want to create your own zone, just edit the file /etc/apt-spy.conf and add something like this:

France-Germany-Netherlands:
  FR
  DE
  NL

The sources.list will be then copied to /etc/apt/sources.list.d/apt-spy.list

As you see, it is really easy to manage, it takes a little bit longer than netselect-apt to run, but also works well.

Note: Remember that during the week, or even the day not the same server is the fastest one for you, as conditions in the Internet change all the time.